# 3D Printing > 3D Printing in Education > Teachers & Professors >  Bat House Project

## reality_boy

This is a 3D bat house I have been working on. I did not want to post the plans until I have had time to validate the design with real bats.  However I need a place to talk about the design, so I'm posting it here.

*Background*

My wife is a 2nd grade teacher and she does a whole segment on bats (she teaches them for about a month).  I have been looking around for a while for a way to give her kids more hands on experiences with bats, beyond videos and books.  One idea was to build a bat house, so I sent off for a copy of BCI's guide to building bat houses (http://amzn.com/0974237914/).  I quickly realized that while the guide was good, the plans were well beyond what a grade school club could put together.  They needed power tools to cut the wood up, and a very serious pole to mount the house on.  Since I was already using a 3D printer as a hobby I wondered if a 3D printed bat house could be made for a low cost and with tools kids could use.

Arial]As I was researching this subject I cam across the plans for the Bat Bunker (https://www.thingiverse.com/thing:2057552).  This was an impressive project by a junior high school robotics club, but looking at the plans it seemed clear to me that this design would not work very well for a family of bats.  Since I could not find anything else, I set out to design and build my own house with the hope that the design could be shared freely and inspire others to put up a bat house of there own.

3D printers are great, but they tend to have a relatively small build volume.  After doing some research on it I decided that targeting an entry level printer with a 150x150x150 mm build volume would allow most users to print a small 2 chamber bat house, and going up to a 200x200x200 mm build volume would let many users with full sized machines print a more substantial 3 chamber house.  Having a small square build chamber lends itself to a rocket box style house (http://www.batcon.org/files/RocketBoxPlans.pdf), and a rocket style house can be mounted on a single pole more easily.  By my calculations the 2 chamber house will weigh less than 1.5 kg (about 3 lb) and the 3 chamber house will weigh less than 2.5 kg (about 5.5 lb) so it does not need a substantial pole.  After searching around and trying several pole ideas I settled on using a 1 3/8" top rail for a chain link fence since it is readily available in 10 foot lengths and is strong enough to hold the house and cost only $13 per segment.

*Design*

The basic design is either 2 or 3 19 mm wide chambers with 1.5 mm deep horizontal groves in the wall spaced 9 mm apart.  The houses are each split up into 5 segments, each either 140 or 190 mm tall for a total height of 660 mm or 860 mm for the 2 and 3 chamber houses respectively.  You could choose to add or remove segments to create a larger or smaller house.  There are three different designs for the center segments, one with a row of 13 mm vent holes in the outside of the box, one with 38 mm passages between the chambers, and one with no holes at all.  These can be mixed and matched as needed for the environment.



Each segment of the house slots together with the segment above.  This interface is designed to create a solid seal to keep the elements out and to help keep the structure strong even if heat causes minor warping of the plastic (although I don't expect any warping, it is good to be prepared).  In addition I use #6 1/2 in sheet metal screws to secure each segment together.  And have a box around the end of the screw that prevents it from penetrating into the bat chamber.  In my tests this provides a very solid structure that could withstand a large impact and hopefully will keep the house sealed up tight for years to come.  Finally the pole is run up through the entire length of the house to add rigidity to the design so that the screws are not the main structural support.  The base of the structure clamps to the pole with 3 screws as well to further keep the structure together. And it also forms a 3" landing strip for bats to land on.

The 2 chamber house made with 5 segments has an outer dimension of  142x142x660 mm (around 23" tall), uses 1.4 kg of plastic (a spool and a half) and has a living space of around 6,860 cm^3.  By my estimates it would cost $26 to print and take about 6 days to print all 5 pieces.  That puts it close to the 6,500 cm^3 space of BCI's single chamber bat house plans (http://www.batcon.org/files/BCI_Sing...se_Plans-3.pdf).  Each additional segment adds around 1,700 cm^3 of living space and 130 cm of vertical height.

The 3 chamber house made with 5 segments has an outer dimension of 189x189x862 mm (around 34" tall), uses around 3 kg of plastic (3 spools) and has a living space of around 16,800 cm^3.  By my estimations it would cost around $60 dollars and take about 16 days to print all 5 pieces.  That puts it close to the 15,000 cm^3 space of BCI's triple chamber bat house plans (http://www.batcon.org/files/FourCham...usePlans-3.pdf). You can save a small amount of money and time by printing only 4 segments, and of course you can add additional segments as well.  Each segment adds around 180 mm of height and around 3,700 cm^3 of living space.

