pic: Demo Transmission 222



I made this drawing of what I thought would be the ideal transmission for showing people how our ball bearing shifting works.

I wanted to get one made up for the 2005 regionals, but due to lack of time and resources, it was never built.

The whole unit was to be made of Polycarbonate and Lexan, with the exception of the ball bearings, bushings, the black locking collar and the main shifting parts inside the shifting shaft.

Instead of gears I just planned on running the Polycarbonate “wheels” by friction, although it wouldn’t work on the robot, it would show how they shift while under some power/load.

I tried to keep this simple and cheap as possible to make.

For more information on these transmission click on any thread that says 222 here:

http://www.chiefdelphi.com/forums/search.php?searchid=455582

Email me at rigdonbrad@gmail.com if you have questions.

I’m wondering if a laser machine would be able to burn out some lexan (0r acrylic) gears without melting it. It doesn’t have to be super precise, just functional enough for a demo box. If not, maybe a waterjet? Do you have access to either of those? With proper indexing equipment and a gear cutter you could even cut your own gears on a mill.

I’m not totally going for the friction wheel thing. I think gears would be way cooler, even if some extra work is involved.

waterjet would not be good for gears. they don’t cut at a perfect 90 degrees.

gears don’t have any 90* angles except for the face of the edge of a tooth.

It’s not going to run under load at any rate, so they don’t need to be perfectly precise.

but if its not a good fit you get serious probles. for example a section of the gear isnt close and it pushes on other gears. it could case a jam, wear, or chipping. with most drivetrains you want close to perfection. look all i know is that you dont use a waterjet to cut gears and this doesnt just come from me.

Since its just a demo gearbox, and they’re using a polycarbonate, precision isn’t that necessary, it just has to work. Even if the tolerances are out of whack, the gears will break-in and all will be well.

And I second sanddrag, gears do look cooler, haha. But that’s my opinion, I’d be too lazy to cut plastic gears and just stick to the plastic wheel ideas, maybe put a layer of epoxy or rubber cement on them to increase friction. I mean, it just has to show the shifting mechanism; if anyone is curious about how it does with real gears, just show them your robot =)

http://www.thefabricator.com/Articles/Fabricating_Article.cfm?ID=646

whoa, wait a minute…i know for a fact that team 42 has been using a waterjet for the past “…x…” season to cut their massive lexan gears. they seemed to work fine and didnt bind or have meshing problems at all.

I have always considered the 222 trans elegant compared to the brute force dog shifters common on first designs. How ever that pneumatic shifting set up is kind of a Kludge. I don’t know what kind of force is needed to move the shifting shaft in and out . In 2005 the number of Hitec servos was not limited. What if you took a plastic cylinder and cut it at an angle. When the 2 halves are twisted you would get the in out motion. One servo probable isn’t enough but, 2 might do it. If it works it would cut out allot of weight and eliminate the need for Pneumatics.


\ / If this makes sense

I agree gears would be cooler to have in this gearbox, but the only machine we could attempt making gears with is the CNC Mill and with limited knowledge on how to use it, the gears would be difficult to make.

The other problem with gears is that it would probably be difficult to see inside were the shifting occurs, this too may also be a problem with just “wheels” in their place.

How ever that pneumatic shifting set up is kind of a Kludge.

Are you referring to the 2004 three speed or the 2005 two speed shifting setup?

We thought about using servos, but we just had too many problems with them in the past when using them to shift the drill motor transmissions.

Not sure exactly what you mean by cutting the cylinder at an angle?

As far as all the extra waterjet discussion is going… we don’t have access to one, a laser mill either. We were also looking into gear cutters to make our own gears once the 06 build rlls around, but we do not have one now.
The tolerances can’t be too wrong, polycarb has a hardness that is measured on the Rockwell scale, so it isn’t exactly going to wear in very easily, but it is after all just a demo transmission. I did like the idea of epoxy or rubber cement. We could probably use the normal tolerances with the 05 transmission plates and use the depth of the rubber cement applied to account for the missing teeth on polycard wheels.

The servo shifting idea was discussed. The shifting is definitly possible with servos, and I bet it could be done reliably with one servo per transmission, but 2 servos per side would be the only safe way to go about it IMHO. That leads to the battery drain. The servos are run entirely off of the backup battery (correct me if I am wrong) so we didn’t want to take the risk of running a low backup and not being able to shift. In the end our discissions boiled down to simplicity. Powerful air BAM one way BAM the other; physical stops each way. Done.
I believe 469 used a leadscrew setup with a globe motor powering the single screw which shifted both of the joined transmissions. I also believe that 571 and 1143 used pneumatics like us. The only other team with this transmission setup is 476 (??) and I am not sure what they use.

-Henry

I have always looked up to team 222 for the way they build their transmission. Specially the shifter.

Just like Henry pointed out before me, that you can shift with globe motors. Team 233, The Pink Team used globe motor to shift or I was told. Take a look at their machine if you get a chance. Or get in touch with someone from their team. :slight_smile:

I got it. Don’t bother with rubber cement or anything. Just put wide rubberbands on your polycarb/acryllic gear-wheels. Make sure you get your center to center distance right though for good contact between the rubber bands. Enough contact to hold, but not excessive friction/binding.

A few notes about laser cutting:
One of our few sponsors owns a shop specialized in laser cutting, so most of our “professional” looking parts are made by him.
He has cut us several acrylic gears and we didn’t have a problem with that (except… acrylic shatters - rookie mistakes :p), though it should be noticed that those were large pitch gears - for the window motor, I think. Not sure if finer pitch gears, like 20 or 32 DP, would be cut correctly.
Another thing to notice is, allegedly, bad gases are released when polycarbonate is heated/melted, so he only cuts it when the shop is closed. Since we are thankful enough for his sponsorship, we don’t ask him to cut any polycarbonate for us. That’d probably be a similar issue with other laser cutting shops: they won’t do it or maybe they’ll charge you a ridiculous amount for it.

Some small timing belt super glued to the circumference of the polycarb would allow a fairly functional gear. No machining required.

The belt idea would probably work, however you would still have to machine something down to accommodate for the thickness of the belt.

I would not use the timing belt as a gear, I would just use the belt for traction. The main I idea of this to keep the shifting part of the transmission clear, so attaching one belt to each of the other “wheels” besides the shifting “wheels” would probably give enough traction.