Best Drivetrain

[EricH]

Originally Posted by Doug G

1) There's no rookie team in Davis, maybe they were referring to a rookie team that attended the Davis Regional.

Yeah, I noticed that. I would suspect that the team in question would be a 2nd-year team now.

Brandon, we don't know anything about the team, other than approximate age. So I called conservatively. If I knew for sure that they had that extra capability, I'd go a little more risky. Some rookies will have the capability and desire to go beyond the 6WD. Most won't.

[Triple B]

233 has used #25 drive chain for 10 year with minimal problems.
This year we used #25 drive chain with no tensioners and have had no problems.
The bot still has the same chains since the mid february assembly date.
mike d

[Lowfategg]

Hey just wondering, how does two wheel rear wheel drive with two non-powered omni wheels up front work? I know in VEX that seems to be the best.

I know this year team 303 used #25 chains (which we did not have problems with) with Mecanum wheels which I really did not like that much.

[Daniel_LaFleur]

Originally Posted by Triple B

233 has used #25 drive chain for 10 year with minimal problems.
This year we used #25 drive chain with no tensioners and have had no problems.
The bot still has the same chains since the mid february assembly date.
mike d

Pink also has some of the best engineering support in FIRST.

#25 chain is strong enough, as long as you understand all the forces and requirements that will be put on it. A rookie team may not have such understanding ... thus the safety margin that #35 chain provides may be wise.

[sdcantrell56]

Could someone from team 233 please post up some pictures of your drivetrain. I have always loved it whenever I get a chance to see it up close but I didn't get a chance to look at it at Championships

[EricH]

Originally Posted by Lowfategg

Hey just wondering, how does two wheel rear wheel drive with two non-powered omni wheels up front work? I know in VEX that seems to be the best.

Ah, the 2WD caster system (without the casters). A word of advice--while it works fine, you want the traction wheels under the CG as much as possible. (Or rather, the CG over the traction wheels.) Not too much, but if you have the traction wheels in the rear, you want your CG aft of center. This allows for better control.

Bear in mind that 2WD can be pretty squirrely. You might want a 6WD with a dropped center--it turns kind of like a 2WD, but has extra wheels that will assist in traction.

[Lowfategg]

Originally Posted by EricH

Ah, the 2WD caster system (without the casters). A word of advice--while it works fine, you want the traction wheels under the CG as much as possible. (Or rather, the CG over the traction wheels.) Not too much, but if you have the traction wheels in the rear, you want your CG aft of center. This allows for better control.

Bear in mind that 2WD can be pretty squirrely. You might want a 6WD with a dropped center--it turns kind of like a 2WD, but has extra wheels that will assist in traction.

On our FTC bot this year the CG was a little bit forwards of the rear wheels so it worked well. My guess is if we did an FRC bot next year we would go with a six wheel drive system using omni wheels on outside with traction wheels in the center. Just on another note whats the best kind of omnidirectional drive in the real world and not just looking a pros and cons of the designs of each.

[Aren_Hill]

little hint, i would advise never to do a 2wd setup with the wheels centered in the bot and 4 casters at the corners, why? because if you get tipped forward or backward at all you have no power going to the ground, reason #2 you have almost no resistance to turning so without some nifty programming and maybe a gyro it will be a pain to control.

If you do a 2wd put the driven wheels at one end of the robot, that makes it so if you tip you have twice the chance of having power to the ground than a 4 caster setup, this also uses the inertia of the robot to provide resistance to turning and results in a much more controllable setup.

I also suggest Omni wheels above casters, as when casters spin around they put unpredictable "whoop de doo's" into you motion.

Also you can power omni wheels to provide additional forward traction rather than wasting weight on dead wheels.

Originally Posted by JVN

Two Words:
Normal Force.
-John

An example of a 4wd 2 grippy 2 omni is our 2006 robot, search for any videos of IRI 2006 and our bots the fridge with the orange bumpers(which by the way is sick)

[EricH]

Originally Posted by Lowfategg

On our FTC bot this year the CG was a little bit forwards of the rear wheels so it worked well. My guess is if we did an FRC bot next year we would go with a six wheel drive system using omni wheels on outside with traction wheels in the center. Just on another note whats the best kind of omnidirectional drive in the real world and not just looking a pros and cons of the designs of each.

OK, that might work. Don't go with a "rocker" system if you do, though. That's too much maneuverability.

Actually, I just remembered. 494 did this a few years ago...
Corner omnis. The idea is a 4WD with the traction wheels on, say, left front and right rear. The other slots are omnis. Apparently it works pretty well.

Omnidirectional drive is the holonomic/mecanum/crab/swerve drives. The best type depends on the game.

Mecanum: 4WD with specialized programming and each wheel independently powered. Oh, and mecanum wheels.
Omni: 3-6 omni wheels arranged so that you can slide. It's a little trickier than mecanum.
Crab/swerve: each wheel turns. 3-4 wheels.

[Cory]

Originally Posted by Daniel_LaFleur

Pink also has some of the best engineering support in FIRST.

Actually Pink has no mechanical engineers.

[Lowfategg]

Originally Posted by EricH

OK, that might work. Don't go with a "rocker" system if you do, though. That's too much maneuverability.

Actually, I just remembered. 494 did this a few years ago...
Corner omnis. The idea is a 4WD with the traction wheels on, say, left front and right rear. The other slots are omnis. Apparently it works pretty well.

Omnidirectional drive is the holonomic/mecanum/crab/swerve drives. The best type depends on the game.

Mecanum: 4WD with specialized programming and each wheel independently powered. Oh, and mecanum wheels.
Omni: 3-6 omni wheels arranged so that you can slide. It's a little trickier than mecanum.
Crab/swerve: each wheel turns. 3-4 wheels.

I think both of you miss understood me but its my fault since I am not quite down with this 2WD, 6WD... etc... lingo.

The best setup I think of for a FRC bot is a 6 wheel tank style bot using omni wheels as casters on the outside wheels and traction wheels in the center. I would also make it so all wheels would be touching the ground.

Also I understand what omnidirectional is and the different types of it but I was asking what seems to work best in different situations.

[BBnum3]

Here's one option that hasn't been said yet: 4 wheel drive, with omni wheels on opposite corners. This worked really well for my team last year, and was easy to maintain. Having the omnis on the corners increases turning ability but not to the extent that your robot turns too fast. It also works well for climbing ramps and such.

[Triple B]

but we gots a good left hook
mike d

[Aren_Hill]

Originally Posted by Triple B

but we gots a good left hook
mike d

i've seen you guys practically do chinups on the overpass, noones doubting your bots, your bots are the only things that could make me "okay" with the color pink

[DMetalKong]

Originally Posted by Lowfategg

Hey just wondering, how does two wheel rear wheel drive with two non-powered omni wheels up front work? I know in VEX that seems to be the best.

I know this year the FRC team I was on used #25 chains (which we did not have problems with) with Mecanum wheels which I really did not like that much.

Team 303 did use #25 chain on our robot and we had only one problem: when a gusset came loose during practice and got caught in the chain. I can assert that our chains were not perfectly aligned, so I am not sure how precise #25 needs to be to be reliable.