To complete the project you need a box of #6 1/2" sheet metal screws and a 10' length of 1 3/8" galvanized top rail, for an additional cost of around $15.  Once inserted in the house the remaining pole will only be about 7' tall, you will need to attach it to an existing pole already in the ground to get the house 12' off the ground.  You can use any pole that is 5' off the ground or higher, or use a second 10' top rail and a $5 panel clamp set to attach the poles together.  Having a split in the pole is actually a benefit, the top pole weights around 10 pounds with the house on it and can easily be lifted and installed by one person, with a little pre-planning.

There are still several unknowns about this design:

I have tried to research how well 3D prints hold up in the outdoors and there are several posts on line with anecdotal evidence that indicates they hold up well for several years, but only time will tell if this is true or not.  The exterior of the house could be painted with an exterior latex paint to ensure a longer life.The house could be printed with any material but PLA is the most common.  I have a test piece outside here in Tucson, AZ  to see how well it holds up to heat.  Again my research indicates that PLA should hold up even in the desert heat, but if it does not we could switch to a stronger plastic like PETG. I verified that PLA looses its integrity at around 130 F, but I don't know if that is enough of a margin to allow the house to survive the summer heat.I'm not sure if the texture I added to the walls of the house is rough enough for bats to grip.  I could go with a different pattern if needed.I'm not sure if it is important to use a dark filament to print the house out of.  The walls are thick so most light would be blocked with any non translucent filament and exterior paint would help darken up any plastic.I'm not sure how well the plastic will hold up to bat guano, or if it is bat friendly.  However it is a solid plastic that is corn based and should be both stable and non toxic.The design of the walls could be reworked to reduce the plastic used and increase the print time.  By my calculations it may be possible to reduce the plastic by around 30%, however that may reduce the strength of the walls and for now I figured it was better to error on the side of caution.  The shape of the walls has a big impact on print time, it is possible that using a different texture on the walls could speed up the prints by a large factor.

I left the outside of the house undercoated on purpose so that others can decorate the houses as they see fit.  Here are a few ideas off the top of my head for possible designs.  You could use a tool like MeshMixer to quickly decorate the walls without a lot of cad experience.



Here are some renders of the final design.  In the first cutaway you can see part of the passage between the chambers, along with some of the vent holes on the lower chamber. And you can clearly see how the segments attach to each other and where the screw blocks are located.





This is a render of the 3 chamber bat house.



Below is a rough outline of the instructions I hope to provide with the plans.  For 3D printers you don't give cad drawings, but rather 3D models in STL format that describe how to print the segments out.  These would be stored on the Thingiverse website under a creative commons licence that lets anyone modify and print the plans without compensating me in any way.

*Print Settings*

*Printer Brand:* Creality
*Printer:* Ender 3
*Rafts:* No
*Supports:* No
*Resolution:* 0.2 mm
*Infill:* 20%
*Walls:* 3
*Filament:*AmazonBasics PLA Neon Green
*Notes:*
This was designed to print on most any printer with a 150x150x150 mm build volume or greater. You should not need any supports at all. I managed to print it fine without a brim, but if you have first layer issues a brim may be helpful.
The models are undersized just a bit, enough so that you can use MeshMixer to decorate the outside however you want. Just be sure to not hurt the integrity of the chamber itself.
By my calculations the house will take around $25 worth of filament to print (1.4kg) and take about six days to print.
It should be OK to print this using PLA, but if you live in a hot climate going with PETG may give you more dimensional stability. I have a test model located at my home in Tucson, Arizona and so far have not had any warping or issues with my PLA print. I will update this if that changes.

*Post-Printing*

*Finishing it up*

The box needs to be mounted between 12 and 20 feet off the ground. This was designed to be mounted on a 1-3/8" chain link fence top rail. You can pick a 10 foot length up at Home Depot or Lowe's for around $13. You will need to either connect two together, or mount the post on an existing pole in the ground.
When selecting a site, make sure the box has good exposure to the sun and that the area around the box is clear so that bats flying in and out will not get entangled in anything. Try to locate the box near a source of water. And if mounting it near a park or school, locate it in an isolated area where kids will not be able to throw rocks at the house, or accidentally come into contact with the bats.

