A little over a year ago Hitec released a new servo. HSR-5995TGThis servo is aimed at the robot experimenter.
Running on 7.2V (6 nicads) it has more than 400 in/oz of torque.
It has titanium gears and 180 degrees of rotation.
Since the servo came out I've been wanting to build an actualted valve with it.
Here is the valve: Top view
Side view
The ballance of the parts came off my mill or out of my junk box.
As you can see in the top view the valve and servo arms are double,
but I only have one set of ball links attached as I broke off my tap in the valve arm.
After playing with it for a couple of hours the aluminum valve arm is loose on the shaft.
I bought some steel stock,and I will make a steel valve arm in the next couple of days.
The valve as photographed weighs 268grams, I've since changed the aluminum arm to stee
and added a 2nd linkage on the other side of the servo so it now pushes and pulls symetrically.
The steel arm weighs more than the aluminum one.
Preliminary test results
I initally tested the unit with the hitec servo tester..
The servo tester has an anemic 4.8V battery and the valve was very marginal.
At 4.8V the valve would operate, but it was slow and getting the ball fully closed was a bit iffy.
I then rewired the servo to use a 7.2V 3000mA car battery pack. That worked much better!
The valve now opens and closes in less than 0.5 seconds and seems very strong.
On 7.4 volts I can not stop the operation with my hands.
After hooking up the 7.2 V battery I attached my astroflight watt meter to see
how much power it was drawing. Operating the valve rapidly back and forth the valve drew about 1.5A.
I then clamped the valve in a vise to see what the stall current is. (I only did this once and very quickly)
Stalled it seem to draw between 3.5 and 4 amps.
I connected the valve to 1500 PSI water (from a hp paint sprayer)
And operated the valve multiple times. It operated normally both opening and closing against a
1500 PSI water source.
Future directions
I've ordered some 2:1 gears from boston gear. Since the servo runs 180 degrees and the
valve only needs 90 degrees I thought I would hook it up to a larger 3/4 ball valve with 2:1 gearing
and see how that works.
For a really big valve you could use:Servo gearbox.
In one of the recent robot magazines these guys were advertising their 5:1 gear box with metal gears and the HSR5995TG for 2000 in/oz of torque.
At some point I will set the valve up on a flow bench and see how linear it is and how much hysterisis it has.
At some time I will test it under pressure with liquid nitrogen to see how eell it would work at cyrotemperatures for LOX etc.
If you have any questions please feel free to ask.
Paul
My email is my first name at the base address for this site.
