pic: 222 3 speed closeup/cutaway

[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

[jskene]

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?

[team222badbrad]

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.

[MikeDubreuil]

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

[Brandon Holley]

awesome awesome tranny...we saw u guyz and experienced you in action at chesapeake. good job. but we still pushed you....j/k j/k, but we did!! no hard feelings

[team222badbrad]

Not really. You guys were chasing us around in first gear. I do recall from the video when both of our robots front wheels were off the ground to form an A. And our base operator knows that we do not get involved with pushing other bots. He knows how easy we tip.
We will have to get in a real match at PARC

I do like your drive train though. Its very sweet that you can change it out quickly if you have too.

[henryBsick]

Originally Posted by team222badbrad

Not really. You guys were chasing us around in first gear. I do recall from the video when both of our robots front wheels were off the ground to form an A. And our base operator knows that we do not get involved with pushing other bots. He knows how easy we tip.
We will have to get in a real match at PARC

I do like your drive train though. Its very sweet that you can change it out quickly if you have too.

Thanks for all the complements and questions. We are always around in the pits too for specific detail. Brad is geting good at explaining these.

As for the pushing...
I was instructed specificly not to push anyone, just to accomplish the task at hand. We do tip, but I have not tipped since practice rounds, note they are practice rounds. I was trying new stuff. I also only ran away in first gear, because well, I am stupid, no, um, i just didn't shift up Figured we were going to the step to climb. It didn't matter when I got there so why risk hitting the corner of the stairs? BUt I will break out second gear some more if anyone wishes to see it. We ran our auton in second and I occasionaly jumped up when making the drive for a distance. Plus, balls +any other gear than 1st = bad, most of the time. We don't run up on them a lot with our lexan teeth but they get bent. So I avaoid higher gears and balls. BAD!!. Anyway, don't worry out there in Philly 11, I will show some more of our machine's capabilities. Annapolis was just a warm up . As Cliff has said. We've got some stuff up our sleeves...

[indigofire79]

amazing design.

We are rookies trying to build stuff in the offseason (yeah for us the offseason has already started and that sucks). Anyway, is the only thing keeping the gears from lateral movement along the axle the pressure from the sides, or it there a locking mechanism? Wouldnt the friction of the gears touching reduce efficiency?

Also, any generic advice on building trannys would be great. We have limited machining capabilities (no high tech stuff i.e. CNC etc.).

[tkwetzel]

Also, any generic advice on building trannys would be great. We have limited machining capabilities (no high tech stuff i.e. CNC etc.).

There are a few white papers on trannys on this site. There are many good white papers. Our team has posted a white paper for our 2-motor, 2-speed gearbox, that only requires a manual mill and lathe to create.

Another good and simple gearbox is team 33's 4-speed automatic gearbox this year. I don't know that there is a white paper available for it, but you might be able to get a lot of information from them about it. It supposedly can be made with a lathe and a drill press with an X-Y table.

Just some suggestions. There are tons of designs out there, as you can see by the variety just this year. A lot of it sometimes depends on the game. Good luck with your offseason work!

[jskene]

I am planning to build one of your transmissions in the off-season, and hopefully develop an automatic shift algorithm for it, which of course I will share on this discussion board. I have a few (actually, several) questions on your design:

1. It looks like you have used a fairly thick walled 1" diameter tube as the main axle. Was this machined out of a 1" rod?
2. What material did you use?
3. What diameter is the inside hole?
4. How far out to the 5/16" ball bearings protrude when they are pushed out by the inner ring?
5. Do you need to have two sizes of holes on the axle to prevent the balls from going in too far? Could you not just have the balls drop down and touch the spring?
6. Does the shifter rod rotate with the axle, and if so, how do you push or pull on it?
7. It seems that the balls might have a tendency to push themselves out due to the rotation of the axle, or at least drop down into a lower notch in a gear when the axle is at rest due to gravity. Do you have any problem with the balls coming out prematurely into the wrong gear?
8. How much force is needed to push the shifter ring against a set of balls to select the next gear?
   

Sorry to have so many questions, but I am quite interested in this design you have some up with, and want to experiment with it. I think it shows great promise for future development.