Electric Motor Secrets

[Peter Lindemann]

Thanks for the Update

Peter, I think that there are two problems. One is that the transistors are not opening fully and the other is that the rotor "locks" on a certain position in the firing zone if the current is too high. I am already using a commutator wheel with only one big 65 degree gap on each side. The resistor values for the MJ2150 voltage divider are 166 Ohms (three 500Ohms resistors in paralell). The resistance of the 2n3055 transistor voltage divider is now 70 Ohms, this makes the over all current draw about 5.2A at 15v if I hold the rotor in the firing position. But if the current is this high, the rotor wont spin, it just locks down ar some point of the firing position. This might be due to the rotor touching the stator slightly. Switched the optotrigger LED resistor back to 500 Ohms.

Jetijs,

Yes, you obviously have enough drive. In fact, I would suggest backing off to single 166 ohm resistors for now. Lock-down of the gap can be a problem with these systems if the frame is not up to handling the stress. If the rotor spins freely when the power if OFF, then let's just work with it for now. Secondly, your commutator wheel with a 65 degree opening is probably to large. The field has no time to collapse before the rotor tries to move away. This is part of the problem with low speed. Make a new wheel with about a 40 degree opening. Then play around with the timing wheels position. Advancing the commutator starts to turn the coils ON before the rotor arrives. This may make for harder starts, but definitely makes for higher revs at the top.

It sounds like you are making a rapid set of changes to the machine without carefully considering the consequences. I assume your commutator wheel with the 65 degree opening was made by cutting the slots off of the slotted wheel. Yes, No?

Like a computer, the machine is just doing what it is told to do by the circuitry and the physical geometry. Trying to get the machine to QUICKLY do what you want it to do is an emotional reaction. It is important to STUDY what the machine IS doing at each stage. It will tell you the conditions it is operating in. But you have to have the patience to LISTEN, and not just JUMP to the next guess at what might work better.

Slow down. Be patient. You have 99% of the work done. We are just tweeking the circuit now. Everything is just fine. Look at what the machine is doing, and deliberately think it through.

Peter

[Jetijs]

Peter, I think that there are two problems. One is that the transistors are not opening fully and the other is that the rotor "locks" on a certain position in the firing zone if the current is too high. I am already using a commutator wheel with only one big 65 degree gap on each side. The resistor values for the MJ2150 voltage divider are 166 Ohms (three 500Ohms resistors in paralell). The resistance of the 2n3055 transistor voltage divider is now 70 Ohms, this makes the over all current draw about 5.2A at 15v if I hold the rotor in the firing position. But if the current is this high, the rotor wont spin, it just locks down ar some point of the firing position. This might be due to the rotor touching the stator slightly. Switched the optotrigger LED resistor back to 500 Ohms.

[Peter Lindemann]

Slow Down

Something is not right. I decreased the MJ2501 base resistor values by half and this resulted in just 1-2mA current draw gain in the optotrigger output. Then I decreased the optotrigger LED resistor value by half, this increased the current draw to 18mA at the optotrigger base. The overall current draw was then 2.4A at 15V each phase. Then I decreased the resistance of the 2N3055 base resistors by half. This improved the situation a little, now the overall current draw increased to 3.4A on each phase. The torque is very weak and the RPM's are low, just 50 or so. The transistors get hot quite quickly. I am out of ideas, any suggestions? Maybe I should decrease the resistance some more?

Here, I made a short video:
YouTube - Lindemann attraction motor V2.0

Just noticed, that you can see in the video how the IR LED lights brightly on the optotriggers. You can not see this without the camera

Jetijs,

Slow down. There are a number of issues here, so let's just take them one at a time. The first is that I recommend you return to the 500 ohm resistor on the IR diodes in the opto units. You'll burn them out if you run them real hot for long.

Second, use 220 ohm, 2-watt resistors in both voltage dividers switching the transistors. That should give you plenty of drive. Also, if you need to, use another NPN transistor to run the first voltage divider and use the output of the opto unit to darlington that NPN.

Third, cut a new commutator wheel with just two openings of 35 or 40 degrees of rotation. In other words, get rid of the multiple slots for now.

Your 2N3055 transistors should be on heat sinks. They are run hot when they are ON, but their duty cycle will keep them cooler during operation. They need the time to wick away the heat produced when they are ON.

