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

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

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... :)

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

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.

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

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?? :)

Glad to share!

Schuffman

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

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)

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

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?

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

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?

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

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?

Re: pic: 6 speed?? Great in theory - lets see 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...

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

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.

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

That's not entirely true.

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

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

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..

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

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 :P

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

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.

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

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.

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

Yeah, that's exactly what I was talking about...
Yay for non-mechanicals chiming in... :p

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

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.

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

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

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

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? ;)

Take Care,
JV

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

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*

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

With two clyinders in of different length in series, you could theroretically obtain four different positions. With three cylinders in series each of different length, you could theoretically obtain 8 different positions.

EDIT: that is the simple answer. The more complex answer deals with "not equal to" issues. For example, if the stroke of the short cylinder plus the stroke of the medium cylinder equals the stroke of the long cylinder then you would have fewer total position combinations.

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

Depending on how relaxed the pneumatic rules are this year there are three position solenoids that have a stopped position. This would be your best option along with magnectic reed switches to tell your stroke where to stop. A little programming and you have a decent solution.

In the past we have not had the three position solenoid and had to refer to using multiple solenoids(best combo is a single and double) to create a hard stop, aka plugging the exhaust tube when we want it to stop and exhausting when we want it to move. This could be used with the magnectic reed switches to create a solution that works. As with most pneumatic one of the biggest keys to this is shortening all your pneumatic tubing so that there is at least amount of slop as possible.

My use of it was not a precise as shifting gears but I imagine if you implement it right with the reed switches and a little programming it could work fairly reliably.

Just a note: Magnectic reed switchs are generally used to tell if a cyclinder is fully extended or retracted to allow automation of pneumatically controlled process. I have not personally tested the above mentioned using magnectic reed switch at mid strokes but it seems that with programming it would work. Also the above mentioned way of stopping midstroke(the second one) is achieved by equally the force on the two sides of the cyclinder. Force in this case is a pressure per area. On the stroke side of the cyclinder the area is reduced by the area of the stroke, the other side remaining the same, this will cause the pressure stroke side to increase. This has caused discussions whether it would violate the 60psi rule. Take this thought in when designing such a pneumatic system. Safety is important.

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

Sean,

Looks very good, but I would like to see more detail on the gears (diametral pitch, backlash, etc.) in order to comment on robustness. With respect to the shifting, I would scrap the pneumatics idea and go straight to a ball screw or a lead screw. You could get VERY accurate positioning from that set-up and you could use the seat motor or globe motor. The issue is speed of shift so the globe motor might be the best candidate. For position sensing you could use limit switches (not what I would use) or a rotational encoder (digikey has a lot of choices). Using a motor/balls screw set-up like this will give you stiffness, accuracy, and repeatability.

-Paul

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

roffle... ever considered hooking up a motor to the shaft that the shifter is on, and making the shaft itself grooved (like a worm gear) and fix it so that the shifter can't rotate (i.e. just throw another shaft through it at a point) so when the motor turns, the shifter will run along the shaft. Probably not the best way, but it's an alternative to all the pneumatics.

Just thought I'd toss something else new and whacky out there since this thread is just asking for that stuff.

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

Here's what I can tell you so far - not that we're trying to keep secrets, but like I said before, this is in the very preliminary stages and I was looking for some input from the CD community (which is exactly what I got). Thanks to all of you!!

1. The drill motor and CIM motor are geared directly to one another. Drill to CIM ratio is roughly 3.2:1.

2. The gear on the CIM motor drives the first in a chain of gear reducing double gears. We are going to see if we can purchase them to our specs otherwise we'll have to mate two gears together face-to-face. Each gear reduction is a step down of 1.67:1. (I will post a screen capture of an end view of the gear train so you can see how they reduce from one to the other)

3. The gears in the gear train all ride on bearings and a simple shaft with thrust bearings separating each pair. The reduction is a stair-step effect from one end to the other. The gears can be replaced by simply removing the plate on the end (clear in the original screen shot) and sliding each gear set off the end of the shaft.

