URGENT- VEX 2 CIM Ballshifter will not disengage

[rajaman0]

Hey everyone. Our VEX 2 CIM ballshifter is under around 80 pounds of force, and it will not disengage unless we push it downward slightly. We measured the force with a digital force gauge, so we know it is accurate, but isn't the ballshifter supposed to be able to take 400 pounds of force. Help please?

[waialua359]

Sounds like you either need to create a lever arm to shift or use a greater bore Cylinder to disengage while under load.

[tag_groff]

a while back, I uploaded CAD files for a dual pancake mod for exactly this purpose.
here is the link for the coupling, but you have to take apart the shell and drill new holes for the standoffs, I can also upload the CAD files for the custom mounting plate. This mod is assuming you have access to a 3D printer. What this does, is essentially put a 1.5" bore cylinder on the shifting mechanism. hope this helps
https://www.dropbox.com/s/4mveor2l36...oupling.SLDPRT

[Chris is me]

"80 pounds" means nothing without the size of your lever arm and the amount of reduction post-shifter that your system has.

We have 80 pounds running on a 1.5" diameter pulley running off a 20:84 reduction between the shifter and the winch. This means we are putting 60 inch pounds of torque on the output. Thus we are putting approximately 14.25 inch pounds of torque on our ball shifter. Under this load, we can release it with about 30 pounds of force. Possibly less.

What I would suggest is either adding more shifting force (though this is a little dangerous as the shifting bearing can't take much more loading) or adding a reduction between your shifter and your winch.

[audietron]

A way to see why it is not disengaging is to take the shifter apart and pull the coupler all the way back and look inside the shaft to see where the flat part of the plunger is located. It is possible to pull too much also if you are using a spool to wind up cord make sure it's a small diameter to put less torque on the balls. If you indeed need a bigger bore cylinder here is one from mcmaster : it requires making a custom bearing block but it should work with a little over 2 times the force for disengaging.

http://www.mcmaster.com/#6113k15/=qqez9a

Good luck!

[Brian_R]

Originally Posted by tag_groff

...

What this does, is essentially put a 1.5" bore cylinder on the shifting mechanism.

...

It's equivalent to putting a 1.06" bore cylinder (calculated as 0.75"*sqrt(2)). Cylinder force is pressure times area, and the circular cross-sectional area of the cylinder scales by the square of the radius. This mod doubles your force - but doubling the piston bore would quadruple your force.

[PAR_WIG1350]

Originally Posted by Brian_R

It's equivalent to putting a 1.06" bore cylinder (calculated as 0.75"*sqrt(2)). Cylinder force is pressure times area, and the circular cross-sectional area of the cylinder scales by the square of the radius. This mod doubles your force - but doubling the piston bore would quadruple your force.

Did you account for the area occupied by the piston rod?

[BBray_T1296]

Originally Posted by PAR_WIG1350

Did you account for the area occupied by the piston rod?

This area loss does not exist for the pushing (extending) stroke, only for the pulling (retracting) stroke. It entirely depends on which direction you are shifting. At any rate, with 2 pistons, both the extending and retracting forces are doubled (just not the same, slightly)

[Answer42]

Just worked on one of these yesterday, same problem. I'm guessing they used the low gear to pull the which back, and removed thier high gear. In which case the shifter has to pull away from the gearbox and the rod area does matter for force. We solved it with a 1.5 inch bore pancake cylinder on extended versions of the original standoffs and an adapter plate. The long standoffs were to move the cylinder back behind the cims where it could fit. Shifts wonderfully now. And didn't require any more gearbox modifications

[rajaman0]

Hi everyone,
Thank you all for your quick and helpful suggestions! We ended up increasing the size of the bore cylinder and making custom standoffs. It works perfectly now!