Learning and Understanding different drivetrains

[Ether]

Originally Posted by Joseph Smith

Widest possible wheelbase...

maximum width wheelbase...

Just to be clear: wheelbase is the distance from the front to rear axles (length). trackwidth is the distance between the two front (or rear) wheels (width).

[theCADguy]

CONS: Medium to heavy weight depending on wheels
All wheels are chained- no direct drive, so it's possible to throw a chain and lose control of one side
Takes up more space
More difficult to swap wheels/tread

Actually, throwing a chain does not cause a loss of control on one side. At the WPI regional in 2013, we (Team 20), lost a chain in our west coast drive during a finals match, and had no time to replace it before our next match, so we played that match without a chain, and we experienced was very little loss of control. In fact, it was impossible to tell (from the stands) that we had lost a chain.

We had a similar situation this year at the Tech Valley regional, were we smashed a drive train bearing, and had to remove the affected wheel, as we had no time to fix it. Our WCD performed just as well with 5 wheels as it did with 6, and we won that match.

[Joseph Smith]

Originally Posted by theCADguy

Actually, throwing a chain does not cause a loss of control on one side. At the WPI regional in 2013, we (Team 20), lost a chain in our west coast drive during a finals match, and had no time to replace it before our next match, so we played that match without a chain, and we experienced was very little loss of control. In fact, it was impossible to tell (from the stands) that we had lost a chain.

We had a similar situation this year at the Tech Valley regional, were we smashed a drive train bearing, and had to remove the affected wheel, as we had no time to fix it. Our WCD performed just as well with 5 wheels as it did with 6, and we won that match.

I think you misunderstand me... Throwing the chain from the gearbox to the wheels in design #1 would result in losing power to the wheels on that side. Of course this depends on how the chain is run, but it's assuming that you have one chain from gearbox to the center wheel and from there the wheels are chained to each other. Also, one of the benefits of WCD that I listed was that throwing a chain wouldn't cause you to lose power on that side because the center wheels are direct driven from the gearbox (in our design at least.)

[Oblarg]

Originally Posted by Joseph Smith

I think you misunderstand me... Throwing the chain from the gearbox to the wheels in design #1 would result in losing power to the wheels on that side. Of course this depends on how the chain is run, but it's assuming that you have one chain from gearbox to the center wheel and from there the wheels are chained to each other. Also, one of the benefits of WCD that I listed was that throwing a chain wouldn't cause you to lose power on that side because the center wheels are direct driven from the gearbox (in our design at least.)

Note that one can direct-drive center wheels on a non-WCD 6WD setup (a la AM14U), so this isn't strictly a WCD benefit.

[EricH]

Originally Posted by Joseph Smith

Of course this depends on how the chain is run, but it's assuming that you have one chain from gearbox to the center wheel and from there the wheels are chained to each other.

Back when I was a student on 330 and we were using that type of setup, we never ran just to the center. The gearbox was independently chained to the center and the back wheels; center wheel chained to front wheels. That way, we'd have to jam a chain when it was thrown, or throw two chains, to lose the side.

[Oblarg]

Originally Posted by EricH

Back when I was a student on 330 and we were using that type of setup, we never ran just to the center. The gearbox was independently chained to the center and the back wheels; center wheel chained to front wheels. That way, we'd have to jam a chain when it was thrown, or throw two chains, to lose the side.

This sounds like it'd introduce a lot of frictional losses over just direct-driving the center wheel and chaining to the two outer wheels.

[EricH]

Originally Posted by Oblarg

This sounds like it'd introduce a lot of frictional losses over just direct-driving the center wheel and chaining to the two outer wheels.

Not too much. And it helped with our weight distribution (we tended to run with the CG aft of center whenever we could). The gearbox was between the center and rear wheels, so we had two short chain runs.

This was back in the day when if you wanted to direct-drive your center wheel, you had to make your own output shaft, if not your own gearbox--we didn't have that type of capability, then. Besides, we were a dead-axle team--that is, at the time we did NOT go live-axle if we didn't absolutely have to. (In my time on the team, I can think of maybe 4 live axles that weren't in a gearbox, none in drivetrain--they were all reduction stages in arms or shooters,)

[topgun]

What about the weight of the bumper mounts? That needs to be added into the weight of the frame as well.

