Servos at higher voltages than they're rated for?

[mstacho]

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

[Soeren]

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?

[billhowl]

How about this "Towerpro MG996R 10kg Servo 55g / 10kg / .20sec"

- 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

[mstacho]

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

[Daanii]

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?

[rbtying]

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. 

[MikeK]

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

[mstacho]

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

[Soeren]

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.

[georgeecollins]

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.