Last night we finished the chassis for our prototype and were reassembling the transmissions after filing down the pin that was sticking out of the dog gear. We noticed the following behavior, and we have no reason to believe this is the first time this has happened:
If we put the transmission in neutral without a pneumatic piston attached, the gears freespun beautifully, even without re-lubing anything
If we put the transmission in gear without a pneumatic piston, the gears still freespin, though the dog gear likes to get caught on the face of a gear on that axle, so it really becomes hard to get it in gear – lubrication should help this
If we attach the pneumatic piston, all of a sudden the gears stop freespinning. We’re still able to turn them without much effort.
If we prevent the shaft of the piston from turning with the pneumatic attachment as we spin the internal gears, the gears get MUCH harder to turn.
In essence, the inside of the pneumatic piston is spinning with the transmission and we want to stop it… so the question is how? If we force it to stop, it feels like something in the piece that attaches to the piston is binding up. Since there are 2 tiny screws that look like they could take a little while to get off and on, we didn’t want to proceed without guidance. Anyone have any ideas?
It is possible that there is something wrong with the bearing in that little black bearing housing, or it is not aligned properly. At tempest 'n tampa this year, one of our shifter shaft bearings blew apart.
You could try removing the piston, shifter shaft and bearing housing from the robot, and seeing if it spins well when not on the gearbox. If it does, I would guess that its an alignment problem. However, if it doesn’t it could be a bearing problem.
What you may want to try to do is to work on the inner workings of the part that attaches the cylinder to the shaft. This takes a lot of patients though, so be careful if you do this!!! I say this because to do this there are two small roll pins which if lost, are near impossible to find.
To start off, you will need to open the gearbox up, make sure to remember where every thing goes. You need to remove gears until you get to the final gear cluster where the dog is attached. Push the bearing out of the side plate to free this assembly of the gear box. Then using a skinny, yet long punch, gently tap the roll pin out of the dog, but not all of the way. I would do this on the skinny side of the dog (the part that doesn’t go into the gear when shifting. Sorry I don’t know all of the technical terms for this). Once you do this you should be able to slide the shifting shaft out of the main shaft. When you do this, take the two screws out that hold the ball bearing into place. Remove the shaft along with the ball bearing (one piece) and you should see a roll pin. Now you have one of two things that are bad. Either A) The roll pin is not centered and is hitting the wall inside of the cylinder attachment, or B) The ball Bearing went bad. If your problem is A), then simply tap the roll pin until it is centered, then reassemble. If your problem is B), then tap the roll pin out (DON’T LOOSE IT!) and replace the ball bearing and roll pin. Either way, reassemble the the gear box the way you found it. NOTE: Make sure all of the bearings are seated, otherwise that nice glide the gears do when you stop spinning them will disappear. Also when you go to put the shifting shaft back into place, put your punch through the hole in the dog AND the shifting shaft (to keep every thing alined).
If this does not fix it, then the cylinder is probably at an angle. You may want to loosen the two 10-32 screws that hold the cylinder brace and try to straighten it out to the best of your ability.
Our prototype has a similar issue with spinning pneumatic cylinders when the transmission is in gear. Is it as simple as the cylinder not being straight?
We are using the bimba cylinder that required us to supply the nut to mount, incase that changes things.
I will double check tomorrow; we chains on the gearboxes at the moment. I do know that this happens on both transmissions, so it may just be a misalignment issue. Thanks for the detailed info!