pic: Mecanum Wheel Module Gearbox

[Joe Johnson]

Originally Posted by Richard

Yeah! What she said!

Bits weigh nothing, cost nothing, and are available on zero lead-time. And you only need two tools to work on them -- the one under your fingertips and the one between your ears.

And anyway, isn't the entire point of this chassis to be able to go in any direction without regard to the orientation of the frame? This magic is going to require tons of software. The least of the problems of the coders will be the (relatively minor) directional bias of the CIM motors.

Back to my points about spacing the plates. I think I get it. The pictures are a big help, but I don't have the CAD in my head so I could be screwed up still.

In general, I think it is pretty nice. I like that you have options if you see flexing.

I am anxious to see the movie of your robot floating around gamefield.

Thanks for sharing your experience with us, M.

Joe J.

[efoote868]

haha... then you'd better give them their own mock-up to play with early... (thats what our team did this year... and we didn't have to spend the bus ride to pittsburgh programming, made for better coding, less stress, life is good. Programmers are people too! )
you'll kill 2 birds with one stone... they'll be able to tweak it better, and they'll also be able to play with the camera, and get the robot moving in the right direction.

Optical encoders --> mecanum wheels scuff. Thats what they're designed to do, so be careful how you approach that.

[Richard Wallace]

Originally Posted by efoote868

haha... then you'd better give them their own mock-up to play with early... (thats what our team did this year... and we didn't have to spend the bus ride to pittsburgh programming, made for better coding, less stress, life is good. Programmers are people too! )
you'll kill 2 birds with one stone... they'll be able to tweak it better, and they'll also be able to play with the camera, and get the robot moving in the right direction...

Good points. Programmers also need a robot to program, which they often don't get until it's about time to put it in the crate!

Our team made a demonstration holonomic drivetrain in the 2005 off-season, and our programmers drove that until we got the competition robot ready. Of course they still needed some time to adapt to the actual robot's quirks. And of course they could have used more time than they got.

These are the facts of life for software engineers: (1) you will be the last member of the design team to get your hands on the system, and (2) it will be your fault if it doesn't work.

[yongkimleng]

Originally Posted by Richard

These are the facts of life for software engineers: (1) you will be the last member of the design team to get your hands on the system, and (2) it will be your fault if it doesn't work.

I very much agree with that. Alot of tweaking of constants and testing and stuff have to be done .. And while you are doing your stuff, everyone else puts pressure on you! Well unless part of the workflow allows the software guys to start early..

[GMKlenklen]

Is this the same design featured in another thread? I know the colors on the cad are the same... and it looks like you even kept the suspention idea aswell! I'm interested to see how easely this works out for you.

And did I hear someone say that the CIM motors move slower or give less torque in one direction than the other? Um... a little enlightenment please?

Thanks.

[Cory]

Originally Posted by GMKlenklen

Is this the same design featured in another thread? I know the colors on the cad are the same... and it looks like you even kept the suspention idea aswell! I'm interested to see how easely this works out for you.

And did I hear someone say that the CIM motors move slower or give less torque in one direction than the other? Um... a little enlightenment please?

Thanks.

The motors have a slight bias in their windings that makes them spin faster in forward than reverse. For the CIM's it's hard to notice. 2004 and prior it was a big deal, as the drill motors had a significant forward bias, and the robot would drift fairly badly if not compensated for.

[Richard Wallace]

For more than you probably wanted to know about how motor performance can depend on direction of rotation, read this thread.

[monty1540]

Originally Posted by Richard

Good points. Programmers also need a robot to program, which they often don't get until it's about time to put it in the crate!

Our team made a demonstration holonomic drivetrain in the 2005 off-season, and our programmers drove that until we got the competition robot ready. Of course they still needed some time to adapt to the actual robot's quirks. And of course they could have used more time than they got.

These are the facts of life for software engineers: (1) you will be the last member of the design team to get your hands on the system, and (2) it will be your fault if it doesn't work.

We avoided this problem this year (after deciding on kickoff weekend to go with mechanum drive) by building a drive-train quickly in 1 week while software worked on the code. Then we let software do as much as they wanted in terms of code testing to make sure that it would work. The early production time frame for our drive-train made certain that that we could switch back to 6 wheel if software couldn't get mechanum code to work. As it turned out, the saturday after kickoff, at about 6:00 pm, about ten minutes after integrating code and drivetrain, this was our result (link at end of post). Pretty amazing result for the turnaroud time. We left it with software for a few days so they could tweak things, and the design/fab team continued on with the rest of the 'bot. This video was taken before we changed gear ratios for a considerably faster robot. We figured we'd start slow, and work out the kinks with the code, then speed it up. And sorry for the bad quality, it was taken with my cell phone.

http://home.comcast.net/~ericmontague/mecanum_drive.mov