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Author Topic: Holding torque after hacking a servo  (Read 523 times)

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Offline ScojoTopic starter

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Holding torque after hacking a servo
« on: October 24, 2013, 02:11:50 PM »
If I hack the HS-5685MH, HS-485HB, or the HS-985MG to operate continuously clockwise and counterclockwise, does the stock holding torque decrease?

Is there a way to up the holding torque on a servo?

Offline Jackson21

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Re: Holding torque after hacking a servo
« Reply #1 on: October 24, 2013, 08:02:05 PM »
Not to sure about the decrease, can't imagine why it would though..
Anyway, why do you want more holding torque?? Just thought that something like a worm drive might be a far simpler option, if you could give more details, would be helpful :P
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Offline waltr

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Re: Holding torque after hacking a servo
« Reply #2 on: October 24, 2013, 09:01:15 PM »
If I hack the HS-5685MH, HS-485HB, or the HS-985MG to operate continuously clockwise and counterclockwise, does the stock holding torque decrease?

Is there a way to up the holding torque on a servo?
1- No, still the same
2- Apply a high Voltage so there is more current to the motor. But if the Voltage is too high it will burn out the servo. A slightly higher Voltage, say ~6V will increase torque over 5V but the servo will not last as long.

Offline ScojoTopic starter

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Re: Holding torque after hacking a servo
« Reply #3 on: October 30, 2013, 04:02:11 PM »
I don't necessarily want more holding torque, but just thought I would ask if it were possible to increase it.

How much holding torque do servos have? Is it a percentage of the max torque?

I'm looking to make a pan tilt camera setup that will operate on a moving craft submerged, so I don't want currents pushing the assembly around. If the holding torque for servos is decent, I see no need to invest in stepper motors.

Offline Jackson21

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Re: Holding torque after hacking a servo
« Reply #4 on: October 30, 2013, 06:10:47 PM »
Correct if I'm wrong, but I believe holding torque is exactly the same as stall torque (makes sense in my head). Still not a lot of info bout the build, but assuming your running servos at 7.4 V you'll have 12.9 kg-cm of stall torque on your HS-5685 (couldn't be bothered researching other two servos but I'm assuming roughly similar specs). So my guess is unless your making a nuke powered sub, I don't think you'll have any issues with water currents or drag. If you're really worried, try to make your camera set-up at aerodynamic (aquadynamic??) as possible as this will also reduce current drain from your stall torque if your robot is in especially strong currents.
 
Hope that helps,

Cheers,
Jacko :D
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Malory: But they were blanksóweren't they?
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Offline jwatte

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Re: Holding torque after hacking a servo
« Reply #5 on: October 31, 2013, 10:52:58 AM »
Quote
holding torque is exactly the same as stall torque

In commercial specifications, the stall torque is the maximum amount of torque the motor can deliver with specified voltage/current. Doing this for a longer amount of time will burn out the motor.

Holding torque is the amount of torque the motor can deliver continuously, without overheating. You will need a regulator to actually regulate the amount of current into the motor (typically using PWM) to actually stay at this level.

Offline ScojoTopic starter

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Re: Holding torque after hacking a servo
« Reply #6 on: November 01, 2013, 09:10:15 AM »
Quote
holding torque is exactly the same as stall torque

In commercial specifications, the stall torque is the maximum amount of torque the motor can deliver with specified voltage/current. Doing this for a longer amount of time will burn out the motor.

Holding torque is the amount of torque the motor can deliver continuously, without overheating. You will need a regulator to actually regulate the amount of current into the motor (typically using PWM) to actually stay at this level.

Any suggestions on a current regulator? I was just planning on putting the servo and my dc to dc converter in line with a fuse to prevent it from burning out.

I would probably want to limit the current to 3 or 3.5 A with my setup if I did.

So how do i get an idea of what my servo's holding torque is?
« Last Edit: November 01, 2013, 09:14:58 AM by Scojo »

Offline jwatte

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Re: Holding torque after hacking a servo
« Reply #7 on: November 01, 2013, 09:52:56 AM »
Any PWM circuit will be able to regulate the current. Note that hobby servos (PWM-style) typically have the PWM bridge already built in, and you can't separately PWM regulate the power to them. You will have to trust that whoever built the servo put in those safeties.
Another way to know whether it works or not is to build the torque in quesiton in a fixture, and keep stalling the servo for five minutes, and see if it burns out or not. If it's an expensive HiTec, perhaps it won't. If it's a Chinese special, it very likely will (unless it turns off itself.)

If the manufacturer is not specifying holding torque from stall torque separately, then the servo is likely not intended to be used in applications where the difference matters.

 


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