View Single Post
  #27   Spotlight this post!  
Unread 10-06-2014, 15:52
asid61's Avatar
asid61 asid61 is offline
Registered User
AKA: Anand Rajamani
FRC #1072 (MVRT)
Team Role: Mechanical
 
Join Date: Jan 2014
Rookie Year: 2013
Location: Cupertino, CA
Posts: 2,229
asid61 has a reputation beyond reputeasid61 has a reputation beyond reputeasid61 has a reputation beyond reputeasid61 has a reputation beyond reputeasid61 has a reputation beyond reputeasid61 has a reputation beyond reputeasid61 has a reputation beyond reputeasid61 has a reputation beyond reputeasid61 has a reputation beyond reputeasid61 has a reputation beyond reputeasid61 has a reputation beyond repute
Re: The in-wheel swerve shifter!

Quote:
Originally Posted by Chris is me View Post
Why are you ignoring the load of the robot and the drivetrain itself? Even with your shifting coupler, it will only disengage as the motor attempts to turn the shaft the opposite direction. Until this is disengaged, as the motor slows the drivetrain slows, and the load of the drivetrain is placed on the motor.

CIMs do not "instantly" switch direction under zero load. Quickly, maybe, not instantly.
Okay, consider this:
As soon as the cim begins to slow, the mated hub/gear will continue spinning at the previous speed, as it is not mated to the shaft except by the dog (which is slowing down). The obtusely angled faces on the dog and hub/gear will contact each other and push the dog into a mate with the other hub/gear, which is spinning in the opposite direction as the original mated gear/hub.
Keep in mind the cim is accelerating to match the speed of the second gear/hub, so its opposite spin, combined with the cim itself accelerating in the opposite direction, will make the shift time extremely low. The inertia of the robot aids the shift.

I said "instantly" as a hyperbole. It was undetectable by the human eye. The only way I knew it has reversed was because I was holding the cim and I felt it shake.

Quote:
Originally Posted by DonRotolo View Post
I share the concerns about the forces seen by the dog teeth; steel or not, the shock loads can easily exceed several tens of LbFt, translating to hundreds of LbF on the tooth.

But that can easily be compensated in the final design. Overall a very ingenious solution!

As for needing a 4-axis CNC: Naah. We got metal files and hordes of Freshmen...
I still want to test this. Like I said, the inertia aids the shift, so I want to test under load to see if it shifts properly.

Freshmen doing this would be interesting.

Quote:
Originally Posted by Seth Mallory View Post
If you took a Sturmey Archer S3X fixed gear 3 speed hub you could make a 3 speed swerve drive. It would most likely be to wide but it would work for testing and as a base for a interesting design. Remove the flanges and mount some tread to the hub and you have a 3 speed wheel. You would want to cut the axils down and a few other things but it would be great for testing concepts and to work from.
Funny story, I was just looking into this. They seem really cool, but I'm worried about it shifting when the motors slow down due to the uncontrolled autoshifting on weird turns. I also am not sure what drives the shift. Love those bicycle gear hubs though.

Quote:
Originally Posted by Jared Russell View Post
I want to see an in-wheel CVT/IVT using two motors and a planetary transmission.
I cadded something like 5 of these for a few weeks before I realized there was no torque advantage to using a planetary IVT. And the only other CVTs I saw were cone CVTs and the like. So I moved onto planetary shifters and swerves.
None of my designs were in-wheel though. That's like... weird...

Quote:
Originally Posted by Greg Woelki View Post
You could certainly test the concept with them like you said, but as far as a competition robot goes they aren't just, wide, they're also two pounds each!
Well, if you can spare the weight. Swerve chassis that don't shift normally can be extremely light (<30lbs with motors).

Last edited by asid61 : 10-06-2014 at 16:12.