Re: Einstein Drivetrains?
 

Jim calls it a Butterfly so a Butterfly it is.

Re: Einstein Drivetrains?
 

Really? I was under the impression this was a butterfly drive...

Re: Einstein Drivetrains?
 

Killer bee joke. Its also a part of BJCs signature: http://www.chiefdelphi.com/forums/member.php?u=36413

Re: Einstein Drivetrains?
 

So from the general conversation, I am guessing that most if not all of the drivetrains had a dropped center. If so, can anyone give me some idea how much to drop the center. On the KITBOT we used I believe all the wheels touched?:confused:

Re: Einstein Drivetrains?
 

In general, 1/8" - 3/16" are very common drops. Unless you're doing anything fancy, I'd lean towards the 1/8" side. Whenever I design using blue nitrile tread on traction wheels, I go 5/32" due to the extra grip from the blue nitrile. If you're doing pneumatic wheels, then 3/16 is one of the most common solutions. Anything else is 1/8 and you're fine.

*Note other people may have other preferences. This is just the general idea I've gotten from talking to many people about their drivetrain preferences and it seems to be the most commonly accepted one.

Re: Einstein Drivetrains?
 

Not sure I buy a trend towards swerve or "butterfly" or octocanum or h-drive or anything else on Einstein. Swerve drives aren't new. They've been around for more than a decade in FRC. While they are often overrepresented on Einstein compared to their general FRC population, they're not an overwhelming presence (2 on Einstein seems about historically normal). The largest population of drivetrain in FRC, even among elite competitors, has remained tank drives and I expect that to continue. Even the best teams often favor the advantages in the trade-off of going for a tank drive. What they lose in functionality, they gain back in resources (weight, space, cost, machine time, programming time, driver training time) they can dedicate to other areas. There's a reason you see teams like 118 using tank drives now, instead of the swerve systems they were famous for in the mid/late-2000s.

Re: Einstein Drivetrains?
 

The AM14U provided as the KOP drivetrain this year had .140" of drop in the center wheels in both long and square configurations. In a wide configuration, it had no drop.

-Nick

Re: Einstein Drivetrains?
 

Most teams use anywhere from 1/8-3/16 for 6wd & 8wd robots. Sometimes how much drop you use can be influenced by your wheel choice. For example a 4in Versa wheel from Vex has a "W" like tread pattern that will dig into the carpet fibers while a flat surfaced Colson wheel will not. Last year we used the Versa wheels and needed 3/16in of drop in the long configuration to get a decent turn while this year we used Colsons with 1/8in drop that turned like a dream. We noticed our issue last year when we put the robot on the field and noticed all 6 wheels were touching the carpet.

Depending on what wheels you use you can adjust the drop slightly. What I love about Colson wheels is you can trim them down by shaving down the OD of the wheel. Our drivebase this year was originally designed without a drop (doh!!) in a wide configuration and it turned similar to last year's long drivebase with 3/16in drop. We shaved down the other wheels by 1/16in to achieve the 1/8in drop and it works great.

Re: Einstein Drivetrains?
 

I wouldn't really consider 1625's 4 wheel tank drive with omnis on the front a 'butterfly-esk' drive. It is far more similar to a tank drive, in my opinion.

I think the biggest take away from that list is 8 6 CIM tank drives compared to 4 4 CIM tank drives. 2 to 1 ratio is pretty significant and very new.

Re: Einstein Drivetrains?
 

Wouldn't having wheels with different ODs make the center and outside wheels have different speeds? Or is it negligible due to the small change? Also, by shaving 1/16" off wouldn't that be a 1/16" drop?

Re: Einstein Drivetrains?
 

Because of the slight change in OD you won't notice much of a difference. IIRC this is how 233 has dropped their tank drives by just machining slightly smaller wheels.

Depends on how you look at the drop. Because we took 1/16th off of both ends and the robot is weighted towards the back there is 1/8in of clearance between one set of wheels and the floor. Another way people look at it is by how much lower the middle wheel is in relation to the other wheels. I've heard it explained both ways.

Re: Einstein Drivetrains?
 

Ahh ok. I haven't heard of the first way.

Re: Einstein Drivetrains?
 

I'll be home in a couple days and I will try to grab some pictures of what I call our "Bullet Omnis" They are ridiculously triangular and its hilarious.

Re: Einstein Drivetrains?
 

We can clear this up easily. 4 omni wheels can be called butterfly, to keep the Bees happy and the 148 style drive train can be called Tex Coast Drive like it should be*.

*For those wondering, I'm going to keep depending it be called Tex Coast Drive for the foreseeable future, so you should probably just get on board.

Re: Einstein Drivetrains?
 

Here is a picture of the drivetrain 2363 used this season. It is 6WD drop center live axle.