I started practicing making custom gearboxes since last season (looking at designs, watching videos, making different versions, etc.), and I wanted to attempt to design, and possible make a custom shifting gearbox. The only thing that confuses me is the pneumatic cylinder connecting to the dog gear. I understand that there is a shoulder bolt typically connecting the dog gear to the shaft within the driving shaft, and then that eventually connects to the pneumatic cylinder, but how does the shift block work? Is that just a bearing inside to allow the shifting shaft to spin and the pneumatic cylinder not rotate? And for most teams that are running custom shifting gearboxes, are you buying a COTs shift block or making your own?
That’s exactly it. Most everyone I know buys theirs.
GRT has been making them for years. Lately the students are making them for our own ball shifter shafts. When designing and building our gear boxes this is one of the simpler parts and we can make ones that fit our designs better. We can also make them quicker then ordering them if we are in a hurry.
I’m interested in learning a little more about this. This shift block is used with this cylinder, is the inside of the shift block threaded? And then you screw the shift block onto the end of the cylinder? We did Evo shifters last year and they came pre-assembled, so I didn’t really look into it that closely.
I recognize that there are advantages and disadvantages to both dog shifters and ball shifters. But as someone who’s had a lot of experience designing shifting gearboxes for FRC using both methods, I’d recommend you switching to the use of ballshifters. There easy to buy from WCP, easy to implement, and I’ve never had one fail on me.
Bimba makes flat cylinders that take a lot less room in your robot. They make the throw of the cylinder to the length that you order…
Adding on, ballshifters make autonomous routines with shifting more consistent and you can shift in more extreme conditions (pushing matches, high speed, etc).They also seem to be more reliable, but failures can be eliminated in dogshifting gearboxes with a bit of precaution.
Edit: The ballshifting gearboxes are made by VexPro, WCP is a reseller.
Is my understanding of how the cylinder and shift block work correct, though?
The shift blocks that come with the ball shifters are “clamshell” blocks (2 halfs split down the long axis of the part). Inside the clamshell are two grooves - one for a small bearing and one for a hex nut. You attach a bearing to the ball shifter shaft. You attach a hex nut to the shaft on the pneumatic cylinder. Then you clamp the two halves of the shift block to the ball shifter and pneumatic cylinder shafts so that the bearing and hex nut are captured in their respective grooves.
Take a look at page 16 of the VEX ball shifter assembly instructions to see how this works.
There are plenty of other ways you could accomplish the same thing. But at the end of the day, you want to have a bearing inside the block to allow the ball shifter shaft to rotate. You could capture the bearing inside a single piece block somehow and then thread the other end of the block to screw the block onto the pneumatic cylinder shaft rather than capturing a nut.
Hi there!
Attached is a few prints of how our newer am-3451 shift block assembly from the EVO Shifter is built, along with the supplementary parts to it. This is a significantly improved design over the older style shift blocks, as the shaft has a lot less play in it with a much larger bearing installed.
Your original thoughts are correct; the key is to create a robust threaded connection between a ‘thing’ to hold a shaft with a bearing in it, and the threaded rod of the shift cylinder so that the cylinder doesn’t rotate.
Hope this helps!
-Nick
P.S. Easter egg; these documents contain the working codename for the EVO Shifter; the GEN3 shifter.
am-3451 GEN3 Shifter Shift Assembly.PDF (52 KB)
am-3452 GEN3 Shifter Shift Block.PDF (43.9 KB)
am-3453 GEN3 Shifter Shift Rod.PDF (68 KB)
am-3454 GEN3 Shifter Shift Block Cap.PDF (40.2 KB)