4. The pink object is the shifting mechanism with a gear in the middle that drives the hex shaft and ultimately the cog on the outside of the gearbox. The jury is still out on how to move to six specific positions consistently but I'm getting some great ideas here!!

Theoretical speed and torque are as follows:
First gear - 16.63fps - 504lb/ft
Second gear - 9.98fps - 841lb/ft
Third gear - 5.99fps - 1,402lb/ft
Fourth gear - 3.59fps - 2,336lb/ft
Fifth gear - 2.16fps - 3,894lb/ft
Sixth gear - 1.29fps - 6,491lb/ft

In theory (which is what much of this is right now) the entire gear box could be built using a drill press and lathe. The lathe is only needed to turn down the ends of the hex shaft where it meets the bearings.

Hope this sheds some light on this funky contraption.

Sean

p.s. No, JVN, I don't have any insight into this years game. Just playing around with some extreme ideas. I think I've been watching too much of the Discovery Channel lately! Although a 1/4 mile drag race between robots is something they should consider for IRI next year! :)

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

Big Guy,

Wow... this is waaay cool. I have a couple of thoughts and suggestions:

• I am wondering how your 6 different ratio gears are meshing. Those cylindrical things with the radial slots are neat, but I have no clue how they work. I guess you can just show us in March.
• 6 speeds? Who is driving this thing, Michael Schumacher? Again, you have some devious plan here with these 6 speeds. Just let us know in March.
• The top left shaft, outside of your drill motor can go away. You can also put a big notch in that transparent plate so you can get at your drill (or whatever motor that will be) motor. This will help with wiring, motor removal, and weight reduction.
• Your shifter device has 1 hex shaft and 2 round shafts guiding it. You only need 2 shafts total. Getting rid of one of the 2 round shafts may make it better, depending on how this mechanism interfaces with the hex shaft. Again, there are some things here that I don't understand with how these "gears" are meshing and how this hex shaft interfaces with these "gears".

It is great to see this sort of design, keep up the great work.

Andy B.

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

why would you ever need a 6 speed transmition in a First Robot?

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

Ooh, that's a neat idea. It's surprisingly simple, and it lends itself well to basically any number of reduction stages. It does have a whole bunch of gears running all at once, though, so it might be a bit more lossy than other designs.

I think with that many positions, an electric motor with position feedback is an appropriate way to shift it. Something like a rack and pinion, or a cam, or even a chain or belt drive. Or perhaps someone can think up a direction-switching ratchet mechanism with mechanical stops at each position, and use a pneumatic cylinder to drive it. I can also imagine a cam shaft controlled by a servo that controls which gear the shifter will stop at.

I'm a software guy without a lot of real mechanical experience, so I don't know how worried to be about the edges of the "power take-off" gear as it moves from one position to the next. It would seem to be susceptible to severe grinding if you don't have the speeds well matched.

What would happen if you moved the shifting mechanism to a spot between the two stacks of reduction gears, so that it could alternately contact either the "orange" or "blue" gears on both sides? You might get away with half as many reduction stages that way. [EDIT]Whoops, they're going opposite directions, so you'd need an extra idler gear to account for it, and the clearance is probably not reasonable anyway.[/EDIT]

I can't remember who posted the three-speed shifter with the internal doglike ball bearing "gear capture" mechanism, but I can imagine putting something it inside the "blue" stack in place of the external "pink/yellow" part. Does that make sense?

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

This might sound crazy but if you just use one piston which has a longer throw... and use a magnetic reader to detect how far you want the throw to go each time... that should work... that is a lot of programming... :)

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

That three speed shifter was from team 968, with Travis Covington as the main designer.

Andy B.

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

Something to think about.
With all that spinning mass could this become impossible to turn due to gyroscopic forces?

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

Ya sure he's not talking about 222?
;)

It sure sounds like it.
But 968's 4-speed was pretty sweet too.

