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Multiple gear motors per output shaft

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jwatte:
Overvolting: Yes, overvolting will reduce the lifetime of the motor, approximately by an exponential function of the amount of overvolting.

1.4x voltage == double power: Ohm's law says power equals voltage squared over resistance. Resistance doesn't change, so multiply voltage by 1.4 means multiply power by 1.4*1.4 which is approximately 2. (You really want square-root-of-two rather than 1.4)

How to find the internals about the servos: It's listed right on the front page of the product listing on the Trossen Robotics site. It's also available in various Robotis marketing literature.

How do I know things? I read, and remember :-)

ErikY:
Makes sense on the overvaulting, thanks for the explanation.

I need to be more disciplined when I read. I read a lot, and usually remember what I actually read, but my brain is always onto the next thing. I have been on that page a million times, and never read the motor, and in turn spent rediculous amounts of time looking for motors!

But I digress, that problem is not one that I think anyone on this forum can help me with!

I am sure this will come back to bite me, but how do you know exactly which Re-max it is? I was on there and there were a million of them, did you use the 225:1 gear ratio from the servo info and the final torque/speed to figure it out, or did I miss this somewhere too?

jwatte:

--- Quote ---how do you know exactly which Re-max it is?
--- End quote ---

I don't know exactly! In fact, all the listed Re-max motors are 24V motors, which makes me wonder whether they got a custom wound version, or whether they use the 24V version and undervolts it for longevity.
You could call Maxon and ask them what they think about your particular application. They probably have sales engineers who answer that precise kind of question!

ErikY:

--- Quote from: jwatte on March 06, 2013, 10:20:45 PM ---
--- Quote ---how do you know exactly which Re-max it is?
--- End quote ---

I don't know exactly! In fact, all the listed Re-max motors are 24V motors, which makes me wonder whether they got a custom wound version, or whether they use the 24V version and undervolts it for longevity.
You could call Maxon and ask them what they think about your particular application. They probably have sales engineers who answer that precise kind of question!

--- End quote ---

Gotcha!

I have been playing with some calculations, and something is clearly off, would you mind taking a look at my calculations and telling e what I am missing?

I am looking at a motor with the following characteristics:

12V
nominal torque: 12.4 mNm
stall torque:  207 mNm
no load speed: 9130 rpm
nominal speed: 8170 rpm

I am using a gear ratio calculator, which asks for the following:

input torque (in/lb's)
input rpm 
Gear Ratio

And spits out an adjusted torque and adjusted RPM

When I look at stall torque, I am converting .207 Nm (from motor specs) to be 1.832104309 in/lb's from a separate converter

So I entered 1.832 in/lb's
9130 RPM's
225:1

And I get the following output:

~ 412 lb's/in stall torque or 6,592 Oz/in
~40 rpm's

This has to be wrong, that is about 6 timex stronger than an Mx106 for $207 at 12V and only 160grams with a 29mm diameter.

What am I doing wrong?

This is the maxon part number if anyone is interested: 226802


jwatte:

--- Quote ---that is about 6 timex stronger than an Mx106
--- End quote ---

One difference is that the MX-206 is run at 12V, not 24V -- this is a 4x difference assuming it's the same motor.

If you also use a different gear box ratio to get to 60 rpm instead of 40 rpm, you get another 1.5x difference.
4x * 1.5x == 6x, so that would almost exactly explain the difference you suggest.

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