We used a 6 wheel center drop dead axle (JVN axle tube style) and the outside edge of our wheels were within a .5" of the frame perimeter. I am not going to worry about that last inch of width but that is important for some teams.

WCD would have the edge in quickly replacing a wheel, though we could change a wheel pretty quick if needed.

We also used HTD timing belts between wheels which are a lot lighter than chains. We used a short #35 chain between the gearbox and the first wheel.

Part of the appropriateness of the drivetrain is what your team can build, and should be a key part of your decision. Determining that is a good offseason project.

[MrRiedemanJACC]

For those of you with WCD I have several questions:
1) How do you locate the wheel in the axial direction? Both inwards and outwards?
2) If you are using the 3 CIM ball Shifter,
a) Do you use the 3rd stage from Vex?
b) Do you only use the support from the bearings in the gearbox or do you add additional support?
3) Is there a set wheel width that you use? (narrower to be able to move the gearbox outward further? ie 1" traction vs a 2" traction?)
4) How much drop do you use for the center wheel?

Thanks! I'm sure as we look into it, I'll have more detailed questions!!

[Thad House]

Originally Posted by MrRiedemanJACC

For those of you with WCD I have several questions:
1) How do you locate the wheel in the axial direction? Both inwards and outwards?
2) If you are using the 3 CIM ball Shifter,
a) Do you use the 3rd stage from Vex?
b) Do you only use the support from the bearings in the gearbox or do you add additional support?
3) Is there a set wheel width that you use? (narrower to be able to move the gearbox outward further? ie 1" traction vs a 2" traction?)
4) How much drop do you use for the center wheel?

Thanks! I'm sure as we look into it, I'll have more detailed questions!!

1. If you custom machine wheels, you usually keep a nub on the wheel to push up against the bearing. If you don't machine your own wheels, you can just use spacers of some type. This year we 3D printed our own. As for the outside, most teams use either e-clips, snap rings or a bolt and washer with the axle threaded on the end.
2. We used the WCP gearboxes, so I don't have much of an answer here, other then you usually would need the 3rd stage to actually have enough reduction for a functioning robot.
3. The wider of a wheel you go, the more grip you can get from that wheel. Since we don't machine our own wheels, we use whatever we can get. This year, that was VersaWheels. The general rule is to have the wheels as far to the edge of the perimeter that is allowed.
4. This year we used 0.1". The old standard used to be 1/8", but with the smaller wheelbases that we are currently seeing, that number has to drop, and we have found 0.1" to work the best.

[Mark Sheridan]

Originally Posted by MrRiedemanJACC

For those of you with WCD I have several questions:
1) How do you locate the wheel in the axial direction? Both inwards and outwards?
2) If you are using the 3 CIM ball Shifter,
a) Do you use the 3rd stage from Vex?
b) Do you only use the support from the bearings in the gearbox or do you add additional support?
3) Is there a set wheel width that you use? (narrower to be able to move the gearbox outward further? ie 1" traction vs a 2" traction?)
4) How much drop do you use for the center wheel?

Thanks! I'm sure as we look into it, I'll have more detailed questions!!

In 2013 3309 used a WCD.
1) snap ring on the outside and the wheel hub was made to touch only the inner ring of the bearing.
2) used a custom gear box but the COTS options are very good.
3)Used Colsons that year, we plan our wheels to be traction limited in low gear. We were geared a little to high so we never added grooves to the colsons or switched nitrile rough top tread.
4) It was 0.125, it worked but was a bit too much. I would not complain if I had to use .125 but if I could get 0.100 I would go for it.


This year my team used octonum which was harder to change wheels. So the biggest thing we noticed was that if you have a practice bot and drive more than 10 hours a week. Wheel changing becomes very important. So next year 3309 is going back to west coast drive. Especially comparing our practice time to elite teams, we need to up our game. We are targeting 20 hours a week (including autonomous work). We are also hoping to practice against more orange county teams next year, so wheel wear will be very high. So changing wheels quickly is a major concern for us.