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

For the shifting..

what if you use a globe motor? They have lots of torque and using a rack and pinion style mechanisim - you shouldn't be backing out anytime soon...?

Maybe even have some limit switches above the positions of the gears so you don't have to worry about timing?

:) Looks good though. Mind if I subsuite it for some of the nastier tranny's I see here in the automotive world?
;)

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

I'm going to chime in on the side of people who know a lot more about these things than I do and agree that a ball screw seems like the best option for shifting to multiple positions. However, since I despise programming and electronics, I'm hesitant to rely on switches and sensing devices to accurately place the shifting collar within the gearbox. That's not to say it's impossible to do it, but only that I do not have the experience to make it work myself.

Instead, to reduce the accuracy in rotation needed by a conventional motor to spin a ball screw and accurately position the shifting collar, you might consider using a geneva mechanism (see also) as an interface between the shifting motor and the ball screw. An indexing device such as that should help to alleviate concern about the shifting collar's position.

Also, it's really cool.

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

Just a proof of concept. The reality is you could change it from a 6 speed to a 10 speed to a 2 speed all by removing a few gears and shortening the shaft lengths.

We're going to prototype it with 2 gears for starters to see how it works and slowly add more gears.

This will prepare us for when the field quadruples in size and we want to get to the other side in 6 very theoretical seconds! :):)

More screen shots coming soon.

Sean

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

In theory, it is possible to have an infinite stage gear. Put threads on a cone and put a FIRST gear (the sideways ones in the kit) on top of it. Adjust its position with a weak motor, and you should be able to deliver the exact amount of torque that you want. I will put up drawings later when I scan them in (yep, i'm a paper and pencil designer), and I may even put it in a white paper. whether it will work.....

basic idea (very ghetto):
/
O/ The O is the sprocket, and the < is the conic gear.
/
/
\
\
\
\

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

If you had free reign to buy whatever you wanted, shifting this thing pneumatically would be very easy. With the parts available to FIRST, i would forget the idea of pneumatic shifting. I can tell you now that if you go that route and try to position a cylinder in that many places soo close together and still have reliable shifting it will not work. It would be much easier with something like a rack and pinion or leadscrew mechanism with a globe motor or similar. The one thing you need to watch out for if you use a motor is that you need to make sure that you are never stalling the motor. You will need to add a spring or something that will compress until the gears mesh.

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

Woo more pictures :)

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

It's possible to have an infinite stage gear system but Im not sure if what you say will work. It's called a cvt or cct. I forget.

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

The pitch and number of teeth would change as you move down the gear...

You really can only acheve infinante gears with a belt - which isn't too good when you have to deal with FIRST rules (Even in vehicles - after so much torque the belt starts to slip. That why you don't see more of them in V-6's and V-8's)

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

CVT - continuously variable transmission.

See http://www.andersoncvt.com/ for a pretty slick variation. I'm not sure if I found this site by poking around or if someone linked to it in a post on CD. It looks good but seems fairly large. For FIRST applications you would have to scale the design down enough to make it practical yet keep it as large as necessary to be robust.

Lots of awesome input! I love how these boards work for all of us!!

Thanks all!

Sean

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

Maybe I'm missing something, but all the gears in your rendering look the same size.

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

A similar cvt is this by Pat Roche posted up on CD a few months ago...http://www.chiefdelphi.com/forums/pictures.php?s=&action=single&picid=7945&direction =DESC&sort=date&perrow=4&trows=3&quiet=Verbose

Wouldn't there be a problem with the FSB (?) that was described on the A+CVT that the belt just slip right off or shear if it push another robot? If it uses a chain like the A+CVT, the FSB would have to be really strong if it hits something at high speed cuz it could bend or snap.

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

I was about to post the same thing when I realized it about an hour ago, but with such detailed discussion (by myself included) into the actual method of shifting and such, I was embarrassed that I simply was missing something. But if it doesn't seem right to you either, maybe this is seriously flawed, or we both are missing something.