All parts below can be easily found at your local Lowes or Home depot, if you live in the United States.
$13.00 1-3/8 in x 10 ft. 6 in. 17-Gauge Galvanized Top Rail$3.50 #6 x 1/2 in. Stainless Steel Pan-Head Phillips Sheet Metal Screw (50 per Pack)
If you don't have an existing post to mount this to you can use the following to install a post into the ground and use the panel clamp set to connect the two pols together.
$13.00 1-3/8 in x 10 ft. 6 in. 17-Gauge Galvanized Top Rail$5.50 1-3/8 in. Galvanized Panel Clamp Set$3.25 Quikrete 60 lb. Concrete Mixoptionally 3 x #6 x 5/8 screws for making the pole clamp stronger
Bats wings are thin and easily damaged. Be careful when assembling this that the screws don't penetrate into the structure and watch for any sharp object near the house or wires that the bat could get entangled in.

You may want to add a layer of paint to the outside of the box to help it last longer in the outdoors. And if you expect a lot of rain you may want to calk the segments when assembling to ensure a more perfect seal from the elements.

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## reality_boy

*Ideas*
Take temerature readings in the house to validate its thermal characteristics.  I plan on comparing that to temperatures inside an inverted 5 gallon bucket and in an insulated thermos as a control.  The idea being that we can't do much worse than the bucket and much better than the thermos.Investigate the temperature effects of paint, both dark and light.  Also investigate roof coating to see if it has any benefits.Experiment with wall thicknesses and layer count to see if it has any impact on thermal or structural characteristics.Experiment with PETG to see if it is stronger or more temperature resistant.Experiment with different wall textures to see if bats cling to one better than another.  I'm most interested in trying a lattice pattern and some sort of random texture.Experiment with adding in more cross bars for larger bats to hang on.Experiment with vertical baffles to help trap the air in an attempt to make more of a temperature gradient.

*Work in progress*

I have access to a 6 element temperature logger, I'm hoping to mount my prototype outside and begin profiling it.  I want to verify that the tall design does in fact create a temperature gradient, and investigate paint and insulation among other things. I have heard that thermal mass is important in a bat house, it is difficult to add mass to a 3D print, but it may be that thicker walls will act as better insulators at least.I need to build a container to house my temperature probe.  Mount my prototype outside and begin to collect data.I also need to find bats to work with.  My hope is to get a hold of a bat rescue that will let me place sample prints in a cage with live bats to see if they are interested in my designs.  It seems the fastest way to verify the questions about what wall texture is best.*5-18-2019*It's alive!  I put the bat house up on a temporary post and went ahead and added my temp logger for some initial validation.  Currently this is on a 10 foot poll that I cut in two to do the initial prototype work, so it is not nearly high enough off the ground.  But it is much easier to reach the house this way, and it verifies that my pole clamps work as expected as well.  My hope is to install this on a proper pole at some point in time, after validating the design.



Them temperature logger is just up temporarily, I wanted to get some base line data to see if it is working or not before making a more permanent install.  This is based around an arduino uno with a real time clock and sd-card board, a LCD board for fun, and a custom built 6 element temperature probe and a light detector.  The probes are accurate to within a single degree and we log both the real time temps and a rolling average to reduce noise once every 30 milliseconds.



I put an inverted thermos next to the pole with a single temp sensor placed at the very center of the container for validation.  I figure the thermos is better insulated than anything I can 3D print so we can use this as a best case scenario.  I added a second temp sensor to the outside of the thermos on the south side so it is in the shade.  And I placed the light sensor at the top so we can see when the sun is on our house.Inside the house I have 4 sensors, one near the top and bottom of each chamber.  These are not currently placed very ideally, the way I mounted the electronics limits how far up the top sensor can go.  I will try to make a proper clamp for the electronics once I validate that this is running correctly and gathering meaningful data.



