Electric Motor Secrets

[Jetijs]

Aaron, I have ordered one, it should arrive any day now
When it does, I will take the temperature measurements and inform you
Edit:

http://www.emuprim.lv/bildez/images/viskautkas_labs/visadi_strunti_1/73_.jpg

In the picture above you can see a scrrenshot of my scope settings and the waveform that shows how the optotrigger LEDs are flashed. These are the settings at which I got one of the best recovery results - 73%. I found the best duty cycle to be around 57% ON time and 43% OFF time. If we have a 50% duty cycle, then I can only get about 50% recovery. Anything past 65% and the recovery results go way down. Also the frequency is important. I found the best results at higher frequencies. I will get some input/output current waveforms at these settings tomorrow
Thanks,
Jetijs

[Aaron]

cold transistor

Very interesting Jetijs!

Do you have an IR thermometer to measure the temp of the transistor? You probably already know but the temp reading won't be accurate on any shiny metal but needs to be on masking tape or something like that stuck to the transistor. Would be interesting to see.

[Jetijs]

Hello,
Here is what I did today. I connected the output to the capacitor in the input section. Then I connected two amp meters. One just before the power supply negative terminal and the other behind the capacitor. This way I could measure the real amp draw of the motor and the reduced amp draw from the power supply. I connected my function generator to the optotrigger LEDs, so I could chop the pulses just as I want. Then I watched both amp meters and adjusted the frequency till I found the biggest difference in those readings. Of course, if the frequency is high, not much current can pass through the coils, I got a high pitch noise from the coils that varies according to the LED frequency and the rotor stays in the firing position. I found that if the square waves on from my function generator are with 50% duty cycle, I can get just about 50% recovery. If i increase the duty cycle to about 60-65%, I get about 60-65% recovery. But If I increase the duty cycle more, the amp draw gets just big enough to move the rotor in a nonfire position. So far the best result I had is 75% recovery. I did not write down at what frequency that was, I will do that later. All I wanted to know so far was how much can I get back. I think that 75% is a fairly good result.

Another interesting observation. If I put the rotor so that one phase is in the firing position and then just pulse the coil with high frequencies so that the rotor can't move because of too small current, the transistor of that phase gets almost freezing cold. I found this very interesting. This is the first time I actually observed this radiant cold effect. I have heard this may happen, but now I witnessed this myself

I will play more with frequencies and duty cycles and keep you informed.
Thanks,
Jetijs.

[Jetijs]

Thanks
I will do that. And get well soon

[lighty]

The changes for 24V will be simple and I already sent you all the necessary parts for those corrections so you won't need to buy anything. I'll contact you via mail with schematic as soon as I get a fever down (I managed to get a flu).

Until then keep playing. BTW- read my post about using DSO to directly measure power consumption and regeneration.

[Jetijs]

Hello,
today I installed a 60v 10000uF across the power supply like Peter suggested some posts ago. Now I can freely change the output as I wish, either to a battery or right in the input section I did some measurements with two commutator wheels - one with just one 40 degree gap on each side and other with six small gaps on each side. I connected the output to the capacitor and measured the current drop. With the first commutator wheel, I observed a current drop of 36.2% (just as estimated before). Then I tried the second commutator wheel the current drop was 51.25%.
Now I will try to switch to a commutator wheel with only one 65 degree gap on each side and to flash the optotrigger LED's with my function generator to find the frequency with the best recovery. This type of MOSFET triggering will make the motor slower and less current will be able to flow through the windings, that is why we will have to increase the input voltage to get a decent current through the winding using the new triggering way. This will require some changes to the circuit. And as long as my new rotor is being made, I will experiment with this one
Thanks,
Jetijs

[Jetijs]

I agree to that, the bent shaft explains all those problems

[lighty]

If you're re-doing whole rotor this time you can have smaller airgap without a need for sanding. It seems it was bent axle that was giving you hard time.

[Jetijs]

sykavy,
Peter already said once in this thread that an S shaped rotor did not perform very well in practice. In the video it is just an idea

Steven, I did not made the shaft by myself, I got someone else to do this for me so I don't know how he made the shaft and of if he dropped it on the floor or something. I already found another guy who can make a new shaft for me and I will instruct him to make the shaft the way you suggested, in one pass.
Thanks,
Jetijs

[nali2001]

Hi there Jetijs,
Too bad about the rotor.
I doubt that it is bend, I mean why would it be, did you drop it or anything?

Are you sure the axle itself in precise? I mean when you machine one side of an axle and then take it out of the chuck, turn it around and machine the other side you already have an off center axle since a lathe chuck is generally not all that precise unless you are using a collet chuck. That is why I always machine the whole axle in one pass without taking it out and such.

Regards,
Steven

[sykavy]

Ok, here's an update.
I sanded off the "hump" on the heavier side of the rotor, only that gave a good balancing.



