03-02-2013 04:04

Mr. Lim

Re: pic: Team 691 2013 Frame

Very neat suspension setup! A lot of people who do mecanum don't realize just how important keeping all 4 wheels on the ground is...

Great work!

03-02-2013 05:44

Tristan Lall

Re: pic: Team 691 2013 Frame

I was thinking the same thing.

I wonder how effective it is? Does it have nice spring and damping characteristics, or do you find that the robot bounces around too much, or not enough?

Care to share any design parameters that you've calculated—especially the specs of any springs or dampers used?

03-02-2013 10:47

Nick Lawrence

Re: pic: Team 691 2013 Frame

Gorgeous suspension setup. I wonder if you guys are having any binding issues with it though?

-Nick

03-02-2013 15:28

Kevin Ray

Re: pic: Team 691 2013 Frame

It's hard to tell from the photo but I'll bet that either bronze or nylon sleeves surrounding the bolts below the springs would work to alleviate any binding issues.

No matter what, that's a very nice design for macanums. I especially like that fact that it looks like a breeze to replace any part on the whole drive system.

03-02-2013 17:33

Garret

Re: pic: Team 691 2013 Frame

Thank you all for the kind words, we are very happy with how this drive has turned out this year.

The suspension on this years robot primarily serves to ensure that all wheels are on the ground, because of that we really weren't too worried about having noticeable travel on the suspension. When driving the robot there is no noticeable bounce as far as we can tell.

We used the same springs in 2011 that we are now (McMaster PN: 9657K255). According to the specs listed the springs have a max load of 21lbs each. With 4 springs per module that would mean a max of 80lbs per module. That's a very high number but realistically you are more likely looking at around 40lbs per module which puts the springs at half compression, this is what you want for any suspension because it allows it to move both up and down to compensate for a non-level playing surface. In reality that's about all the math I ever do when I am looking at our suspension springs (that's all that is needed), to us the suspension is basically just an assumed part of the robot, we have done it on regular skid steer drive trains, swerve, and mecanum.

We had bronze bushings in the drive last year, however we removed them at the tournament because they really weren't necessary (as long as you use partially threaded bolts and slightly oversize holes). With this type of module it is easy to add bronze bushings or sleeve bearings if deemed necessary (only requires the holes to be enlarged). The idea behind the suspension is literally a "poor man's" solution to mecanum drive (or any drive that benefits from all wheels on the ground) with a stiff frame. When we first did this in 2011 it was done as a replacement to using shims to fix "bad pillow blocks" so that the drive would sit right.

So far we are quite literally amazed by the performance of this drive so far, especially the Vexpro mecanum wheels. We are getting surprisingly large pushing force right now with the base shown we were getting around 60+ lbs of pushing force (I don't have a weight on the robot right now but it is considerably less than 60 lbs. I am happy to answer any other questions about the drivetrain and suspension system.