Hey,
So what has your team used for the suspension? Specifically, how much was it able to move. Does a tennis ball work well, like 488 is using, or do you think you need more springiness.
I’ve been thinking about testing:
I’m sure this will be useful to a lot of teams using mecanums this year. Thanks!!
Just from reading this, I’d suggest steering away from RC shocks. They can’t hold the weight of a first bot, unless you wnat to pay hugely. Also, they’re very expensive.
our wheels were retractable last year… so i guess our “suspension” would’ve been the pneumatics… I would steer clear of that again… pretty heavy, and it takes the cylinders a long time to fill back up after using it just once.
Also, we got it wrong, so one wheel was 1/32 or so above the rest… and made our robot go in arcs most of the time.
We found that the racquetballs, though giving a larger range of motion in a suspension, cannot withstand the torment of being on FIRST machine. After only about fours hours of run time, they’ve begun to tear and crack and will need to replaced.
The tennis balls, on the other hand, are holding up quite well. They’re a bit tougher to compress, but our chassis is still lighter than a completed robot.
We used rubber slugs 1"x1"x1". But coming from a team that used mech wheels. Team 868 had the best design with retracting wheels.
I am truly clueless as to what any of you are talking about. I understand that all 4 wheels of a Mecanum drive need to maintain equal contact with the ground for the system to work properly but what in the world are all of you talking about? Pneumatically retracting wheels??? tennis balls??? rubber slugs???
Huh???
Anyone have a picture to share?
Our team build a mecanum drivetrain this fall. A photo and link to video can be found here: http://www.chiefdelphi.com/media/photos/25886
On one end, we placed racquetballs between the pivoting wheel module and the frame. On the other end, we placed tennis balls.
Other teams have used a split chassis, round rubber rings, and pneumatics to achieve the same result.
Ahh, I now see the racquetballs and tennis balls and more importantly understand how they are used. What are the advantages of using a tennis ball for this purpose over a spring or a split chassis?
I avoided a split chassis in the end because I felt that attaching upper structure to it would become troublesome, given its flexibility. It’s possible to integrate the split chassis into a larger, stiffer frame, but that comes with a significant weight penalty.
I think a spring is an ideal solution, but I didn’t feel comfortable making assumptions about how much travel and force would be appropriate from a spring. The tennis ball and the current arrangment allow for us to quickly try different objects. With sufficient testing, I’d feel more comfortable approximating the characteristics of, say, a tennis ball with a spring.
Thanks Madison! We have no experiance with nor plans for Mecanum this season but I really think they are wonderful. I am just trying to understand some of the design issues. I can see how a split chassis could limit the upper structure and without knowing the game requirements it is probably safest to put the suspension at the individual wheel. I love the tennis ball as a low tech but effective solution. Truly K.I.S.S. at work. Thanks teaching me something new today!
How are you attaching the tennis balls to the frame?
Last year my team used a tennis ball for a universal joint for the shooter (worked great and was cheap). We drilled 3 holes around the ball, which allowed it to bend more. Unfortunately, I don’t have any pictures. A little wear was evident by the fall, but that was after many, many rotations at 2000 RPM. Don’t know if it would work with this, because the forces are in another direction, but you may want to try holes in the top, bottom, or sides of the tennis ball.
Also how much vertical motion do you think is required?
Currently, I have been CADing a different type of suspension, which I will hopefully post soon. My main difficulty is a material for the suspension and the distance a suspension would need to be able to move.
Thanks a lot to everyone who replied!!
edit: I uploaded a pictureof our 2006 robot. If you zoom in you can see 1 of 3 holes in the tennis ball - it seemed to work well.