pic: 254/968 Transmission
 

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That looks very clean, is it only one speed transmission though?
The entire thing's only 1 lb, what are the sideplates made of? Looks like some kind of polycarbonate to me.

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I think someone must have accidently turned down the gravity in your shop...

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Wow, I would call that an engineering marvel. A 1 lb transmission.. really goes to show how light you can actually get. Great job, if someone came up to me and told me they are going to make a 1lb transmission, I would ask them to sit down, drink some water, and rethink their statement. Man, this is amazing. Nice job, bravo. :)

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did you guys zero it before putting that caliper on there? or is that 1 lb including its weight? Because that would put your tranny at even less then 1 lb...

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ahhh, I think your scale is broken.

Re: pic: 254/968 Transmission
 

We zeroed with the calipers on it. The sides are made of Delrin. It does shift. It may be a little deciving because that is the weight without the shifting piston and the scale goes in half pound increments. It is really about 1.2-1.3 pounds.

Re: pic: 254/968 Transmission
 

we have that same scale, and the same problem. I constantly have to remind everyone that 2.5 lbs over could be anywhere between 2.3 and 2.7 over.

Re: pic: 254/968 Transmission
 

Wow. I want one.

Re: pic: 254/968 Transmission
 

Our scale looks exactly the same but it doesn't go in .5 incriments, but it goes in .2 incriments.

Which actually just as unhelpful as the .5

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I bet two would be more useful.

If any one other than 254/968 posted this I am not sure I would believe it, any chance at getting a top view?

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Sure. I'll post one when I get home from work.

We'll probably have a full bot picture up in a couple days. We didn't remember to take any pictures of the comp bot before ship, and we havent yet fully assembled the practice bot.

Re: pic: 254/968 Transmission
 

I will be posting more pictures and details of the transmissions in a few days when I have some free time.

For reference, this gearbox is Kirk Oden and my senior project as Manufacturing Engineering students. As such, be prepared for some rather detailed analysis and explanations of chosen materials and processes as well as work study and analysis simulations of assembly and maintainence times. At the very least we plan on sharing our findings and suggestions on possible changes/improvements that people may want to make if they chose to pursue something similar.

In the next few days expect a new post in the technical discussion with many more pictures of the assembly and detailed part pictures, as well as explanations of the manufacturing processes, coatings, material selections and properties, part weights, etc.

Re: pic: 254/968 Transmission
 

That is neat and incredibly light. Wonderful

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Sounds Awesome. You go to Cal Poly Pomona right?

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Yes

Re: pic: 254/968 Transmission
 

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?

Re: pic: 254/968 Transmission
 

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.

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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

Re: pic: 254/968 Transmission
 

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.

Re: pic: 254/968 Transmission
 

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

Very nice job, looks cool too.

Chris

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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.

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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?

Re: pic: 254/968 Transmission
 

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.

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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?

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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.

Re: pic: 254/968 Transmission
 

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.

Re: pic: 254/968 Transmission
 

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?

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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.

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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 ^^

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Ok, I understand the pillow block now, but how exactly does the shifting rod work? I dont see how anything is or can be connected to the dog except for the output shaft because it spins with the shaft. You said it was inside the main shaft, only its only connected to the dog and not the other gears?

Edit:
I think i can see the shifting rod here, but im still not sure how it connects to the dog.

Re: pic: 254/968 Transmission
 

We use a screw to connect the shifting shaft to the dog. There is a slot in the output shaft which gives the screw/shaft/dog clearance to slide back and forth, engaging one or the other gears.

Here is a cutaway that team 45 posted a few years back showing how it works.

Re: pic: 254/968 Transmission
 

How are the gears holding up for you guys? I saw what I consider significant wear on the Poof's practice robot, but I am no expert on gears.

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The teflon dry lube was wearing off, I assume. The comp bot has some of that, too. It really is of little concern. The teeth on all four of our bots are in better condition than the steel gears that we ran last year with the same amount of driving time. I am quite surprised with how well they are wearing. The 20 pitch gears show absolutely no wear whatsoever. The 32 pitch show some wear on the endges, but only slight anodize and drylube wear. Again, the teeth look pretty good on all of them though.

Re: pic: 254/968 Transmission
 

After reading the poster, I was wondering what you meant by "clutchless" since you are using a positive clutch for dog shifting.

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It isn't really a clutch. This transmission design is most commonly found on motorcycles, with the addition of a clutch of some sort. An electric motor allows you to remove the clutch, simply due to the fact that the motor works from 0 rpm onward. An IC engine on the other hand, has an idle that would otherwise prohibit the vehicle from stopping completely without a nuetral position or a clutch. The starting and stoping are the primary needs for a clutch with an IC engine/motorcycle tranny. It is quite common to not use the clutch when shifting a motorcycle by simply easing off the throttle and engaging the next gear so long as you are already moving.

By clutchless, I meant lacking a means to engage or disengage the power coming from the motors feeding the output shaft.

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Have you posted your actual gear ratios and final specs for this transmission yet?

If not, please do so. I was very impressed with the design! I'd specifically be intersted in the gear ratios. Thanks

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deleted - nvm

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irrelevant. -mk

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Got an drawing of it by any chance? Just curious.

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We still have not completed our final technical paper on the transmissions ourselves for school, so it'll be a while til we make any sort of white paper to post here on CD.

As for the ratios, the initial 32 pitch reduction has 20 tooth pinions and an 80 tooth driven gear. High gear reduction is 45:30, low gear is 60:15, driving a 4" diameter wheel.

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Could you just post your paper for school when it is done?

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We haven't decided. Most likely, if anything, we will write a brief overview of the FIRST related uses of what we did. The rest of the paper really isn't useful or appropriate for the CD community.