So I want to design a 2 speed gearbox and I can either do a ball shifter or a dog shifter. I can see that a ball shifter would be more compact but the issue I see with making one is that the long shaft isn’t really long enough for a wcd. A dog shifter seems harder to design especially since the shaft is 2 different sizes at 2 different points and the dog gears are a lot more expensive. The ball shifter gears also appear to be cheaper so they have that going for them. Because of this, I am leaning towards designing a ball shifter but how would I overcome the short shaft issue? While I am here, is there some groundbreaking benefit to a dog shifter that would make someone choose that over a ball shifter? Since looking at team gearbox designs, I’ve personally noticed more teams choose to do a dog shifter over a ball shifter if it is a custom gearbox.
the long shaft isn’t really long enough for a wcd.
I may be mistaken since I’ve never attempted this before, but I believe all v2 ball shifter shafts have pinned output shafts that allow you to swap it for your own.
Ball Shifter v2 (Note the 3mm X 18mm COILED SPRING PIN and diagram of hex shaft on 2nd page)
Alternatively, you can design the gearbox such that the ball shifter output shaft is not the shaft on which the wheel is attached to. My team did just that this previous season, (albeit it was the much heavier solution, and less compact vertically):
So what I’m guessing is use a pin punch and remove the coil spring. Then drill a hole in the new shaft for the coil spring.
If you decide to make a 2 speed dog shifter, they aren’t too difficult, but making the shifting shaft is the worst part. We used 4140 steel I believe for ours which gave us a little bit of difficulty finding iirc. We used VexPro gears for most of the gears, the 4 tooth dog and gears from AndyMark, and then the SMC shift cylinder used on Vex and WCP gearboxes. We did run into the shoulder bolt used as the pin with the dog loosening up, and then breaking, requiring us to drill the last bit of threads out and screw a new one in. Since we were using our gearbox to climb, if that happened in a match, we really wouldn’t notice until the end when we went to climb.
There’s also a bit of machining you’ll have to on the end of the thunderhex shaft that interfaces with the shifter shaft body. (left section of image)
The “traditional” dog shifter layout with the 1st stage bull gear fitting between the two dog gears doesn’t work with the vex ballshifter, but there’s a pretty simple workaround with a .3" spacer plate that also reduces forces on the end of the motor shaft.
(ignore the pink/purple circle)
What do you mean by bull gear, is that the gear that moves back and forth? Is the .3" spacer placed between the 2 ball shifter gears? Also, I’m assuming a 3rd stage will be necessary in order to have proper speeds and not a robot that trips the breaker? I was playing around with JVN’s calculator and under no circumstance could I think of a reasonable speed without using a 3rd stage. I’m asking cause 330 used a custom ballshifter as seen on behind the bumpers and you’re profile says you’re from 330 so I guess you might have experience here.
The bull gear is the larger of two gears in a pair. In the above image the “1st stage bull gear”, is the rightmost gear on the upper shaft. The .3" spacer is the purple plate that holds the bright green .5" ID bearing for the dogshifter shaft, attached to the gearbox motor mounting plate.
This isn’t really a VexPro ballshifter in a different box, it’s more of the ballshifter mechanism made to work in a traditional-ish two stage reduction gearbox. It actually uses almost all the same ratios as the WCP SS box. With 6" wheels, we geared for around 8 and 18 FPS using the new 10t pinions.
8" wheels would certainly be a stretch, but I think you could make it work with the 9t pinions and some adjustments.
Btw, I’m the guy who designed that gearbox and the guy in the Behind the Bumpers video. I’ll probably post the CAD for it soon, just got bogged down with school and work stuff.
Ok, so I’m assuming the bull gear would act as a 3rd stage in a way. The Vex gearboxes have the motor pinions directly driving the same gear that would interface with the ball shifting gears. Oh, so the spacer is able to shift the ball shifting assembly forwards which allows the use of the bull gear. Correct?
Kind of. The normal ballshifter has a very unique layout which makes terminology a bit weird.
On the nose for the 2nd part. There is actually a more efficient packaging method with the 1st stage bull to the left of the dog gears in that image, but it involves custom pinions, weird adaptors, or a legal way to have longer motor shafts. (Or just flipping the motors, kind of like this but in a normal flipped GB layout)
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