Even if the gears were different sizes, the bright green gear in between the pink "slider" would have to be of varying size each time it shifted.

A transmission of this style can difinitely be fabricated, but it woul dhave to be done so in a matter similar to that of 222, that ball and plunger design.

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

I thought the same thing you did, and actually sat on it for 24 hours before I realized what the designer was trying to do and posted my comment.

However, the transmission is possible with different sized gears and minor modifications. Lets call the input shaft "shaft 1" and the other shaft "shaft 2". Now, if you stripped the hubs off of all the gears on shaft 2, and attached a larger gear to each of the six existing gears (with all six larger gears being the same size), the gear in the slider could interface with the larger gears by sliding back and forth.

Although that isn't what is in the drawings, as far as I can tell, that may have been the design intent.

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

Thank you. My train of thought almost got there but it derailed. Thanks for getting it back on track. I'm not sure if that is the way the drawing is but that is certainly the way it would be done. Mystery solved by ahecht.

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

I hope this comes across as a simple explanation for the 6-speed transmission - you know how us teachers can complicate even the simplest of things! :)

First off, I've posted a new picture of only the gear reduction system of the transmission. The first gear (top red) on the primary shaft (on the left) is an initial input- from the CIM and drill motors. It is a 1.25:1 reduction from the gear on the CIM motor.

From the first double gear there is a simple tranisition of 1:1 to the first double gear (top blue) on the secondary shaft on the right. The overall reduction from the original input is now 1.25:1.

The first doulble gear on the secondary shaft reduces the speed (1.67:1) back to the second red gear on the primary shaft. Overall reduction at this point is now 2.0875:1

The second primary red gear transitions back to the second secondary gear at 1:1.

The second secondary gear reduces back to the third primary gear at 1.67:1. Overall reduction to this point is now 3.486:1.

The reduction continues down the system to the sixth gear.

The gear on the hexed output shaft (shown in the original picture) slides across the six blue double gears and engages at each one of them to provide six different output speeds.

Friction, while a concern, is negligible since all of the gears on the gear train (red and blue) are pressed on bearings and rolling rather freely. Granted the friction between the gears from one end to the next creates quite a bit of friction, I don't think it will be a huge concern. Like I've said before, we're going to start with a two-speed variation and work up from there.

I hope thsi explains how this system works a little better. Once you understand the stair-stepping concept between the gears, it is easy to see how you can set this up with as few or as many speeds as you need without great modification.

I will keep you all posted as we progress with the fabrication, construction and testing. I will also update the model to include gears with actual teeth so it is easier to see what meshes with what and how it all plays together.

Sean

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

There are threads about multi positioning with air cylinders. If I was going to do it that way I would use a control valve with a center off, no power all ports closed. A slider pot attached to the piston, and a really good programer.
You can stop a piston in any point of it's travel with the first, you can tell where it is with the voltage generated from the slider on a analoge input to the controler. The bounce and drag may cause occilation problems. And if your coding is not up to it, all bets are off. Other wise I would use shaft with very coarse thread, almost like that of a Yankee screwdriver, and a multi turn pot; driven as suggested by a globe motor. Good luck

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

I like the concept, but there are a few little things that I'd watch out for when finalizing the design.

I'm making a couple of assumptions about those gears, namely that they're 1/4" face width, and 24 pitch (the pitch is a guess, based on the face width, and the face width is an estimate based on the size of the other components). Using a spreadsheet which calculates the number of horsepower that the gears can accept, using the Lewis formula (let's all hope that my spreadsheet skills are up to par), those gears would have to have approx. 85 000 psi tensile strength. (The Lewis formula isn't perfect, but it ought to be fine for these purposes.) Fortunately, SDP/SI sells gears that exceed that spec nicely at 180 000 psi, but at around $50 (USD) each, you'd be spending vast amounts of money. (Backtracking a step, I'm only saying 180 000 psi, because SDP/SI quotes min. R_C 35 [Edit: That's the Rockwell C hardness scale] or so, which, in steel tends to exhibit strength of 180 000 psi. Actually, they quote R_C 55 for the teeth, but I'd rather not use that number, for safety's sake. Note that I've never tested this, or received verification from SDP/SI!) Are you planning to make your own gears (slices of gear stock, maybe?), and have them heat-treated?

