Your welcome Jay
And what you are talking about using a DC motor with a variable resistor will work just fine. And would be cheaper than using the brushless motors. And just for thought the DC motor would be easer to control than the brushless motor as for as loading the nitro motor. There is one problem that you will encounter and that is heat on the loading device. But this will be true with any true dyno that will load a motor.
I built a dyno to use in my shop about fifteen years ago to test electric motors. It will test a motor at 350KW for however long that I want to test it for and it will peak at 500KW in short burst. The loading device is what we call a edy current coupler. The way it works is there are two drums, one runs inside the other with shafts coming off the drums on each end of the device. One shaft is tied to a torque arm and a load cell. The other couples to the machine that we are going to test. In the middle of the drums is a DC coil that when a DC voltage is applied to the coil it tries to turn the shaft the the load cell is tied to. The type of magnetic field is call edy currents thus the term edy current coupler. Even thou there are not friction parts other than the bearings there is a lot of heat made in the coupler. The coupler that I use for this dyno has got a water jacket so we cool it with water. I use a encoder for the tach signal that has 3600 pulses per rev along with the load cell all goes into a logic controler. Then I process the math on the numbers and then transmit them to a computor with some pretty graphics on it.
But it is like this. If you were doing this all of the time you might want to build a dyno like this. But a DC motor with a variable resistor for load device. A set of digital postal scales, a hand held tach, a calculator, pen, and some paper. You have got you a very good dyno that will give you some very good numbers.
And I would trust these numbers over anyone else numbers.
Mark Bullard
In 1980 I built a dyno from a GM power steering pump ( the one with a resevoir ) with a valve between the pressure line and the return line. This was the variable load. The pump was driven by the engine through a 10:1 reduction using gear belts. The pump assembly was made to pivot on its center by mounting it between a front and rear bearing. A torque arm was connected from the pivoting pump to a Ford ( Holley ) carburator accelerator pump diaphram that was fastened to a resevoir filled with fluid ( WD-40 ) that was connected to a pressure gauge. This was the load cell to measure the torque. The gauge was calibrated using an inch- ounce torque wrench and a paper overlay using these figures was made and glued to the pressure gauge dial. The RPM was read using a Globe DC permanent magnet motor as a tach generator driven directly off of the shaft that was connected to the engine. The voltage went to a DC volt gauge that was calibrated to the voltage output of the DC motor ( I think it was 1.25 volts per 1000 RPM ) again made into a paper overlay and glued to the volt gauge dial face. As the load was applied by gradually closing the valve the pump pivoted in its bearings, through the torque arm to the load cell on to the pressure gauge. This dyno had 2 control levers. One for the load and one for the throttle. This was a crude but simple device that worked without a glitch. I did not use it for horsepower #'s rather to confirm or reject changes that I made to the engines. I only used this dyno on 21 and 45 size engines. I did not try it on the high powered larger engines. This worked for me and I learned a lot. I was able to seperate a lot of the sh.. from the chaff so to speak. Charles Perdue
Charles,
That was great thinking outside the box and if it told what you wanted to know that was the important thing. There is no secret to dyno's. They have been around since the day that we came up with the measurement of Horsepower. You got to have some way to load the motor that you want to test, measure torque and rpm.
Now let put something else into the box. Maybe Andy Brown can step into this if he would like. He may have thought of this or he may have not.
What if we turn a prop in a water tank with a device that would turn the prop the rpm's that we want to turn. We would want the device to turn the prop with variable rpm's. We would also want to measure the torque and rpm's that where required for the prop's load. Now we could take this torque curve and design a motor to run in that torque curve. Just thinking outside the box. Next!!!!!!!!!!
Mark Bullard
