pic: 1683 8 wheel drivetrain completed

[EnderWiggin]

Every good 4+ wheel drive train has an odd number of wheels on each side. This is because the center wheel is dropped to allow the robot to "spin on a dime" because it rocks on the center
When you start pushing someone or they start pushing you, the robot basically turns into a 4 wheel drive system by falling to one side. Either the front or back wheels barely touch the ground when this happens.

In your system here, you COULD drop the two sets of center wheels if you so desired (this is what team 48 did with their tank drive system) but i doubt it would rock very well on those four wheels unless you move them closer together.

[sdcantrell56]

We used bushings this year and they seemed to work very well. Switching out to bearings would work but the cost would be much greater, also how thin of bearings can you buy? I am wondering because the plates are only .25" thick. I do agree that they would probably be more efficient, but honestly bushings worked so well for us and really didn't have much friction. I will definitely look into bearings though.
The total weight for the drivetrain is around 40lbs. I believe each module is about 17lbs in inventor. That weight is with motors. It uses the andymark 2 speed transmissions, and on the design as pictured the speeds are around 5fps and 12fps, but we might up the speed a little.
The 2 middle wheels are lowered on each side to provide some rocking effect. There shouldn't be much problem with it turning as the middle wheels have a larger track width than the length. Essentially it is a wide 4 wheel drive base which generally doesn't have any problems.

Originally Posted by sdcantrell56

We used bushings this year and they seemed to work very well. Switching out to bearings would work but the cost would be much greater, also how thin of bearings can you buy? I am wondering because the plates are only .25" thick.

We used bearings for half inch shaft that were .25 thick total, and 1/16th of that was a flange, so press fitting isn't necessary. We still press fitted them for more security though...

[sdcantrell56]

Could you tell me where you got them from and how much. The thinnest I can find are 7/16". 1/4" would be perfect and would allow us to press fit them. Also why do you not like bushings? Multiple teams use them including 121 and they seem to work well. Just wondering. Thanks for your help.

Originally Posted by sdcantrell56

Could you tell me where you got them from and how much. The thinnest I can find are 7/16". 1/4" would be perfect and would allow us to press fit them. Also why do you not like bushings? Multiple teams use them including 121 and they seem to work well. Just wondering. Thanks for your help.

I can't find the flanged ones right now, but as for normal ones, you can get them from McMaster. The part number for an open one is 60355K15, the shielded is 3760T15, and the double sealed is 3760T31. If you go with these, you'll need to pocket the hole so that the bearing won't get forced out in a heavy defense match. Either that or search around for a bearing maker that sells flanged ones.

[sdcantrell56]

I looked at mcmaster and I saw those bearings. If I were to use bearings over bushings, they would have to be flanged, and be thinner than 1/2". Also I can't tell if the electronic thing is a joke or not but I think there's plenty of space for electronics. The controller will probably be on a second layer above the rest of the stuff.

[AdamHeard]

Originally Posted by EnderWiggin

Every good 4+ wheel drive train has an odd number of wheels on each side. This is because the center wheel is dropped to allow the robot to "spin on a dime" because it rocks on the center
When you start pushing someone or they start pushing you, the robot basically turns into a 4 wheel drive system by falling to one side. Either the front or back wheels barely touch the ground when this happens.

In your system here, you COULD drop the two sets of center wheels if you so desired (this is what team 48 did with their tank drive system) but i doubt it would rock very well on those four wheels unless you move them closer together.

His method of dropping the four center wheels will work just fine. Several teams have done this before and it provides the performance of a 6 wheel while eliminating any possible rock that some drivers find annoying.