I'm really starting to like the possibilities here, especially because of the expandability of the thing. It would be a trivial matter (except in terms of weight) to increase the face width of the gears to 3/8", if you needed to.

Make sure that you verify your gear strength calculations, and take into account the fact that the gears will be "crashing" together a little bit, due to the teeth engaging one gear after another (sideways). I don't know how durable the gears will be under that kind of loading, especially when shifting on the fly. Those through-hardened gears are rather brittle--this is definitely a good reason to test them!

The lead screw idea sounds good, and M's suggestion of the Geneva mechanism is an interesting one.

Finally, what's the purpose of the small slots in the sides of the gears? Some sort of aperture for an optical or Hall effect sensor? I don't think they'd be necessary everywhere, in that case.

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

Couple of clarifications -

1. The drawings I have posted are for illustration purposes only. It was, more or less, a quick and dirty way to prove a concept. And, I'm pleased to say, it worked. At least in the theoretical universe of Autodesk Inventor 8 Pro.

2. The slots in the gears (the blue and red components that are missing actual gear teeth) are there so it is possible to see the rate of rotation of each gear as it steps down. Motion constraints have been applied to all of them so you can actually see the reduction taking place when the constraints are driven.

3. I am working on a four speed variation (can't imagine the need for 6 gears unless, as JVN pointed out, the field gets REALLY big!) of the same design using actual gears so the concept is a bit more clear. The assembly is about 90% complete and weighs in at just a shade over 8 pounds without motors or a shifting input device (pneumatics/lead screw/etc.). I'll post a pic after I submit this post.

This new design uses standard hubless spur gears (20 deg. pressure angle) ranging in size from 15T to 45T. Their face width is 1/2" and they are tied together in sets of two (face to face) using drilled holes and roll pins. I can probably reduce a fairly significant amount of weight by dropping down to 3/8" face width. I've tried to standardize as best I can for ease of component acquisition.

Tristan - thanks for the insight into the Lewis formula. I'll have to keep that in mind when selecting components that can withstand the abuse of FIRST robotics! $50 each - YIKES! I better find a more financially responsible solution!

Sean

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

If there's a way you can keep the tolerance to press in dowel pins I would recommend that over roll pins. They have a much higher shear strength.

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

Depending on what sort of gear strength you actually need, you can use cheap (and relatively soft) gears in the high-speed stages (where they are less stressed) and only go with high-strength gears for the lower reductions. Also, though I've never tried it myself, getting carbon steel spur gear stock and having it hardened is probably an excellent way to control cost here. SDP/SI (and others) typically sell several inches of the stuff for the same price as a single gear. All you need to do is machine the bore, cut off a reasonable length, and add a keyway (or dowels, or whatever is necessary). Then find somewhere to get it hardened, or maybe do it yourself (and hope it doesn't distort--you'd have to inquire about the specific hardening process to find out if that's an issue).

By the way, for a 6- or even a 4-speed version to work well (it seems to me, anyway) that you'd need to be able to shift on the fly, even while pushing something, or crashing at high speed into something. (Because the chances will be higher that you'll be in the wrong gear for something, as you're doing it.) I think you've addressed that, but just in case it wasn't a priority--please make it one! Part of that involves using sufficiently robust gears, since a partially engaged gear does not evenly apply its load to the entire face width!

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

The design intent is shift-on-the-fly capability. How well it works will remain to be seen. We plan on auto shifting - requiring a driver to also manage which gear he/she is in is not something we want to do.