I had also to sand off a little corner. Anyway, I assembled the motor again and this time it did not have any vibration and ran alot more quiet. But occasionally the motor got louder like every 10 seconds or so and then again it got quieter. I checked everything and saw that one of the bearings tends to rotate into the bearing holder, when it gets to a certain position, the motor gets louder and then, when it goes past that position, the motor is quiet again. This is a good indication that the shaft in fact IS bent. Also there is no way that the plates were cut so inprecise that there is need to sand off so much. It's a shame I did not check this when I got my shaft made. I will have a serious talk to the engineer who made this shaft for me

I guess I will have to make a new rotor. Must check if I have enough rotor plates left to do that. Also, I verified the motor speed. It indeed is about 1600 RPM, I counted the output pulses on a scope and measured the speed on different places with the laser tachometer. Also I guess that we will need to move up to 24V eventually.
Ok thanks,
Jetijs.

Hi Jetijs,
I know you probably want to perfect this design you are using but could I make a suggestion that may help? If your going to make a new rotor maybe an "S" shape rotor could help. It may give you an easier time setting-up the timing. You then could grind down your electromagnet lips making coil replacement easier as Lighty suggested earlier. Your plate construction would also seem good for the "S" design. Or maybe wait till you do another one. I don't know as much as all of you on here but Peter did suggest this design once in his video. If anyone hasn't bought the video I would suggest you should ASAP. It is so important for this topic.

Anyway great job so far keep up the great work

[Jetijs]

Ok, here's an update.
I sanded off the "hump" on the heavier side of the rotor, only that gave a good balancing.



I had also to sand off a little corner. Anyway, I assembled the motor again and this time it did not have any vibration and ran alot more quiet. But ocasionally the motor got louder like every 10 seconds or so and then again it got quieter. I checked everything and saw that one of the bearings tends to rotate into the bearing holder, when it gets to a certain position, the motor gets louder and then, when it goes past that position, the motor is quiet again. This is a good indication that the shaft in fact IS bent. Also there is no way that the plates were cut so inprecise that there is need to sand off so much. It's a shame I did not check this when I got my shaft made. I will have a serious talk to the engineer who made this shaft for me

I guess I will have to make a new rotor. Must check if I have enough rotor plates left to do that. Also, I verified the motor speed. It indeed is about 1600 RPM, I counted the output pulses on a scope and measured the speed on different places with the laser tachometer. Also I guess that we will need to move up to 24V eventually.
Ok thanks,
Jetijs.

[Jetijs]

well,
I removed the rotor and put it on two parallel sharp blades to see the balance. I must say that there is a serious unbalance in the rotor, no wonder the motor vibrates so much.

It might also be that the shaft is bent Because all the parts are more or less symmetrical for a disbalance this big. You can see how many magnets I need to put as a counterweight to get the rotor more or less in balance.
here is a video:
YouTube - Unbalanced rotor or bent shaft?

[lighty]

The difference between ordinary diodes and hyperfast diodes can be easily noticed in the voltage spike peak when the reversion of flux on current turn off is very fast. It's hard to notice when voltage impulse is already converted to current. There are some advantages to using hyperfast diodes but I won't go into that in this thread.

Also, you can use math function of your software to see power graph directly. Use CH1 probe to measure voltage on input (or output) and use CH2 probe to measure current with shunt resistor (you should use 0.1 Ohm carbon resistor-you should never use wirewound type). Then use math function to multiply CH1 with CH2. The red graph you'll get is the power graph. Then turn on RMS measurement and you'll get RMS values of the power graph (it will be in red letters). In this way you can directly see any change in power in real time when you change something in motor configuration (recovery, load etc.).

You can also measure time periods with your software by using various time measurements (duty cycle and period comes to mind) or by using measurements cursors you can move over the scope screen. Either way you won't dealing with estimations then but rather with precise values.

Ah, and one more thing- whenever possible use differential probe configuration with appropriate math function (CH1-CH2) in order to reduce noise at least to some level (when measuring just one value at the time, of course). Also, I just noticed that when you using Channel setting you can turn Bandwidth limit Off. That's a great function to capture fast impulses (as much as your DSO sampling rate and input circuitry allows) although you might get some additional noise.

[Jetijs]

Hello,
Today I made some tests before removing the rotor for balancig. Firstly I measured how much energy I am getting back using the same 40 degree gap on each commutator side. I put a better battery on the output that that what you saw in video. Here is the input current waveform measured across the pinput section amp meter, like I did with my first motor.



We can see that the overall ON time is a little smaller than the OFF time. This is because we have two 40 degree gaps, that is 160 degree per revolution. So the ON time is 160 degree and the OFF time is 200 degree.
And here is the waveform of the output pulse measured across the amp meter on the positive line of the output. This is using the IN4007 diodes on the output:



And here is the same only this time I am using the ultra fast diodes on the output, you can see that there is almost no difference:



After some crude current/voltage measurements I got the following results.
Input 12.24V, 1.81A
Output 13.5V, 0.6A
That is 36.6% recovery.

Then I switched to the commutator wheel with six smaller gaps on each side. All these gaps fill about 65 degree of the 70 degree firing window. Now the input current looked like this:



And this is the output current:



This time the current draw on the input was just 0.75A and the motor run very slow, loud and was easy to stop, I mean it was easy to stop in the NO fire zone, but it was not possible to hold the rotor in the firing position with hands.
This time the crude calculations showed 45.5% recovery.

That is it for now, I will now remove the rotor for balancing.
Any comments?
Thank you