I am planning to build a simple motor tester. I wouldn't call it a DYNO as I have no way as of yet to measure torque nor graph it out. I need this built fast so V1 will be made from passive components, switches, and such. The objective is to get baseline data on motors using another motor as the generator. As research and discussions with others have shown, using the motor under test to turn a second motor is one way to find the amps under load. I realize I could use a Raspberry PI, or any other such device to do this but I don't have time to learn the programming language. I will save that for V2 or V3. The basic design will start with a main power switch that allows the input batteries to operate. I will use a 2 pole switch to choose between an external battery pack or the internal 12V SLA. I have some LCD panels that show voltage for the battery in use, and two panels that show volt/amps for each motor. Any other ideas let me know. Parts will be here by Saturday and I will start putting it together then. Thanks El Gato
What are you trying to find out? Just getting Amps under whatever arbitrary load you happen to put on it isn't going to tell you much/anything about how it is going to preform in your desired application. (Unless the loads match perfectly which seems unlikely) Sure you'll be allow to rate which motor is "better" at whatever load you happen to be running but I don't see how that helps you in the real world.
I should be more helpful, sorry. Put some sort of tach on the shaft so you can get rpm too. Then you can get rpm and amps at different loads , or the same load for different Motors, you could start building real motor curves from there and those could actually be useful.
Absolutely! Not at an engineering level but when you buy a batch of unlabeled motors then you need something to baseline the motors tell them apart then it will help alot. I am using a 35 turn crawling motor as the generator and if you have a high speed low torque motor turning the generator, the tested motor would most likely pull a lot of amps and possible generate very little voltage on the generator. A high torque motor would in theory have low amp load on the motor but higher voltage on the generator motor. In that case it will give me an indication of what the motor can do without having to take it to the pond and waste 2 hours trying it out. Jeff has been using this system for a while. I will give it a try and see what happens.
Yes building motor curves is on the list.. didn't know how but when the time was available I would research it. V2 will utilize an rpm sensor so perhaps that would do what I had hoped to get.
My biggest issue with MOUPs (motors of unknown providence) is how fast they will spin. I'd put a tach as a high priority Even if I cheated and bought a phototachometer (I think that's the wrong word, but it uses light )
Buying unknown motors is dicey at best....Mabuchi let me order an "engineering sample" for the motors i wanted to use in my VDT. 10 really nice motors (with specs) for $50. Finding a good motor was a tough one when I was setting up the bismarck, thats one of the reasons I went brushless. Even with the few stats that are generally available for them it was easier to make better choices and compare/predict what a motor would do. but I digress... If I was going to build a RPM counter for this and wanted to keep it as simple as possible i'd probably do something like this: get a small wood disk that you can mount on the shaft securely, put 3 or 4 little rare earth magnets spaced evenly around the circumference, and use a hall effect sensor to sense when the magnets pass. I'd use a little microcontroller to count and spit it out to an LCD or a few seven segment displays but I know there are ways to do this fully analog as well if you dont want to program anything. if you painted the disk black and white in quarters you could do an optical system just as easily.
Is that different from a laser tach, or are they one in the same?? I know I acquired a laser tach that *seems* to work well for under $20 on Ebay. I say seems because I can't really verify the accuracy.
Heck for ~$20 Cannonman is right, just buy a laser tach, Amazon Prime and you'll have it this weekend.
Interesting.....could this $20 laser tach be hacked to control max revolutions and therefore max speed?
The "generator" is a fix known motor. So by turning this motor with the motors you are testing you will get a poor mans tach by measuring the voltage it produces. Also you are getting an idea of amps under load condition. Even though it is not the load in which it may be applied you are at least begging to look into the window
If I were testing random motors, I would probably measure a few things at a fixed voltage. Free RPM (no real load), amps at free rpm. Those two could be measured dry and on the bench. Then I would probably have a little thrust testing tank and rig to mount the motor to and take some measurements for thrust and current draw with a given prop or range of props. I think @rcengr has a thread somewhere here with a thrust testing setup when he was playing with some motors.
Put a gear set between the test motor and the generator motor. Then you can simply change the gear ratio to change the load on your test motor. Measure volts generated and Amps drawn at a few different gear ratios ( loads) and you should be able to piece together a motor power curve which is probably what you are really looking for. Much more useful than a speed/torque curve when picking out a motor.
Or wait till the ice melts and put it in a boat and run it around with a data log, then download. More REAL less fake.
