Team 3489 Category 5 Presents Storm Drive
 

Hello CD Community,

Inspired by a trip to CMP in 2013 and the chance to spend time with the nice folks over at FRC Team 148 (Robowranglers), and the innovative gearboxes from FRC Team 192 (Gunn Robotics), we were inspired to push our creative envelope a little bit and come up with our own version of Butterfly Drive. Attached here is a representation of our competition "Storm Drive" from our 2014 entry, "Floyd Scaryweather". It utilizes a COTS worm gearbox with a 10:1 reduction, and HTD Timing belts driving 6 inch Omni wheels, along with a set of pneumatically actuated drop-down traction wheels with a 2.1:1 reduction. The theoretical top speed is 14ft/sec in high speed, and 6.7ft/sec in traction mode. With the fully enclosed gearbox and belt drive, the robot is eerily quiet. The gearbox utilizes a 3-start worm, and can be pushed (not easily) after a break-in period.

The main goal of this design was to utilize the space between the frame rails in a way that the center of the chassis could be largely open. Our results were largely positive. The main issue encountered was with ratcheting encountered during a quick change of direction. We attempted to control acceleration/deceleration through software, but we're unsure if it was effective. We didn't encounter a lot of pushing matches in competition, but the low speed operation seemed to work as intended. Future iterations would likely include larger pulleys for greater engagement, closer c-c distances (0.5mm "slop" seems to be too much) or possibly converting from 9 to 15mm wide belts.

So, please ask and comment away!

Re: Team 3489 Category 5 Presents Storm Drive
 

Wow. This is really cool. Do you have any video of it in action?

Re: Team 3489 Category 5 Presents Storm Drive
 

I know what I want for Christmas

Re: Team 3489 Category 5 Presents Storm Drive
 

Why are the traction wheels more inside than the omnis? Having the traction wheels on the outside would provide more stability.

Re: Team 3489 Category 5 Presents Storm Drive
 

How much does a module weigh?

Re: Team 3489 Category 5 Presents Storm Drive
 

Wouldn't this depend on what you plan on having for your primary drive wheels?

Re: Team 3489 Category 5 Presents Storm Drive
 

Exactly, We use an orientation similar to this. It works well.

Re: Team 3489 Category 5 Presents Storm Drive
 

Not really. Having the traction wheels on the outside makes you more stable when they are down. You are less likely to be spun (longer moment) and, have a bigger contact patch to keep your CG inside and prevent tipping. You don't need to worry about either of these with omni wheels due to them being slippy by design. (It's real hard to tip an omni bot due to them just sliding away and their habit of preserving their inertia, and spinning them is almost always easier no matter their contact patch)


Basically, there's design benefits to having your traction wheels on the outside. I can't come up with any obvious ones to having your omnis on the outside.

Re: Team 3489 Category 5 Presents Storm Drive
 

I personally haven't driven a multiple wheel type robot in a while, but I would think that, depending on the game and your strategy, having a slight bit of turning ability in traction mode could be helpful to reduce the amount of wheel actuations.

Re: Team 3489 Category 5 Presents Storm Drive
 

The problem with having traction wheels on the inside is that if your getting pushed its not uncommon to be tipped onto the outer omni wheels negating the effect of the traction wheels.

Re: Team 3489 Category 5 Presents Storm Drive
 

I can think of a number of times when locking my orientation is beneficial. Auton being the obvious one but any game wherein I have to line up to score while NOT in a safe zone.

If you are using small cylinders for actuation the air use is minimal. Add another tank. To me the benefit of knowing that I physically CANNOT turn under my own power far outweighs the downsides of adding a half pound of air tank.

Re: Team 3489 Category 5 Presents Storm Drive
 

If you would like to be able to turn while in the traction mode putting your traction wheels on the inside might be a good idea. Like you said, the longer the wheelbase the harder it is to turn. Sometimes that's a good thing, sometimes not so much.

The designer needs to identify what they are trying to gain by having two separate sets of wheels and make decisions accordingly.

, Bryan

Re: Team 3489 Category 5 Presents Storm Drive
 

I should be able to dig some up tomorrow.