My next step is to start experimenting with the variables.  I plan on printing with different thickness of walls, painting the exterior both black and white, and trying out some elastomeric roof coating on the outside as well.  I don't expect the roof coating will have a significant improvement over white paint, but I want to verify that.  The roof coating is rather expensive, so if it has no benefit it would be great to know that up front.I will probably make a cross bar for the pole with small spikes that i can mount test prints onto rather than messing with the prototype house.  Hopefully that makes it simpler to iterate over designs and reduces the cost as well.

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## reality_boy

*5-19-2019
*
First Data! I need to clean up my logging code a bit, and work out a better way to visualize the temperature differentials, but we have data! 

Looking it over it seems that the outer chamber is heating up a bit over ambient. I think that is because this material is not completely opaque but instead lets a small amount of light through. Painting the outside of the chamber would help, as would using a darker material like black.

Also for some reason I expected the upper segment of the chamber to be cooler, even though heat rises. Of course the ceiling is always hotter than the floor in your house, when the sun is out so I was just thinking incorrectly. I need to see if building a taller box makes a difference on the temperatures, it may have an impact.

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## reality_boy

*5-19-2019

*Here is the same data as above but as a delta relative to the ambient temperature.  It is interesting to look at it this way.  You can see that the bat house offers very little insulation at night, and it is a somewhat poor insulator of radiant heat since the upper part of the outer chamber is heating above ambient.  What is odd to me is that the cooler is heating above ambient several hours before the light detector sees the sun.  That makes me question the accuracy of my sensors so I put them all in the cooler in a closed room of my house to see if they can all hold a stable temperature.  After that I will try adding cold or hot water to the bottom of the cooler to see how they react to changes in temperature.

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## reality_boy

Question for later, does the pole absorb heat from the bat house via conduction.  Figure out how to mount a temperature probe to the pole to see if it is cooling below ambient.  This would only happen if the ground was absorbing energy.

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## curious aardvark

Okay - first, I take it you haven't done much research in to bats ? 
The reason they usually rest in caves, roof spaces, tree holes etc is that those are shaded places that retain heat in winter and stay cool in summer. 
A solid chunk of plastic in the open arizona sun - will not attract any bats. 

Secondly, most bats are very very small - their bodies are smaller than most mice. They tend to go for very small spaces and can crawl through cracks smaller than you would believe. 

Your house would be better, both smaller and made to attach to buildings below the eaves, or on tree trunks in shaded areas.  Places nearer where they would naturally roost. 

A big cylinder on  a pole in the open in arizona (of all places :-) will not attract bats, as it's clear it will be too hot during the day. 

So that's my first suggestion, do some research on bats, then redesign the box to suit the bats.

You don't need the pole. 

Secondly - why on earth does it weigh -2-3 kg ? That's a lot of money in filament. To get it that heavy it must have a lot of solid shells and really dense infill. 
Thinner shells and a lower density infill mesh will not only make it cheaper and lighter (able to be mounted more places) but the larger mesh will increase the insulation properties of the box. 

Bats like small tight spaces that daytime predators can't easily access. 

Thirdly (lol) bats crap during the day, so the box should be fitted with a way making it easy to clear it out. a hinged trap door type base would be favourite.  

Different bats will like different box types - so make small ones for small bats and larger ones for larger bats - though there are a lot less of those generally.

Pipistrelles are the most common bats in the uk - and a cigarette box sized house with a 5mm entranceway could easily house a half dozen bats. 

Also a small, building mounted box, could have a micro camera built in,  so the kids could see whether or not it was occupied.  

I applaud your project - but you probably need to start with the bats and then design a house. Than work on the principle: 'If I Build It - They Will Come' :-)

Oh yeah, like most small mammals bats have claws and can climb what looks like smooth walls to people. Print the b at houses at a fairly large layer height and fast and the natural grooves will be sufficient for most bats to easily hang on to. 
The majority of bats don't sleep hanging upside down from the ceiling.

Something like this:

with a trapdoor base would be quick ad simple print and easily attached to buildings, trees and shaded areas.

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## reality_boy

Thank you for taking the time to look over my project.  You raise good questions, hopefully I can try to answer some of them to the best of my ability.

