N20 gear motors from China...

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MarkR
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N20 gear motors from China...

Post by MarkR » Tue Mar 20, 2018 1:53 pm

Hi, this is a general warning.

I ordered a total of 6 motors from China, 5 of them are working normally.

If you measure the resistance with a good quality meter, 12 Ohm is normal. This one is showing a short circuit.

*do* measure the resistance of every motor before wiring it up :)
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Paulmchurd
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Re: N20 gear motors from China...

Post by Paulmchurd » Tue Mar 20, 2018 2:09 pm

I have a few that measured 30ohm. Or some where around that. Is this because they are rated 3-6v ?

Ant Ipodean
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Re: N20 gear motors from China...

Post by Ant Ipodean » Wed Mar 21, 2018 2:33 am

On a related note re the N20's ..
I have had the simple "bent metal" brushes fail on these.
There appear to be some N20's made with "proper" carbon brushes.
Does anyone have more info about this, sources, etc?

Mike.

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MarkR
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Re: N20 gear motors from China...

Post by MarkR » Wed Mar 21, 2018 8:36 am

I found that my cheap home meter behaves somewhat like a random number generator, my guess is that it's putting AC or some switched voltage through.

The good meter (pictured) is in Reading Hackspace and consistently gives 11-12 Ohm for the good motors. It also depends slightly on the shaft position, because not all the windings may have the same resistance.

After I have finished dealing with Banggood about getting a replacement, I will post a tear-down of the failed unit.
Robot: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?

Paulmchurd
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Re: N20 gear motors from China...

Post by Paulmchurd » Tue Apr 17, 2018 8:53 pm

Any further tests on the motors?

I’ve just received 3 that have 4 ohm resistance.... and the 4th one is 12ohm.

They make an absolute racket the 4ohm ones. So loud

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MarkR
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Re: N20 gear motors from China...

Post by MarkR » Tue Apr 17, 2018 9:03 pm

Update:

The 0ohm short-circuit motor, I decided to use as a "mechanical prototype" that I could bash around as much as I wanted, trying to make it fit.

Essentially, I connected it mechanically to my flipper and started bashing it around a bit.

To my extreme surprise, it seems to have "recovered". I tried powering it from a bench supply, and it now runs!

So I guess it was an internal mechanical problem with the brushes which fixed itself with enough abuse. I didn't open the motor.
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DieGracefullyRobotics
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Re: N20 gear motors from China...

Post by DieGracefullyRobotics » Wed Apr 18, 2018 8:08 am

Essentially, you abused it til it behaved.

Should we be calling the robot equivalent of Childline? Ha. Mind you, I guess we're all guilty of machine abuse here.
Dave
Die Gracefully Robotics - Barely Even a Proper Team.

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