Is there a way to set up an am14u5 without the drop center? I’m hoping to do it (with omnis on the corners of course) to eliminate some of the rocking we experienced while accelerating.
Plenty of teams make it a four wheel drive.
With a wide wheelbase and the power you can get from brushless motor drive, instead of CIMs, you don’t even need omni’s. Although, depending on your driving and wheels, without omni’s it can wear out your tread rapidly.
The caveat is that you need to test whatever solution you arrive at,
- at full robot weight
- on carpet
- and test turning while standing in place
1 Like
Sand down the center wheels a bit, or try different wheels. 6" is a nominal size; on a few 0"-drop, corner omni drivetrains I’ve hilariously seen that the center wheel doesn’t even touch the ground.
Are you sure the rocking is due to the center drop? Could it be due to violent acceleration? You can reduce the rocking by designing your robot so the center of gravity is lower and by ramping your power up and down. I saw swerve drive robots rocking when changing direction violently and they, by definition, do not have center drop.
1 Like
From my experience in FRC, I would say that the violent rocking can be caused by 3 things:
-
Too much of a dropped center wheel: to which I’d say the KOP drive base is not. I think it’s only like 1/8”-1/4” which is more than reasonable.
-
Too high of center of gravity: if your CG is too high, no matter how you drive, you’re going to rock as you accelerate. And since people tend to drive full speed in FRC, this would be worse.
-
Inexperienced drivers: by far the most common reason for this is having a driver that is inexperienced and changes directions way to fast. Essentially whipping the robot the direction they want. This is made more apparent this year than most because of hard collisions plus having to react to where balls are coming from/landing.
The reason for a west coast drive (6 wheel drop center) is to make sure that you’re always driving on 4 weeks rather than 6. This greatly increases you’re turning radius and in turn, your driving and maneuverability.
2 Likes
This is what we have done with our KOP drivetrains for the past 4 years. We found that we definitely didn’t have a low CG on any of our robots, so we compensated by “removing” the drop by shaving down the center wheels. This made the robot significantly less bouncy, and with omni wheels on one side, far more maneuverable.
The KOP drop distance is 1/4" if I remember it off the top of my head. We shave down the center Hi-Grip wheel until the rectangles are all gone, and the wheel is “smooth”. That is typically enough to eliminate most of the drop. Also, if you’re trying to add omnis to a corner, I’d advise against using the Andymark DuraOmni wheels for the job. They are wider than other omni wheels, which means that they can’t really be used as a drop-in replacement for the Hi-Grip wheels without modifying the spacers on the axle. We’ve had better results using the Vex Omni wheels as their form factor matches the Hi-Grip pretty well.
Of note: this definitely did not stop our robot from this season from bouncing a bit. All of that was caused by a combo of a decently high CG, and a driver that liked to quickly go from forward to reverse.
If you’d like pictures of our setup I’d be happy to snap a few for you. We love the KOP chassis, and this is pretty much the only change that we make to it every season.
Our robot rocked a lot while turning because of our high center of gravity. Our fix was taking out the center 6" wheel and replacing it with a 4" wheel. Basically the middle wheels only made contact with the bump in the middle of the field, but it greatly helped stability. However, the trade-off was we had a wider turning radius. We believe the plusses outweighed the minuses and had a much better performance in our second regional. At Champs, we did break 2 or 3 of the plastic pulleys and we had a gnarly wheel break that Andy of AndyMark himself took home to have his engineers look at. 
Does anyone have experience with an 8-wheel drop center (where the middle 2 are lower than the outer 2)? My team was considering doing this for a kitbot chassis mod to remove the rocking but still keep all traction wheels in the case that next year’s game has a metal bar as a bump (like 2020 or 2019). The 2 middle wheels being a drop center would give it a small wheel base but still prevent hard rocking in theory, but we’ve never built it before.
This is what my team did. The rocking still exists, but only while accelerating/decelerating, assuming your CG is in the right place, which ours probably wasn’t.