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??
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?
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.
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.
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…
Except resistors are tiny and pistons are not
You are talking about fitting 5 or 6 pistons in a gearbox that’s supposed to be a few inches thick…
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
PS: It’s pretty late and I’m an Electrical Engineering student, so bear with me for any major mechanical inconsistency in this post
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.
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?
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.
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