[TikiTech]

Originally Posted by MrRiedemanJACC

For those of you with WCD I have several questions:
1) How do you locate the wheel in the axial direction? Both inwards and outwards?
2) If you are using the 3 CIM ball Shifter,
a) Do you use the 3rd stage from Vex?
b) Do you only use the support from the bearings in the gearbox or do you add additional support?
3) Is there a set wheel width that you use? (narrower to be able to move the gearbox outward further? ie 1" traction vs a 2" traction?)
4) How much drop do you use for the center wheel?

Thanks! I'm sure as we look into it, I'll have more detailed questions!!

We went to a 6 wheel WCD this year and are very happy with the results.

Now that VexPro and West Coast Products produce easy to incorporate parts for west coast drives, just about any team can upgrade.

You can use the Versa rails and Versa blocks to create the drive rails. In fact you can get everything for a WCD from VexPro and West Coast Products.

We did not use the Versa rails as they are, in my opinion, not strong enough for this year’s game. You can make your own frame rails very easily with just a good drill. The VersaBlocks center the bearings and create the offset by their orientation so perfectly drilling the rail is not required. Just a hole big enough for the axles to fit through. Normally the offset is about 1/8" between the center and outer wheels. If you center your weight you will have no issues with turning with all traction wheels.

We are using the West Coast Products 3 CIM 2 speed transmission with the 3rd stage. It is geared to run at 5fps and 15fps on 4" wheels.

You will want to get the third stage, as mentioned before.

The 3 CIM is quite heavy and you should definitely add additional support. With so many different gear selections available for these transmissions you can tune your drive speed for whatever wheel size you are running.
We LOVE these transmissions!!

At our regional we ran the 4"x1" Versa wheels. These were OK for a first attempt but were fairly easily worn out and did not give quite the traction we wanted. The wear was easily overlooked since the Versa wheels are quite inexpensive.

We have upgraded to 4"x1.5" Colson wheels for the championships.
We would of gone wider but our drivetrain is set and wasn’t sure if the 2" wheels would fit without major modifications.
Since the change to the event times we were not sure that there would be time for it.

Good luck with your drive train change. PM me if you have any questions. I can send you our CAD files or talk more in length on you first try at WCD.

After our first attempt was so successful we doubt we will ever go back. Unless of course it is a water game, then all bets are off.

Aloha

[Clem1640]

WCD is a great tank drive-train. Love it.

But we use 4-wheel independent swerve. It works for us. It carries a high cost; brings significant benefits for those who execute it well.

For a perspective, see: http://wiki.team1640.com/index.php?title=Swerve_Central

[DampRobot]

Originally Posted by TikiTech

We went to a 6 wheel WCD this year and are very happy with the results.

Now that VexPro and West Coast Products produce easy to incorporate parts for west coast drives, just about any team can upgrade.

You can use the Versa rails and Versa blocks to create the drive rails. In fact you can get everything for a WCD from VexPro and West Coast Products.

We did not use the Versa rails as they are, in my opinion, not strong enough for this year’s game. You can make your own frame rails very easily with just a good drill. The VersaBlocks center the bearings and create the offset by their orientation so perfectly drilling the rail is not required. Just a hole big enough for the axles to fit through. Normally the offset is about 1/8" between the center and outer wheels. If you center your weight you will have no issues with turning with all traction wheels.

Few people realize how revolutionary these blocks and the whole Versa system are for drivetrain design. You can literally buy a WCD off the shelf, with a lot of features designed for easy customization and to be really easy for low resource teams to use.

By the way, we used .0625" 6061 2x1 this year in a standard WCD and in the rest of our frame. No bending, breaks, cracks in the powdercoat, etc. They are behind strong full perimeter bumpers, but nothing that the average team couldn't create. Even for a game like Arial Assault, the VP tubing is more than thick enough. IMO, you can go thinner (like we did) and save a ton of weight without running into strength problems. We had a sub-10lb frame, all because we used 1/16" tubing everywhere and relied on strong geometry rather than tubing to make our frame robust.

[Oblarg]

Originally Posted by DampRobot

Even for a game like Arial Assault

I chuckled.