pic: 222 3 speed closeup/cutaway



This is how our transmission looks close up. The picture also includes an Inventor cutaway which shows how we change gears. Most of us know gears connected to 2 shafts with different gear ratios will not spin.

The 4 gears on the right are all keyed to a 1/2’’ shaft. The 3 gears on the left spin free on the 3/4’’ shaft that steps up to 1’’ so that we can place our ball bearings inside. There are 4 holes drilled 90 degrees apart on the 1’’ shaft. Each gear has 4 slots 90 degrees apart which allow the ball bearings to pop up inside. The shaft is also hollow which allows us to place a shaft inside of the drive shaft. This shaft pushes the bearings up inside the gears when moved in position.

This link will give you a better idea behind this simple idea:

Feel free to contact me by Private Message: team222badbrad, AIM: bsrtunkpa, or in a thread.

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.

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?

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

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.

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.

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…

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.

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.

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.

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.

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.

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?

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. :cool: Even if they did push out the balls would be forced back in by the rotation of the gears and shaft

Thank you for the clarification.
From what you are saying, am I to imply that you use pneumatics to control the balls? (you wrote: The ball bearings remain in the shaft until the air inside shaft pushes the balls out and locks the gear.) Henry seemed to indicate that there was a central rod in the axle that slid back and forth, and somehow pushed the balls out.

Did you use a water jet to cut the slots in the gears?

Sorry for the typo…

I ment to say that the rod is used to push the ball bearings inside the slots in the gears. The air cylinder moves the rod between high and low and a 2nd cylinder wedges it in 2nd gear.

We made the slots in the gears using a manual mill. Most parts were made by hand and the side plates were done on a brand new CNC.

Very cool, I think I might even understand how it works. Thanks for the explanation.

[quote]
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?[/quote]

This would seem feasable, but we do not have a neutral postion between gears with our pneumatic positioning. We could use a simple current sensor or two and a staement in the program that would be something like "if amps are greater than or equal to 35, shift down to next gear; if amps are less than or equal to 5 amps shift up to next gear " I know that is not how it would look in the code because i do not know C or any language for that matter. But it is the basic idea. And i think it is atainable with any shift on the fly tranny and a bit of testing.

Sorry for the misplellings i am not the greatest with techinical terms and such.
-Henry

Awesome design, but I have to agree with Joe…seems like the simplest & most robust robot always wins. We had an awesome 3 speed planetary gear, shift on the fly tranny two years ago. Debug period was horrible, but once we got it fixed it was great. I just hate wasting a regional to debugg. ROBUST, ROBUST and ROBUST if you want to win. If not, at least have a lot spared parts pre-made and assembled for quick change.