First the house you are showing is considered a poor design by current standards.  Both because it is too small to house a nursing colony, and because it lacks enough variance to allow the bats to find there ideal temperature in any weather condition.  The current recommendations call for at least a 24 foot square house with 2-4 chambers, that is a substantial thing!

An alternate design is called a rocket box, it is basically the above house wrapped around a pole.  This is nice because it is simpler to mount away from a building and it tends to be simpler to construct as well.  Rocket boxes tend to keep the same internal volume as traditional houses, they just build up rather than out.  My larger bat house design mirrors one common rocket box design in size and livable volume.

How rough to make the sides of the house is a big unknown.  Right now I'm using horizontal groves to increase the roughness, but there are probably more efficient textures that would both use less materials and be faster to print.  My design requires the walls to be around 4 mm thick, rather overkill otherwise.  

As for material, I'm using as little material as I possibly can without compromising the integrity.  I am fairly new to 3D design, so I'm sure someone else could optimize the design even better, but I have tried many variations in an effort to reduce the material count.  The truth is that this is a really large print.  However I am aware that getting this shrunk down so it only takes one spool of filament would go a long way towards making others interested in printing it.

I'm experimenting now with ways to improve the insulation on the house.  I think what I have now is actually holding up fairly well. At least if my thermos test from above is to be believed.  The house is nearly as good at keeping the bats cool as the thermos is in direct sunlight.  At night the thermos seems to have the advantage, but in my defense I left the lid on it, so it  was not open to the night air.  I suspect paint is going to matter more than anything, but I do need to build a wooden bat house for comparison to see if I'm in the right ball park or not.

Finally, my hope is to find some bats to validate this all with, and redesign as needed if it does not hold up.  My goal is the bats,  not the house.  If it is not helping bats then there is little point in publishing the design.  That is why I am being cautious and holding off on releasing the stl files.  I don't want to release a bad design into the wild.

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## reality_boy

I managed to clean up the images above, the way I was hosting them before I could see everything but no one else could.  Hopefully that clears up some confusion.

I ran two temp tests overnight.  First I placed all my temp probes in a sealed thermos in a closed room.  You can see from the plot below that the sensors are all reading a bit off from each other. This is a plot of the difference between the first probe and the others, basically a measure of there relative error.  They should be accurate to within a degree but they are fluctuating by 2 degrees instead.  Considering we are seeing only 4-8 degrees of temp differential in the house that is not nearly sensitive enough.



Next I filled the bottom of the thermos up with ice, while keeping the probes dry, and let it sit for a while.  Here is a plot of the difference in readings from the first probe to all the others.  You can see that there is no consistent pattern to the temp offset, we can't just subtract or add a degree to bring them into allignment.



I don't think I can really move forward with these probes.  So I'm looking into some i2c temp probes that have a 0.3 C accuracy and a finer resolution.  Hopefully they are close enough.  On top of that I'm considering building a wooden rocket box to compare the temperatures against.

In the meantime while I'm waiting on parts I will make a test print at various thicknesses, and look into alternate ways to texture the inside of the house.

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## curious aardvark

what species of bats are you aiming to house ? 

Also are you looking at permament colonies or simple shelter for transient bats. 
I've done a little study of bats over the years (yes I have a bat detector :-) ) 
Obviously a lot will be country specific, but overall bat habits should be fairly universal. 

The bats that are in decline and need help tend to be the very small species that tend to have a variety of roosts that they move between over the year - even a small bat can roam as far as 30 miles in an evening. Because of habitat loss, over urbanisation, improvements in building insulation and materials and techniques. The traditional roosting places are in decline, also predation - particularly from domestic cats - accounts for a huge decline in bat numbers. 
Obviously in the states there are snakes, raccoons, tarantulas etc that will also prey on bats.

These bats do not need huge living spaces and tend to avoid them - for the obvious predation reasons. 

It just seems that you're concentrating more on the actual build - with an emphasis on large, inpractical housing for a very small segment of the bat community - rather than the species that really need transient shelter. 

The other thing is that your emphasis is purely on 3d printing as much of the house as possible. I find with larger projects that you can usually source the larger parts from something that's cheap and readily available and use 3d printing to fix things together, make joints, brackets etc. 

Why print large cylinders when your local hardware store already sells plastic pipes/tubes in a huge variety of materials and diameter and colours - both stronger and cheaper than you can print. 
Throw in  a hacksaw and a drill - and the 3d printing becomes minimal and more practical. 

