Combo Drive --- Swerve Decision

[Chris Fultz]

(NOTE: I am not questioning the decision you made at all, I am just asking for you to share, if you will, what went into your decisions.)

I have noticed several Ocotcanum drives, a combination of Mecanum and straight traction drives. For these teams that made this choice, or discussed it and did not make this choice, what were some of the factors behind your decision for this combo drive compared to a standard swerve system or 6WD?

It is a very interesting drive, and we discussed it as well. Curious to what others thoughts were.

[Jonathan Norris]

I know our team talked about it for a while as well. What we really liked about it was the combination of the maneuverability of a swerve and the power of traction wheels. We had it planed where the traction wheels would be geared slower for more torque to be able to push through defense, while the mecanum would give us speed and maneuverability.

The main advantages I saw over a pure swerve drive was reduced complexity of the overall system. However, the system would be pretty heavy, probably require two big pistons or four small ones, and to do right would need to have side supports to support the side loading while trying to turn with the traction wheels down.

I like the concept of the design, but as always it comes down to design and execution to make it worth the extra weight/effort.

[Alpha Beta]

I am curious as to what the gearing between the two wheel sets are on the 3 Oct-canum drives posted thus far. One of the advantages of a 6WD is the ability to add two shifting transmissions.

Are these teams getting a similar bennefit by having their traction wheels geared for a different speed than their mecanums?

If so would you choose to have your traction wheels geared faster or slower?

• I was under the impression that mecanums could only be geared so fast before the torque requirements for strafing were compromised. It might be nice to have the extra speed then placed in the traction wheels.
• I've also been under the impression that mecanums have more difficulty pushing than traction wheels, and it might be nice to have more torque under the tracton wheels for those pushing battles.

[Jonathan Norris]

The majority of the systems I have seen so far use smaller traction wheels, with some gearing to have more torque with the traction wheels.

[Chris is me]

I could be completely misremembering, but it was very briefly discussed with some members of my team at least in part before our Kickoff meeting. The obvious use to us was to push or dash past defenders and just get to the scoring zone, then switch to the mecanum drive to reorient and strafe within the scoring lane. For all the flak I've given mecanum, this isn't the worst year for it.

However, our team has incredibly limited resources and we did not want to take a risk with our drivetrain this year. Also, the zone at the end of the field is a whole seven feet wide... Thus six wheel drive was the immediate conclusion.

I'm all in favor of calling the drivetrain "octocanum", "wave drive", "XDrive", or whatever silly name people want as long as it's catchy.

[Madison]

We discussed early the need for maneuverability in the scoring zone. Because there are three unique game pieces and because there is incentive to score each type of piece in a particular location, we understood that this conveys significant advantages to defending robots. They'll know exactly where you're headed and might more effectively impede you from getting there. With the ability to strafe or otherwise maneuver easily within the scoring zone, it allows some flexibility in getting our robot into place in the zone while avoiding defense.

Given that, our options narrowed to mecanum or swerve drive. We didn't really consider using an omniwheel-based holonomic platform. Swerve is the clear favorite here and many students argued passionately for it. Unfortunately, I'm working with a much stricter budgeting/spending policy this season and purchasing two robots' worth of swerve gear was a bit too pricey. Additionally, since we have no prior experience with swerve, I was a bit concerned with developing the framework required to adequately support it.

Mecanum wheels then emerged as a plausible alternative. After a more careful examination of how we thought things will play out, we decided that we weren't ready to give up the benefits traction wheels had to offer, so we looked at combining the two. We called it Mecatank on the first day, but Paul Copioli mentioned Octacanum here on CD, so 488's Octacanum was born.

Personally, this may be the last FRC robot I ever build, so I'm pretty exciting about doing something a bit different than the status quo. I think the decision to use mecanum was a risk -- but so far we're really happy with our implementation and our programming team and its fancy field-oriented drive have made me a believer that, at the very least, it's going to be a fun robot to watch out on the field.

[Ether]

Originally Posted by Madison

We called it Mecatank on the first day, but Paul Copioli mentioned Octacanum here on CD, so 488's Octacanum was born.

I've heard it called MecaTrac (Mecanum+Traction). Rolls off the tongue a bit easier.