Best Drivetrain

[Lil' Lavery]

Originally Posted by vivek16

I have actually been thinking about that. Couldn't you lock the wheels of a crab in a 4wd orientation and (if you have each side independently driven) just turn like a 4wd bot?

Has anyone attempted this?

-Vivek

Yes, teams have done this before. Look at 111's swerve drive for a great example.

Swerves have a great deal of flexibility in how they perform and how they are built. Each configuration will result in different strengths and weaknesses.

[thefro526]

Originally Posted by vivek16

I have actually been thinking about that. Couldn't you lock the wheels of a crab in a 4wd orientation and (if you have each side independently driven) just turn like a 4wd bot?

Has anyone attempted this?

-Vivek

You can do pretty much anything you can imagine with a swerve. Just if you have a coaxial like 148 or 118 where there's only one central gearbox providing power to all of the wheels you can't turn like a tank. With some tricky Programming and the ability to steer either side independently then you could turn in theory but it wouldn't be easy. My suggestion would be, if you have a vex kit you could prototype a bunch of swerve drives and try different motor configurations and control systems.

[Pat Roche]

Originally Posted by thefro526

You can do pretty much anything you can imagine with a swerve. Just if you have a coaxial like 148 or 118 where there's only one central gearbox providing power to all of the wheels you can't turn like a tank. With some tricky Programming and the ability to steer either side independently then you could turn in theory but it wouldn't be easy.

That's not necessarily true. The reason 148 or 118 can't turn like a tank is because it has on central gearbox powering the entire drivetrain (not the rotation but the wheels). Coax crab can still be accomplished using two (or more depending on your preference) independent gearboxes that control the wheel nodes independently. If you only have one gearbox then regardless of programming you won't be able to turn like a tank.

[AdamHeard]

Originally Posted by Pat Roche

That's not necessarily true. The reason 148 or 118 can't turn like a tank is because it has on central gearbox powering the entire drivetrain (not the rotation but the wheels). Coax crab can still be accomplished using two (or more depending on your preference) independent gearboxes that control the wheel nodes independently. If you only have one gearbox then regardless of programming you won't be able to turn like a tank.

If the wheels are steered separately in pairs, one pair can be turned 180 and steering in place is possible.

[Pat Roche]

Right, exactly. You also don't necessarily need to limit them to 180 degrees of rotation (I understand the argument of why you would I'm playing devil's advocate). You could use a coaxial style setup (shaft inside of shaft) and run two sides of the robot independent of each other. In that case you are still doing a 'crab drive' as we have coined the term. The difference being the two sides are independent of each other rather than being run all off the same rotator and power transmission.

[thefro526]

Originally Posted by thefro526

With some tricky Programming and the ability to steer either side independently then you could turn in theory but it wouldn't be easy.

lol that's what I said earlier, but it's still only spinning in place.

[Andrew141WOBOT]

It really depends on the game... our 2008 bot drove like a car. 2 Cims, direct drive, to each rear wheel, with an electrical differential. The front wheels drove used the acrynom principal, so when the bot was turning left, the Left front wheel turned more than the right. It was really strong this year, but it probably won't for any other game.

[Rick TYler]

Originally Posted by Andrew141WOBOT

The front wheels drove used the acrynom principal

Ackerman principle, not acronym principal.

[Aren_Hill]

Originally Posted by vivek16

I have actually been thinking about that. Couldn't you lock the wheels of a crab in a 4wd orientation and (if you have each side independently driven) just turn like a 4wd bot?

Has anyone attempted this?

-Vivek

We did, We had one gen2 driving the front two wheels and one on the back two. So if we wanted to "tank drive" we just pointed the wheels sideways and drove around like a wide bot (wider=less effort to turn). This setup also enabled us to create "drift" buttons, We had 2 buttons on the joystick base and each one cut power to the respective transmission. So when we were going sideways we could kill a gearbox and the other one would drag its end around. This enabled us to effectively reorient on the fly, which greatly decreased our lap time.

[R.C.]

I was wondering, what if you leave omni's in the front and put one dewalt to each of the remaining wheels. Direct drive or chain drive???

[Aren_Hill]

Originally Posted by rc_cola1323

I was wondering, what if you leave omni's in the front and put one dewalt to each of the remaining wheels. Direct drive or chain drive???

I'm guessing your talking 6wd? If so this would create a very robust drive if done correctly, yet i suggest you mechanically link the driven wheels on each side so if one set is off the ground all the power still is driving the wheel touching the ground. I believe RUSH 27 has used a similiar setup before, at least in '06.

[R.C.]

So youre saying to power each wheel but link them by using chain and would this style of drivesystem be more effecient than the standard gearbox on each side thing

[EricH]

Originally Posted by rc_cola1323

So youre saying to power each wheel but link them by using chain and would this style of drivesystem be more effecient than the standard gearbox on each side thing

I'm not sure about efficiency, but you don't have to worry as much about putting, say, 2 CIMs into one DeWalt. On the other hand, you just added 2 DeWalts to your robot, which adds weight. (Assuming a 6WD.) You may gain efficiency (fewer gears in interface) or lose it (chain slop, twice the gears for the same amount of power). You have a fully redundant drive system, though; theoretically, any one motor can power the entire side even if the other motor's gearbox explodes all over the field.

[R.C.]

It still wouldn't be as much weight as a supershifter and i remember that rush got up to 18 to 20 feet per second with drive system and Erich, you are right about the slight chance of losing efficiency

[AmoryG]

Now I've done searches, but I've never seen any team attempting a "ball drive" drive train. It might be under a different name, but it's simply a drive train that uses spheres for wheels. I've tried to think of a few ways of doing this, but because I have no examples to follow I can't say any of my ideas would work.

With spheres you could rotate the ball in different directions without having to rotate the thing that holds the ball inplace. The ball wouldnt have to be a complete sphere.

Has anyone tried to do this successfully?