Teams in Israel have to wait until tomorrow to get their Kit of Parts, so I was interesting in hearing from teams that have, how are the HiGrip Wheels included in the KoP? Are they a legitimate alternative to traction wheels?
First look (no testing), says yes (for traction purposes).
They have ~1/8" deep rectangles embossed into them that take half the width of the wheel and alternate.
However, we don’t plan on using them because we doubt the strength of the spokes.
Edit: according to Andymark, they don’t have a better CoF than roughtop or wedgetop tread.
They look sweet. The good old drag across the carpet test showed they were quite grippy. But we most likely wont use them because they are only 6in diameter wheels making getting over a 4 in bump quite iffy. But I like them very much and hope they will make other sizes soon.
One of our mentors thought they looked like LEGO wheels.
I agree with Jacob; maybe we’ll wait for next year.
The HiGrip wheels seem nice. They’re lighter than the 6" plaction wheels on AM by 38% (.5lb each as opposed to .81lb).
A google search for TPU Rubber wheels went nowhere. Is there any indication that it will be offered in larger sizes? Smaller sizes?
The size of the wheel does not necessarily keep you from going over the bump. Just build a slippery ramp in your chassis in front of your wheel so you slide up and over. That being said, we are using 8 inch wheels.
We played with them a bit. I’m not certain that they’ll see use on 2815’s robot this year (in COTS or modified form), but they do look like an upgrade over prior designs with the divider as it is.
Teams I’ve been on have used variations on modern kit wheels for several years with no issue on the spokes. If we chose another wheel, it wouldn’t be on that.
Our Team was in two Regionals one at Medera, CA, Central Valley Regional and the last in San Jose, Ca, Silicon Valley Regional. Our 6’ HiGrip KOP Wheel worked great in the first regional. While we at the second Regional the Janksters, Team 1976 reported that they had a wheel failure and ask us to borrow a wheel. However, we did not have a spare wheel. We took a look at our wheels and fould a broken spoke on a rear wheel. Upon further investigation we noticed the wheel was split across the tread. We did not have enough time to change this wheel until the next match. Thank you 2144 for giving us a wheel. The Janksters broke two wheels at SVR. I will not use these wheels next year.
Have you contacted AndyMark? Inform them of the problem (pictures should help), and hold off on declarations of not using the wheels next year until AM has had a chance to look into why they are failing. You’re not the only team with these failures, as you know. AndyMark likes feedback, and likes to fix problems with their products promptly.
And two competitions on a single set–back when I was a student on a team, we could go through two sets of AM and McMaster wheels in an event, minimum one set. We’d usually take some time on practice day to change out from the previous event, wear through the wheels by the end of elims if not before, go to the next event, repeat. (We’d also buy quite a few spares.) You guys put a ton of drive time on those wheels, so I’m not terribly surprised that they would have broken eventually–fatigue plus impact will take down quite a few things, let alone a wheel.
Thanks for the quick response. Like I said two teams at SVR had problems with these wheels. Our team 2643 and 1976. Team 1976 was paired with 254 and 118 to win SVR. But they broke two wheels. Yes, I am waiting to hear from Andy Mark. These wheels seem to be pretty grippy. But I think the drive train can over power the cross section.
It was 1967 that had suffered the wheel failures, the wheels survived CVR without a problem, the students then added an extra pair of cims (4 total with the kit bot transmission), and added a little more defensive components that moved the CG up slightly. This caused a more hoppy robot, which also got into a few serious pushing matches. We actually broke 3 wheels throughout the event, one being last year’s high grip that another team had loaned us. I don’t think the wheels were bad, just didn’t survive the abuse we were putting it through…
Here is an example…
Thanks to the 3-4 teams that loaned us wheels (the team didn’t think the wheels would break and didn’t pack any extras), including 692, 3933, 3482?, and others!
We broke 5 at the Sacramento, Andy Mark replaced them. Had no problem at CVR. We did get hit pretty hard when a nameless team ram us as we were tipping over. They have some bad reviews on the AM site.
During the past two weeks, 3 teams have contacted us regarding some durability problems with these wheels. I have recently talked to one team today who had broken wheels at SVR. This is the same wheel that was used in 2012, with the same HiGrip tread. The only difference is that the tread is colored white this year. In 2012, we did not receive complaints regarding the durability of these wheels.
From my experience at regionals this year, there is much higher speed being reached by the robots in this open playing field. Robots are hitting each other at high speed within the field, and there are not field barriers (steps, etc.) present to slow them down. During these collisions, the wheel is getting a high side load. Combine this side load with a high tractive force of the wheel, and we have high stress on the wheel bore, spokes, and rim.
We have a short term and a long term plan to fix this wheel.
- Short term: We suggest putting some 2-part epoxy in the area immediately outside of the bearing bore rim, in the pockets next to the screw holes. Putting a filler material in this area will help decrease the chance that the bore will break down.
- Long term: We will improve the mold this summer for this wheel, beefing up the bore area, the rim, and the spokes. We may even try some other plastic co-polymers to see what has higher strength and higher impact resistance. Our current material is polycarbonate.
FYI, here’s a picture of the wheels team 1967 broke at SVR.
The one on the right broke in match 28 and prevented us from driving. The middle one is not fully broken yet but has cracks on the spokes where they meet the outer rim so we replaced it. The one on the left broke in the elimination matches and we could still drive because every spoke completely broke so we were driving with 5 wheels.
Overall, we’re very happy with the belt drive system, but this year we’re able to drive much more aggressively than in the past due to the field and due to our robot having a much lower CG. So, while I think we’ve never seen anything like this (and we’ve used these wheels in the past), I also think we’re abusing the wheels much more than in past years.
We’re definitely considering metal wheels for next year already!
And, we’re ordering spares for the championships (which we’re VERY excited to be able to attend)!
Oops - I hadn’t realized Alvin had already posted a picture. Sorry for the repeat.
Does anyone know what the Coefficient of Friction for the HiGrip Wheel is normal to the direction of travel? I know AnyMark has 0.95-1 listed as the coefficient of friction for the wheels; however, I don’t know if that is for the direction of travel exclusively or both.
Or is there an effective coefficient of friction due to the “biting” in the carpet normal to the direction of travel? Essentially in an equation what do I use for Mu_x (direction of travel) and Mu_y (normal to direction of travel)?
A bit off topic from what the OP has started
An interesting side note. Team 225 had a KOP 6-wheel chassis, with 4 inch wheels to help keep our center of balance lower. However, we discovered at our first competition that the sharp edges of the wheels mean they bite into the carpet when pushed sideways, which contributed to our tipping in a couple matches. Roughtop wheels move sideways more easily, which helped us stay up.
5545, a rookie at our first event also had an issue with them. They were a defensive robot that got slammed around a lot, and they managed to shatter the center of the wheel so that the bearing had nothing to sit in, and they flopped around the axles.
I am very surprised to see so many complaints with the HiGrip wheels. Team 3958 really loved using them this year. We had them in a 4wd with a wide (32x24) robot. Turning was very easy because of our short wheel base, and our robot was really good at pushing and resisting getting pushed. The first half of this video is a good example.
We can’t really speak for durability. We had absolutely no driver practice during the build season, and we missed half of our matches during our first of two competitions. We also did not make it into eliminations for our first competition. And because we were a floor pickup robot, we were not subject to lots of crossing the field at full speed. So we were not putting the wear on our wheels that most teams were.