Motion Magic with Mecanum Wheels?

So we’re using mecanum wheels this year, and we just got a set of new Falcon 500 motors to play around with. We were wondering how we would be able to make use of all of the aspects of mecanum wheels with Motion Magic using the TalonFXs built into the Falcons.

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I think you are being pretty biased here. We have been using mecanum wheels for a long time. With a great driver, they can guarantee you very small cycle times and great opportunity to rotate around defenses and keep on going. We have even won events with our beloved mecanum wheels. So you can be very competitive with mecanum wheels and a good driver. Switching to WCD for our team would be a total failure right now. I do not know why there is so much hate against mecanums but they are great for teams who are not ready for swerve but have an awesome driver who can handle defense with mecanum.

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I would actually agree here. The reason I don’t recommend mecanum nowadays doesn’t really have to do with traction as much as it has to do with driver skill. You have to have a very very skilled driver in order to pull off mecanum. If you do though, you can really reap the rewards. There’s nothing like seeing a skilled driver juke a defense bot with a mecanum drivetrain, there are just few that can.

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Thanks for the completely unnecessary post in a thread by someone asking for help.

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As far as hot takes go, this is a really bad one, for several reasons.

  1. It’s false. If they’re going mecanum anyway, the other advantages of the Falcon (weight, efficiency, simpler wiring, integrated encoder) are all things that will make their mecanum drive better than it otherwise would be.

  2. It’s utterly unhelpful. okthx asked a question, and you had no intention of answering it.

  3. It’s mean-spirited. The only purpose of your reply was to mock their design decision.

It would be better to say nothing at all than to be a jerk just to be a jerk.

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Which button do I click for the opposite of a like?

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That’s quite irrelevant to okthx’s question. They didn’t ask, “What do you think of our decision to use mecanum wheels?” or “What are the pros and cons of using mecanum drive vs. other drive systems?” or anything even kind of like those questions.

They asked a technical question about to get started using Motion Magic with TalonFXs on their mecanum drive.

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On the topic of the thread - I haven’t had experience with a mecanum since 2008, but I would assume that apart from motion magic profiles using straight up tank drive, you would need to create a function that accounts for the “slip” of the wheel when strafing when using encoder feedback in order to follow a path correctly.

You can still at least just use the mecanum in tank drive with Motion Magic to ensure your wheel speeds are synced up for more smooth movement on the field.

A large part of how well this goes will be up to the variable of wheel contact. By this I mean if your frame isn’t allowing consistent contact with the carpet on all 4 wheels you might not get the exact movement you want. This is why in the past teams with mecanums have run them in small suspension systems. (or a less rigid frame, but that’s not really a great solution)

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If you wanted to use the motion magic capabilities of the falcons for path finding in auto, I would honestly recommend taking a look at wpilibs trajectory generator and their example mecanum project. What they do is PID control their heading separately from their x,y global coordinates.

I know this isn’t using motion magic, but you would still use the talons velocity control mode to tell the wheels what speed to move at.

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I hid the pointlessly divisive / off topic / noncontributing post, but kept the responses as there was some good information somewhat relevant in those posts. Let’s move on.

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I sort of agree that this isn’t a field well suited for mecanum. But that is not the question. The extra power that the Falcon has probably isn’t needed. But the compactness and lighter weight is certainly a plus. If we ever use mecanum again, I know what motors I am using. :slight_smile: You probably want to incorporate a navex in your control strategy. Wheel speed is not necessarily speed over the ground so the wheel encoders are less than useful. You are also control each wheel independently. I am not sure of the solution, but the problem is very interesting. Motion control has probably gotten to the point where is solvable. Good luck with it.

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As other said, due to wheel slip and roller angle, mecanum wheel speed isn’t going to be the speed of your bot so you can’t really used motion magic. Other options would be to use a set of omni wheels with attach encoders to track ground speed/motion and/or a combination of gyros/IMU, distance sensor(s) and camera(s) to determine location.

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We ran octocanum for several years, and had a blast with it. My experience with that drive train leads directly to this assessment:

  1. It’s pretty easy to program a robot with mecanum wheels to drive like a (holonomic) first person shooter, with one joystick for movement and another for facing, using the WLILib resources. We could, at the time, give any kid a PS3 controller, tell them it was a Fallout or Call of Duty robot, and watch them drive really well with basically no practice, and without using any of the encoders on the drive train. The notion that mecanum is particularly hard to drive is nonsense—your average gamer will find it much easier than tank drive.

  2. Autonomous can be pretty easy if you ignore the holonomic aspect and just treat the wheels as tank drive. It’s not ideal, but it might be enough for whatever your routine is, and is likely compatible with Motion Magic.

[For the peanut gallery, please note that I’m deliberately ignoring whether or not mecanum is the best choice (or even a “viable” choice Per CD zeitgeist). This is not an invitation to start that argument.]

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Thanks for the support, everyone! It’s alright to share opinions but I was wondering if anyone had any ideas for holonomic drive trains using motion magic? It’s kind of the point of the thread :slight_smile:

Thank you so much for your support but I really wanted to try to do holonomic motion magic :frowning:

You are missing the point of what everyone is trying to tell you. If you go to the motion magic docs it tells you that all it does is automatically create a motion profile and move your motor to a certain encoder count. This would let you move A WHEEL to a certain position. But you then miss out on the inverse kinematics portion of mecanum. You need a way to calculate, given your “joystick command” what each motor VELOCITY should be. If you wanted to manually go ahead and calculate that beforehand and have each wheel move to a position that’s fine. But honestly that seems way more painful and tedious then doing what others have recommended in this thread

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Alright then, thanks for the help!

I suggest you begin here with a classic Ether paper on the kinematics of mecanum. With a bit of skull work, this will tell you how to convert your desired motion profile for the robot into a motion profile for each wheel. That said, expect to have to iterate a good bit before you really end up where you desire.

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