SG90's at high voltage

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barryg
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SG90's at high voltage

Post by barryg » Fri Jan 04, 2019 12:21 pm

Hi all,

Looking for a little advice on a particularly cheap spinner setup. I have an SG90 that i have wired with a relay so that i can give the motor max volts without burning out the PCB. my question is, has anybody got any idea what voltage these tiny motors will handle before producing lots of smoke? I have seen some comments that say the servos aren't happy above ~6v, but i figure its the PCB that fails and the motor will have a higher capacity.
Any advice/experience very welcome!

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MarkR
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Re: SG90's at high voltage

Post by MarkR » Fri Jan 04, 2019 3:02 pm

I run my flipper N20 motor at about 17v. It hasn't burned out yet, but I run it at a low duty cycle controlled by the microcontroller, so the driver can't just hold the stick to maximum.

I am more worried about the gearbox than the motor, I think the metal gears might fail eventually (testing this morning was ok though)

Mark
Robot: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?

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Team RobotMad
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Re: SG90's at high voltage

Post by Team RobotMad » Fri Jan 04, 2019 3:54 pm

(N20 motors are completely different from SG90 servos)

we used to use SG90 servos a long time ago but found that the gearboxes were incredibly week but you said its for a spinner so you have probably removed the gearbox, in which case the motor will have such low torque that it probably wont spin anything that has any mass.

the circuits in sg90 servos are designed for about 5v and thus i would image that the motor is not going to be over-spec as to not increase cost that the motor will probably burn out above 6 volts. but i haven't personally tested this, just my theory.
Lincoln Barnes
Maker of "SmartAnts", and autonomous Rover project, "Geoff".

barryg
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Re: SG90's at high voltage

Post by barryg » Fri Jan 04, 2019 4:37 pm

"we used to use SG90 servos a long time ago but found that the gearboxes were incredibly week but you said its for a spinner so you have probably removed the gearbox, in which case the motor will have such low torque that it probably wont spin anything that has any mass"
I have indeed tried using it without a gearbox, at which point it takes about 30 seconds to spin up. As a results i am using a speed-modded gearbox, which may well be the weak link. If so i can always change it out for a metal gear setup (although the proper solution would be to get a decent weapon motor)

"the circuits in sg90 servos are designed for about 5v and thus i would image that the motor is not going to be over-spec as to not increase cost that the motor will probably burn out above 6 volts. but i haven't personally tested this, just my theory."
This is a sound bit of logic. I think im still going to crank up the voltage booster until i get a failure of some description..... i just wanted to know when to expect a failure, although that may be the gears from what you have said.

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MarkR
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Re: SG90's at high voltage

Post by MarkR » Fri Jan 04, 2019 6:27 pm

Looking at the spec of the SG90, it looks like the gearbox is a crock of sausage, so it's not going to last very long if the motor gets overvolted.

I have some of those continuous servos which I used on an earlier (non-combat) robot at 5v, they are poss weak (but very easy to control from a gpio on a microcontroller)

If you want a simple way of doing a spinner, maybe use a low gear ratio (10:1) N20 motor and overvolt that, it's going to give loads of torque and probably won't destroy itself in 1 second.

I wouldn't recommend using a relay though, I suppose any ESC which is rated at the appropriate voltage would be ok.
Robot: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?

barryg
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Re: SG90's at high voltage

Post by barryg » Mon Jan 21, 2019 1:09 pm

Just to close this one out for anyone scanning through the forum in the future:
-Yes you can run the motor from an SG90 at a high voltage (tested up to 11v stall without any issues)
-At around the 11v mark the pinion gear on the motor starts slipping, which effectively protects the rest of the gears (i know, not exactly robust)
-gunna attempt to run it at ~20v for AWS 57 and accept the slip, replacing the pinion between battles
-I fully expect running one of these motors at 20v for more than 2mins to kill the motor, but it should be fun until that happens :-)

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