Re: Team 3489 Category 5 Presents Storm Drive
 

Yes, having the traction wheels outboard would improve stability. It's just a compromise. Having them inboard allows both ends of the axle to be supported, and reduces the torsional moment on the traction wheel assembly. It also allows some semblance of turning in the traction mode. Mostly, it's about packaging as most of the goodies are contained inside a 3inch wide channel.

Re: Team 3489 Category 5 Presents Storm Drive
 

I haven't weighed an individual module, but our entire chassis, including all wiring and controls, sans battery and bumpers weighed in at 61lbs.

Re: Team 3489 Category 5 Presents Storm Drive
 

You should be careful with worm gears in your drivetrain. If you slam into a wall (or other robot) at full speed, there could be a tremendous axial force applied directly to your worms.
Also you may be unable to push the robot around in your shop/etc

Re: Team 3489 Category 5 Presents Storm Drive
 

Actually, it turns out that, once broken in, these gearboxes can be back-driven with some effort. We don't want to make a habit of it, but it's possible. The spider couplings also help with some of the shock load. We disassembled 1 gearbox after 2 (often rigorous) regionals and a few demo events, and the gears showed no visible damage.

Re: Team 3489 Category 5 Presents Storm Drive
 

Come by our pits sometime. My kids would like to show you the advantages of a small traction wheelbase octocanum.

Re: Team 3489 Category 5 Presents Storm Drive
 

Or you could tell me and save me a trip... I'll ignore that I said nothing about mecanum wheels.

Re: Team 3489 Category 5 Presents Storm Drive
 

Both have their advantages and disadvantages. It really depends on your end goal. Putting the traction wheels in the center gives you more turning ability with more control over where the robot ends up (no drift due to omni wheels). You would probably be using the omni's to escape a t-bone or something like that.

On the flip side, putting the traction wheels on the outside means you are primarily using the omni's most of the time. I believe this is what most teams who use butterfly do, because of the reasons Andrew Schreiber said - you have a longer wheelbase for stability when you're pushing or being pushed, and are less likely to be spun around.

Re: Team 3489 Category 5 Presents Storm Drive
 

Hope this works.........

http://youtu.be/arKL5XCXGfU?list=UUZ...8THLwUgtdjtgdg


You may notice a lot of "power slide" maneuvering with the 4 omnis. What you probably won't notice is much audio, and yes it was on. The team decided to go with 4 omnis rather than 2+2 omni/traction, which would have made the driving dynamics very different. The 4 omnis did make it much easier to place the robot on the field (by pushing it sideways) since the gearboxes were hard to backdrive, at least early on. The chassis has since been converted to 2+2 for demo events, and the chassis can be maneuvered in any direction now that the gearboxes are broken in.

Re: Team 3489 Category 5 Presents Storm Drive
 

Looks nice. Have you tested it on carpet? One thing I noticed is that it is so quiet!

Re: Team 3489 Category 5 Presents Storm Drive
 

This is great. Omni wheels are a lot of fun once you get the hang of them.

Re: Team 3489 Category 5 Presents Storm Drive
 

We've used it in 2 regionals this year, so absolutely.;) The carpet provides better traction and stability than on the polished concrete.

Re: Team 3489 Category 5 Presents Storm Drive
 

I am just going to put it out there. When your traction wheel and omni wheel are this close together, wouldn't it make more sense to put packaging of the system over the traction wheel base? Especially for the drive this thread is about, moving the traction wheels to the outside could net you about an extra inch at most of traction wheel base. While moving the traction wheel out would appear to make it more difficult to package.



Also, do you have any video of the drive at competition weight. It would give us a much better idea of this drives capabilities.

Re: Team 3489 Category 5 Presents Storm Drive
 

From my experience, many drive train modifications/features provide only marginal gains, but when you look at the sum of all the little details, you will see a noticeable improvement.

Successful sports teams often use this principle of "aggregation of marginal gains", it works just as well in the FRC world.

Re: Team 3489 Category 5 Presents Storm Drive
 

Looks sweet. I would like to see the worm drive gearbox in action, it looks interesting.

Re: Team 3489 Category 5 Presents Storm Drive
 

Very cool looking! Do you have and specs in CAD for the individual module weight?
The use of a worm gearbox plus the cim mounting... such a beatiful combination.