12" I3V Build

[Dustin B]

You want the wheels to spin but not wiggle or be loose on the rail.

By spin do you mean you start them turning and they will continue to spin on their own, or just that they turn with minimal force? Seems tricky to get them tight enough to not wobble and still spin freely enough to continue turning on their own once started.

[printbus]

What do I set "#define POWER_SUPPLY" to in the configuration.h file using this power supply?

The short answer is the POWER_SUPPLY definition likely won't make a difference to you. Unless you've added some power control mechanism onto the printer, that power supply and your printer will be on whenever there's AC on the power cord, and there's nothing firmware can do about it.

In at least older versions of Marlin... Firmware control of the power supply needs to start by having the printer electronics core always powered up, even when the printer power supply is off. The 12V supply on the printer is then used for just heaters, fans, and motors. ATX power supplies have a standby 5V output that often gets used for keeping power on the electronics. For non-ATX power supplies, you need to provide some other dedicated 5V source for the printer electronics. Power from USB is one way, at least until more 5V load like an ABL servo gets added. With that problem solved, then you have to identify an Arduino pin that can be allocated as the output used to control the power supply. This is done through the PS_ON_PIN definition in the pins.h file. If the pin definition is -1 (the default), there's no firmware control over the power supply and the POWER_SUPPLY definition isn't used.

When a pin has been allocated for the power control function, the POWER_SUPPLY value defines whether the control will be active low or active high. A POWER_SUPPLY value of 1 means a low logic level output will turn the power supply on, which is what you'd use if you're wanting to turn an ATX-type power supply on and off. A POWER_SUPPLY value of 2 means a high logic level will turn the power supply on, which would typically be used if you're using a relay to switch the AC power input to the power supply on and off. If using a relay, people are then often surprised to learn that they have to add a MOSFET or some other driver that can interface between the Arduino processor pin and the high current draw of the relay.

Only a few people bother with firmware control over the power supply. Some have wanted to turn the power supply on and off from the printer LCD panel. A menu item will appear for this once a pin is allocated for power control in the pins.h file. Some others have added remote print capability (typically with a Raspberry Pi) and want to be able to turn the printer on and off remotely as well.

Marlin has been undergoing some major overhaul over the last several months. I have no idea how much this changes in the newer versions.

[tsteever]

I too had the question of how tight the wheels should be when building. What I found to be a good tension was tight enough to take the wobble out, and then just a tad tighter to keep things in control. You still should be able to spin the wheels with minimal force. They will not spin freely at that point. There is a small window on spinning smoothly under control and binding. If there is wobble, they are too loose. If they spin freely when you flick them...too loose.

[Dustin B]

K, that's along the lines of what I was currently thinking. I think I have them slightly too tight right now. They currently don't take constant force to turn. It goes up and down slightly. I think I want to back it off until they require consistent force to turn rather than jerk a bit through turning as they currently are. I might end up talking to my father in law (designs and sells hydraulic systems) and see what he can get for replacement bearings that might work better.

Thanks for the great explanation printbus. That helped a lot.

[printbus]

I'd argue that something is wrong if tightening the wheel mounting bolt changes how freely the wheel spins. The only way it should make a difference is if the nut is backed off enough that the inner race isn't held tight and it's spinning on the bolt. IMO that's way too loose; I prefer for the bolt to tighten solidly on the inner races. That said, there's a few things to note.

These are greased bearings, which do require some run time to loosen up.

The OD of the inner races are pretty small, and don't clear the rotating part of the bearing by much. Make sure the nut, bolt head, spacer, or anything else mating with the inner race ONLY touches the inner race. You don't want anything rubbing on the rotating part of the bearing beyond the inner race. Add some shims if there's a doubt.

Did your wheels come preassembed? It might be worth taking one apart to make sure there's a proper shim washer installed between the two bearings. The problem here is that the wheels are wider than the two bearings are, and the shim washer is required to make up the difference between the two bearings. If there's no shim washer installed, the bearings aren't fully seated in the wheels, or the shim washer isn't thick enough, tightening the wheel mounting bolt puts axial pressure on the inner and outer parts of the bearing, which will cause binding in the bearings. Note that openBuildsPartsStore has precision washers for this - http://openbuildspartstore.com/precision-shim-10x5x1mm/

[Dustin B]

Ah, now I get it. They came assembled and I never took one a part. There is definitely a washer between the bearings but it must not be thick enough compared to the ridge in the middle of the wheel (I didn't know there was a ridge there, but makes complete sense it has to be there after I think about it, how else would the wheel be captured). So ya the ridge being thicker than the washer between the bearings means tightening down will pull the inner races closer together than the ridge in the wheel allows the out races to come together causing all the issues. Someone else mentioned using the 5mm washers supplied to replace the washers between the bearings in the wheels. I'll see what's up with mine tonight. I might have some shims from my RC stuff that will allow me to fine tune it, if not I'll be doing some looking around tomorrow after work.

[Dustin B]

And I just realized that my Traxxas Slash RC uses 5x8x0.5 teflon washers in the wheel hubs. So maybe just adding one of those to the washer that's there will solve my issues. If not, 2 or 3 of the teflon ones likely will. A package will be a couple bucks at any place that carries Traxxas parts.

[Dustin B]

1/8 scale nitro clutch bell shims are 5mm inner too. Easily found down to 0.1mm thickness too.

[Dustin B]

So the bearings in the delrin wheel measure 11mm. The bearings by themselves measure 10mm. The washer they came with is 0.8mm. Add a 0.2mm clutch bell shim, tighten down nice and firm and it turns completely smooth, no binding at all. Two teflon washer from the slash are a little thicker than 1mm and seem to compress. There was no binding but not as smooth as the metal clutch bell shim. The precision 1mm washers recommended above are highly recommended. Colin should be sending these kits out with those. I'm not going to wait for them as I can get enough 0.2mm shims from a local hobby shop that's minutes from my house.

[Dustin B]

So didn't work out that 0.2mm shims worked every time, but with enough playing around with combinations of shims I got all the wheels turning completely smooth after being really torqued down tight with no side to side play. I highly recommend picking up some shims, the extra effort is well worth it (5x7x0.1 : 5x7x0.2 : assorted set) Should finish up most of the mechanical assembly this afternoon and later tonight, then it's on to assembling the extruder/hotend and wiring it.

The relay had solder on both sides of the board and I was unable to get it cleanly removed. Ended up cutting it off and then getting the pins left behind out. Little work with a reamer and a 14 gauge sold copper wire just fit in the hole. Got that soldered up and continuity still checks out.