hey got a tech question about AM Trannys

[Holtzman]

For the people who have had issues breaking roll pins in the shifter assembly, are you sure that the shifter was properly adjusted and that the nylon stroke limiting spacer was installed?

I have seen these roll pins break if the nylon spacer is omitted, or if the shifter is adjusted poorly.

You should be able to adjust the Shift Block such that when the cylinder is at full extension, the dog gear is nearly flush against the 48 tooth gear, and when the cylinder is retracted against the nylon spacer, it is again nearly up against the 35 tooth gear. When adjusted properly, the roll pins only see significant load during the shift. If they aren’t adjusted properly, the roll pins are loaded constantly, and this can lead to premature failure.

In the first match of the GTR finals, we broke the 1/16" Roll pin in the shifter block. This was caused by omitting the stroke limiting spacer. After re-installing the spacer, and replacing the roll pins, and properly adjusting the cylinder, we’ve experienced no further issues.

Also, the 3/32" Roll pins through the dog gear can be replaced with these "High Strength" roll pins from McMaster Carr. Part number 95755A131. They seem to be a tighter fit than the pins that come stock with the gearboxes. As for whether they are actually any stronger than the ones that come stock with the gearboxes, our very limited testing says "So far so good".

These shifters are quality engineered and built products. If your breaking roll pins, you’ve probably got something put together wrong.

[Uberbots]

Originally Posted by Holtzman

For the people who have had issues breaking roll pins in the shifter assembly, are you sure that the shifter was properly adjusted and that the nylon stroke limiting spacer was installed?

I have seen these roll pins break if the nylon spacer is omitted, or if the shifter is adjusted poorly.

You should be able to adjust the Shift Block such that when the cylinder is at full extension, the dog gear is nearly flush against the 48 tooth gear, and when the cylinder is retracted against the nylon spacer, it is again nearly up against the 35 tooth gear. When adjusted properly, the roll pins only see significant load during the shift. If they aren’t adjusted properly, the roll pins are loaded constantly, and this can lead to premature failure.

In the first match of the GTR finals, we broke the 1/16" Roll pin in the shifter block. This was caused by omitting the stroke limiting spacer. After re-installing the spacer, and replacing the roll pins, and properly adjusting the cylinder, we’ve experienced no further issues.

Also, the 3/32" Roll pins through the dog gear can be replaced with these "High Strength" roll pins from McMaster Carr. Part number 95755A131. They seem to be a tighter fit than the pins that come stock with the gearboxes. As for whether they are actually any stronger than the ones that come stock with the gearboxes, our very limited testing says "So far so good".

These shifters are quality engineered and built products. If your breaking roll pins, you’ve probably got something put together wrong.

Well i dont remember any spacers on the piston, so i guess that needs to be put into the wiki for next year (=
And yeah, we tried stronger pins, but then the next weakest thing broke- the bearing the the pin holds against X=

[Pat Roche]

We actually ran into the pin issue at NYC. The robot shifted for the better part of two competitions before finally shearing a roll pin in our last qualification match. We are currently looking into replacing the roll pin with a hardened dowel pin to give it some strength. Be careful doing something like this though, because the shaft is so small at the hole's location. You need to make sure you won't damage(via shifting not installation) the shaft changing to a dowel pin. At the competition we would have normally just changed the air pressure but it was needed for other parts of the robot.

[Travis Covington]

Are any of you limiting the piston stroke to ensure that the piston isn't shoving the dog into either dogged gear?

I have never worked closely with the AM trannys but on our own gearboxes we pay very close attention to the side load that the dog puts on the gear, making sure there is a gap of some sort so that the dog doesnt physically push on the dogged gears when the dog teeth are engaged. We use 1/4" ID nylon spacers to limit the pistons stroke to just under the distance required to move from being fully engaged in one gear to being fully engaged in the other.

I should note, we run at a full 60 psi and use a #3-48 stainless SHCS instead (which is MUCH weaker than the included roll pin) We have yet to break a screw under normal conditions. A few times we failed to tighten the jam nut on the piston rod which allowed the dog to push on the dogged gear, and only during those few times did we have any problems.

Couldn't hurt to throw it out there...

Edit: Oops... I didn't even see Tyler's post. This just reaffirms what he said though!