Draw up these changes to the schematic and let's see what they look like. This will give you a circuit I have successfully used in the past.

Peter

[Jetijs]

Something is not right. I decreased the MJ2501 base resistor values by half and this resulted in just 1-2mA current draw gain in the optotrigger output. Then I decreased the optotrigger LED resistor value by half, this increased the current draw to 18mA at the optotrigger base. The overall current draw was then 2.4A at 15V each phase. Then I decreased the resistance of the 2N3055 base resistors by half. This improved the situation a little, now the overall current draw increased to 3.4A on each phase. The torque is very weak and the RPM's are low, just 50 or so. The transistors get hot quite quickly. I am out of ideas, any suggestions? Maybe I should decrease the resistance some more?

Here, I made a short video:

http://www.youtube.com/watch?v=zvCnPIV7dvs

Just noticed, that you can see in the video how the IR LED lights brightly on the optotriggers. You can not see this without the camera

[Jetijs]

Hi,
I am convinced now that the problem is that the transistors do not open fully. I measured the current on the output of the optoswitch and it was just 10mA at 15V. But it should be at least 30mA. So I will buy some more 1K resistors and put them in parallel to those I already soldered to the board, this way I can decrease the resistance twice. This should give an improvement Also I checked the coil series arangement - it is right.
Thanks,
Jetijs

[Jan H]

hi jetijs,
I know what you are going through..... fiddling for hours and still not finding out where the problem is....try and shake it off... it was just a ****ty day

I think the problem is probably not in the motor itself or the windings for that matter.
I think you have to look in the direction of the commutating.. sensing bit. Like you suggested the transistor not fully opening. or anyway not working like it should. Because you said that a manual delivered pulse to the coil made it spin really well. And everything in the motor looks so neat and tidy! It looks like its off the shelf

[Jetijs]

Hi all,
today I re machined the shaft of the rotor so that the commutatro wheel can be attached nicely, this gave me a chance to wight the rotor, it is 614 grams light. So, I assembled everything and fired it up. The results were very bad. If I left the rotor at the firing position and then slowly increased the voltage, the rotor started to move only at 8 or so volts, but just till the end of the gap as if there was a great friction. If I held the rotor steady at the firing position, the amp draw at 10V was 1.8A. I could not get the thing to rotate by itself until made a new commutator wheel with only three but wider gaps. Then, only at 15V it started to rotate continually at very low speed. Then I increased the voltage to 24V and the current draw then was 1.7A and the speed increased a little bit. I could not make the tests for long time, because the transistors got hot quickly and I did not have any cooling fans. Then I made a new commutator wheel with only one 65 degree gap on each side. This improved the situation a little bit. Now I got the rotor to rotate continuously at 14V and the current draw was about 1.3A.
There was a 12v light bulb connected to the output. I thought that maybe the output wires are connected wrong with the diode on the wrong side of the coil, so I switched the leads, but that was not the case, because then the neon bulbs would light up at each pulse, so I switched the wires back.
Also, when I had the commutator with the 6 gaps, I noticed, that the rotor tended to lock on one of the gaps with the transistor ON. I rotated the rotor with hand and listened carefully, I could hear that on some part of the rotation, there is a slight hissing sound as if the rotor is touching the stator very slightly (could not feel any increase of friction). This might be the problem, because at this point there could happen this locking effect. Seems like I will have to increase the air gap a little bit. I double checked everything, the wiring seemed fine. Also the current draw, when the transistor is ON, is too small, it should be at least 8A or so, might it be that the transistor does not open fully? What could you suggest? Cold the problem be that the two poles in series are not connected right and has two N or two S poles facing each other (I will double check that)?
Thank you,
Jetijs
Thanks,

[sykavy]

Video of air hybrid

sorry I posted on the wrong thread

[Peter Lindemann]

Step by Step

Jetijs,

Great work! Just take each step necessary to move the project forward. In the meantime, we'll all just die from anticipation.

Peter

[Jetijs]

Hi all
I had a very bad cold and was on antibiotics for a few days, so I could not do much about my motor, but today I finally felt well enough to work. So here's an update.
I made the timing mechanism and the timing wheel. I also soldered the circuit. At the end I decided to use the circuit just like my previous one, since that worked well and can shut off the transistors faster. Here's the circuit:



And the rest:









The timing wheel has gaps on each 70 degree area. I could fit in 7 gaps on each side, that is 5 degree ON time and then 5 degree OFF time and so on seven times. Basically everything is ready for testing, but it is already late today and I am tired, so I will make the last checks and first tests tomorrow. There are some issues that might cause trouble, but we will see that tomorrow.

