pic: drivetrain idea (comments please)

[R.C.]

If you use 2x1 and at a 1/16" for the frame, make sure if the shaft is live put bearings in the frame. But if the wheel rotates on the shaft, put bushings in those spots where the shaft rests. If you leave the shaft by itself in the frame, over time it will eat away at the frame. I prefer to stay away from direct drive because you either have to hex or key your wheels.

[sdcantrell56]

I feel like broaching your wheels and sprockets for hex shaft and using live axles is actually potentially more reliable. At least you dont have to worry about the bolts holding the sprockets to the wheels from loosening. Another thing they could do is have simple bearing blocks machined out of 1/4" thick aluminum to give something a bit more substantial for the bearings to sit in. Although I would agree that if they are using the kit wheels it makes more since to go with dead axle since you would then have to use a keyed hub of some sort.

[R.C.]

Direct Drive is awesome, but a the drive he has set up will be fine and will work just as good. As long has he has aligned the sprockets up and the chain, he will be fine. Nice drivetrain and keep cadding.

[pakratt1991]

I saw someone mention tracks in this thread a ways back, and they didn't provide much of a competitive advantage in this years game as it has in some, although were fine tuning and improving upon what we had.

[bmarick]

the one advantage to this idea i can see and have found out from discussing this with other is that you can add a second gear ratio to the spin. But i see no problem in your design other then i would think about not dropping the center wheel at all. keep up these ideas because they cause great discussions. I know I learned alot.

[sdcantrell56]

Originally Posted by bmarick

But i see no problem in your design other then i would think about not dropping the center wheel at all.

Unless you want to not be able to turn well at all and potentially trip the breakers whenever you attempt to turn you have to lower the center wheel. We lowered it 1/8" last year with 6 kit wheels and it was perfect. No noticeable rocking but it could still turn perfectly. The only way to not lower the center wheel is to use omni wheels in the corner to allow slip while turning.

[EricH]

Originally Posted by sdcantrell56

Unless you want to not be able to turn well at all and potentially trip the breakers whenever you attempt to turn you have to lower the center wheel. [...] The only way to not lower the center wheel is to use omni wheels in the corner to allow slip while turning.

Careful about blanket statements like that. Team 25 doesn't exactly drop their wheels (to my knowledge) and they still turn easily. I'm not sure exactly how they do it. It sure doesn't affect the rest of the robot, though. There may be one or two teams who use similar setups.

[bmarick]

oursystem did not need a drop but we used omni for comp. as long as you reverse the direction of one side to turn you should be fine. only you gent more friction thus lower speeds

[Cory]

Originally Posted by EricH

Careful about blanket statements like that. Team 25 doesn't exactly drop their wheels (to my knowledge) and they still turn easily. I'm not sure exactly how they do it. It sure doesn't affect the rest of the robot, though. There may be one or two teams who use similar setups.

I don't know of teams not named 25 who have been able to skid steer with a 6wd with no dropped center and no omnis. I'd say it's a pretty safe blanket statement.

[EricH]

Originally Posted by Cory

I don't know of teams not named 25 who have been able to skid steer with a 6wd with no dropped center and no omnis. I'd say it's a pretty safe blanket statement.

They've been telling other teams how they do it. Then again, not many have copied the design.

I'd also guess that many who try it for the first time (without asking advice here first, that is) quickly find out about the scrub and the "fun" associated with it, and change to an omni/drop configuration.

[sdcantrell56]

I would say it is a very safe blanket statement. I was waiting for someone to chime in with team 25 as an example. Yes they do not drop the center wheel and they do have 6 traction wheels but as far as I know, they and maybe 103 who share a similar drivetrain are the only teams that don't drop the center wheel and have had success. I would say unless you are team 25, which no one is and very few are at there level, then I would recommend dropping the center wheel. You are not sacrificing any performance and in fact are improving your ability to turn and not trip the breakers.

[=Martin=Taylor=]

Originally Posted by sdcantrell56

I would say it is a very safe blanket statement. I was waiting for someone to chime in with team 25 as an example. Yes they do not drop the center wheel and they do have 6 traction wheels but as far as I know, they and maybe 103 who share a similar drivetrain are the only teams that don't drop the center wheel and have had success. I would say unless you are team 25, which no one is and very few are at there level, then I would recommend dropping the center wheel. You are not sacrificing any performance and in fact are improving your ability to turn and not trip the breakers.

World Finalist 348 also used a team 25esque drivetrain. Having experienced their defense, I can attest to the speed and pushing power of this design. However, it did have a tendency to buck back and forth violently.

[R.C.]

I was just watching a video of Team 25's match on the blue alliance and man they are spectacular.

[s_forbes]

As the conversation has drifted more towards true skid-steering drivetrains, I thought I'd point out my favorite: 1662 in 2006. Their drivetrain was very similar to the one posted at the beginning of this thread, but instead of six kit wheels, they had a four-wheeled drivetrain with 2"x8" IFI wheels. Talk about a robot that's hard to turn!

For those of us that aren't able to pull of such feats, six wheel drive with a dropped center works great. I would just recomend (as several others already have) that you add some bracing between the side rails of the chassis. I would prefer stickier wheels, too, but as it sits it looks like a solid base for your bot.

[Daniel_LaFleur]

Originally Posted by bmarick

definitly the cross brace or extra bracing is going to be needed. Otherwise it will bow over time. Can some one explain the degrees of rap to me. I'm still a little new to the drive train systems.

A sprocket is basically a circlular object (360 degrees). You want the chain to wrap around at least 1/3 of the sprocket (120 degrees). I personally suggest at least 150 degrees wrap with no more than 180 degrees.

The more wrap you have the more forgiving your drivetrain will be, but you trade off that forgiveness with added drag and friction. Going less than 120 degrees of wrap invites the chain to jump off of the sprocket.