Colson Wheel and AndyMark HTD Pulley

[Oblarg]

Just want to get some thoughts on something;

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.

[Redo91]

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.

[Mark Sheridan]

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.

[sanddrag]

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.

[Oblarg]

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.

[Mark Sheridan]

Originally Posted by Oblarg

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?

[Oblarg]

Originally Posted by Mark Sheridan

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.

[Mark Sheridan]

Originally Posted by Oblarg

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.

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.

[pfreivald]

Our octocanum drive last year used 2" Colson wheels with aluminum 1 3/4" pulleys and belts, and we had no problems...

Not to say that we *couldn't* have problems on a different drive surface, just that we didn't.

[AdamHeard]

Originally Posted by pfreivald

Our octocanum drive last year used 2" Colson wheels with aluminum 1 3/4" pulleys and belts, and we had no problems...

Not to say that we *couldn't* have problems on a different drive surface, just that we didn't.

What do you mean by 1 3/4" pulley?

What was the pitch and toothcount? flange diameter?

[BBray_T1296]

Originally Posted by Mark Sheridan

you may find your self your supporting the robot with your pulley more than your wheel.

Then you have yourself tank treads!

[pfreivald]

Originally Posted by AdamHeard

What do you mean by 1 3/4" pulley?

What was the pitch and toothcount? flange diameter?

I meant a 1-3/4" pulley on a 2" wheel. The flange came to 1-7/8". Couldn't tell you the tooth count off the top of my head.

[Mark Sheridan]

Originally Posted by pfreivald

I meant a 1-3/4" pulley on a 2" wheel. The flange came to 1-7/8". Couldn't tell you the tooth count off the top of my head.

If that works, then a 3" wheel could work too especially if its a butterfly drive.

[AdamHeard]

Originally Posted by pfreivald

I meant a 1-3/4" pulley on a 2" wheel. The flange came to 1-7/8". Couldn't tell you the tooth count off the top of my head.

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.

Originally Posted by Mark Sheridan

If that works, then a 3" wheel could work too especially if its a butterfly drive.

3" is MUCH too big for a butterfly

[Mark Sheridan]

Originally Posted by AdamHeard

3" is MUCH too big for a butterfly

Did your team run a butterfly drive on one of your summer robots? Do you mind sharing your specs?