For a school project - starting with cheap readily available materials, and adding a few easy to print parts to convert it into a bat house - would make a lot more sense. Both from the cost and practicality side of things.   

It would also be very easy to scale up or down for different species and usages of bats.

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## reality_boy

I have been looking into various ideas on how to control temperatures in the house.  Here are some potential ideas to explore

 - Print a shade on the outside that  keeps direct sunlight off the walls of the house.  Ideally the overhang would be designed to reduce shade in the winter months to help heat the house.
 - Build an outer chamber with a solar chimney built into it.  The idea is to use convection from solar energy to cool the air around the house.
 - Build in an attic with a plug of foam insulation.
 - Experiment with aluminum foil as a radiant barrier. It is suppose to act as a one way heat valve to reduce the temperatures in the house during the day, without adding thermal mass for night.  This may help in some humid and hot climates where heat builds up excessively.
 - Experiment with exterior color, white for cooling, black for heat and to produce a solar chimney effect.

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## reality_boy

While waiting on the new temperature sensors I thought I would do a little bit of a design sanity check. I modeled the house in one piece as 3-4 cylinders at the final height with no internal bracing, no textures on the walls, and no seams at the interface.  The idea being to measure how much cost is involved in my design work, vs just the cost of printing anything of this relative size.  

To analyze the results I created a fake printer with a 800 mm cubed build volume, big enough to print all the parts out.  The numbers below are what cura reported for this virtual printer to print the design.  The times are all quite long because I used a much slowed down profile that I'm currently using with my ender3, a better tuned printer could take less time.  However what matters is the relative change not the total time taken.

Here are my results for both the 2 chamber and 3 chamber houses:

3 chamber
 - Simple 4 walls, slow speed
   315 hour print time
   3633g / 1218m material
   $70

 - Full model 4 walls, slow speed
   412 hour print time
   4044g / 1356m material
   $77

 - Increase by
   31% more time
   11% more material

2 chamber
 - Simple 3 walls, slow speed
   136 hour print time
   1569g / 526m material
   $30

 - Full model 3 walls, slow speed
   183 hour print time
   1801g / 604m material
   $34

 - Increase by
   35% more time
   15% more material

Basically the cost of finishing the design is not a big deal, it is the overall size and shape that dictates the cost and print speeds.  This was all done with 4.5 mm thick walls.  I could go down to 2.4 mm thick walls to see if that speeds things up any.  With a 3 shell thickness that essentially results in solid walls with no infill.  Infill is set to 20%, so the savings can't be too great, but it may speed things up by a larger amount.

---

Edit, I ran a quick test and reducing the walls to 2.4 mm reduces both the material cost and print time by about 20%, basically the amount of infill in the walls.  I will do some strength tests to see if reducing infill has a significant impact, a 20% savings is not amazing but definitely worth something.

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## reality_boy

My thermisters came in, I picked up 8 thermisters with 3 meter cables that are housed in metal pipes and epoxied into place.  That should be safe enough to leave in the house even with bats (if I ever get so lucky to have bats).  The up side is these are dirt cheap, it cost $9 for 8.  The down side is you need a MUX or a device that can log analog voltages from 8 or more inputs, and they are uncalibrated so I have to go through that step.



I'm still waiting on my i2c temperature probes.  I went ahead and picked up 8 of those as well, at around $30.  The nice thing there is they can share a single wire for the data bus, and are easily to gaing together.  They are also calibrated and have there own 12 bit A/D converter built in.  The down side is the cost and the slightly larger size.  Also they are exposed, so I would need to print a housing if I was to leave them permanently in the house.  For now they are good enough.

I also picked up several light sensors to see if I could work out the thermal load on the house.  My light sensor from above is not good for much more than a binary on/off value indicating the sun is up.

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## reality_boy

Our agave plants are starting to bloom.  They rely heavily on bats to help them go to seed.



The rest of the hardware came in, and I managed to wire things up.  I'm just finalizing the logging code and working on a more permanent mount.

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## reality_boy

I finished up my arduino code and calibrated my analog temperature sensors.  I still need to finish wiring up the other digital temp sensors and see how well they compare to each other.

