16-03-2010 13:23

thefro526

Re: pic: 2791 At WPI

Chris, the bot looks good! Strangely enough, we lost the ability to climb over the bump between ship day and our first regional. We think the reason is two fold for us. The first part of it is because our drive chains are routed in such a way that does not allow for proper chain wrap on the center wheels so the chains can jump under high stress (cresting the bump). The second part may have been due to the way the carpet was mounted on our practice bumps, because apparently our carpet was mounted one way and the carpet on the field was mounted another. (This was told to me by another mentor on the team so I don't know much more than that) We have a solution for it, that I'm sure you guys are more than capable of implementing since your drive seems to be nearly identical to ours. PM Me if you want to know more...

16-03-2010 13:47

MrForbes

Re: pic: 2791 At WPI

Nice!

The bump problem is probably due to the interesting things that happen with 8wd and the center of mass of the robot, and the angles at which the forces work when the bot is at a 45 degree angle.

I suggest you draw a free body diagram of the robot in the position where it gets stuck, and figure out the tractive force on each pair of wheels, and compare it to what is needed to get over the bump. Might be that adding some weight at one end of the robot, down low, will fix the problem.

16-03-2010 13:54

Chris is me

Re: pic: 2791 At WPI

Hmm. As we moved around all the heavy stuff, this explanation makes a lot of sense. Since I can't calculate the CoG (something about the robot being crated), I think I'll do the math with various weights, locations of the center of gravity, etc. and see if putting a bunch of weight on the front or back would fix it. While planning specifically where to put weight isn't possible, doing the math should help me figure out how to fix it on Thursday at CT.

16-03-2010 14:14

MrForbes

Re: pic: 2791 At WPI

You should be able to make a close approximation of the CoG by just sketching the robot, and estimating the weight and location of each major subassembly. Then draw a FBD, and look at the normal force on the wheels, and calculate the tractive force using the published CF specs for the treads.

16-03-2010 14:58

sgreco

Re: pic: 2791 At WPI

I still love your bot. That 8 wheel drive is really nice. I hope everything works out for you guys in CT because you will certainly be a force to be reckoned with there. Good luck!