pic: Version 1.1

[Max Lobovsky]

There is probably room in the gearbox to shift ratios so that the shifting gears are spinning faster with less torque. Specifically, increase the size of the CIM pinion, then increase the final stage ratio.

I assume this is all 20 pitch? As I'm sure you know, make sure to buy the strongest material that you can find the shifting gears in.

A good question that I can't answer is wether extra backlash is a good idea for the shifting gears. More backlash means they will be able to shift faster (less friction, more time to do so), but more backlash also means they are slightly weaker. I'd guess a few thousandths extra is a good idea, but this is definitley a question to ask someone who has built a sliding gear shifting gear box.

Also, where are you purchasing that long gear in the final stage?

[Cory]

Originally Posted by Max Lobovsky

Also, where are you purchasing that long gear in the final stage?

Spur gear stock... available from SDP-SI, McMaster, etc

[Alex Golec]

Structurally, the position of the CIM motor just sticking out on a sheet of (I'm guessing) about 1/4 aluminum just seems like a hazard to me... but then again I have little engineering knowledge to judge this by. Also, as Tytus mentioned, I think the extra material from the gears needs to be removed and the pieces holding the plates together should be a little bit thicker.

Arefin, Great job on the drawing; it looks great!

_Alex

[jimfortytwo]

If I'm looking at this right, it seems that in the transition period between high gear and low gear the motor shaft is locked, because both gears are engaged at the same time. Is this actually what is desired? It seems needlessly cruel to the motor, and I would think actually makes slipping into the new mesh more difficult.

By all means lighten the gears if it is easy for you to do, but I suspect that the inertia of those disks is negligable in comparison to the momentum of the 130 pound robot, or even just the wheel attatched to this gearbox.

[Arefin Bari]

Originally Posted by jimfortytwo

If I'm looking at this right, it seems that in the transition period between high gear and low gear the motor shaft is locked, because both gears are engaged at the same time. Is this actually what is desired? It seems needlessly cruel to the motor, and I would think actually makes slipping into the new mesh more difficult.

By all means lighten the gears if it is easy for you to do, but I suspect that the inertia of those disks is negligable in comparison to the momentum of the 130 pound robot, or even just the wheel attatched to this gearbox.

you are very right... it is locking.. thanks for bringing it up to my attention. umm... solutions.. there are two. one, either stop and shift. or space the gears out more. decisions will be made soon. most of the modifications will be made and will post a Version 1.2. I pointed this out in my posts before that i am going to make holes in the gear. please understand that I am a newbie to inventor, in fact i started working with inventor on thanksgiving night.

Edit - Sanddrag, if i use any steel on the transmission it will just be the shafts, because i have experienced shafts bending inside the transmission. but i do consider using steel if i have enough weights left. our 2003 transmission was first made out of aluminum. it did work ok. but then we switched to steel.

[henryBsick]

Weight issues from my critique point.
The third shaft is the output shaft and is geared down from the second shaft's spur gear by what seams 1:2 maybe 1:3. There isn't a whole lot of reduction and a lot of weight. Possibly eliminating the third shaft and making the second shaft longer to attach a sprocket... but then that wouldn't work because the shaft moves and the sprocket would need o be mobile. SO maybe if you made the first shaft move with a spur gear straight from the CIM the one of the 2 gears on the first shaft. That would make the first shaft mobile and you could then attach a sprocket to the immobile (laterally, not rotationally) second shaft. In essence that would reduce the size of the big middle spur gear originally on shaft 2 and the gear it connected with on shaft 3 would no longer be necessary.
Its kind of a radical change, but just an idea of other possible means to reduce weight.
Also, the hubs on the gears can be reduced. a lot. They are pretty huge massive in the pic. a simple trip to the "digital lathe" could fix that.
my $.02
Good luck with version 1.2 Arefin.

[Andy Brockway]

Originally Posted by Arefin Bari

you are very right... it is locking.. thanks for bringing it up to my attention. umm... solutions.. there are two. one, either stop and shift. or space the gears out more. decisions will be made soon. most of the modifications will be made and will post a Version 1.2.

Nice design, of course I always advocate that you build and test.

I am hanging the CIM motor off 1/4" plates and think your design will be OK. If you include a mount to the frame of the robot close to the CIM you will definitely have enough support.

As for stopping and shifting with the current spacing....depending on the ratios the chance that both sets of gears will have teeth lined up is slim. This would prevent the shift from occuring. Designs with the shift dog have broken themselves when a "neutral" is not included and the shift is done on the fly. (It may have been JVN who told this story )

[tiffany34990]

good job so far-- you have been working hard arefin as i well know-- good luck w/ the next version--hopefully it won't drive you nuts


enjoy designing....

[ZACH P.]

You need to adjust the spacing on the shifting shaft. By the picture you posted, I can see that there needs to be more lateral play on the shaft. The current setup allows for both gears to be engaged at the same time. You need to have space so that one gear is fully disengaged before the other is engaged.

[David Guzman]

Ok... this might be a dumb question but what controls how much the piston goes out? Is it controled so that it goes out just emough to move the gear or it will just stop when it hits the aluminum on the sides?

Maybe I just don't see it.

[Arefin Bari]

Max, Thanks for your input... yes those are all 20 dp gears... but i am thinking about switching them to 16 dp gears. the shifter works fine. and thanks cory for answering the last question.

Edit - Also there will be holes in each gear just not to reduce weight but for what tytus pointed out (look at his post above). Each gear will be anodized.

EDIT- didnt want to post again... so here i go replying to alex from 469. yes i am considering what tytus has said. Also (if you see in the description of the picture) i am planning on moving the motor between the two plates. if i leave it like that i will sure mount it on the chassis somehow to make it stronger. thanks for your inputs.

[sanddrag]

Originally Posted by Arefin Bari

Each gear will be anodized.

If your gears are steel, I don't believe they can be anodized. And if they were aluminum, why would you anodize gears? It would add extra "thickness" on every anodized suface (not much but enough) which could cause a problem with teeth meshing. The only anodized gears I've ever seen are made from stock that is already anodized, then the gears are cut leaving a fresh precision surface for the teeth.

Perhaps you meant hardened?

[Arefin Bari]

Originally Posted by sanddrag

If your gears are steel, I don't believe they can be anodized. And if they were aluminum, why would you anodize gears? It would add extra "thickness" on every anodized suface (not much but enough) which could cause a problem with teeth meshing. The only anodized gears I've ever seen are made from stock that is already anodized, then the gears are cut leaving a fresh precision surface for the teeth.

Perhaps you meant hardened?

yup .. sorry for the confusion... i meant to say harden the aluminum gears...

[sanddrag]

Originally Posted by Arefin Bari

yup .. sorry for the confusion... i meant to say harden the aluminum gears...

Why aluminum and not steel? I'm always a fan of saving weight (aren't we all) but I like to keep a bit of "beef" in areas prone to failure, or where I have seen failure before.

I don't know enough to do the calculations, but if someone can mathematically convince me that aluminum 20P gears are suitable in a FIRST robot gearbox application (even say non-shifting), then I'll run right out and by some.

But, because I can't mathematically prove or disprove the success of aluminum gears, I always just opt for the safer side and go with steel, as do most teams I assume.

If someone has done an aluminum geartrain and it worked, I'd love to hear about it and see some pictures. If anyone thinks it will work, I'd love to see some calculations. I'm not by any means saying it does or will not work, I am saying I have no clue and would really like to find out.