Caveman optical sensor RC controller concept.

[spinningmagnets]

I am a newb to electronics, and my old brain is slow, but...

I believe gas prices will spike up again, and every time that happens, hub-kits get quickly sold out and back-ordered. I believe non-hubs will eventually provide an E-bike solution that is better and cheaper than the most common hub-kits. Towards that end, I think the next year here on ES will result in open-source plans for a DIY-motor that is scaleable in size and power.

Though I am no expert by any means, I think the axial-flux motor with optical sensors will end up the best DIY by far. Removing hall sensors from the inside of a hub might mean adding external trigger-magnets, which could then accumulate debris. Optical sensors have no problem being external.

I have been assured by an RC enthusiast that his very affordable DIY optical sensors ran a motor at 6,000-rpm with no switch timing issues.

In humid weather, moisture is almost impossible to keep out of the inside of a hall-sensored motor, and on occasion I recall someone posting that his halls shorted out. Though I "think" DIY halls could be potted, having external sensors completely eliminate any brushless sensor heat issues.

External photo-sensors should be easy to make completely rain-storm ridable. I have heard of an LED shining light onto a white/black decal, which reflected back onto a photo-sensor. Also a disc and caliper arrangement where the light shined through holes in the disc. Apparently both types worked well.

I can't afford a proper RC build yet, and I won't have my own shop again for about a year, but...I CAN build a DIY axial-flux with optical sensors inside an apartment, and I think a lot of other people can too.

Whether adding sensors to an RC motor or a DIY axial-flux, I think optical sensors will end up being the hot ticket.

[Kburn77]

I really like the idea of a interupter/encoder style disc, here's some really cool optical sensors that would be easy to implement on an encoder disc. http://www.jameco.com/webapp/wcs/stores ... eyCode=PDF
it uses a 5v supply but maybe the controller already uses 5v for hall sensors?

[Jonathan in Hiram]

The trick to getting phototransistors to respond quickly is making the load impedance as low as possible. One way to do that is using an op amp as a current to voltage converter, with a current to voltage converter, the load impedance is essentially zero.

An LM3900 or an LM324 quad pack op amp will work, the 3900 has a bit better specs but requires a bit more external circuitry, they both will work on a single supply. It's been at least a decade since I fooled with this stuff, I'm sure there are better choices out there today.

[vanilla ice]

A splash guard thingy could help with sunlight too. I know the sun screwed with our optical rear wheel slip sensors at work.

[John in CR]

LFP,
It sounds great. There's something about the hall sensored commutation that just doesn't seem right at take off, so a more positive control over commutation may prove very beneficial. Also, going with a brushed type commutation without the brushes may prove to be a real winner too, because firing all the coils all the time instead of only 1/3 or 2/3rds has to be a more effective use of the copper. Cheap labor down here too, hint, hint.
John

[fechter]

Optical sensors will be just as prone to moisture damage as a hall sensor. Either one should be fully submergible if properly sealed.

On the other hand, I can think of a few motors that got hot enough to fry the hall sensors, which are typically located right in the windings. By using optical sensors outside and away from the heat generating windings it should be immune to that failure.

I'm not sure if they would need a buffer amp. That might help. You might be able to do something real easy with a logic inverter chip. This would also speed up the swtiching.

Here's one that Mouser has for $0.76 ea. http://www.vishay.com/docs/83760/tcrt5000.pdf
That's cheaper than a hall sensor. I bet you could interface those directly with a "standard" brushless controller by just adding a few resistors.

A few other thoughts:
The disk or drum with the pattern needs to be fairly large in diameter to maintain precise timing with a reflective sensor. You might be able to use a single pattern and stagger the senors to get the right output phasing. This is the equivalent of how hall sensors would be placed. This would require a greater spacing between the sensors. With a single pattern, the dark and light sections would correspond exactly to the north and south magnet poles.

Keeping the sun out is essential, and not such an easy thing to do in some cases.

The power consumption of the IR emitters is quite a bit higher than your typical hall sensor, so the 5v supply may be strained. The forward voltage of the emitters is low enough that you could possibly put 3 in series and still run them off 5v, which would cut the current draw by a factor of 3. I think you'd want to run them somewhere between 10-20ma.

I think it make sense to try this with a regular brushless controller. The cave man commutation scheme would be great if you had to make the whole controller from scratch, but it' so much easier to just get one already built (I know, it takes half the fun out of it).

[liveforphysics]

I've seen some motors with optical sensors. Usually they use an interrupter disc, but I don't see why a reflective sensor wouldn't work. Just need to shade it so it doesn't screw up when it's in the sun. A bit of felt draped over the sensor holder and glued to be snug up against the motor should solve ambient light problems I think you could do it with just 3 sensors and use a standard sensored controller.I'm not all that impressed with TO-220 fet packages used in all other controllers, not too impressed with poor use of space in board layout and weak traces. I bet you could run the optical sensors directly to the hall wires (with some resistors). If your pattern was black against a shiny metal background, I don't think you'd need reflective paint. Timing could be adjusted by moving the senor mount. Yep, that's what I currently do with my external hall sensor retro-fit RC outrunner.

A similar approach would be to use a disc rather than a drum for the pattern. This may allow for mounting the encoder on the motor shaft externally or on the end face of the rotor. More needless complexity IMO.

