pic: 6 speed?? Great in theory - lets see how it works!



Theoretical model of a 6 speed/2 motor transmission. Speed ranges on a 5.25" wheel with a 5:1 redution from transmission to wheel - high 16ft/sec. - low 1.5ft/sec.

Still needs a great deal of tweaking including how to shift to six different locations on the output shaft!!

Questions? Comments? Clarifications??

Holy snap… a 6 speed tranny… looks awesome…

question… how much does the transmissioin weight… once you get it manufactured and test it please let us know if it works or not… thanks… :slight_smile:

6 speeds, sounds awesome. I’m not really sure about how to get it to six different points on the shifter, but I’m certainly no expert in tranny’s.

My guess - and it is ONLY a guess - is about 8 pounds without the motors. I’m probably ballparking high at the moment. Once all of the details are filled in I will give you an actual weight including motors and shifting mechanism. All of this is very much in the preliminary stages.

Does anyone know how to stop a pneumatic cylinder at 6 specific, pre-determined points in the stroke?? :slight_smile:

Glad to share!

Schuffman

ehh. looks awesome but i dont really understand it… im guessing the pink part is the ‘shifter’ and the blue and red are different ratioed gears? but whats meshing with what? awsome how you got it so compact!. very nice how your drill and cim are so close… can you get a close shot of the gearing there?
and one point youd probably want to notice… the drill motor… IF it burns out, its gonna be hard to access… prolly want to widen that hole behind it a bit more…
and how are you mounting the drill?
and as in how to get 6 positions, ive been thinking a ratchet design maybe. one in out stroke of a piston moves the ratchet one “ratch?” … so as like in a sequential… you wont be able to skip through gears, but its definitly doable even if it may be quite heavy too. to go the other direction through the gears, maybe another ratchet/piston thing going in the other direction…(think grandfather clock)

That sounds awsome! As of right now you are planning on using drill motor… but we are not getting any drill motor in the kit of parts this coming season… what would you do in order to change it once you get the new motors?

to get the 6 points on the cylinder…

im guessing have 3 pnu lines going thru the robot, each with a different PSI. (maybe 40, 60, 80) Then you connect a solenoid to each one of those, and output all the A’s to one side of the cylinder, and all the B’s to the other. Then switching some on and off may do it.

Actually, i have no clue. but that may work.

anyone wana disprove it?

Has anyone ever seen a video clip of a driver of a Funny Car shifting. It is a clutchless transmission and they just move the shifter back and forth all the way through 4 or 5 gears. Boom forward 1st gear, Boom back 2nd gear, Boom forward 3rd gear and so on. It doesn’t actually go Boom But does anyone know how it works?

Don’t have time to build a model ant test it but a pneumatic cylinder in theory (disregarding friction of course) should fully extend or retract no matter what the pressure (or the switching of a solenoid) because as long as there is a difference in pressure it will move all the way until the end of the cylinder stops it. Now, on these boards a lot we have talked about “multipositioning wit pneumatics” and I believe that is achieved using muliple solenoids and timing(or limit switch and program) them correctly to make sure both extend and retract ports are open (at equal pressure of course) when the cylinder reaches a certain position. That is just a guess as to how it works as I have not had time to actually read the multipositioning thread.

Now, it could be linearly actuated by some other means than pneumatics you know…

I don’t know about strength or anything, but what if you had a rack-and-pinion system with the shifter on the rack You could test and program or have limit switches or something and have a motor move the rack along to a certain point. (i.e. where the next gear is) Sorry if that wouldn’t work, but its the best I could come up with at the moment.

That’s not entirely true.

We wont be getting any of the same drill motors. We very well could be getting a different model.

The only way i have seemed to get a pneumatic piston, like those in the kit that only have 2 ports to move to more then 2 positions well requires multiple pistons. Take 3 pistons, and put them in series (like one after the other). So when you have the all retracted its on the first length, piston a extended and piston b and c not extended is length 2, piston a and b extended with piston c not extended is length 3, having a not extended with b and c extended is length 4, having a and c extended with b not extended is length 5 and having all a b and c extended is length 6. Its actually works really well you just have to tweak it before it goes on the bot. So like resistors in series, you can get pistons in series in a way to act together like a single piston with multiple positions…

Hope that helped…

Except resistors are tiny and pistons are not :wink:
You are talking about fitting 5 or 6 pistons in a gearbox that’s supposed to be a few inches thick… :slight_smile:

I would go with a lead screw with a huge pitch, so that rotating it a few degrees would make the shifter move a considerable amount. Depending on the forces involved, a servo could be used to precisely turn the lead screw, sliding the shifter and making an accurate change of gears.

BTW, your design looks very good :wink:

PS: It’s pretty late and I’m an Electrical Engineering student, so bear with me for any major mechanical inconsistency in this post :stuck_out_tongue:

the only part that has to be in the transmission is the shaft on the end piston that will be acting as the shifter, and also you can get pistons with as small of a stroke as 1 inch that have been legal before for use on the robots.

I’m not particularly mechanical but I’ll give it a shot…

I’m going to call the pink piece that is supposed to move the output head. If you were to run a threaded piece of round stock through the tapped output head, and then turned the round stock the output head would move. A good choice of motor would be the globe motor to turn the round stock. If you added a rotation sensor to the round stock you could create some software to fairly accurately shift the transmission for you.

Yeah, that’s exactly what I was talking about…
Yay for non-mechanicals chiming in… :stuck_out_tongue:

According to my i-Cylinder inventor model from firstcadlibrary, even a 1/2" stroke cylinder still measures over 4.5 inches in total length retracted.

I still have no idea how that shifter engages different sets of gears. Anyone care to explain?

Sean,
I agree with Mike.
This is the best method I can come up with.

Get 3 different length pistons.
(I recommend as small as you can.)
Put them in series. As long as the pistons are all different lengths, you now have a 6 position shifter, with a high repeatability (the important thing.)
The only tricky part would be pulsing through the gears without the shifter “back hopping” on it’s way forward. (as in, if you have a .5 and 1" cylinder, 2nd gear would be .5 out, 1 in… 3rd gear would be .5 in, 1 out… so to shift from 1-2 you’d need to grind into 4th or into 1st.)

With this method, you could shift both gearboxes at once to save on the total # of cylinders on the robot. Mount the cylinder centrally, and run it to both gearboxes, such that it pushes out, or pulls in on both equally.

Another option is “pulsing a pneumatic” using 2 solenoids on the same cylinder. I am NOT a pneumatics whiz, but someone else can tell you the pros and cons of this method.

Also… what about a servo?
How much torque is required to shift?
I always think of pneumatics as being better for shifters, but I hear 226 had some luck converting their tranny to servo actuated. Maybe that would be good for your application.

Also… Sean… 6 speeds? Is the field a 1/4 mile strip now? Do you know something we don’t? :wink:

Take Care,
JV

From what I see I’m going to make an educated shot at this. You could do this with a single piston using multi positioning…you would have to use the speed control valves and set them very very low if not all the way. I don’t see how three pistons would help you much though. I’d be interested in learning more about this shifter first before i finalize my statements.

-Pat

EDIT Just rethinking about it…you could also use a rodless piston. That would slide along top. It would also have to multiposition. The only problem with that is that it isnt legal as of the 2004 season. Just another idea.EDIT