pic: 2 speed tranny



3.32 lbs without cims
1/4" aluminum side plates
pneumatic smash shifting

why not big cim little cim combo?

A better question would be why use the big-cim little cim combo, if you don’t need 2 small cims elsewhere?

Very nice, and very light! Is there a reason you switched to aluminum side plates and returned to bronze bushings?

Probably because that is significantly heavier, and a bit weaker.

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Its hard for me to judge from the angle, but it looks like you will not have much room for an output sprocket due to the encoder. I could just be look at a bad angle. Whats the gear ratios?

Bronze bushings work well for shafts that have to slide as well as turn…

It does look that way. However, I’d say they aren’t planning on having a sprocket directly attached to the output shaft. The encoder and shifter would get in the way except in a fairly narrow angle. Plus that’s a pretty small sprocket. I’m going to guess that they use a coupler to a longer shaft that can either direct drive a wheel or connect to a sprocket.

My question is, are the side plates going to be hogged out to save weight? Those are some heavy trannies!

The plastic plates we used last year flexed and allowed everything to become misaligned. In years past, everything spun on brass bushings except the motor combiner. On this design, everything is on bearings except the shaft for the smash shifting, however the gear cluster on that shaft has bearings inside of it.

The transmission is designed to be modular so we’ve put all the drive sprockets on the same shafts as the wheels (6wd).

http://www.flickr.com/photos/jdebner/397162975/in/set-72157594547502324/
here’s a pic of last years bot. you can kind of see how where the tranny links to the center axel.

.925:35 in low and 3:35 in high

If needed yes, but I was under the impression that 3.32lbs per side was light.

Im with you on this one. 3.2lbs perside is quite light especially since your getting 2 speeds out of it. I do think you could get a bit more weight out of it though, maybe 3/16" sideplates?

Weight wise, you’re carrying about 3 small CIM motors with the drive motors attached. Mind you, if you can get the rest of the robot to also fit in the weight budget, I’d rather have the weight in the trannies where it’s low to the ground. If not, remove some of the “extra” wall material away from the bearing areas. There’s a lot of weight there.

I wouldn’t go so far as to say ‘a lot of weight.’ I can see this getting into the mid to high two pound range. That’s, at most, a 1lb saving for the entire robot at the cost of significantly increase machining time. As drawn, the plates could be made on 195’s EDM, if you add pocketing that significantly increases manufacturing time and adds another machine. (unless it is already being milled, then it just adds time)

If that middle plate can be eliminated though, that would save weight and make it easier to machine (one less part). I can’t really see what that plate’s purpose is so I don’t know how easy that would be.

The middle plate supports the shifting axle. If it were removed then that axle woudl have to be supported by the other 2 plates. When you shift, it would then hit the 70t gear.

We have both a cnc machine and an EDM, but some of the advisors were looking into using the AM Super Shifter this year to decrease machine time. When I designed this I had to keep this in mind and balance weight and machine time.

Why do people always say our [insert here] weighed [insert here] without motors? What good is a transmission without motors!

If I designed a drivetrain that only used two small CIMs and was able to push around all the multi-motor drivetrains in FIRST wouldn’t that be a lot lighter and simpler than a drivetrain that used many motors?!

Sorry about getting us off topic. I actually think this is a pretty nice transmission - a crash shifting transmission looks simpler to build than a dog-shifting one. I wonder why more teams don’t do it. Why did you choose crash-shifting over dog shifting?

This transmission was meant to be an improvement on last years design which was smash shifting. I wanted to get something together before build so I went with what I had experience in.

Can somebody clarify the differences between crash shifting and dog shifting for those of us in the peanut gallery?

Crash shifting (also sometimes referred to as blind shifters, 116-style shifters, sliding gear shifters, and gear munchers) is when you have gears slide to engage a different set of gears like so:

Dog shifting (also sometimes referred to as 45-style or 716-style shifters, depending on the dog design) engages a set of gears by using a ‘dog’ to lock to the shaft one of a pair of freewheeling gears. Like so:

The orange part is the dog, green and blue are the freewheeling gears, red part is the output shaft, and the yellow part is the shifting rod that actuates the sliding action of the dog. (The shifter appears to be in the middle of shifting and the dog isn’t really engaging either of the gears)

While that piston orientation save a ton of space, it looks like a royal pain to install and maintain. Is there a good reason not to just turn your two clearance holes into notches so the piston can be removed with the pneumatic fittings still in place?

Very nice! Not sure what all the complaints are about, this looks like a very solid design! 3.2 pounds is amazingly light for a 2 speed shifter. I believe the only thing lighter was the 254/968 gearbox, but that thing was just insane.

Looks very, very nice. What made you go with crash shifting, instead of dog shifting, or a ball lock alternative?