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 Post subject: Motor experiment
PostPosted: Aug Wed 09, 2017 5:25 pm 
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Location: Warner Robins, GA
Off and on over the last few years I've been experimenting with this kit

http://simplemotor.com/shop/motor-kits/kit-6/

Making my own refinements such as using a shaft and bearings, using two better coils and using a 7805 to regulate the power to the hall IC since the motor can run on up to 30Vdc.

The motor itself when unloaded will spin so fast on higher voltages that I had to glue the magnets down with gorilla glue to keep them from simply flinging off as the motor sped up extremely fast.

Surprisingly the rotor is fairly balanced.

The fan is just there for looks and so the motor does something besides spin itself. Plus when I had the motor driving the spindle motor from a CD rom drive which was used to light an LED it helped to keep the transistor cooler.

Attachment:
Motor.jpg
Motor.jpg [ 164.27 KiB | Viewed 1386 times ]


I initially thought of building a second kit, coupling it to the first and offsetting the rotor so that only one set of coils are on at a time in order to make it better, but that wouldn't be easy.

I then thought of this.

Why not use something that I can mount at least 8 magnets to?

I would need these parts:

1. Premade rotor with at least 8 sides.
2. Neodymium magnets.
3. Coils.
4. Hall effect IC.
5. Transistor.

The only issue is finding something with 8 sides that is small enough so the magnets are not too far apart which is non-metal and has a center hole in it.

I'm figuring it may cut the maximum speed in half, but it may be a little stronger.

If I can get the parts cheap enough I may eventually build one with 12 magnets.

One thing I could do is offset the two coils so that only one coil is on at the time which will require another hall IC and transistor, but I would then have a two phase brushless motor that would be a little stronger.

Any other ideas on how to improve such a simple motor?

Found some magnets.

These can attach with glue.

http://www.goldmine-elec-products.com/p ... ber=G21654

These I can use a non-magnetic bolt or screw to attach them.

http://www.goldmine-elec-products.com/p ... ber=G21668

Which would be the best choice?

EDIT:

Got the parts ordered.

I just ordered the magnets on the simple motors website.

Here's the circuit schematic.

Any way to improve the design or is it already as good as it can get?

Attachment:
Simple motor circuit.png
Simple motor circuit.png [ 9.92 KiB | Viewed 1317 times ]


Would there be any benefit to moving the coils to the collector? I then would need a resistor in series with the hall IC output and base though.


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 Post subject: Re: Motor experiment
PostPosted: Aug Mon 14, 2017 12:29 pm 
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Location: Warner Robins, GA
Decided to bring the motor to work so I could measure the frequency of the hall sensor, but it isn't that simple.

The measured frequency doesn't seem to increase as much as it should as the speed increases.

I did notice a high positive pulse to the waveform measured at the coil and said pulse starts to get wider until it is a complete square wave.

Now if I put a diode across the coils so that it is reverse biased in normal operation the pulse is eliminated and I'm just left with the normal square wave signal on the coils, but the speed of the motor is negatively affected by quite a bit at higher B+ voltages.

At first I wondered why the transistor didn't self destruct given the positive peak is around 40Vpk, but looking at the datasheet it looks like it has a built in protection diode from collector to emitter.

http://www.mouser.com/ds/2/149/TIP107-1012682.pdf

I'm wondering if moving the coils to the collector side would make the transistor have lower on resistance given it will take less base voltage to turn the transistor fully on, but I wonder if that would cause there to be a higher momentary reverse voltage on the coils when the transistor switches off. What I did do initially was to install a NE-2 neon lamp across the coils so that any high peak voltage would be limited to the neon lamp's firing voltage.

EDIT:

If the coils are in the collector circuit the transistor simply does not turn on.

Also with no load I can get the motor up to 6,105 RPMs briefly. The limiting factors are.

