pic: 2 Speed V.2
 

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arefin, what did i tell you about square holes?

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...that they work better for square pegs than round holes?

(sorry, couldn't resist)

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lol... I didn't want to make it look like CHEESE. Ofcourse the squares can be changed to different shapes. (When I will take weights out of the plate, I will take it out from anywhere possible)...

Anywho... I made the pocket bigger for the dog shifter to fit better. Took some weights out (Gears and plates). Also made it thinner (modified the gears hubs, shorten the shafts). V.2 is 6.25" by 5.5" by 2" and weighs 4.5 pounds. :)

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wow, it just keeps on getting better! great job =)

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The thing about it is that it cannot be machined (by traditional methods). It is fine if you plan to laser or waterjet it but an endmill no matter how small will always have a radius. Another option would be some sort of custom broach, or machining it with a fillet and filing it square (not too hard and comes out pretty good if you use a nice sharp file).

Of course the easiest thing to do would be to just draw in a fillet and live with a filleted rectangular hole. :D

As for the lightening, I would recommend a pocketing pattern over a hole/cutout pattern. Even just .063-.090 of material left in the bottom of the pockets will add a lot of strength. Then you leave ribs of the full thickness. Sort of like this: http://www.chiefdelphi.com/forums/sh...ad.php?t=34384

This keeps a uniform plate with no holes (which I think looks nice) that will be stronger than one with holes, but a very close if not the same weight.

Of course, it is all up to you and while it will be stronger without through holes, in this application it probably makes very little difference, when I see transmissions like the AndyMark running .090 plate with no problems.

I'm still curious as to how those dog gears spin on their turned down (to round) portions of the hex shaft.

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If I am understanding what exactly you are curious about... those two dog gears (30, 60 tooth) are always spinning... When you engage the shifter in one of those gears... the hex shaft starts turning. (ofcourse the dog is always engaged either with the 30 tooth or the 60 tooth gear).

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Typically teams will put a bushing, or bearing inside those gears, to reduce friction. 229 used a bronze bushing.

Do you have something like that?

(I believe this is the question sanddrag has been asking...)

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A bronze bushing John... sorry for not pointing that out earlier. I hope that answered your question Sanddrag.

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Looks good. Maybe while your in design mode you could add a take off on the output for an encoder or hall sensor. The output RPM is a little high. Might need a reduction for both. Could be done with plastic gears to keep the cost and weight down.

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You are right... it is high. I made this transmission to be used with 4" inch wheels. If you do a reduction of 10:24 (sprocket), with high gear you get the output rpm of 742.5 and with low gear you get the rpm of 185.63 which will make your robot go 13 fps on high gear and 3 fps in low gear with a lot of torque.

Please read posts 6, 7, 8, 9, 10, 12, 14, 15 in this thread to get more specific specs on the transmission. :)

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I was referring to a second output shaft to drive an encoder for autonomous mode. If only low gear was used for autonomous the 1 to 1 on the output shaft for the encoder would be OK. If high speed was used for autonomous, the interrupts per second could be a little high. If you do design in an encoder shaft there is some planning as to how fast the robot will go, the precision that is desired and the interrupt load that can be placed on the controller. If additional reduction is needed for the encoder shaft, then plastic gears could be used.
As for the high speed gearing, 13 fps is fast. It takes a very good driver to control the bot at that speed and may be unusable in a crowded obstructed playing field. It's main use is a mad dash to the end zone at the end of the game. The high gearing also affects the acceleration and responsiveness at the lower speeds most of the game is run at. They are all design choices. I personally go for about 10-11 max. This years kop gear box I believe was 8.3 fps and was very usable. Of course if the next game was all about mad dashes from one end to the other you would have that covered.

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Now I totally understand what you are trying to explain. This transmission is in the very early stage of design. I just designed it to learn how to do a dog shift. As time pass by, I will improve it. There is no plan of this transmission to go on the robot just yet. It all depends on the game. I do appreciate your comments. Thanks. :)

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Edit, don't put too much analysis into this post. I forgot about crucial center to center distances. See my "fixed" recommendations on the next page of this thread in my next post

I'm thinking you could drop that 60T gear down to something like a 45T. This would keep your high gear ratio the same but increase your low gear rpm (decreas the ratio) and decrease the ratio between them making for a 3:1 difference.

I'm fairly confident that you could even fit a 40T in between the CIMs if you wanted to as long as you keep the axes of rotation of the CIMs and the 40T gear all in the same plane. (my rough calculation shows you should still be left with about .080 between the CIMs).

This would give you a 2.67:1 difference between high and low which I think is pretty much optimal. This would bring your low speed up to around 4.5-4.8 fps which I think is much more useful.

Have you determined that you must be geared for a low 3fps before you can slip the tires without tripping breakers? I'm thinking you can gear a little higher than that and not trip breakers and still slip the wheels.

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Off the top of my head... ;)
With 4 CIM motors, a 130lb robot and a coefficient of friction of 1.5...
I'd say you can be at around 6 ft/sec.

(I have run these numbers, once of twice before.)