I was wondering of anyone has made a two speed transmission and if so how you managed your shifting. From what i understand there are multiple ways of shifting, but the only one I understand is crash shifting due to it’s simplicity. I would love explanations on different methods and pictures if possible would be super helpful.
Thanks
Do you want specifically custom shifters or would COTS transmissions work? If you want COTS, you could look into both the AM Super shifter and the VEXPro BallShifter. I think there’s also a video or two floating around YouTube that explains ball shifting. Never bothered looking for dog shifting. The CAD for both products are on their respective pages, so if you’d like you can download them and take one apart without actually buying the gearbox.
I was kinda hoping for custom builds just to see how people did it, but thanks to the link to the ball shifter I had only seen the andymarks shifter and the supershifter whih I think are both dog shifting
You might have to do some digging, but you can find some shifting gearboxes on FRC-designs.com
Somewhere out there is 33’s 4 speed transmission… I know it’s in the white papers some where.
Here is one that one of our team member built http://www.chiefdelphi.com/media/photos/24580
Its a dog shifting design, you can see the the dog in the pictures.
I could get more pictures if you would like. Basically both the gears spin freely from the shaft and the dog is attached to the drive shaft. The dog will latch onto the first or second gear transmitting that power to the driveshaft
Looking at the dog shifter if I understand correctly all the gears are free spinning on the shafts and the dog is attached to the driven shaft. the dog meshes with one of the two gears to spin the driven shaft. Is that right?
Yup, that is correct.
Great thanks i’m like 90% sure I understand now
The one you see most often nowadays is dog shifting: the dog gear is (with the teeth on the side face) engages a recess on one of two output gears. I’ve built one of these with 188; it worked great. I’ve also bought these off the shelf.
Captive-ball shifting is once again popular, with the release of VexPro’s kit. Previously, 222 used this design. Here, balls are displaced in and out of recesses in the central shaft, to engage gears with slots in their bores.
You used to see axial-engagement (“crash”) shifting more often. There, the gear teeth themselves slide in and out of mesh. I’m not a huge fan of this, but implemented with fairly large gear teeth, it works fine.
Rarely, you see tangential-engagement shifting. I tried it once with 188 and it didn’t work properly (the gears wouldn’t stay in mesh). However, knowing what I know now, I think I could probably make it work. However, I don’t see any particular advantage to doing so.
You also used to see planetary shifters more often, when the Nothing But DeWalts modification was popular. (A DeWalt XRP drill transmission, shifted with a servo by sliding the device that locks and unlocks its planetary gearsets.) I’ve implemented this, again with 188, with two CIMs feeding a single DeWalt. Everything worked reasonably well, except the custom output shaft. (It needed to be hardened alloy steel, not hot-rolled free-machining steel.)
I’d be interested if it were possible to use a linear electric solenoid to shift instead of a servo or pneumatics. The bad part is that they have maximum “on” times (duration the plunger can be “out”), which can be between 1 and 2 minutes or shorter (which is a problem in our application) because they need to cool down. It would be useful for teams who don’t want to deal with pneumatics, especially if shifting would be their only use, and want to have fast shifting, because servos are sloooooow (in comparison)
Could use a window motor/cam linkages to shift both, or a faster motor with a leadscrew.
Dealing with pneumatics isn’t that difficult. Don’t need an on-board compressor.
Has anyone tried using a shifting bicycle hub? The kind that bikes without derailleurs use?
I realize pneumatics isn’t difficult, but it’s A LOT of overhead weight (even without on-board compressor). You’ll need at least the manual relief valve, emergency relief valve, pressure gauge, storage tank, solinoid, tubing and your actual pneumatic cylinder. That’s quite a bit when all you want to do is shift!
I suggest looking at Team 254’s shifters on their website (www.team254.com)
Here’s their 2012 transmission: http://media.team254.com/2012/08/gearbox.jpg
Also, a bit unrelated, but did you use to have a MC server?
The question is if the extra weight is worth the extra performance. Pneumatics means faster and more reliable(imo because there is little chance to shear a dog gear) shifts. In addition to that, pneumatics can be very useful for simple, 2 position operations, can be used as springs, and can be actuated after the buzzer. This gives pneumatics tremendous versatility. I personally think pneumatics gives enough benefit to outweigh the price.
I realize that. I’ve used pneumatics on every robot I’ve been associated with building. I’ve just seen a lot of teams staying away from pneumatics because of either difficulty or weight.
The biggest issue with derailleurs is that it is a single direction gearbox, and most FIRST applications are bidirectional.
