I have been doing some load tests of servos. I am using a Vexa ServoXciter to generate the pulse and a digital fish scale as the torque readout. I drive the servo thru a heavy duty y harness to the servoXciter for the pulse with the + lead disconnected. The other input to the Y harness is connected to a 1500mah ni-cd with the pulse lead disconnected. This way the servo gets the pulse from the ServoXciter and its current supply from the battery. The servo is connected to the digital scale with a kevlar string attached to a H9 servo pull-pull wheel.
I have been unable to get the rated torque from the high torque servos. For instance the 9206 is rated for 133 oz-in. The best I can get is 100 oz-in. I have two 9206's and two 9204's that show similar results. The two 9250's that I have run about 10% low. I have 9202 that is better than its spec by about 10%. The standard servos I have tested show results exactly as the specifications read.
Do you have an explaination for this?
Richard H. Kelly
[email protected]
PS I am a retired graduate electrical engineer. During my career I performed many such tests in the engineering department of the Boeing Co.

Hi dirtybird,

The higher current demands of the digital servos may be drawing down the battery supply voltage. This drop in voltage will effect the torque of the servos. You may want to try a high quality regulated power supply as a source voltage. This should solve the problem of lower torque readings that you are experiencing.

I hope you find this information helpful. You can also reach our Futaba support technical team at 217-398-8970, or via fax at 217-398-7721.

Sincerely,
Krysta
Lead Futaba Customer Service and Programming Technician

I am monitoring the battery supply voltage with a DVM. I quit testing when the voltage drops below 4.8 volts. Most of the time its above 5 volts. I am using a new 1500mah Ni-Cd connected to the servo thru a heavy duty y harness. The other lead of the Y is connected to the pulse generator.
9204 and 9206 servos are coreless non-digital servos.
If its necessary to use a high quality regulated power supply to get the rated torque from the servos how does one fit it in the airplane?

Futaba servos are tested with a digital torque meter. We use a Shimpo TS-50J Remote Torque Sensor connected to a Shimpo DRI digital remote indicator. The servo is clamped into a fixture and the torque sensor is attached to the output shaft of the servo under test. The servo is attached to the torque sensor in the center position. The servo is then given signals to drive it to the extreme left and then the extreme right. The torque sensor measures the stalled torque of the servo. The torque readings for driving the servo to each extreme should be close.

For consistency and repeatability of all tests, the input voltage is regulated to 4.8 V and 6.0 V, depending upon which voltage we need the torque for.

The published torque numbers for Futaba servos are those determined in testing with the above equipment and method. Because the actual conditions in any particular installation will not conform to the test conditions, results will vary from the test results. In otherwords, "Your mileage may vary".

OK now I understand why I am not getting the published results.
Your testing method, while it shows what the servo is capable of performing in the lab, does not represent what it will do in the hands of the average modeler under operating conditions.
Its sort of like the way they used to test the engine of your car for HP. They took all of the accessories and fan off of it. Then the tuned it up to the teeth and ran it bare with not even a water pump on it. In the car it was not able to produce 1/3 the HP they claimed.