whew hoo... so good to be seeing results for so much hard work......

@Jetijs

Since you didn't have the opportunity to use preformed coils you could have tested resistance between wire and stator after every turn of the coil. That would have saved you some time if you found out compromised insulation section straight away. You could have even simply additionally isolate only that section of coil. Please don't take this as criticism- it's just a suggestion for people reading this thread that will hopefully follow your lead. Good work m8!


Anyway- I suggest that you weigh the rotor before you assemble everything. In that way you would have some numbers in regards to the inertia of the rotor. With that value and rotor RPM one could calculate the amount of kinetic energy.

BTW- a strong impulse and heavy rotor will easily overcome bearings friction if it's not too excessive. When I made Tesla induction motor and turned it on for a first time I was astounded at the amount of accumulated kinetic energy when the device was turned off. All because momentum gained with the action of the rotating magnetic field was stored in the weight of the rotor core and copper windings.

Flywheel aspect of rotor does have it's merit in rotational engines and especially in pulse driven ones since it smooths out the mechanical impulses transients and makes it easier for rotor to overcome possible rotational dead zones.

I'm talking too much anyway- you're doing an excellent job Jetijs.

Horray!!
congrades on your hard work!!

Hi all and thank you
Here is a very basic schematic that I would like to use. Since we have only one transistor per two coils, I think that we do not need any amplification, those optotriggers should be able to trigger the transistor by themselves. I intend to use the MJL21194 transistors with apropriate heat sink. For the first tests I would like to use a secondary battery on the isolated output. The optotriggers will be placed 90 degree apart from each other to get the right timing and the comutator wheel will have two slots on each side.



So can I use such circuit, or should I use the voltage divider on each transistor base like in previous circuit? Any other comments on the circuit?

Thank you.

Jetijs,

You can try it. The main problem is the low current the output section of the opto-interrupter provides. The max collector current is 20ma. See what happens. Up-grading the circuit for more gain later is simple enough.

Peter

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.

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

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,

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

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

Jetijs,

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

Peter

sorry I posted on the wrong thread

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,

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

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

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,

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