pic: 222 3 speed closeup/cutaway

[CD47-Bot]

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[Kevin Sevcik]

Sweet looking tranny. I like the idea, it's nice and simple. I'm just curious if you guys have any bearing surface between the free spinning gears and the output shaft. Is it just steel on steel with lots of lube, or is there a bronze bushing in there?

Also, how do you guys index it so that shifting rod only moves part way?

Other than that, it's a really awesome, simple idea.

[tkwetzel]

Sweet looking tranny. I like the idea, it's nice and simple.

I agree that it is a sweet tranny and an amazing idea, but is it really that simple? The concept might seem simple, but the production seems very difficult. Kudos to team 222 for doing it though.

Also, are those trannies powered only by the CIM motors?

[team222badbrad]

Yes the shaft and gears are steel on steel. Both of which I think are heat treated. We also used some kind of spray on lubricant that sticks to the gears.

If you look on the other pictures there are shifting stops to keep it from shifting too far.

Since this is our first year ever building a tranny we went overboard. The production could be simplified greatly. There are lots of different things we could modify such as the side plates and the whole shifting mechanism could be redesigned!

Once I finish the inventor award (due 3/15) I hope to find time to make a white paper and redesign it!

thanks for the comments

[tkwetzel]

I hope to find time to make a white paper and redesign it!

I'm looking foward to seeing a white paper on this beautiful tranny.

[Kevin Sevcik]

In that case, for your redesign I'd suggest a bronze bushing or some such between those free running gears and the shaft. I just got lectured by my design prof about galling, and it wasn't pretty. Apparently, two very similar metals have a tendency to stick together. Thus, if your lube ever gives out, the gears will sieze and bad things will happen. so as a corollary, check the lubrication whenever you get a chance, just in case.

[Joe Johnson]

I hate to say this because I think I am only adding fuel to the fire* but... ...I like it!

The part I like best is your method of transfering the torque via the balls. Very elegant.

Nice job.

Joe J.

*I have discussed in many posts that I question whether all this shift on the fly mania (yes, I say mania) is worth the bother when you consider that you can make a relatively robust transmission shifter with a standard drill gearbox and servo.

The only thing that has me thinking is Jim Zondag's 4 speed with automatic shifting (and I suppose your 3 speed would work about as well). Perhaps there is a game where such things make sense. I am still pretty much for simplifying things, but perhaps I was too hasty to close my mind. Time will tell...

[henryBsick]

Originally Posted by Kevin Sevcik

In that case, for your redesign I'd suggest a bronze bushing or some such between those free running gears and the shaft. I just got lectured by my design prof about galling, and it wasn't pretty. Apparently, two very similar metals have a tendency to stick together. Thus, if your lube ever gives out, the gears will sieze and bad things will happen. so as a corollary, check the lubrication whenever you get a chance, just in case.

As you can somewhat tell, the word, well, name "FRED" is on the inside of the tranny. I just noticed it myself but, I believe it is there because he is NOTORIOUS for greasing, greasing, and well, greasing. We should be ok and he should have some fun this year, but thanks for the heads up.

[Andy Brockway]

This is certainly a nice, compact design. Reminds me of my dual range Suzuki I had in the late '70's. I have looked at how to easily do the machining and am very interested in seeing your white paper.

As for the lube. We are lucky that we run short matches and that the total life of our robots is measured in hours. Greasing on a regular basis allows us to run on the edge with our designs. I do agree with Kevin's professor provided this was on production equipment. The Suzuki I had (actually I still have the motor and gearbox) was steel on steel but ran in an oil bath.

[Kevin Sevcik]

Speaking of Kevin....

I just had a test today in that class, and it reminded me that the issue is worst if the metals are of the same or similar composition, same hardness, and relatively low hardness. The threshold for same hardness is within 5 HRC of each other. Soooo.. if you have a hardened steel shaft there, and the inside of your gear isn't hardened you should be reasonably ok.

Also, I'd still be concerned even though this isn't production equipment. Our prof showed us a few examples of some coupling threads that suffered from galling, and that's obviously not a high-cycle kind of thing. so mostly, I'd just keep it lubed and keep these things in mind in your white paper.

[team222badbrad]

Thanks for the heads up guys. We tried filling the bottom with oil but that got too messy.

We ran the trannies for hours and didnt have a problem. We give our robots the robust test every year...

Our robot never missed a shift once and that is almost amazing considering we always had problems with shifting the drills in previous years.

[MikeDubreuil]

Preface...Control systems guy with fetish for understanding mechanicals.

How do the balls capture the gear? And how do you control which gear gets captured?

[henryBsick]

Originally Posted by MikeDubreuil

Preface...Control systems guy with fetish for understanding mechanicals.

How do the balls capture the gear? And how do you control which gear gets captured?

In the picture, the balls in the shaft sit down in thier holes, not above the exterior surface of the shaft. We have a rod that moves in and out of the shaft which pushes the balls up locking them into the little notches in the gears. The rod is on springs so when it touches the 4 balls (on one gear) on the inside of the shaft the balls do not jump up into the gear by force they go when ready so not to grind. the balls fall back into place once the rod is removed. So by moving the rod to different places it locks in different sets of gears choosing our speed.
I hope i didn't confuse anyone to badly.

[jskene]

How do you prevent the balls from moving radially outward when the shaft is spinning? I would think that the centrifugal force on them from the spinning shaft would tend to push them out into the slots in the gears.

I (and from reading this thread, many others also) would be very interested in seeing a photo or drawing of how your sliding rod works to move the balls in and out. I would also be interested in knowing how you cut the slots in the gears.

If you put a sensor on both shafts, I think you could make a really slick automatic transmission with this gearbox.
When the software figures it's time to shift up to the next higher gear, indicated by high motor speed, the control computer would put the gearbox in neutral, then drop the motor speed down so that the input shaft speed, as measured by the period between sensor input triggers on the input shaft, matches the period measured on the output shaft, adjusted for the gear ratio of the next desired gear. At this motor speed the desired input/output gears are spinning at exactly the same speed. Then the contoller would shift to the desired gear, the balls pop into place on the output gear, and the controller applies power to the motor, accelerating away in the higher gear. A similar sequence can be used to down-shift, where the motor speed is increased while in neutral to match gear speeds. The system would work like a sensor-controlled synchromesh. (I would call is "automatic sensor synchromesh" if not for the unfortunate acronym . Maybe "sensor controlled synchro - SCS would be a better term.)

In any case, this would be a neat project to work on. Any chance of getting some more details?

[team222badbrad]

The force your refering to is just inertia (a body in motion will remain in motion unless acted upon by an outside force). This is a comon mistake that people make mistaking intertia with centrifugal (which does not exist). The ball bearings remain in the shaft until the air inside shaft pushes the balls out and locks the gear. Even if they did push out the balls would be forced back in by the rotation of the gears and shaft