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  1. #1

    Bat House Project

    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.

    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.

    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.
    Last edited by reality_boy; 05-21-2019 at 12:08 AM.

  2. #2
    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.5-18-2019It'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.
    Last edited by reality_boy; 05-21-2019 at 12:13 AM.

  3. #3
    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.

    Last edited by reality_boy; 05-20-2019 at 11:41 PM.

  4. #4
    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.

    Last edited by reality_boy; 05-20-2019 at 11:39 PM.

  5. #5
    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.

  6. #6
    Super Moderator curious aardvark's Avatar
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    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.
    Last edited by curious aardvark; 05-20-2019 at 09:21 AM.

  7. #7
    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.
    Last edited by reality_boy; 05-21-2019 at 12:59 AM.

  8. #8
    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.

  9. #9
    Super Moderator curious aardvark's Avatar
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    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.

  10. #10
    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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