Weird Behavior - Vex Pro Ball Shifters

[tag_groff]

Originally Posted by Brian_R

Yes - if I recall correctly, tightening or loosening this nut can change how the coupler assembles relative to the piston.

We ended up using two of the stock pancake cylinders in parallel with a 3D printed coupler (graciously made available by user tag_groff of 4265 here ). This required us to mount the standoffs for the cylinder in new holes in the ball shifter, and make a plate to hold the pancake cylinders side-by-side.

Depending on the forces in your winch, these might still have trouble shifting. For TESTING purposes, my understanding is you can run these pistons up to 120 PSI to see if they have enough force to shift. This is equivalent to a single 1.5" bore cylinder at 60 PSI, which you could order after ship and swap out at competition.

Note that I'm just a guy on the internet - check all the safety stuff (pneumatic component ratings especially) before trying anything out of spec like this. Also, since this is well out of the expected usage of the ball shifter, be prepared for possibility of these big forces damaging the ball shifter over time. With our brief testing of 2 cylinders at 60 PSI, we haven't encountered any issues... yet.

Even though our team has moved away from a winching catapult, I am really glad to see that the work I did for this mod is being utilized by other teams. Thank you very much.

[DampRobot]

If the problem is solved by upping the pressure above 30 PSI, why not just crank it up to 60? We've had problems with out Vex Pro Ball Shifters not shifting correctly when they don't have full pressure. There's probably enough separation forces in the shifter that you need that extra pressure from the piston to keep it locked in gear.

[Paul Copioli]

Originally Posted by DampRobot

There's probably enough separation forces in the shifter that you need that extra pressure from the piston to keep it locked in gear.

In normal use, this is just not true. The ball shifter is set up such that when the shifter is in each position the balls are sitting on the flat area of the plunger. This means there is no separation force at all.

As some of the people using this as a pull back device, the normal force between the flat area of the plunger and the balls and the side of the ball pocket in the gear at high (externally applied) torque conditions, the plunger does not want to disengage.

The critical dimension on the layout drawing on the vexpro.com web site must be met if you are using your own gearbox.

Also, I have found that the SMC solenoids are not that happy at anything under 40 psi.
Paul

[audietron]

another thing to remember is the radius of the spool you are using to wrap a strap around if that is your way of pulling. We over looked the diameter of the spool and use a 2 inch diameter spool. If it is 1 inch diameter than you are halfing the torque put on the balls allowing more force for releasing and using the cylinder set up.

[Nunners]

Gearbox is functioning as it should now. We opened up our gearbox and made sure that the cylinder was pushing and pulling at the correct distance. Also, we fabricated some more exact spacers to input onto the hex shaft where our wrench is mounted. It seems like both of these modifications fixed the problem.

Even without applying any PSI, the shifter is no longer pulled into the gearbox.

Thanks for all of the suggestions!

[Brian_R]

Originally Posted by tag_groff

Even though our team has moved away from a winching catapult, I am really glad to see that the work I did for this mod is being utilized by other teams. Thank you very much.

No, thank you! That little tweak took us from not firing to firing.

We plan to put a sticker on the coupler to acknowledge the borrowed design work - Would you prefer your name, team number, Chief handle?

[tag_groff]

Originally Posted by Brian_R

No, thank you! That little tweak took us from not firing to firing.

We plan to put a sticker on the coupler to acknowledge the borrowed design work - Would you prefer your name, team number, Chief handle?

team number please