With the 6 sensor approach and the right FETs, you could essentially turn a brushless motor into the equivalent of a brushed motor by using the sensors and FETs for commutation. This is like the eCycle silicon commutated motor. http://www.ecycle.com/motorgenerator.html With this setup, the commutation is done separately from the PWM and you just use a (cheap) brushed motor controller. Of course it would make sense to just gate the high side FETs with the PWM signal to avoid the losses in a separate controller. In this kind of a setup, I think you'd want to add some kind of logic latch that would prevent shoot through if a sensor screwed up. Yep, hence the part where I suggested driving a 6 channel H-bridge fet driver with built-in no-passthrough protection.

[kfong]

Luke,

Cool idea, optos should have no problem in this application. There are already opto sensors that have transmitter and receiver pairs so it will reflect on the surface easily. If you know what the hall effect outputs are, it might be just an easy substitution. This optocoupler uses plain paper as the contrast media. Would be easy to create a pattern on the motor and secure it with clear tape or paint. You would need to know if the motor algorithm uses edge or pulse width detection. Keep the sensor on the underside or on top so it gets less sunlight, so as long as there is good contrast it should work out fine. It already has a daylight filter.

http://search.digikey.com/scripts/DkSea ... -1239-2-ND

With the large motors it would be easy to create a circuit board with a strip of these. Let me know if you plan to pursue this. I can help by making a simple 2 layer circuit board with my milling machine. Just attach it length wise to your motor and print out a pattern.

Kin

[kenkad]

Kfong,
Thank you for the Osram SFH 9240 reference. I was planning to use the RPR-220, which has a slower response and no Schmidt trigger. I have changed my layout to use the SFH 9240. Again thanks. I have enclosed a JPG of how I will be mounting my motor controller to the motor shell and sensing the reflective spots on the rotor disk. You can see the reflective spots in the circular slots in the JPG. I also plan to be able to adjust the timing by rotating the motor (+/- 10 degrees) controller on the motor shell. The motor controller (as shown) is setup to allow up to six 3phase drives. This is a long term research project for me. I have not started to cut any material yet. I still have some small details to work out. I have provided this JPG simply to give others ideas they can implement in their designs. Keep up the good discussion.
kenkad

[deVries]

November 29, 2009...

I've seen some motors with optical sensors. Usually they use an interrupter disc, but I don't see why a reflective sensor wouldn't work. Just need to shade it so it doesn't screw up when it's in the sun. A bit of felt draped over the sensor holder and glued to be snug up against the motor should solve ambient light problems I think you could do it with just 3 sensors and use a standard sensored controller.I'm not all that impressed with TO-220 fet packages used in all other controllers, not too impressed with poor use of space in board layout and weak traces. I bet you could run the optical sensors directly to the hall wires (with some resistors). If your pattern was black against a shiny metal background, I don't think you'd need reflective paint. Timing could be adjusted by moving the senor mount. Yep, that's what I currently do with my external hall sensor retro-fit RC outrunner.

A similar approach would be to use a disc rather than a drum for the pattern. This may allow for mounting the encoder on the motor shaft externally or on the end face of the rotor. More needless complexity IMO.

With the 6 sensor approach and the right FETs, you could essentially turn a brushless motor into the equivalent of a brushed motor by using the sensors and FETs for commutation. This is like the eCycle silicon commutated motor. http://www.ecycle.com/motorgenerator.html With this setup, the commutation is done separately from the PWM and you just use a (cheap) brushed motor controller. Of course it would make sense to just gate the high side FETs with the PWM signal to avoid the losses in a separate controller. In this kind of a setup, I think you'd want to add some kind of logic latch that would prevent shoot through if a sensor screwed up. Yep, hence the part where I suggested driving a 6 channel H-bridge fet driver with built-in no-passthrough protection.

Luke,

Cool idea, optos should have no problem in this application. There are already opto sensors that have transmitter and receiver pairs so it will reflect on the surface easily. If you know what the hall effect outputs are, it might be just an easy substitution. This optocoupler uses plain paper as the contrast media. Would be easy to create a pattern on the motor and secure it with clear tape or paint. You would need to know if the motor algorithm uses edge or pulse width detection. Keep the sensor on the underside or on top so it gets less sunlight, so as long as there is good contrast it should work out fine. It already has a daylight filter.

http://search.digikey.com/scripts/DkSea ... -1239-2-ND

With the large motors it would be easy to create a circuit board with a strip of these. Let me know if you plan to pursue this. I can help by making a simple 2 layer circuit board with my milling machine. Just attach it length wise to your motor and print out a pattern.

Kin

Bump.

Has anyone pursued this optical sensor-controller to get a working model yet?

Or, does someone have an ETA when this might happen for RC motors?

TIA

[gwhy!]

Bump.

Has anyone pursued this optical sensor-controller to get a working model yet?

Or, does someone have an ETA when this might happen for RC motors?

TIA

I think this idea sort of went away, it was talked about before anyone really had a working hall sensor setup working well on rc motors using standard sensored speed controllers.

[heathyoung]

Its a cute idea, but optical always tends to fall over in implementation - it was tried with very limited success in automotive applications, for stuff like crank angle sensors etc. but as soon as crap falls into it - it falls over. The majority of stuff is hall effect for good reason. The 'cave man approach' is nice, but you could do the logic with something as simple as gates or heaven forbid something as primitive as a GAL.

The heat effects on LED's - visible or infra-red are also well known. If heat is that much of an issue, then perhaps pickup coils are more appropriate.