My team has recently started experimenting with Mecanum wheels. Driving straight and strafing is working as expected, but we are having issues with turning. The best way I can describe it is “jumpy”. Speeds are very inconsistent throughout the turn, shaking the robot and making it hard to control. Any ideas on how to solve it?
Did you have mecanum wheels attached per instructionsy?
They must look like X from the top. Then see this post for the drive code: Vexcode Mecanum Wheel Program
Yes, they are mounted that way.
Strafing works fine. Only turning does this.
Turning with mecanums is nothing special, you drive both wheels on the left side in one direction and then you drive right side wheels opposite.
Mecanums are known to be slow turners. Do you have all four wheels contacting the ground equally well?
They are all touching the ground equally. I’m moving them the same way I would any wheel to turn.
I’ve checked the rollers on all of them, some of them have a bit more friction but they all roll fine. Could that cause issues?
mecanum wheels having issues turning is one of the main downsides to them. compared to Omni wheels the rollers don’t freely spin.
here is a diagram on the force vectors of a mecanum drive. the rollers apply force diagonally and the forces equal out so that it can drive straight. so when you want to turn, the vectors are kinda weird. with omni wheels don’t have to worry about the weird vectors it takes to turn because rollers take care of it.
though this probably isn’t what you looking for, this is one of the reasons why omnis wheels in direct or chained configuration are the most popular drive.
This diagram has the wheels placed completely backward. The rollers need to make an X pattern at the center of the bot.
I don’t think it actually matters which way u do it. Some one might wanna fact check me tho
It does matter, if the wheels arent positioned correctly, then you cant strafe
Ours is bumpy, but I wanna think that it’s from the big rollers from mecanums, besides that does it turn fine?
This is more accurate diagram, because it clearly indicates “Top View” and force vectors are drawn for the case of turning:
There is more information in the linked topic, but TLDR is that Mecanum wheels will exert large forces inline with axles onto the wheel bearings. If you don’t have well lubricated teflon washers between wheels and bearings, then you are going to have a bumpy ride with a lot of power losses due to friction.
Also, Mecanum wheels only make sense for heavier robots, because of the way they convert robot weight into forward traction. Only use them if your gameplay calls for a slow heavy robot that needs to move sideways without much turning.
Mecanums behave like traction wheels when turning as they have to drag the rollers sideways across the tiles. This will create lots of friction and burn out your motors if you are not careful.
We discovered this last year with our 8 motor 1:1 turbo chassis which would burn out ~30s into matches due to the friction of turning.
You could possibly put omnis in between the mecanums on each side to take some of the load off the mecanums but if I were you I would just make an omni/bling chassis and don’t bother strafing. I have found that with enough driving practice, strafing is unnecessary anyway.
It doesn’t matter if the rollers are in an x or facing outwards. They just all have to be the same and you should be fine
On our holonomic drive we can turn easily, you might want to look into it @wewered
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