How would you feel about putting one of AndyMark’s plastic 42-tooth kitbot HTD pulleys on a Colson 3’’ wheel, given that the flange diameter of the pulley is 2.9’’, which leaves only .1’’ of clearance between that and the ground?
I think it’d probably be fine, but would like to get some more thoughts on it. It’d be very convenient, as the AndyMark pulleys are cheap, have the correct bolt-circle for the Colson dead-axle hubs, and we already have a bunch lying around.
I believe you only have .05" of clearance. But if it clears, it clears. I have never used Colsons. Would a Colson compress .05" from the weight of the robot? How far into the carpet would the wheels sink in? How far below that lip does the belt sit on the AM pulley?If I had the parts sitting around, I would just build it and try it out.
Your pulley will probably will get damaged from ground debris.
We ran 3.5" colson wheels this year with a west coast drive. with the 1" by 2" box tubing frame, we had 0.5" of ground clearance. For us this was right at the threshold of getting hung on debris or the steel plates under the carpet at the pyramid corners. So if there was a wad of tape or a piece of broken #35 chain at the pyramid corner, we usually would get hung up on it.
So if you want to run 3" wheels, you need this on some low profile pillow block or something to create space for the frame. Also, you will have the pulley touching objects on the ground. I think you will risk unnecessary wear and tear on you pulley and belt from running over debris. Lastly, I think your wheel will compress the carpet a bit so the flange of the pulley will touch the carpet. Colson wheels wear a bit to, so the gap will be reduced. So you may find your self your supporting the robot with your pulley more than your wheel.
Going up to and 3.5" to 4" wheel should solve most of these issues. Personally, I would stick with 4" but there are several teams that run 3.5" wheels effectively.
We originally started with 3" colsons on a typical WCD. On carpet, we were dragging, and we couldn’t make it over the “bump” around the pyramid, so we upped it to some custom ~3.4" wheels. For an upcoming parade, we’ll be running 4" Colson wheels.
It’s worth noting that this would be for a traction wheel in a butterfly drive assembly, and thus I’m not too worried about wear on the belts/pulley as we’d be on these wheels a small minority of total driving time.
Well sounds like a butter fly drive set up would be perfect for 3.5" wheels. The extra .25" clearance over the pulley OD will help keep the pulley and belt safe and since the wheels are capture in a module, you could rise the frame a bit to give it a good gap over the the carpet.
You still don’t want the belt the scrape the ground even if its not common. the 3" wheel has no margin for that. Do you need a smaller wheel for more gear reduction?
3.5’’ wheels aren’t compatible with the dead-axle Colson hubs from WCP. 4’’ could work, but are bigger than I’d like (smaller module = less weight) and I’d have to change our planned gearing.
That said, 4’’ might end up being the way to go. Our initial design had us making our own ~2.8’’ wheels our of delrin and plaction tread with custom pulleys out of pulley stock, and while we’re going to be building that initially I’m trying to move later iterations towards as many COTS parts as possible (I’d have designed for Colsons originally, but was not aware of the COTS hubs for them and thought we’d have to turn our own).
As it stands, it seems that with 4’’ Colsons, everything except the side-plates of the modules (which we can make ourselves to high precision) will be COTS.
I think i would actually work. I don’t have my CAD with right now so don’t quote me on this, but our drive used our own custom press hubs for the 3.5" Colson wheels. Looking at WCP, the OD for the dead axel hub press is 1.2" OD which is close to what we used, I think we did 1.1" because the wheel begins to taper at 1.2" so we made is smaller for weight, aesthetics and using the wider part of the hub as a stop. So if you machine the wheel to 1.2" all you need is a washer or don’t press the hub all the way into the wheel. There should be enough material for it to work even if it is tapered at that section of the wheel.
Assuming 5mm pitch (GT2 or HTD), that’s a 28T pulley. 1.754" PD, 1.875"
Flange diameter (per sdp-si spec). Just posting this so people have a data point to compare to.
I’m really surprised by a 1-7/8" flange on a 2" wheel. That flange is DEFINITELY touching carpet from my experience, but since the traction portion of an octonum is so rarely used I can see that not being a big issue (especially if metal flanged pulleys are used).
For future reference, I bet the c-c is small enough that if there is a flange on the pinion pulley and the belt is reasonably tight no flange is required on the traction wheel pulley.
Honestly, I’m not seeing the ground clearance issue with the belt; if that were a problem, you wouldn’t have people running VexPro 72t gears direct-mounted to 4’’ omni-wheels, which I have seen work with no problems. Besides, if anything contacts, it’ll be the flange, and given the near-redundancy of a flange in this setup anyway it’s not exactly clear that there are any real wear issues with that.
Also, while it’s nice to keep the traction wheel in a butterfly drive small, 3’’ isn’t exactly “much too big” - I’ve seen teams run butterflies with two 4’’ wheels which worked fine and weren’t particularly heavy.
A pair of 1.5" diameter, 6" stroke. Ummm…not sure if Parker or Bimba. We’ve got the setup down to ~50 lbs for the drive train including electronics and compressor, and absolutely as cheap as we can possibly make it. (Well under 50% the cost of our first go.)
