Last year we had great success with the KOP chassis. This year we are getting a lot of shaking as we turn. We are in the longer configuration this year, but it’s still more shaking than I would expect. Strangely, it seems to be worse when our COG is behind the center wheels (when we lower our intake, we shift to the front 4 wheels and it seems a bit better).
I’m suspicious that it has something to do with us not having any lateral cross members due to our intake/indexing. Are we experiencing torsion? Has anyone else experienced this with the KOP chassis?
Edit: we were originally shaking with the pneumatic upgrade kit, so we switched to the 6in higrips. It got better, but still pretty shaky.
What type of surface are you having this problem on? What if you try on a smooth surface i.e. not carpet? What happens if you put a layer of duct tape on the treads of your front and rear wheels?
Have you ruled out voltage issues? You may be browning out. Make sure your batteries are charged and your electrical connections are all solid. Also verify there are no mechanical hiccups in the drivetrain that might be causing excess current draw. If none of those things are the issue, you might want to try adding cross member support.
Edit: also, are you using the same batteries you had success with last year? If you’re using new batteries or old worn out ones they might be the issue. If you have a battery beak check the internal resistance of the batteries. I want to say it should be between .009 and .015 Ohms but I could be wrong. Last year all of the brand new batteries we had bought for the season were measuring at about 4 times what the internal resistance should’ve been and that caused severe brownout problems and stuttering like you describe.
We tried the duct tape when we were running the pneumatic wheels. It helped, but not enough. We also tried sanding down 2 wheels to increase the drop. Still problems. Thats when we switched back to the original KOP wheels, noticed an improvement, but still not like last year.
It’s more of a shaking, not stuttering, so I dont think its voltage, but I will look into that. I will also try running on a smoother surface than carpet, and see what happens. Perhaps getting some slo-mo video.
That’s a really strange issue. Is it possible a misplaced spacer is causing belt misalignment? I haven’t fully assembled a KOP chassis since around the 2016 offseason so I don’t even know if that could be in the ballpark or not. I wish you luck in working this out!
I agree that this is unusual. With solid wheels, I haven’t seen this with the AM14U series chassis. Then again, all of the long robots I’ve built or helped build since 2015 have had some cross bracing. I don’t think any have had the long churros, but all have had some angle/channel/tube that spans the chassis to support manipulators above. Especially if you have an opening in your chassis, get the cross frame plate or a piece of extrusion to provide some stiffness. 3946 did not properly back up the gap at chassis altitude in the rookie (2012 Rebound Rumble) chassis and had this issue, so yes, that is definitely something to check.
After seeing some video of your team’s robot on social media, I think your suspicions about torsional flex while turning are correct. Too much flex causes opposite corners of the chassis to touch, creating the ‘rodeo’ effect you’re seeing. The pneumatic wheels hide a lot of it, but I see some flex on turning when lining up in the video I saw. The back and forth rock has much more to do with the height off the floor your COG is.
You might be able to offload some of the torsional structure work into your bumpers. We did this in 2018 with a welded 2x1 frame to stiffen up the chassis, as we had similar rodeo issues too. Worked great, YMMV.
Omnis on one end might help as a band aid, but I’d be a little concerned with plastic omni wheels on the steel berms this year.
Thanks for the input Nick. I appreciate the professional opinion.
By “offloading the work to bumpers,” do you mean just increasing the strength of connections and rigidity of the bumpers?
Also, today we realized that one of our SparkMax’s had accidentally had a way too low current limit set (5A). Fixing this has helped quite a bit. Those who suggested brownouts and battery issues were not far from the truth.
We do still “rodeo”, but not as quickly. We will work to improve torsional rigidity. Maybe we can even return back to pneumatic wheels.
Could you post a video of the chassis shaking please?
We are having a similar problem on our custom chassis that only went away when we switched to omnis on all four corners, which we’d rather not do. Maybe we can use some of the solutions presented by others in this thread.
My team had this issue a few years back with the pneumatic wheel upgrade, with us we needed to beef up our gearbox. The standard gears on our max weight robot did not work.
Also make sure you moved your center wheels lower then with a standard chassis, this may be your issue.
If you do return to pneumatic wheels, fully pressurizing the middle wheels and somewhat underinflating the corner wheels helps reduce scrub and rodeo by effectivly increasing drop center.
We tried many solutions in this order to get the pneumatic wheels to work
Duct tape on the outer wheels
Over inflating center wheel and under inflating outer wheels
Sanding down the tread on the outer wheels, also reducing the diameter
Putting duct tape back on the outer wheels
After all this we still had the rodeo problems and ended up making the switch. Then that brings us to wear we are currently and all the problems @suPURDUEperAndy mentioned. Here is what it still did after these changes.
This effect was exaggerated when spinning in place, and we only seemed to turn well while driving. I’m sure a lot of it accounts to the high COG we might have.
How certain are you that the chassis center drop is the right way up? I see you’ve made changes to try to bring make it larger, so you’re aware of it, but just going to ask the dumb question anyway…
With the AM14U series kit chassis, it’s just about impossible to invert the drop center, because the gearbox mount is integral with the inside sheets, so the gearbox would then extend too far below the axle to drive.
Just to be clear, that gif was from before we discovered the current limiting mistake on a motor controller. We haven’t gone back to using pneumatics since that fix, as we are still trying to reduce some minimal rodeo and dont want confounding variables.
No good places for cross members, but we might try adding a bit of bellypan. We’ll keep everyone updated, but are decently drivable now!
Are you able to add a second panel on the top surface of the chassis rails to form a box with the side chassis rails and the bottom? That should further increase the rigidity of the frame.
