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Author Topic: Making your own "gearbox" is hard... (And my omniwheeled robot is coming along!)  (Read 1465 times)

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Offline corrado33Topic starter

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I've FINALLY started building my robot that I planned years ago!  Except right now the only thing the same as the one I planned is the shape.

Anyway, I'm building a 4 wheeled omniwheeled robot, and I just finished assembling the first motor/gears combination.  I think it looks AWESOME, and I just wanted to share.  I pretty much just built it as I went.  I didn't plan anything and it got me into trouble a couple of times.  So if you look REALLY closely you'll see most of my holes for the screws are ovals, to give them some play so the part would end up in the right place. 

Anyway, I'm just going to disassemble it and make 4 more sets just like it.  Oh it works too, and that little tiny motor is sweet.  At 12V it's spinning REALLY fast.  I forget what the final gear ratio is, but it's manageable.  At 5-6 volts I think it'll be pretty slow, but that's where I'm going to start.  Then I might power the motors by 12V and have to use a lot lower duty cycle for the PWM.  I think at 12V the wheels will have a max RPM of 2720.
 
(Off the top of my head the motor spins at 13,600RPM with no load, and the gears are 12, 20, 30, and 40 teeth, so
13600x12/30 = 5400 RPM. 
Then the next two gears spin on the same axis and are joined, so 5400x20/40 = 2720RPM final, at 6V it's a little less than half of that) 
So assuming 2 inch wheels,
Pi*d = 3.14 * 2 = 6.28 * 1350ish RPM = 8482 in/min  / 60 seconds = 141 inches/second / 12 inches = 11ish feet per second at 6V. 

I think I did that right.  I guess that's not that slow, but the motor will most likely be spinning slower with load.  And since it's omniwheeled, it'll probably never travel on the same axis as the wheels are pointed, (unless I program it that way), so I'll need more speed to get a decent net velocity. 

Anyway, here's what I came to post about.  I know it's not perfect, but it works, and I'm happy with it.  The next 3 should be a ton better.




Oh and I wish I could weld, cause it took 12 threaded holes to put this together.  Do you know how annoying/hard it is to thread holes in steel?  The bulk of the body is built from aluminum, but I built the brackets from steel, as I was afraid aluminum wouldn't be tough enough.  (Yes I know different metals don't play nice together, but I doubt this thing will be together long enough to start corroding.)  I threaded the steel cause for some reason I remember reading somewhere that aluminum strips easily? And it looks much cooler to have the bolt heads on the outside of the robot than to have a bunch of bolts sticking out from the inside.  AND it makes it REALLY easy to take apart.
« Last Edit: July 02, 2011, 01:05:53 PM by corrado33 »

Offline corrado33Topic starter

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Double post, I know.... sorry  :-[

But I'm 3/4 of the way done with my second set.  I made a template of the drill holes from the first one, and while some things do still need tweaking, holes moved over a mm or two, it's only a couple of the holes, and not all of them.  Which is good.  Hopefully by the third set I'll have the template perfect and it'll just go together with no modification.  So far this set moves a LOT easier than the first set.  As I took care of the main hole that the axle comes out of better.  Since I'm not using bushings or bearings of any kind, I have to be REALLY precise when I drill the two holes that hold the axle.  

Anyway, all that's left to do is thread 4 holes and bolt them in.  (I'm waiting for the drill battery to charge)

Now if I could just get real time communication between my computer and my palm pda working.... I could control the robot wirelessly.... hmmmmmmm  Well maybe I should get communication between the palm and MCU working first  ;)

EDIT: Finished set 2
You can see in the top down view my second one turned out MUCH straighter than the first.  The motor at least lol.



« Last Edit: July 03, 2011, 12:09:37 PM by corrado33 »

Offline Aberg098

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Good stuff, impressive considering the "rudimentary" means at your disposal. By the time you get two more done you should have manufacturing down to a tee.

Are you considering some lubrication for those? 10k rpm is pretty quick and I'd hate to see that work wear out prematurely. I've seen graphite powders do an okay job for that type of box, without making too much of a mess.

Offline corrado33Topic starter

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Good stuff, impressive considering the "rudimentary" means at your disposal. By the time you get two more done you should have manufacturing down to a tee.

Are you considering some lubrication for those? 10k rpm is pretty quick and I'd hate to see that work wear out prematurely. I've seen graphite powders do an okay job for that type of box, without making too much of a mess.


Hmmm, haven't thought about lubrication, I'll have to look into it.  I think I might leave them run a bit without any lubrication just so they "wear in" if you will, then I'll put something on them.  I actually love the gears though, I think they're really cool.  Sure I could have spent some money and bought motors with gearboxes on them but this way is much more fun, plus I get to learn about gears in the process. 

I'm kind of opposite of a lot of people here.  I don't build something just to GET to the final product, I build something to learn everything I can along the way.   ;D  I mean sure I'll eventually build purpose built things, but that's not what this project is for. 

Offline Soeren

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Hi,

Oh and I wish I could weld, cause it took 12 threaded holes to put this together.  Do you know how annoying/hard it is to thread holes in steel?  The bulk of the body is built from aluminum, but I built the brackets from steel, as I was afraid aluminum wouldn't be tough enough.
Perhaps a bit late for this build, but if you want threads in thin aluminum plate, you can get threaded bushings that you pop-rivet into the holes.
It's just drill, pop and you have a solid, long lasting thread with minor weight gain.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline corrado33Topic starter

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Hi,
Perhaps a bit late for this build, but if you want threads in thin aluminum plate, you can get threaded bushings that you pop-rivet into the holes.
It's just drill, pop and you have a solid, long lasting thread with minor weight gain.


Yep, I've used them before for thin sheet metal in my car.  They're actually REALLY nice.  However I don't have the rivet gun and it's probably cheaper this way anyway.

Thanks for the tip though.   :)

 


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