pic: Shifting Mechanism 222

[team222badbrad]

loading photo ...

[tkwetzel]

How much of that shaft did you manufacture yourself? I am especially interested in the internal shaft.

[Andrew Schuetze]

Kudos to your design team ,

My question for you, "What device do you use to engage the three detent positions on your shifting shaft?" I've seen small pnuematics on two speed trannies and even built a CD two speed using the drill planetary set using a servo. I have some doubts about a servo having enough torque for this applicatin

APS

[team222badbrad]

I didn't machine the shafts because of the level of accuracy that they needed to be; I was busy making other components of the robot/transmision.

Everything on our robot is built in Tunkhannock High School by students with the help of mentors.

The only thing we had to "outsource" for these transmissions from the school was the shafts and gears to get heat-treated, since our school does not have this capability.

They were made in the school and then taken to some company for the heat treating.

Shifting Question:

Our transmission really does not take that much strength to change gears. The main thing they need to shift is accuracy. We used two small pneumatic cylinders to shift.
On cylinder moved the transmissions to either first gear or third gear; the other cylinder was used to wedge the shifting forks into second gear. This required the cylinder that shifts the gears from first to third to become pressureless.

Here is the best pic I can find at the moment:
http://www.tigertrons.com/2004/2004bot3.JPG

Also more pictures can be found here:
http://www.tigertrons.com/pictures.htm

[Stu Bloom]

Very, very nice ... do you have any drawings and/or CAD files you wish to share??

[team222badbrad]

No drawings that we wish to share with other teams on the shafts sorry...
We have drawings, but I and I think WE (THE TIGERTRONS) feel that you should do some designing/calculating on your own.
I feel that building/designing a transmission should not be something that you can just build from a piece of paper.
Our team went out on the branch in the 2004 season and built this transmission from scratch with little help from outside sources. This was the first transmission we have ever built; we always used the drill motors and transmissions on our robot since 1996, up until the 2004 season.
None the less they worked!

I will give you these important dimensions though:

The biggest part diameter of this shaft is 1''

The smallest is 3/4'' to allow for output gearing/smaller bearings

The ball bearings we used were 5/16''

The inside hole for the shaft is 33/64''

The plunger that pushes the ball bearings into the gears is approximately 1/2''

The smaller hole that keeps the 5/16'' ball bearings from fall through the shaft is 9/32''

[[527]phil]

I'm assuming that whoever machined that part either used a horizontal swiss type cnc lathe, or a 3 axis vertical milling machine with an A axis mounted table. also a part like that doesn't have an extremely hight tolerance space, I'm used to alot more, where the part has to be within 300 thousands of the original, but nonetheless it is a precision part. I'm curious of whether the main part of the internal shaft, is that created of a single piece of material?, or is a couple threaded together?

[team222badbrad]

Nope, we used regular lathe and a 3 axis mill with a digital readout!

All we have at the school to used that is computer controlled mill. The thing is that we do not really know much about how to use it. We did make some simple gears and plates on it last year though.

I can make parts, but I would hate to mess something up that we or I spent hours machining, therefore I let the more experienced machinest make it!

The shaft pictured above is all one piece. It is A2 tool steel.

The main problem was that after machining it the dimensions changed after being hardened.

[[527]phil]

The dimension change is inevitable with a hardening process. And don't worry about messing up part, last year i made axles out of aluminum bars by milling the key slot with my max NC cnc milling machine and when i was setting it up i adjusted for the width of the material, but forgot to adjust for the width of the endmill so they didn't fit into the sprockets .

[Max Lobovsky]

Did you find it was really neccesary to use tool steel (that must have been fun to machine...) and harden it? Was there enough wear to warrant it?

[team222badbrad]

You could probably get by a season without hardening the shaft, but since we have not tested doing so I could not tell you what the results would be.

Here are the measurements I got from the gears; I do not have the shaft measurements for between each gear.

Third Gear:
1.014''

Second Gear:
1.001''

First Gear:
1.001''

Being that we used second gear the most it had the least amount of wear because it was not able to "freewheel'' on the shaft.

Overall the shaft was at 1.008'' in diameter, I am not sure of what it was when it was after being machined.