pic: FRC 1923 chassis v2 Progress



How much do the grooves cut in the Colson wheels actually improve traction? Have you done any comparisons against standard Colson wheels or other COTS wheels (say W-tread Versa wheels)?

We actually set up the cut wheels on the comp bot and the regular wheels on our practice bot and the comp bot was able to easily push the other. We estimate it to be a 15% improvement with the pattern that we use, but unfortunately we weren’t able to get any concrete numbers since we were already strapped for time. It was well worth it considering it only took about 5 minutes on a bandsaw and was an easy freshmen job :slight_smile:

Any advice on keeping the cuts regular, if you just do them on a bandsaw?

I am clearly not on their team but a way that I think could work is to 3d print a template that goes around the wheel with slots in it that are then cut on the bandsaw.

Our team used colsons for the first time this year and are also interested in some quantitative differences between the slotted colsons and smooth ones.

Also, from the looks of things this chassis doesn’t seem to have much rigidity in terms of torsional stresses, did you experience any problems with this design in competition? Also the front and back plate look incredibly week in the center, do you strengthen the chassis with different sub-assembly’s or is it strong enough by itself? These assumption are form anecdotal data that I have experienced through my time in FRC and I am genuinely curious how this design can hold up.

Thanks, Michael

I don’t know about the safety aspect, but 228 cut their’s like this in 2012.

http://i.imgur.com/lKI3OhB.jpg

I also remember seeing a photo of the jig that 25 uses to cut their Beadlock wheels but can’t seem to find it.

As a person with an unnatural fear of chop saws and giant blades I don’t think you could get me to do that if you paid me.
That being said the results are very nice.

Exactly. We just set up the bandsaw fence at the correct distance then used a 3d printed jig that the wheel keys into.

Also, from the looks of things this chassis doesn’t seem to have much rigidity in terms of torsional stresses, did you experience any problems with this design in competition? Also the front and back plate look incredibly week in the center, do you strengthen the chassis with different sub-assembly’s or is it strong enough by itself? These assumption are form anecdotal data that I have experienced through my time in FRC and I am genuinely curious how this design can hold up.

This isn’t the entire chassis, since there are outer plates that key into the front and back plates (where you can see that little 1" cutout where the outer plates goes. I’ll post a picture when I can.

The front and back plates were kinda weak and we had some bending problems after a hard hit with 56 at DCMP. We unbolted the plate and bent it back with a hammer at comp and it was fine. For worlds we just reinforced the bumper with L-angle and it stiffened it up a lot (we have one piece bumpers). If that hadn’t worked we have holes on the front and back where we could rivet versa.

This looks great! What’s up with the omnis in the background? They seem to be powered, so follower wheel seems unlikely.

They are actually drop down omni wheels for getting out of pins. They are unpowered, since we have 8 wheel tank drive when we drop down we ride on them and thr front 4 wheels, so it isnt necessary for them to be powered. They worked pretty well for the 1 or 2 time someone was dumb enough to try and t-bone us :).

:eek:

No, no no no no no.

Rings on fingers when power tools are being used is a HUGE safety issue. Google image search ‘ring skinning finger’ if you don’t believe me. Rings can turn normally minor cuts into serious injuries.

The picture is poorly timed. The wheel is being indexed in the photo, and the saw is not on. Note how the blade isn’t spinning.

The most recent year we did this (2016), we used a face cutter on a manual mill with the wheel held tilted in a rotary indexer. Made for a cleaner, more precise cut.

GUS’s traction tests with freshly cut wheels were done before I was on the team, but the data collected showed a 25-30% increase in pulling force on carpet vs uncut wheels. It really is a big difference, though it does become less pronounced as the wheel wears in.

We didn’t cut the wheels this year, mostly due to time constraints. If the team does it again, the straight cut will probably be what we try next just because the diamond cut pattern is a bit of a hassle.

Ummmmmmm ouch?

And he’s about 1 second away from pulling the trigger on the saw and cutting a wheel…

I’d love to heard an argument that says it’s okay to be wearing a ring in a shop with power tools. Safety glasses go on; rings, jewelry, loose clothing, come off.

Was this a “head-to-head” pushing match? Or something more akin to a “T-Bone?” If the latter, which robot was T-boning and which was the recipient?

Basically, I’m curious how much these grooves help in terms of both longitudinal and lateral traction.

Separate from the wheel discussion… is that frame made out of 1/4" Aluminum?
How much does each of those side plates weight after you’ve pocketed them like that?

It looks quite beefy. :eek:

This was head to head. With cuts perpendicular to forward motion, lateral traction would not be improved, but that was not our objective. If you want improved lateral traction then you need diagonal cuts to make a diamond pattern. This can also be accomplished on a bandsaw rather than a mill if you dont want to spend so much time on it.

That being said, lateral traction isn’t great for a tank drive, because it just makes it easier for someone to lock you in a t-bone and may also increase wheel scrub. It would really only help in a swerve drive, IMO.

Yep. It came out to about 10 pounds for the 6 plates, which isnt too bad for our first custom CNC drivetrain. It’s also our first parallel plate drivetrain, so there are definitely a lot of improvements to be made.

I’d disagree with you there. I don’t think lateral traction is always bad. But for it to be good you need a lot of it. If you have no lateral traction it’s really hard to get t-boned because you just slide out of the way. If you have some lateral traction you can get locked in a moving pin or a t-bone with no way out. But if you have so much lateral traction that you can’t be pushed at all, no one can t-bone you.

TL;DR Lateral traction can be good in a tank drive. But you need a lot of it.

I guess that is true in some regard, but the way I see it it’s easier and faster to slip out of t-bones rather than just kinda sitting there. In any case, it definetely was not aligned with our robot’s design since we have drop down omnis and it was designed to be fast across the field. (9 ft/s Low 19 ft/s High)