pic: Can anybody give me advice on my Butterfly drive that I am working on?

[JesseK]

I'm curious whether he intends to do a 4-speed or not. The major tactical advantage of keeping a 1:1 ratio between the omni & traction wheels is to be able to change from one to the other at full speed. There is also another (huge, IMO) build advantage to this setup which should help answer the actuation question, and it is outlined on slide 3 of this paper:
http://www.chiefdelphi.com/media/papers/2968

I think I need more detail on how the drive train will be run before commenting further. For example, do you plan to use 1 serpentine belt or two belts per side?

[Ty Tremblay]

Originally Posted by JesseK

I'm curious whether he intends to do a 4-speed or not. The major tactical advantage of keeping a 1:1 ratio between the omni & traction wheels is to be able to change from one to the other at full speed. There is also another (huge, IMO) build advantage to this setup which should help answer the actuation question, and it is outlined on slide 3 of this paper:
http://www.chiefdelphi.com/media/papers/2968

I was just musing on the idea of pulling off a mostly-COTS 4-speed with this design.

While I agree that you could change modes on the fly, I don't see a major advantage of this. If you're changing to traction mode, you're either trying to push or not be pushed. In that case, it'd be better to have the switch to low gear already built into the change of modes than to have to switch to low gear after changing modes. To put it simply, what advantage would low-gear omni mode give you? What advantage would high-gear 4-wheel traction give you?

From my experience, a major goal when developing a drivetrain should be to reduce the mental load on the driver. Having 4 possible drivetrain states for the driver to keep track of sounds like too much.

Originally Posted by JesseK

I think I need more detail on how the drive train will be run before commenting further. For example, do you plan to use 1 serpentine belt or two belts per side?

Based on the size of the pulley on the gearbox, I'd say he's going for a 2 belts per side system.

[JesseK]

Originally Posted by Ty Tremblay

To put it simply, what advantage would low-gear omni mode give you? What advantage would high-gear 4-wheel traction give you?

From my experience, a major goal when developing a drivetrain should be to reduce the mental load on the driver. Having 4 possible drivetrain states for the driver to keep track of sounds like too much.

Low-gear omni provides safe-zone agility while lining up on a precision game piece or goal, like 2011, 2012 or 2013 (2012 in particular).

High-gear traction provides faster straight-line movement since the 4 traction wheels on the corners make it harder for the robot to turn itself. This is tremendously useful in autonomous 'drive straight' routines like 2011.

Changing to high-gear traction at speed can prevent a robot from being knocked off course while still beating a defender to a point straight ahead.

On the surface I agree with your last point, that 4 modes is a bit much. Yet for the team to be successful with any "butterfly" drive, they will need practice. The modes I've described are fairly intuitive, so it wouldn't be an issue for a team with a nominal amount of practice. I've driver coached lots of students over the years only a few of them would not have been able to handle a more intuitive setup of the modes.

From a mechanical maintenance perspective, 4 modes can be a nightmare given that there are 6 subsystems* with 6 actuation points in the current CAD above and 4 subsystems with 4 actuation points in the 624 design. I like that your design has only 4 subsystems with 4 actuation points and is effective yet simple, but I also know how my team does autonomous and driver training, so it wouldn't be right for us. That's a tradeoff the OP has to decide on as well.

*subsystem here is a contained system which is actuated (i.e. not the drive train frame or wheels which are not actuated). Each shifting gearbox is 1 subsystem, but a non-shifting gearbox is not.

[mlantry]

aside from some of the points people have had you are gonna want to put some kind of support between the ballshifters because just having those angle bracket supporting the shifter won't be enough on their own to be supported well