Modifying Vexpro Ball Shifter transmissions
 

Hello,

Last year, Team 1676 used Ball shifters as seen here: http://www.vexrobotics.com/vexpro/ge...l-shifter.html

We had two stage transmissions, and used the standard pancake cylinders to shift from high to low. These were great on the field and relatively easy to maintain, until at Lehigh, and more frequently than not at Monty, we lost air. As most of you using the transmissions probably know, when you loose air, the transmissions shift to neutral; Thus my question: Has anyone come up with a reliable way of inserting springs into the transmission to default either a high or low gear when air is lost? beyond that, has anyone come up with a way to modify the transmission without compromising the structural integrity of the transmission case? Any suggestions?

Thanks,
Let me know

Re: Modifying Vexpro Ball Shifter transmissions
 

Is the Cylinder designed with a spring return to center. We used them, but I haven't checked the specs on the cylinder?

Re: Modifying Vexpro Ball Shifter transmissions
 

Specs on the cylinder. Looks like there's currently no springs.

You could switch from single rod to double rod configuration and connect springs from the chassis to the unused rod ends.

Re: Modifying Vexpro Ball Shifter transmissions
 

How did you lose air? (I'm assuming you made a type when you said "loose".) If it was through a problem with your pneumatics system, it may be more important to secure the whole system rather than trying to rig the shifters to default to one position. (Personally, I see the default neutral as a feature, not a bug, and I wonder if 1678 might be able to take advantage of it in the future...)

Our team ran with the ballshifters last year, and though we occasionally had pneumatics leaks elsewhere in the system, the gearboxes themselves didn't present any issues in that regard. If it really concerns you, I'm sure you can rig some springs to the cylinder-pin coupler.

Re: Modifying Vexpro Ball Shifter transmissions
 

You can probably just tie a piece of surgical tubing to some other part of the frame, then around the tip of the cylinder.

However, it's totally possible to have a pneumatic system where there are NO leaks throughout the whole season, it just takes some time. Make sure the teflon tape is applied well and in the right direction, and test ALL parts with 120 psi, and make sure that they don't drop more than 20 psi over a few hours. Use soapy water to check for leaks. Also, remember to make a tubing cuts perfectly perpendicular.

Re: Modifying Vexpro Ball Shifter transmissions
 

These are an inexpensive way of ensuring your tubing is all cut square:

http://www.mcmaster.com/#8288a51

Re: Modifying Vexpro Ball Shifter transmissions
 

I don't think 1676 would argue that it's not possible to avoid leaks. I don't think they're planning on allowing the leaks to continue with this robot and most likely will do everything in their power to avoid them in the future.

However, in the event a leak does occur, I think they want a fail safe so they don't also lose their ability to drive when they lose pressure.

Re: Modifying Vexpro Ball Shifter transmissions
 

Precisely Sean.Modify them to do what? That might help us help you.Between my team and yours, we'd have to ask FRC 1677...:p

We lost air because of a failure. That failure mode has since been eliminated, but no doubt there are others.

I was thinking that a plain rubber band would do the trick.

Re: Modifying Vexpro Ball Shifter transmissions
 

I would advise against it. Our team missed a potential division win in 2011 because of rubber bands. Springs are your friends.

Re: Modifying Vexpro Ball Shifter transmissions
 

I would assume (I don't know the situation you were in) that rubber bands had nothing to do with missing out on a win, rather how you used them caused your problems. Rubber bands are great tools when used wisely. They are cheap, plentiful, and easy to work with. At your next competition try walking around the pits to find a direct replacement for that critical spring that you used, then try finding a rubber band... Springs are not quite as friendly going around objects, you can't tie a spring to something without using another material or drilling a hole, and if a spring breaks or deforms you have to have a replacement that is the same size and strength. We never plan to use them, but rubber bands have been necessary additions to our robots all three years and have performed near flawlessly when taken care of.

Re: Modifying Vexpro Ball Shifter transmissions
 

I wonder if there is a way of modifying the ball shifter to avoid pneumatic shifting all together, even something like using window motors(servo might not be powerful enough to shift on the fly).

Re: Modifying Vexpro Ball Shifter transmissions
 

Absolutely there is, but for most, pneumatics are far more reliable, simpler, and lighter. These can easily be shifted with a servo, it that servo used, say, a Chap-Stick "extender" mechanism to do the actual pushing.

Re: Modifying Vexpro Ball Shifter transmissions
 

Can't ball shifters be purchased with a servo instead of pneumatics anyways?

EDIT: 254th post goes out to the cheesy poofs. I love those guys.

Re: Modifying Vexpro Ball Shifter transmissions
 

No.

Re: Modifying Vexpro Ball Shifter transmissions
 

You're thinking of AndyMark's shifters (though given past rules on servos, every year we've used AM shifters we've used pneumatics).

The VexPro line is pneumatics-only.