pic: 254/968 Transmission

[Travis Covington]

Originally Posted by AdamHeard

Sounds Awesome. You go to Cal Poly Pomona right?

Yes

[cire]

That is quite amazing, but why #25 chain? We used it our rookie year and it broke almost every match we had (However mind you we were using a plywood robot and had a heavily cantileavered kit drill motor transmission, and a really bad tensioner!). Has 254 and 968 had those problems?

[Cory]

Originally Posted by cire

That is quite amazing, but why #25 chain? We used it our rookie year and it broke almost every match we had (However mind you we were using a plywood robot and had a heavily cantileavered kit drill motor transmission, and a really bad tensioner!). Has 254 and 968 had those problems?

Nope. No problems. In the two years I've been on the team, we've never broken a chain. As long as it's properly aligned and tensioned it should be fine.

[Ben Piecuch]

Travis,

This is just another beautifully made/designed part of your robot. While building our robot, we're almost always limited by our machine shop, and the time spent on the machines. Do you know how much weight all the lightening holes and treepans remove? I'm trying to determine how much "time for weight" is involved in these transmissions. (I won't even ask about all the heat treating and anodizing time!)

Also, I believe this is a single CIM gearbox, right? Have you found any lack of pushing power even when you're in low gear? We used the Dewalt 3-speeds with a single CIM last year and found that we were still being pushed (well, rammed) around by kitbots.

Thanks,

BEN

[Travis Covington]

Lightening the aluminum gears doesnt have nearly as big of an impact as lightening the same sized steel gears, obviously. The weight was removed because it could be. For the designed power constraints and face widths, the added material in the web was of no real benefit. For most of the gears we designed, we were able to remove more than half of the total gear weight using pockets and holes.

These gearboxes have 2 small CIM's per side.

[ChrisMcK2186]

I figured out how it weighs so little! It doesn't weigh in lbs., it weighs in # of transmissions on the scale.

Very nice job, looks cool too.

Chris

[chaoticprout]

I told Kirk this in LA when he was showing it to us, simply amazing. I'm very saddened to hear that you guys are not going to Atl this year. Awesome job in general, the gearbox is awesome.

Just a question for us in the California area looking to improve our transmission weight for next year (aka me)...

Where did you guys purchase your delrin sheets? And how did you go about getting the 7075 and 7068 gears?

[Travis Covington]

We got our delrin from mcmaster.

The gear blanks were all made from round aluminum barstock, turned, milled, hobbed, pocketed, and anodized by either Kirk or one of our teams few local sponsors.

SDP and others sell some aluminum gears, but nothing in the face widths, pitch, or materials that were required to build the transmission we wanted.

Say I were interested in finding my own way to get gears this light... Would it even be plausible to look around at local companies to have them done? Basically, what kind of cost went into these, and was the weight loss worth it?

[pepe]

I'm sure if you look around you can probably find some company who may offer to sponsor you with some materials. The majority of the cost went into the machining process, which was graciously donated by the sponsors.

The reason we cut down the weight on the gearboxes (from 4.6 lbs to 1.3) was to have more room to work with weight-wise.

[Travis Covington]

I have told this to those who asked me similar questions in person, and I will go ahead and say this to everyone interested.

If this were not Kirk and my senior project, there is no way we would have taken on this much work for this much (little) weight savings. While 2+ lbs per transmission is significant, the 500+ hours that went into getting these made was most definitely not worth it. For us, we were killing two birds with one stone, which made sense. We would have had to put in a similar amount of time doing a senior project totally unrelated to FIRST, so why not spend that time on the robot?

Bottom-line, for a FIRST robot, this is beyond overkill. Next year we will be designing everything around what andymark already makes and sells for a ridiculously low price. A few of his gears with our own sideplates and shafts, and I am a happy camper. Time and resources are spent much better elsewhere, take my word for it.

[Henry_Mareck]

How does the output shaft work?

And by that i mean, it appears the shaft with the dog is the same line as the output shaft, from looking at this picture.
Because the shaft moves side to side to actuate the dog it would seem that the entire output shaft would shift from side to side. It would cause a problem if a wheel was attached to a shaft that slides from side to side each time the transmission is shifted. What kind of mechanism keeps this from happening?

Also, apparently there are two sprockets on the inside, (or one double sprocket), but there is also that big red thing sticking out one end. Is is right to assume that the red thing powers the center wheel and the two sprockets power the front and rear wheels, and that the big red thing also contains the mechanism i was wondering about earlier? and if so, why does the blue one shown on the scale not have the this mechanism?

[Travis Covington]

The shaft does not move. The shifting shaft (not shown) which the dog screws into moves inside of the output shaft.

The red thing is stricly a bearing housing which mounts to the side rail. The center wheel mounts on the smallest hex of the output shaft. The front and rear wheels are powered with chain and sprockets, as you guessed.

[sanddrag]

The output shaft does not move axially/linearly. There is a hole drilled in the back end of it, and a "shifting rod" inside it which connects the pneumatic cylinder to the shifting dog. Just like any other dog shifting transmission I've ever seen (andymark, etc)

The "red thing" is a pillow block that carries the outer bearing for the output shaft. It does not move. The wheel is driven by the hex milled in the end of the output shaft. Not shown is the frame rail to which the gearbox face mounts. The frame "red thing" goes through the frame rail. Tha flange sits on the outside, and the face of the gearbox sits smack up against the other side of the frame rail. Very clean.

EDIT: Travis beat me to it. But yes, what he said ^^