IR phototransistors are commonly used in automotive cam position sensors (albeit in transmissive fashion through slotted discs, rather than in a reflective configuration.)amberwolf wrote:The only question I have is: Is the response time of the optical sensor fast enough for extremely high-rpm motors?
Right-on Luke... Super-Glad to see Burtie move ahead with this too.liveforphysics wrote:Yes, Burtie, first let me say, you're exceptionally awesome.
It makes me super super happy to see somebody doing this!
Check this thread out I did clear back in 2009 on this exact topic, but then never got time to try it out.
https://endless-sphere.com/forums/viewto ... controller
Power to the Burtie!November 29, 2009...liveforphysics wrote:fechter wrote: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.by deVries Â» Sat Jun 12, 2010 7:02 pmkfong wrote: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.
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?
Brilliant find! and at a reasonable price (US$43)for a tiny (37mm x 11mm) self contained bolt-on product that provides direct outputs compatible with any device requiring encoder or commutation U/V/W signal input at standard TTL logic levels! Super high resolution as well (1,024 PPR [positions per revolution] Thats accuracy to 0.35 of a mechanical degree)!flathill wrote:
Whilst it's true that the limited size range of the shaft couplers is only 2mm>8mm, there is nothing stopping users drilling and tapping a centred hole in the end of larger diameter shafts (ie common Astro 3/8" shafts), screwing an appropriately sized smooth shank bolt partially in till it bottoms out (with loctite), cutting the head off the bolt, and there you have it. You can now slide your coupler over the excess shank protruding from the end! You would probably need a lathe to get the centre accuracy required, but thats a small issue compared to fabricating something like this from scratch!flathill wrote:.....a single magnet on the end of the shaft seems simpler than screwing around with shaft adapters
Yeah, they are interesting. However you would still have to build a housing for the board.bigmoose wrote:Take a look also at the Renishaw RLS AM4096, it has a RMK4 development kit that is ready to rock and roll. Only goes to 8 pole pairs however.
These look really cool. I looked at them a while back but had a concern. There is only one thing that makes me question their reliability for our application. It appears that it's using a compression fit on the plastic adapter that interfaces the shaft. I didn't see what material was specified for the adapter but it would have to be some kind of sticky urethane or something to work. When I was setting up and messing with the encoder I made for the 3220, I tried to tighten the magnetic trigger disc that bolts to the end of the shaft up just enough that I could try slight adjustments by holding the shaft with pliers and rotating the trigger ring with another set. It was way too tight to turn by hand but the acceleration of the motor would cause the mag ring to slip. I had to loctite it and tighten it down all of the way each time I tried a different position. If I had cut the adjustment slots in the sensor module a little longer, no mag ring adjustment would have been necessary........Anyway, that adapter needs to really grip the shaft and using the smaller shaft contact area and a friction fit adapted to a larger motor might not work. When the motor is actually installed, it won't be able to accelerate fast enough to cause slip 99% of the time though.......I guess I'll just have to order one and see how it works. Building everything from scratch takes too long. Being able to order things like this gives me more time to figure out other stuff!flathill wrote: