Re: pic: FRC 2869 - 2016 Offseason bot
 

I haven't yet heard anything bad about DARTs; do you have some discussions to link to on that? Would be good to know for the future.

As you've probably learned, rotational arm joints are sometimes tricky and require some care to do with the standard sprocket at the pivot point method of rotation. You could probably have attempted something with pneumatics, which simplifies control and is easier to make strong. Stack two pistons of different throw length on each other and now you have a four position actuator.

Re: pic: FRC 2869 - 2016 Offseason bot
 

The DARTs have several eccentricities you need to work around -- they aren't "plug and play" and require a level of hardware and software understanding. If anyone is interested in details, you can PM me and I'll detail our experience. We used 2 on our arm last year.

It may change for next year, I know AM is working to make them better based on team feedback.

Also, thanks for using us as an inspiration! :)

Re: pic: FRC 2869 - 2016 Offseason bot
 

What gearbox are you guys using for manipulating your arm and what is its reduction?

Re: pic: FRC 2869 - 2016 Offseason bot
 

The Versaplanetary has 2 10:1 stages for 100:1. It then goes into a 24t gear which goes into a 60t gear which brings the reduction to around 250:1. A chain is then driven by a 12t Sprocket which goes to a 36t sprocket making our end reduction about 750:1.

The reduction was pretty much perfect for the arm (It originally had a giant cylinder mounted to the back). The biggest issue that we cantilevered a shaft which had to deal with loads that big on a plastic gearbox.

Re: pic: FRC 2869 - 2016 Offseason bot
 

How did you guys get the motors and gearboxes in with that tubing in the way? It looks like it would take quite a while to replace anything should a motor go out or something similar.

Re: pic: FRC 2869 - 2016 Offseason bot
 

Attaching everything was very simple but repairing? Not so much. We were pretty confident that the gearboxes wouldn't break in the 1 offseason they were used at, but... They did. Ended up taking us about an hour and a half which involved taking the entire side of the chassis off, sliding out the output shaft and then carefully reassembling everything. We will definitely design stuff to be more easily repaired in the future.