1. Rotor is ever so slightly out of balance.
2. Bearings aren't real secure in their mounts which affects speed slightly.
3. Limited to 30Vdc given I use a 7805 (max spec 35Vdc) for the Hall sensor.

Their website does list a kit capable of 5,900 RPMs without bearings, but I personally am a bit leery of operating one that fast which only uses super glue to hold the magnets on as I've had a magnet fly off one of the earlier versions of the current motor I have.

Now would the coils used affect the maximum speed?

What I don't quite understand is why putting a diode across the coil so that it is reverse biased when the coil is on is affecting the speed as much as it does.


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 Post subject: Re: Motor experiment
PostPosted: Aug Mon 14, 2017 4:06 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: S. Dartmouth MA 02748-1225 USA
I consulted at Vectrix electric motor cycle in 2012&13. All the electric bikes used a 27hp brushless 3ph electric the could reach 5500 rpm. It was combined with a motor controller that also functioned as the control for regenerative braking. System voltage supplied by lithium tractions cells was 158 VDC. Search any VX-1.

http://visforvoltage.org/book/ev-collab ... books/7869

Early motors had problems retaining magnets too. The mechanical design of the outer perimeter of the rotor was altered as well as the shape of the magnet such that non-magnetic retainer rings were pressed on. The rotor was assembled with magnets that were not charged. So powerful was the rotor that when removed from the bike the rotor could support the weight of a 150 lb man. It had to be pried off the steel bench into a wooden box...

I would suggest going to 3-phase, looking at semi circular magnets and a retaining scheme.

Chas


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 Post subject: Re: Motor experiment
PostPosted: Aug Mon 14, 2017 5:01 pm 
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With mine I used some Gorilla glue to hold the magnets in place. Seems to work quite well.

The website does list a kit using lego bricks and that one does have a retaining ring for the magnets, but sadly no such thing for the type I have.

I've thought about perhaps duplicating the transistor, hall sensor and two coils and have them offset so that when one set of coils is off the other set is on.

That would get me more torque, but I don't know if the speed will increase.

When I get the 8 magnets I gotta find some sort of 8 sided non-magnetic rotor to put them on. I'll then have an 8 magnet motor.

This isn't something I'd use for normal things where a motor is used. It's more of an experiment as to the effects of adding more magnets and perhaps more coils.

One issue is in finding coils already built that will work.

The two I am using now came from Electronics Goldmine a few years ago. I have two more somewhere, but I gotta find them.

I don't want to use the coils they have with the kits as they are all for low voltages and cause the transistor to heat up much quicker plus they draw more current.

That said would the lower voltage coils make the motor faster when run on the appropriate voltage for the coils?

Now the original motor I plan on possibly tweaking it to get the motor as fast as possible.

I want it so fast that even gorilla glue won't hold the magnets in place :mrgreen: :lol:

The one with 8 magnets I may use it to drive a fan blade or something.

I may eventually build one with 12 magnets as well.

The slowest the current motor will run is 1,050 RPMs unloaded on a B+ voltage of 7.28Vdc. Below that the motor slowly stops which could be partly due to the 7805 for the hall sensor.


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 Post subject: Re: Motor experiment
PostPosted: Aug Mon 14, 2017 7:40 pm 
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Add more poles to the field. Use old relay coils, extend the pole face. commutate the field pulses. There are IC's that will do that. Like the ones in a hard drive, there may be an IC that is dip so easy to connect. Try to shape rise and fall time of pulses... Lower the impedance of the power supply and use heavier wire from source to driver, to motor coils, keep leads short too. More poles, the Hall sensor can go away and the rotating field will take over. Look at different magnets with poles arranged differently...

Chas


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 Post subject: Re: Motor experiment
PostPosted: Aug Mon 14, 2017 8:39 pm 
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Location: Powell River BC Canada
"I want it so fast that even gorilla glue won't hold the magnets in place :mrgreen: :lol: "

Don't even think of proceeding with the project without first constructing a guard to contain
flying off parts.


