"Load Master"
 

As requested I am posting this in the electronics sub forum.

I am have built a load tester "Load Master" thanks Bsthetech . The Load Master is a simple design, the idea is to put a load on a motor under test when using a Trinity Motolyser 2 or SkyRC motor analyser. The test motor is coupled to a slave motor which then has resistors connected to the phases and then wired together. I do not take credit for the idea, I've seen it while researching dyno alternatives in the many threads and forums I have been learning through. What I have done is put in the leg work to test this with the Trinity Motolyser 2 and the SkyRC Motor Analyzer. I have also designed a 3d printed motor mount that will hold the motors and attach to the analyzer without alligator clips or having to solder anything to the tabs. You can still solder to the tabs of the motors if you want, you just need to take off the spring clips and the top cover of the mount.

The unit will also work with an R1 digital 3 esc and wifi module.

Hobbywing support response for the Tunalzyer:

Tech Support Dept (HOBBYWING)

Jun 14, 2023, 10:42 AM PDT
Hello,

12 amps is what we see most often as the max. There are some variances, but typically it's right around there when the safety kicks in. Made for no load testing more so than "dyno" type usage.



Here is a pic of a completed unit.
https://cimg9.ibsrv.net/gimg/www.rct...782eb8924f.jpg





Here is a pic of a 13.5 under test by a Motoyser II coupled to a USGT motor attached to 2 ohm 100 watt resistors.


https://cimg6.ibsrv.net/gimg/www.rct...df563cd9fd.jpg



Here is a pic of the same 13.5 being driven by the SkyRC analyzer, coupled to the USGT motor and connected to 1 ohm 100 watt resistors.

https://cimg9.ibsrv.net/gimg/www.rct...2207c01a7c.jpg


My ultimate intention is to make a unit that will drive the setup without the need for a external motor controller. However that is going to take a bit. More realistically though I am designing an Arduino interface that can read the RPM, current draw, and voltage of the system while connected to an ESC. Below is my prototype.

https://cimg9.ibsrv.net/gimg/www.rct...cc03189434.jpg


And finally, here is my current schematic for the design.
https://cimg7.ibsrv.net/gimg/www.rct...a61604839f.png



If people are curious, I can go through how I am calculating current, voltage, and rpm. I would also like to add sensor angles to this at some point.

Well, with my tiny knowledge of electronics I think you will not read any voltage :sneaky:

Voltage is being read on Pin 1 through the voltage divider in the circuit...

I have code setup in the arduino that uses the voltage divider formula to return the correct voltage.

Here is a pic that has everything...

EDIT: My schematic is off, sorry...

https://cimg6.ibsrv.net/gimg/www.rct...e6b5b999eb.jpg

Fixed the schematic...


https://cimg0.ibsrv.net/gimg/www.rct...da9c9c2ef8.png

Here is a pic comparing RPM and Current from my prototype to the Motolyser. I just got the voltage setup last night so I haven't had time to tweak the code yet, so no comparisons for that.

https://cimg1.ibsrv.net/gimg/www.rct...069a72b424.jpg

Here are some pics of the output of the current reading on my scope. This has been fun, lol.

https://cimg2.ibsrv.net/gimg/www.rct...874e38fb26.png
https://cimg3.ibsrv.net/gimg/www.rct...744d50505e.png
https://cimg4.ibsrv.net/gimg/www.rct...340afeda72.png
https://cimg5.ibsrv.net/gimg/www.rct...4a295a627d.png
https://cimg6.ibsrv.net/gimg/www.rct...1cdaff62d0.png
https://cimg7.ibsrv.net/gimg/www.rct...bb133546e9.png


The RPM sensors are so much easier.

https://cimg8.ibsrv.net/gimg/www.rct...35ef157f0e.jpg

No problem. I figured it sounded better than “Loader McLoaderface”.

I plan to mainly use it with my 1s 17.5 motors. Should I choose a different load for the slave motor?

I think the 1 ohm resistors will be fine for 1s 17.5. If you are using a 21.5 for the slave, then the bemf will be around 4.5-5.0v. Power dissipated by the resistor will in the ball park of 20-30 watts. You could go down to 0.50 ohm 100 watt resistors for more of a load. Power dissipated will be around 50 watts. These are rough guestimates, but should be close.

EDIT: Are you going to be using a 1s for testing? The above statement is based on using a 1s.

What are you ultimately trying to measure here? You'll be able to measure electrical power in, but you won't be able to measure mechanical power out.

Basically he can measure the mechanical power. When using a 3 phase rectifier making DC he can easily read the current and voltage generated by the driven motor. Comparing the powers on both sides you can determine the efficiency.

Current and voltage generated by the driven motor doesn't give you mechanical power, without knowing the efficiency of the conversion. And that conversion efficiency is not linear.

R1 Wurks can say it better than I can.
YouTube video

In that video they didn't measure the load output, they just had it as a generic load and to hold the motor in place. There was no explanation of how they're measuring the output or how they're choosing the resistance for a proper equivalence load. Just lots of ums and ahs about using it to choose out of 2 motors which one is best. The only data used in this video was input current and output RPM vs timing endbell. And given how low the input current was in their data, the slave motor doesn't appear to have been putting much of a load on it.

The idea with this is to put a load on your test motor. Why is that important, I don't know, go read through the many posts that state how motor analysers give unloaded outputs and how they would be better if there were a load on them. But regardless, one of the things you can do is see how much of an rpm drop you have under certain loads. If you are looking for top speed down the straight use a lower load or higher value resistors. If you are looking for more pull out of corners use a lower value resistor for more load. Compare rpm drop from different timing settings. You can also do the same old test where you plot the rpm vs current draw for different timing and find where the current goes up with not much rpm gain. And you also have the benefit of knowing it was with a load.