Author Topic: Servos at higher voltages than they're rated for?  (Read 858 times)

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Offline mstachoTopic starter

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Servos at higher voltages than they're rated for?
« on: May 05, 2011, 07:55:43 AM »
Can I hook up a 6V servo to a 7.5V power supply and get a servo with more torque?  I know that when you do this for a regular DC motor you get more torque at the expense of life of the motor, but with the servo electronics I am not sure if this will work.  Any thoughts?

Alternately, does anyone have a link to a high-torque servo that's inexpensive :-P  I probably need around 50 oz.-in

MIKE
Current project: tactile sensing systems for multifingered robot hands

Offline Soeren

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Re: Servos at higher voltages than they're rated for?
« Reply #1 on: May 05, 2011, 09:06:21 AM »
Hi,

Can I hook up a 6V servo to a 7.5V power supply and get a servo with more torque?
No, you get a servo that's dead.


Alternately, does anyone have a link to a high-torque servo that's inexpensive :-P  I probably need around 50 oz.-in
Why not make one yourself?
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline billhowl

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Re: Servos at higher voltages than they're rated for?
« Reply #2 on: May 05, 2011, 09:18:46 AM »
How about this "Towerpro MG996R 10kg Servo 55g / 10kg / .20sec"

Quote
- Operating speed: 0.17sec / 60 degrees (4.8V no load)
- Operating speed: 0.13sec / 60 degrees (6.0V no load)
- Stall torque: 13 kg-cm (180.5 oz-in) at 4.8V
- Stall torque: 15 kg-cm (208.3 oz-in) at 6V
- Operation voltage: 4.8 - 7.2Volts
- Gear type: all metal gears
- Connector wire: 30cm

http://www.focalprice.com/YO146B/Genuine_TowerPro_MG996R_Upgrade_Digital_Metal_Gear_Hispeed_Servo_for_Helicopter_Black.html
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6221
http://www.dealextreme.com/p/mg996r-metal-gear-digital-torque-servos-with-gears-and-parts-35763

Offline mstachoTopic starter

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Re: Servos at higher voltages than they're rated for?
« Reply #3 on: May 05, 2011, 09:21:05 AM »
Awesome, thanks guys. 

Haha Soeren, I guess it's a good thing I asked before I just hooked a servo up to my 7.5V supply :-P

MIKE
Current project: tactile sensing systems for multifingered robot hands

Offline Daanii

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Re: Servos at higher voltages than they're rated for?
« Reply #4 on: May 05, 2011, 02:28:11 PM »

Alternately, does anyone have a link to a high-torque servo that's inexpensive :-P  I probably need around 50 oz.-in
Why not make one yourself?


How does one make a servo oneself? Any advice on how to do that?

Offline rbtying

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Re: Servos at higher voltages than they're rated for?
« Reply #5 on: May 05, 2011, 03:29:26 PM »
You take a high-torque gearmotor, hook it up to an H-Bridge, attach a potentiometer (or rotary encoder) to the output shaft, and use a microcontroller to ensure that it stays at a given position.  Usually a PID algorithm is well-suited to the task. 

Offline MikeK

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Re: Servos at higher voltages than they're rated for?
« Reply #6 on: May 05, 2011, 04:00:58 PM »
Alternately, does anyone have a link to a high-torque servo that's inexpensive :-P  I probably need around 50 oz.-in


A standard servo is around 47 oz.in.  Here's a 69: http://www.junun.org/MarkIII/Info.jsp?item=10

Offline mstachoTopic starter

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Re: Servos at higher voltages than they're rated for?
« Reply #7 on: May 05, 2011, 07:40:41 PM »
as for making a servo: Yeah, all of my other motors are using PID, but that's because I also need torque control.  Problem is...I have 7 motors + 7 encoders, and I'm worried about scheduling issues using webbotlib and an axon.  I figured that the 7th motor is actually not something that I need torque control for, so I'd just use a servo and call it a day, having the servo deal with its own encoder.

Of course, I could just break up the control to have two uCs or something...and I'm not actually sure if the Axon *will* have scheduling issues, but Admin seems to think it might and until I get the whole robot hand hooked up (in a few weeks...) I won't know :-P

MIKE
Current project: tactile sensing systems for multifingered robot hands

Offline Soeren

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Re: Servos at higher voltages than they're rated for?
« Reply #8 on: May 06, 2011, 01:38:59 AM »
Hi,

How does one make a servo oneself? Any advice on how to do that?
Something along the lines of what rbtying describes should work and by making it from the ground up, you have several options for each part of it.

You might wanna visit the OpenServo project as well.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline georgeecollins

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Re: Servos at higher voltages than they're rated for?
« Reply #9 on: May 06, 2011, 02:54:58 PM »
Some digital servos and robot servos, like a hightec HS-5685 are made to be able to run at 7.4v so that they can accommodate LiPo batteries.  Since a fully charged four cell LiPO pack often goes over >7.6v I don't think 7.5v would be a problem.  It is not the cheapest option. 

 


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