This I learned +60 years ago, scar will follow me to the grave. :mrgreen:

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 Post subject: Re: Motor experiment
PostPosted: Aug Tue 15, 2017 12:45 am 
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Agreed. Pretty sure I could not get the motor that fast unless I spun it with a dremel or something.

Even with the gorilla glue holding so good I still take precautions when running it at full speed.


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 Post subject: Re: Motor experiment
PostPosted: Aug Wed 16, 2017 5:54 pm 
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Chas wrote:
Add more poles to the field. Use old relay coils, extend the pole face. commutate the field pulses. There are IC's that will do that. Like the ones in a hard drive, there may be an IC that is dip so easy to connect. Try to shape rise and fall time of pulses... Lower the impedance of the power supply and use heavier wire from source to driver, to motor coils, keep leads short too. More poles, the Hall sensor can go away and the rotating field will take over. Look at different magnets with poles arranged differently...

Chas


Very good information.

Those are things I may look at in the future.


The bearings were a little loose in the mounts which was because I had to enlarge the original holes in the round pipe included with the kit so the bearings would fit.

That caused a bit of noise when at a fast speed so I epoxied the bearings to the pipe making sure to align them properly.

I can now achieve a maximum speed of 6,720 RPM.

The slight imbalance of the rotor is still limiting the speed somewhat.

Unfortunately with the coils in place and no easy way to remove them I cannot balance the rotor.

I doubt I'll ever much run the motor that fast anyways since when I do the transistor on its heatsink gets quite warm.

With the fan blade installed I get a maximum of 3,210 RPM at 34Vdc input.

EDIT:

I remembered I had a brass piece from a VCR video head motor that I had on the motor's shaft for a flat belt when I drove the spindle motor of a CD ROM drive to light an LED.

It has a set screw so I knew the piece would not be perfectly balanced and I figured I could use it to offset the imbalance in the rotor.

I have now achieved a maximum of 6,945 RPM.


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 Post subject: Re: Motor experiment
PostPosted: Aug Mon 21, 2017 5:40 pm 
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Ok screwing around with the motor again today after replacing the hall sensor here's what I get.

I use the current limit control on the supply as it's easier to adjust the voltage that way.

At 16.53 Vdc 118 mA I get 6,330 RPM.

At 27.6Vdc 500mA I get 6,870 RPM

So for an increase of 11Vdc I only get an increase of 540 RPM.

I've drilled several holes by hand with a small drill bit looking for an increase in frequency as I go meaning a faster speed. I still have some vibration, but not nearly as bad as it once was. Still may play around with drilling holes in an attempt to get the rotor as perfectly balanced as possible for maximum speed.

Now would the imbalance be the only thing causing a lower speed difference with the increase in voltage or is it getting to the point that the field in the coils cannot collapse enough causing less of a speed increase as the voltage increases?

Here's an example of the waveforms I get.

The left one is the lower voltage. The right one is the higher voltage. The green line is the center of the scope display.

Attachment:
waveform.jpg
waveform.jpg [ 11.36 KiB | Viewed 1144 times ]


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 Post subject: Re: Motor experiment
PostPosted: Nov Mon 06, 2017 3:31 am 
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You asked a while ago about how the snubber diodes across the coils might be impacting motor speed. The diodes don't just 'keep the voltage from spiking' they provide a path for the current to flow as the magnetic field of the coil collapses. (Since the collapsing field is a changing field in the coil, it is generating current flow.) The current flow slows the decay of the field. This is commonly seen as a delay in the drop-out of a relay that has a clamp diode on the coil.
The coil magnetic field is lasting longer, after the switched drive current is off, so it still has a grip on the magnet. I expect that is the mechanism of the slowing.

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 Post subject: Re: Motor experiment
PostPosted: Nov Mon 06, 2017 11:21 am 
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Thanks for the explanation.

Now I understand it better.


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