At the same time I designed a small prototype box that is hopefully large enough to measure some benefits, yet small enough that it is inexpensive to replicate.  I plan on printing it out with multiple wall thickness and line counts.  The hope is to work out what the minimum wall thickness is for both temperature control and structural integrity.  Finally I hope to paint these to see how that effects things.

I'm currently struggling with my 3D printer, I consistently get under extrusion at times and nothing I do seems to help it along.  I have tried new nozzles, new hotends, new extruders, new bowden tubes, hot/cold pulls, rolled back the software, and so on.  Nothing seems to cure the problem.  Im going to experiment with drying out the filament, maybe that is the issue? Something is causing too much back pressure at the extruder, at times I can hardly push the filament through manually.  Anyway I need to work through this issue before I can do more serious testing.

Finally my test bat house is cooking along (literally) outside and showing no signs of warping so far.  We have only hit 107 F, but there is plenty of summer left!

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## reality_boy

I went ahead and published my code, it is still a bit rough and lacks proper documentation, but it should work.  This is built around an arduino uno and a Adafruit data logger shield.  Add on top of that some analog thermistors and up to 8 MCP9808 i2c temperature sensors and either a VEML6075 UVA UVB and UV Index Sensor or VEML7700 Lux Sensor to track the thermal radiance.

https://github.com/reality-boy/tempLogger

I have been down on my health for a while, but I think I'm turning a corner.  Hopefully things here will pick up now that I'm on the mend.

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## curious aardvark

just out of curiosity, now you've got all this data -  have you considered going back and actually making something that fits your original brief ? 

Ie: something cheap and easy for kids in a primary school to make ? 

You're clearly having lots of fun :-)
But it's so far from your original starting point, it'll probably never see light of day in an actual school.

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## reality_boy

I redesigned my sample prints to be both skinnier and taller,  I think that more closely resembles the real thing.  I then made them with a 1.6mm, 2.4mm, 4mm and 8mm thick outer wall, and 2-3 0.4mm walls when printing.  The first two effectively have solid walls when printing with either 2 or 3 walls (that is getting confusing to say!).  The other two have some percentage of infill between the walls.One of my questions is how much plastic is needed to make a solid outer wall.  Ideally we use the bare minimum that gets the job done, it makes printing faster and reduces the cost.  Anyway the first two samples while stiff can still be flexed with moderate pressure while the 8mm sample is rock solid.  The 4 and 8 mm prints also block significantly more light than the thinner samples.  I am curious to see how much paint will improve that.  I still need to finish printing out the full samples and stick them outside to see how well they stay cool.

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## reality_boy

I wanted to test out how well different wall geometries block out light, so I printed a 100x100 mm square that was built up out of 4 different thicknesses.  Then I painted the flat side with two different types of white paint and finally used a light box to view how well the bare plastic and painted plastic block the light.  The results are interesting and highlight that I need to switch to a different plastic, this one is much to translucent.  Even the thickest walls and the best paint combined failed to block out all visible light.


I tested out some generic white spray paint and some rubberized spray on roof sealant. The roof spray is super thick and very flexible, however it does a poor job of blocking the light and does not stick well to the plastic.  I can scrape it back up easily with my nail.  It may stick better to a primer, maybe a coat of black would help with blocking the light as well.Anyway I'm picking up some black PLA plastic, and will repeat the experiment with that.  Hopefully that blocks the light completely.  If not I will try some black primer as well.  I also want to try scuffing the paint to see how well it sticks, and placing it over a heat lamp and measuring how well each wall and paint combo blocks heat.

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## reality_boy

I also finished printing my test containers.  The above test brings there value into question, but I will test them out as is and after painting them just to see if we can detect a benefit.  The test will need to be re-run using the final plastic and paint as well.

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## reality_boy

I got some black PLA, it blocks the light 100% even with only 2 perimeters.  I also tried painting my green PLA black and even with one coat of paint I was able to block out 100% of the light.  So basically use black as a base paint before painting the exterior of the bat box, or go with black PLA.


Interestingly enough both black pieces warped in the sun on a 100 degree day here in Tucson.  The test print I have outside in green PLA has not warped at all, I need to do some more investigation to see what temperature black PLA can handle.  Of course in 100 degree weather we want the house painted white, and I suspect that will survive even a 120 F degree day.