We would like our shifting mechanism to be fast AND accurate enough to engage the vast majoirty of the gear even in the heat of battle. Double-edged sword whether to go with wider or narrower gears. Wider gears mean more strength but also mean more travel to fully engage and more weight. Narrower gears are lighter and quicker to engage but may not have the necessary strength. Time to add some math to the design mix.

Sean

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

Just one question..... why?

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

I just ran across this old thread... Very cool idea.

OOC, Did it ever get made? If so, how did you solve the shifter problem?

My $0.02... Several methods of shifting immediately come to mind:

Method 1 - Threaded rod, Globe Motor and 10-turn pot feedback:

Use a high pitch threaded rod to drive the indexer, such that the entire run from one end to the other is less than 10 rotations.

On one end, attach a Globe gearmotor, with a "slippery" fitting (ex: use a short section of vinyl tubing as a "coupler"). This prevents damage in case of a software error, as the drive will slip if it hits end of travel.

On the other end, attach a 10-turn potentiometer. Wiring: one end to +5V, other end to Ground, wiper to an analog input. Attach it with a hard coupling, but set it so that the pot never over-runs. This gives you an analog voltage into the RC, proportional to the position of the indexer.

Calibration: Manually set the indexer into the center of each gear position. Record that voltage value into a table. Jog it around to record the RANGE of values that still legitimately set a solid gear ratio for each gear setting as well. Taking these error values (epsilons), look them over and decide upon a good maximum error band value you'll allow that still guarantees you are In Gear no matter which gear you select. Call this your Epsilon.

(I'm assuming here all of your drive motor Victors are set to "coast", to protect the gearbox from meshing damage.)

Now, to shift: Your software simply "hunts" for that value, within "+/- Epsilon". Look at the current pot value. Idle the drive motor, Turn on a "Shifting" light on the Operator's Panel. Move the Globe motor in the right direction to increase or decrease the value. Once within Epsilon, STOP, turn off the Shifting light, and re-enable the drive motor. This helps keep you from tearing up the gearbox while shifting, no matter what the operator is requesting of the drive.

Method 2 - Threaded rod, Geneva Wheel idea for indexing, Globe Motor, 10-turn Potentiometer, Home Switch for Geneva drive wheel:

Use a threaded rod for the indexer motion, and add a 10-turn pot to it for feedback, as before. This is now your "gear selected indicator"

On the other end, design and add a Geneva Wheel as an indexer.

See: http://en.wikipedia.org/wiki/Geneva_mechanism
Mechanism: http://upload.wikimedia.org/wikipedi..._animation.gif

Drive it with a Globe Motor. On the drive wheel, add a notch for the green wheel's "the pin is away from the Geneva Wheel" position, and monitor it with either a micro switch or an opto interrupter, connected to one bit of Digital Input. This forms the Home position of the drive wheel for each gear position, where you will stop the motor. (I can show you how to wire this, if you need more information.)

Software: Again, record the pot's analog value for each gear position, and calculate the overall Epsilon.

This time though, the analog value will be used as an INDICATOR of which gear you are in. You still need the Epsilon, as the analog input values WILL drift with slightly with temperature shifts (a known effect of A/D conversion systems). That is easily implemented by a CASE statement, that says if whenever the values is BETWEEN (value-epsilon) and (value+epsilon), AND the HOME is hit (IOW the globe shifter motor is OFF), then it's in THIS gear...

Shifting: As before, coast the drive motor, turn on the SHIFTING indicator, and use the current value to determine which way to kick on the shifting motor. Once the HOME switch is off, use that signal to keep the motor on until the HOME switch is hit again (one gear step). If you're still not in range, keep going. Once the POT is in range, keep going until the HOME switch is off as well, then stop. Turn off the SHIFTING indicator, and re-enable the drive motors.

Method 3 - Two Indexer Cylinders (Up, Down), ratchets, and a Potentiometer or switches for feedback

Two tiny cylinders: 3/4" bore, and 1/2" or 1" stroke (whatever the design calls for). One cylinder is INDEX UP, the other INDEX Down.

