Modifying Vexpro Ball Shifter transmissions


Last year, Team 1676 used Ball shifters as seen here:

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?

Let me know

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

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.

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.

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.

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

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.

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…:stuck_out_tongue:

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.

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

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.

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).

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.

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.


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.

Yes thank you. I knew there were servo operated shifters somewhere!

Absolutely, leaks in general can be fixed. The only issue is that the solution to the problem is active, such that it can be applied in the event of a leak. As everyone knows, pneumatic systems pop; It is inevitable. I have thought about the spring/elastic solution but the one drawback is that regardless of what is modified, it is subject to the conditions within the gearbox. I am thinking that the fix (if internal, which I currently favor) should be subjected to a long term test. Perhaps a pre-Prototype phase.

I did see that the transmissions came with a servo option (has anyone used it?) - I just find that I am not quite in love with servo functionality in general. And is anyone considering other transmission options?

Pardon the “loose” earlier.

I would like to hear a bit more about neutral being a feature. I can only imagine it being used in one paradigm.

Where did you see this? I can’t find it on the vex pro page.

I’m not sure, but I think that team 67 might have used a motor to shift a ball shifter this year, but just ended up using a zip tie to lock it in high gear because it didn’t work well, so you might want to ask them about that.

I don’t know for sure if this will be an option next year, but did anybody try using an electric solenoid this last year, particularly for shifting? They were legal.

Thinking that might be a smidge easier than modding the transmission for a spring.

This thread will answer a few questions:

Specifically, regarding 67’s shifting this year:

Regarding electronic solenoids (Adam touched upon it in the above quote, also):

In conclusion, window motor shifters are very large, VEX motor shifters fry up a lot, VEXpro doesn’t make servo shifters (and 67 had issues making a replacement), and electronic solenoids aren’t strong enough.