Author Topic: Basic gear confusion  (Read 1533 times)

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Offline Vilos EngkorTopic starter

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Basic gear confusion
« on: May 30, 2011, 03:14:39 AM »
Someone please help me!!!!

I don't need a full explanation because I know the basic just been confused by some other "theories" which make me not confidence with my calculation.

I have a motor and the torque is 40.5mN-m(millinewton-meter). Then i have a gear and the radius is 22.9mm. Hence the maximum load it can lift is 1.76N. Am i right?

Then the problems comes. The load is too low which i have to design a box as a weight with other mechanism inside it. My aim is at least 1kg.

And then i found this link and i read the compound gear section.

The system is quite similar to mine.

After i asked around about how to increase the amount of load, at least double it; but the the torque of the motor remain the same. Some told me to use gear ratio. It that possible?

By the way, 40.5mN-m is my stall torque.

Please help me!!! :'(

Offline mstacho

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Re: Basic gear confusion
« Reply #1 on: May 30, 2011, 09:45:00 AM »
Yes, what you describe is theoretically possible.  By using the right gear ratio you can up the torque -- but you also reduce the speed, and the gears might get really, really big..  

I assume you're trying to LIFT 1kg against gravity, which would mean you'd need 9.8N.  But the lifting ability of your motor depends on the radius of the gears, so let's just play with torques (you can deal with the actual forces once you choose the radii of the gears):

If you have 40.5mN-m torque and you want 405mN-m, I need a gear that has ten times as many teeth (and is 10 then times larger).  Just as a rough calculation, it seems that you'd need a 10:1 gear ratio (and that 405mN-m is about right to be safe), but as you can see this would require a 229mm gear!  Also, your larger gear would be spinning 10 times slower than the smaller one, so if the smaller one is only going 1rpm, it'll take a LONG time to get that 1kg up there!


**EDIT: Screwed up my units, changed 22.9mm to 229mm.
« Last Edit: May 30, 2011, 10:28:26 AM by mstacho »
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Offline Gertlex

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Re: Basic gear confusion
« Reply #2 on: June 02, 2011, 07:11:13 PM »
Instead of doing one big gear, large gear ratios are accomplished by using a series of gears.  Look at pictures of the gears inside servos and you'll see how that works.  (a big gear and a small gear on the same axis will turn at the same rate.  Connect a bunch of these and large gears are avoided.)


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