Mechanically set it up such that each full cycle of one of the cylinders runs a ratchet step system, that either increases or decreased the gear by one step. ("The design of which shall be left as an exercise for the reader"... Don't you just HATE that when your teachers do that???) :rolleyes:

Current position is indicated by either switches, or a potentiometer. One way to connect the potentiometer is via an inverse rack and pinion system, watching the throw of the shifter. An alternative is to use micro switches at each position.

If you use switches, but become short of digital input lines (you need them for other reasons), wiring lines can be saved by:
a) attaching the switches to a Priority Encoder chip, which converts single lines into a binary value. (This is roughly a $1 IC in most logic chip families.) or:
b) attach the switches to an R2R resistor ladder to encode them as an analog voltage, which is then connected to one channel of Analog Input. Decode like a pot as with method 2 (bands of values equal each gear position), as again the A/D converters do drift, and values are rarely EXACTLY the same from one sample to the next.

For safety to keep the mechanism from tearing itself apart if an indicator switch fails, I'd also make sure you either have some End of Travel switches, and/or set up the mechanics such that attempting to index beyond the end of travel will cause something to slip, vs tear up.

Does this make sense?

- Keith

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

I dont see the value of anything more then a two speed unless u want to waste a lot of weight

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

Well, for most of the contests I've seen to date I'd agree, but I can imagine exceptions.

The two primary gears I want are of course "dash around unhindered - high gear" and "position yourself for scoring - low gear".

However, having a "sumo fight - VERY low gear" can be extremely useful in some contests, where you have to hold ground or displace another bot from their scoring position, but it's too slow for efficient scoring. (But that can often BE the low gear...)

Beyond those cases though, the only time I'd want more than three gears would be in a contest where you could score in more than one way and they require different speeds not easily attained by the two (or three) gear system.

One game that comes to mind is Zone Zeal. It could easily use up to 4 ratios, optimized for minimum time consumption at full speed:
- Dash while empty
- Drag 1 loaded goal as quickly as possible without stalling
- Drag 2 loaded goals as quickly as possible without stalling, and
- SUMO mode - tank crawl against a blocker while holding 2 goals (or displacing an opponent holding 2 goals).

<edit>
I do have a hard time envisioning use for anything over a four speed transmission, though.
</edit>

- Keith

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

oh that would be better than just two, and i have a feeling we will be doing something like zone zeal pretty soon:rolleyes:

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

It seems to me that a better way to get four speeds would be to use two dogs, that way you do not have the gears smashing into each other. You could just have something like this:

X's are interfaces between the gears,
D's are the dogs,
----- is a gear,
| is an axle.

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

Use a leadscrew on a banebot or other low-gear motor.

Doh - looks like kmcclary beat me to the punch.

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

Excellent concept. Though I worry about the end loss of the final gearing stages. Usually gears are averaged to a 97.5% efficiency per gearmesh reduction, yet you have 12 possible gearmeshes at once. Even at a very generous 98% efficiency per reduction (which must include bearing losses as well) it's still 0.98^12, which is only a 78% efficiency regardless of what gear it's in (since all of the primary and secondary gears are always connected).

This isn't to say that this isn't a fabulous design -- it simply says that there is a point where it will become highly impractical to keep adding stages to the transmission. Due to traction, current draw under load at max speed, and other issues, I'd expand the gearing in between stages and go for (max!) 4 stages that vary from 3-4fps to 13-15fps.

Regards

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

Hey, I like the dual dog concept! (VERY cool!) :)

Bottom line though: This thread started out a few years ago, and I'm curious! DID any version of it ever get built, for that original (or subsequent) contest???

... and if so, what was the final solution???

- Keith

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

I would recommend PMing Sean Schuff to see if they ever built it. It looks like he was the one that originally uploaded the image. I know he is still active on the forum.

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

I'm pretty sure this was never built. 171 has former 93 members and none of them has ever said anything about this. But I could be wrong.