Servo operated ball-valve

Help & Support Robot Parts
1

Hi,
I need some help with a servo operated bal-valve that I want to build.
At the shaft of the ball (valve) I want to mount a (large) gear.
The gear will be driven by a servo with a small gear.

I want to modify/hack the servo rotating continuously and detach the internal servo-potmeter.
An external potmeter (same value) will be attached to the shaft of the large gear and the leads will be connected to the same points
as the internal potmeter was. (in fact I just add an extra external gear to the servo’s gearbox)

Questions:
Can I operate the servo in a standard manner now (PWM pulses - 0° - 90° - 180° -) ?
I need quite a lot of torque to operate the ball-valve:
Can I calculate the servo strength and the gear(s) ratio ?
Maybe the idea is over-dimensioned and is it better to operate the ball-valve directly with a strong torque servo ?

By the way I am new in servo’s.

Henk Wijtman
Rotterdam
Netherlands

Ball-valve

2

@dikkehenk Welcome to the RobotShop Community. It sounds like you want to do exactly this:

https://www.robotshop.com/en/sg20-series-servo-gearbox-51-ratio-504-rotation-2360-oz-in-070-sec-60.html

Similar, but no external potentiometer. It does allow for virtual multi-turn though, and can be changed to accept RC input:


  1. Can I operate the servo in a standard manner now (PWM pulses - 0° - 90° - 180° -) ?

Yes.

  1. I need quite a lot of torque to operate the ball-valve: Can I calculate the servo strength and the gear(s) ratio ?

Multiply the servo’s torque by the gear ratio to get the torque after gear down on the second shaft.You need to divide the speed by the gear ratio too.

  1. Maybe the idea is over-dimensioned and is it better to operate the ball-valve directly with a strong torque servo ?

Possible too, like:

3

cbenson,
Thanks for answering (very rapid)
I have looked at al suggestions but they are all quite expensive. I did not ask but I was looking for a cheaper solution. I think the toque the servo has to deliver depends on the turn-stiffness of the ball-valve. I have to figure out something to measure it.

regards
Henk

4

As you said, you’d need an idea of the torque.
What is the total angle of rotation?

5

Final angle on the big (extra) gear is 90 degrees (valve open/close). I also noticed that the start of rotating the handle of the valve by hand needs more power. (you a small pop).

I found a way on the internet how to measure the power that’s needed to turn the ball valve. I have to enlarge the handle of the valve to (for instance) 1 meter. Than fasten the valve sideways in a vise. Than put a weight at the end of the lenghtened handle and when the handle comes in motion with that weight I can calculate which power/torque is needed to operate the valve.

I am also looking into a way to loosen up the valve a little bit. But not too much (leaking).

Henk

6

If it really requires a significant force, you might want to consider using a linear actuator.