Go Down

Topic: Controlling a servo motor with an external H-bridge (Read 403 times) previous topic - next topic

roadstar93

Hello, I have a question regarding control of a servo motor with external h-bridge.
So here it goes, can I connect the + and - to the H bridge and make the servo work like DC motor? I know that servos have no need for an h-bridge but for my project I am required to use one.

This is the servo I would be using: http://www.amazon.com/TowerPro-SG90-Mini-Servo-Accessories/dp/B001CFUBN8 and for my project I would ignore the control pin.

Zarolis

if you're planing on using it for continuous rotation than you reconsider. if you took the servo apart, in the gearbox there would be a gear that is connected directly to a potentiometer. on that gear there is a pin than physically limits the rotation. and secondly, since it is connected to a potentiometer and it cant rotate continuously, that would also cause a problem to you. im not sure what youre planing on doing, but, there are a few ways to make the servo go round. there are videos that explain how to modify it:

 take it apart, cut of the before mentioned pin on the gear, take out the pontetiometer, solder it out, solder a couple of resistors in its place, and that way you would get a motor that if you type in 90 degrees it would not turn, if 0 degrees than it would turn max speed in one direction and if 180 degrees max speed to a different direction. however if you need accuracy than i do not recommend this, because the dead stop would not be at 9 degrees, it would be slightly off. i tried building a robot like this and that was a disaster, it was immposible to sync two of those motors and each time i turned it on is spun at different speeds.

but if you have a h-bridge, you can simply solder off all the unnesecary electronics and a have a quality dc motor with a spare wire and a good gearbox. worked for me, still glad i did it.

but again im not sure what youre doing wth it so i dont know if this is of any use to you.

roadstar93

if you're planing on using it for continuous rotation than you reconsider. if you took the servo apart, in the gearbox there would be a gear that is connected directly to a potentiometer. on that gear there is a pin than physically limits the rotation. and secondly, since it is connected to a potentiometer and it cant rotate continuously, that would also cause a problem to you. im not sure what youre planing on doing, but, there are a few ways to make the servo go round. there are videos that explain how to modify it:

 take it apart, cut of the before mentioned pin on the gear, take out the pontetiometer, solder it out, solder a couple of resistors in its place, and that way you would get a motor that if you type in 90 degrees it would not turn, if 0 degrees than it would turn max speed in one direction and if 180 degrees max speed to a different direction. however if you need accuracy than i do not recommend this, because the dead stop would not be at 9 degrees, it would be slightly off. i tried building a robot like this and that was a disaster, it was immposible to sync two of those motors and each time i turned it on is spun at different speeds.

but if you have a h-bridge, you can simply solder off all the unnesecary electronics and a have a quality dc motor with a spare wire and a good gearbox. worked for me, still glad i did it.

but again im not sure what youre doing wth it so i dont know if this is of any use to you.
Thank you for the quick answer.

I need to turn a panel 90 degrees left or right so there is no need to make it spin 360 degrees. Thats why I decided to use a servo instead of a bldc motor.
So if I want to use it with an H-bridge I still have to take it apart and connect the wires from the H-bridge directly to the motor ?

Robin2

Why do you need to use a H-bridge when there is already a perfectly good one inside the servo?

if you must use a H-bridge then just use a simple DC motor.

However from your description of the project requirement a servo (without an external H-bridge) seems ideal.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

Go Up