Re: 2015: Year of the Mecanum
 

Absolutely. It's not terribly complicated either. After all your meCHanum motor set speeds are calculated, mix in a component from the gyro useing a PID. Only do this when the driver is using the strafe functions. Disable it when he is turning.

Easy Peasy.

Re: 2015: Year of the Mecanum
 

We did mecanums for logo motion with a flat-floor and they worked fine, but for rebound rumble, trying to climb the 'bridge' in the middle they were really problematic, even with suspension.

Remember that with mecanums, the left wheel is always pushing against the right wheel to make it go straight. So if one wheel gets off of the ground, your robot turns by itself.

Methinks that with a stack of totes on a forklift, the back-two wheels will be bumping off the ground regularly, and if you try to cross a platform at any kind of angle other than 90, you'll lift a wheel.

Last year I saw four wheel mecanums in the IAM14U frame, and maybe more often in 'butterfly' and 'octanum' drives. That that was acompletely flat floor. My recommendation is that if your heart is set on mecanums, use a butterfly or octo so you can put regular wheels on the floor when you need to. Also, note, the new frames are much more stiff than the old channel sections ones, so you'll need to do Something to keep those wheels on the ground. Something like independent suspension.

Mecanums work really well with Banebot transmissions too.

Last thing. Mecanums running over a noodle a problem? I think so . You tell me?

Re: 2015: Year of the Mecanum
 

My interpretation of the above is:

1) calculate the 4 motor speeds using the X and Y translation commands

2) calculate the motor speeds for rotation using the output from a PID

3) add the the corresponding speeds from (1) and (2).

Wouldn't it be more straightforward to compute the 4 motors speeds just once directly from the X, Y, and rotation commands?


BTW, what's the significance of the CH in caps?

Re: 2015: Year of the Mecanum
 

What I was thinking was a way of dealing with imperfect results from mecanum, i.e., if simply using WPILib's mecanum drive function results in the robot turning when it's supposed to be straight strafing. When the driver is trying not to rotate (the "rotate" value would be zero), store the current gyro heading. Then have a PID controller that tries to maintain that gyro heading, by setting the "rotate" argument for the function. So the PID would find the value that counteracts any undesired rotation caused by mechanical issues.

Re: 2015: Year of the Mecanum
 

This is exactly what we did in the past for our mecanum drive, and it worked wonderfully. We didn't have to obsess nearly as much about perfect weight distribution.

Re: 2015: Year of the Mecanum
 

See attachment

Re: 2015: Year of the Mecanum
 

Nice chart--That's exactly what I was trying to describe!

Re: 2015: Year of the Mecanum
 

We've used mechanums for the last couple of years with success. Last year we made our own gearboxes and built them into our chassis. They worked exceptionally well but, obviously, were a huge drain on time. Other years we used Andymark ToughBoxes and those worked well for us. I'd recommend them unless you'd like the challenge of the custom gearboxes.

Re: 2015: Year of the Mecanum
 

Thanks, that diagram is helpful.

Re: 2015: Year of the Mecanum
 

Hi Aedan. Just for future reference, it's spelled mecanum. It's an easy mistake to make.

Is anyone using 6 inch mecanum wheels with CIMple boxes? We will be and are going for ~11 ft./s.

Re: 2015: Year of the Mecanum
 

I think we may also going the CIMple Box route with the 6" standard Andymark mecanum wheels, with HTD belts geared for 12.5 fps.

In the past I have used a gyro just as stated above to keep the robot driving straight. It worked so well that we had a motor come disconnected and didn't notice for a few hours. :)

Re: 2015: Year of the Mecanum
 

Wouldn't another option be to treat the feedback loop as the "rate controller" for the yaw axis? The rotation command from the joystick would be sent to the yaw controller. If it the command is zero then it will work as described in the attachment. If the command is greater than zero, then the controller will allow for more predictable rates of rotation based on the joystick command.

I believe this is how yaw control is managed on most RC Multicopters.

Re: 2015: Year of the Mecanum
 

What you've described¹ would work; but if you're trying to hold position, it's best to close the loop on position, not velocity.


¹ ... http://www.chiefdelphi.com/media/papers/download/2796 ...... http://www.chiefdelphi.com/media/papers/2390

Re: 2015: Year of the Mecanum
 

That makes sense. Thank you for creating these great resources.

Re: 2015: Year of the Mecanum
 

We have 6" VexPro mecanums on our 2013 robot and we drove it over several noodles with no problem. There is a bit of bumpiness when you go over, so you might want to either stabilize the stack or just drive around the noodles when loaded, but that is true with any wheels unless you have suspension of some sort.