Edit:
I found a bug on the shaft that needs to be taken care of. I made a new commutator wheel with only 6 gaps, because 7 gaps was too much and when I tried to align the wheel according to the stator fire positions, I saw that this last gap will just fire the pulse a little bit after the rotor has passed the stator, so it will pull the rotor back. This new wheel is not easy to attach to the shaft (so was also the first one), because there is not enough space to press this wheel on to, only 0.5mm on each side, this makes the wheel turn wobbly and touch the optotriggers. I will give the shaft to re machine so that there is a 6mm thread on the commutator wheel side (instead of 8mm), this will give 1.5mm area for the wheel to press on and align perfectly. So unfortunately I wont be able to make the tests today
But the good news is that I tested the circuit along with the optotriggers. Instead of motor windings as a load, I used a LED just to see if everything works, and it does


Thank you,
Jetijs

[elias]

Turning of the transistor

Jetijs,

You can try these things, but the reason I have suggested the circuits I have is to provide for a rapid TURN OFF of the transistor. This markedly helps with energy recovery. The Darlington arrangement is fine for increased gain, but not so good for rapid shut off.

Build it and see.

Peter

Peter,

The schematic I used for my motor can turn the transistor off rapidly by using a transistor to discharge the base of the power transistor. Maybe It would be better for Jetijs to use a type of circuit I suggested.

[I am only able to check this forum once a week so ... I may not be able to respond in time]

Elias

[Peter Lindemann]

Turning the transistor OFF

Hi lighty
I just had a coversation with my friend, who is smarter in these things than me. He said that the MJL21194 has a rather small amplification coefficient (25 to 75). This means that with 20mA on the transistor base, I would get only 0.5-1.5A collector current. He also suggested using two transistors but in following configuration:



This way, if I use two MLJ21194 transistors the amplification coefficient is multiplied (625 to 5625), this means that in theory I could get 12.5 to 112.5 collector current. Of course the max current would be about 17A at 12V due to the coil resistance. Since the MJL21194 transistors are rather expensive, I will probably use two 2N3055 transistors in such arrangement.
I hope I understood everything right. I remind you, that I am a noob in electronics
What do you think?
Thanks,
Jetijs

Jetijs,

You can try these things, but the reason I have suggested the circuits I have is to provide for a rapid TURN OFF of the transistor. This markedly helps with energy recovery. The Darlington arrangement is fine for increased gain, but not so good for rapid shut off.

Build it and see.

Peter

[lighty]

Your friend suggested using Darlington pair configuration while I opted for inverted transistor gate. Those are both perfectly valid solutions but I draw the schematic to allow for a simple replacement of BJT power transistor with MOSFET or IGBT without any change of components. When experimenting I always prefer more versatile solutions, that's all. It's your choice really.

[Jetijs]

Hi lighty
I just had a coversation with my friend, who is smarter in these things than me. He said that the MJL21194 has a rather small amplification coefficient (25 to 75). This means that with 20mA on the transistor base, I would get only 0.5-1.5A collector current. He also suggested using two transistors but in following configuration:



This way, if I use two MLJ21194 transistors the amplification coefficient is multiplied (625 to 5625), this means that in theory I could get 12.5 to 112.5 collector current. Of course the max current would be about 17A at 12V due to the coil resistance. Since the MJL21194 transistors are rather expensive, I will probably use two 2N3055 transistors in such arrangement.
I hope I understood everything right. I remind you, that I am a noob in electronics
What do you think?
Thanks,
Jetijs

[lighty]

You could use voltage divider to properly bias base of the power transistor but why don't you simply add one transistor switch in between photo-transistor and power transistor.

So, you simply have to add one resistor to the collector of the photo-transistor then take that signal via the base resistor to some intermediate transistor (really anything that you got at hand would do). I have a number of good old BD135, 137 and 139 laying around so I would use one of them. Then you put another resistor on the collector of the intermediate transistor and take that signal to drive the power transistor.

Now, the photo-transistor would produce inversed logic at it's output and intermediate transistor would convert it back to the normal logic so no problem there.

Look at the simplest example without any recovery or other components added.