I'm planning on printing my thinnest test tube twice in black PLA, and paint one white.  I will put those two up with the green PLA to see if any will warp in the sun in a stronger circular configuration rather than as a flat sheet.


I also need to finish putting my temperature probes together.  I'm 90% done, but I have a bit of work left to do.  Just need to get off the couch and do it.  Then I can quantify how much the color of the PLA affects the interior temp relative to the air temp.

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## reality_boy

I got my sensors all wired up.  Well all but one, I managed to pop one of the digital temp sensors.  I will need to order another one.  Anyway I ran a test overnight with the sensors in a closed container and logged out the temperatures from all 7 digital sensors and the 4 analog sensors that I can hook up at the same time.  Here is the raw temperature readout.



I then analyzed the data and calculated a new scale and offset that would bring all the sensors into a closer line with the first digital sensor.  Here is the corrected data.



And finally I worked out the difference between the reference sensor and the rest.  The analog sensors lag behind the digital ones, probably because of larger thermal mass.  That is why the error grows so large during times of fast change (sunrise).  When the temperature is stable the error is within 0.2 degrees C.  It is even smaller for the digital sensors, I may leave the analog sensors off or use them where direct comparison is not important.

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## reality_boy

It has gotten up to 109 F here, very hot indeed!  However my test house is holding up well.  There are no signs of warping and there is only a slight discoloration on the plastic. 


 I did notice that at the hottest time of the day the metal pole is heating up hotter than ambient temperature and radiating heat into the house.  I suspect painting the pole white would help.  On the flip side in a cold environment painting the pole black probably helps get heat into the house, even on a wooden rocket box.  I did not measure this but it was quite warm to the touch, I estimate it was 8 degrees hotter than ambient.


I have my temp sensors all set up, and I made a mount for my test houses.  I just need to put the whole thing up and let it run.  One problem is that we are only days away from the monsoons kicking in so we now have heavy cloud cover and should be seeing quite a bit or rain for the next few weeks.  I really should have put this all up two weeks ago to catch the high point of summer heat...

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## reality_boy

Life got in the way of this project and I have not been able to post here for a while.  However I did manage to get some more work done on it.  In particular I finished up my experiments using different colors of PLA.  I have found that using black PLA and painting the outside white (or brown, as needed for your environment) provides the  greatest light blockage.  In addition I printed out some sample tubes using different color PLA and painted as needed.  Below is a shot of the samples after spending a month in Arizona summer heat (over 115 F at times). You can see that the black PLA deformed just a bit, while the rest remained stable.  I also checked by hand to see that the PLA was not softening up and it always felt solid to me.  I'm confident that this material will survive the summer in Arizona, and therefor would make a good material for any region.





I have been turning my attention to new ways to add texture to the interior of the bat house.  I experimented with a lattus pattern and was able to optimize this to print in a continuous loop with no infill.  However while it is very strong it feels very clunky to me.  Next I experimented with the 'fuzzy skin' option in Cura, that adds random offsets to your print to create a rough texture on the wall.  That produced a very interesting texture that while not quite rough enough to use without any sort of additional structure is still very promising.  I started to go down the path of learning to code macro scripts in Fusion 360 with the idea of being able to selectively apply a fuzzy skin type effect.

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## reality_boy

I have been struggling with serious under-extrusion on my Ender 3 for a while now.  I tried changing out the extruder, swapping hotends, new PTFE tubing, cleaning the hotend, new nozzle, and changing the print temperatures by a lot, but nothing seemed to work. I suspected the extruder was not producing enough force, but blindly swapping out parts was not giving good results.





Finally out of desperation I came up with a novel way to measure the force output of the extruder.  Basically I pulled the nozzle off the hotend, blocked up the z-axis so it could not move up, and extruded a length of fillament into a scale placed on the bed.  From there I can directly measure the extruder force.  I combined this test with the new dual drive extruder from Creality and was able to dial in the spring tension to triple the force over the default extruder.  That seems to have cleaned up my under extrusion for now.  I do think the extruder is only half the issue, the hot end also is poorly designed and tends to clog up.

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