Mecanum Wheel questions

This is our first time using mecanum wheels and the way we built the chassis the wheels are off set about an inch from each other (the back ones are a total 2.5 inches closer that the front ones) we were wondering if there would be a performance decrease as a result of this offset spacing.

closer to what?
performance decrease during what activity?

You shouldn’t notice any difference when driving forwards, but there are a couple of other things that might come up:

  • When trying to travel straight but not forwards, your drive will sometimes generate an imbalanced torque instead of simply translating. For example, when travelling diagonally two diagonally opposite wheels do not rotate, while the other two rotate at full speed. On your robot these two wheels are at different distances from the centre of mass. Since both wheels exert the same force, they will generate different amounts of torque. This might cause unexpected rotation.

  • When turning, the front wheels will need to trace a larger arc than the back ones. This will force the motors driving them to run at different speeds.

It sounds like your wheels are probably offset by a small enough amount not to matter, especially with regard to the second point. As for the first, holonomic drives rarely have their centre of mass perfectly centred between their wheels anyway and if you notice a problem it should be correctable with driver compensation or code.

Of course, the best way to know whether there will be a problem is just to test the robot. Good luck :slight_smile:

we tested it, it dose not seem to make a huge difference but more torque seems to be required to strafe, so were working out those little bugs

having your wheels offset like your talking about should not make any difference at all. as long as your wheels run at the same rate you will be alight.

For the reasons that Vex Mundi pointed out, there is a theoretical difference. The wheels placed farther away from the center of turning have a longer “moment arm” that they need to push on to tun the robot.

Awesome :slight_smile:

We’ve noticed that the mecanum wheels strafe a lot slower than they drive forwards as well. The main reason, I think, is that strafing they have to overcome roller friction wheras travelling forwards they don’t. If a team you know also has mecanum wheels, comparing to them might tell you whether the difference is something you’ve done or the wheels themselves.

Yeah we noticed that the strafing is a lot slower and takes a lot of torque, so we usually don’t do it to avoid tripping the breakers on our drive, however the mecanums do allow for turning directly on the base without the all-omni setup that allows a robot to be easily pushed.