Optical Rpm Sensing

I think most of the automotive sensors are TTL. It might take a little research to confirm.
 
wa5cab said:
It only takes one transistor and three resistors to make a level changer. However, I am not certain about the I/O requirements of the ABS sensors. They are certainly cheap enough. And definitely sturdy enough.
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The sensor from my Dodge minivan is a Hall effect device. I had just connected 12 volts to the power lead and checked the output lead with a scope. As I recall, there was no level shifting.
 
sounds like a fun project, but a cheap eBay tach and a magnet on the bearing spacer under the gear cover works just fine for me. I haven't even made a proper mount for the pickup, just glued a magnet onto it to hold it to the headstock. Works as well as I can tell (from memory it displayed the correct speeds for each pulley as detailed in the manual) and no chips so far as the gear cover is usually closed. I think it was $13 or so. I have another one I'll be putting on the drill press when I get the motor conversion done.
 
Quick update, I had just glanced at the gears and thought there was enough room to do as I planned. After more careful measuring I don't believe there is enough gear above the bearing housing to fit an optical sensor . However I finally got the Hall Effect sensor to read correctly and will use it. I plan on epoxying a small neodymium magnet to the face of the gear and if that fails I will inset the magnet. Now that family have started to arrive all work has come to a stop until after the new year begins.
 
wa5cab said:
Inside the headstock is a pretty dirty environment for any kind of optical sensor. Unless you never grease or oil anything in there. I would recommend a reluctance or an eddy current sensor counting the bull gear teeth. Plus as Jim indicated, that would give much higher resolution which could be important at very low spindle RPM.
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Real cheap 3M retro-reflective tape
 
I personally would have kept it much more simple and just ran a tach generator off the back of the spindle. I doubt you will have goodluck with a retroflective photo eye trying to count the bull gear at 2k rpm. The solid state electronis wont cycle fast enough and you will just end up with a constant on signal. The optical route isnt going to work will with 2 pulse per revolution. You near much more resolution that that. I would want at least 50 pulse per revolution for low RPM accuracy.

If your not looking for a perfectly accurate reading and you just want to know the ballpark RPM say +or - 5 % then you can do that without any type of instrumentation. All you need is a VFD upgrade. Run the motor control set up as sensorless vector and you will have very good accuracy for motor RPM right off the VFD. Just figure out what your conversion factory is for each belt combo ( though you wont be switching pulleys because vector drives make peak torque from 0 RPM to basically redline). You could just run the middle of the field pulley combo and run the drive motor at more than 60Hz when you want spindle speeds over 2k rpm and you could also run at 20Hz and still have all the torque you need. Basically all you need is a vector or vfd specific motor and a drive cable of vector contorl. Most of the cheapy drives you see are V/hz control but spend a few buck more and you will accomplish your goals for for a speed output and also have variable speed and torque control.
 
Nitmare67, where would you suggest I place this tach generator on the spindle? I have a MK2 and there is no shaft beyond the Direct Drive coupling to attach anything to. I have placed a magnet to the Spindle back gear to read spindle speed whether or not the back gears are in use. This is the only place I see to directly read the spindle. I had thought about reading the motor pulley and with software convert the reading but both being possible, and being simple were not going to happen. As to low RPM accuracy, testing shows I get a stable enough reading at 17 RPM and a 3100 RPM reading from the drive motor. I am using a treadmill motor/controller as a cost saving solution, the price of a VFD motor alone was more than I paid for the lathe. My original problem was not getting a stable signal from the Chinese hall effect sensor (you get what you pay for), however I was using the wrong datasheet. After a slight redesign have changed back the hall effect sensor. Now to build the sensor mount.
 
I didnt realize you were using an MK2. Sorry I was up all night working on my own lathe and running off a total of 1 hour sleep from the night before lol. Dang kids decided to wake up at 5am so I didnt get my normal 4 hours minimum. My thoughts were pretty foggy as I tried to complete that post last night!

I thought about this a little bit now though and i would agree on not doing a VFD on an MK2. The Hall effect sensor is a great idea. Another low cost sensor you might could use is a cam position sensor that comes in any ford 4.6/5.4 from 96 to current. Those are driven off 12-24 volts and will switch extremely fast... must faster than you will ever need to in your application.

For the sake of keeping thinking simple you could also consider just usings some sort of capacitve prox sensor and glue a small plastic square onto the back side of the chuck and have the prox switch sitting back behind the lathe out of the way. I would have to get more familiar with the MK2 to offer much more help. I can help you run down which control devices are good and bad though if you need help with that. Its too bad you cant pick up the speed on the back side of the spindle.. the gear side on a regular altlas 12". it would be easy to machine a press fit end piecd to go into the spinde and the tach could be mounted onto the cover so that it engages when the door is shut and this would keep it out of your way. Or drive the tack off same same pitch gear on the spindle gear and have it offset.

I will try to find some MK2 pictures so I can better help.
 
Nitmare67, I appreciate any help I can get. I am using an Arduino so 5 volt logic levels for me. I have the display built and only waiting for my son to mill the hole in the enclosure for the LED display. Just today I built the sensor using the hall effect sensor embedded in some pvc sheet. I have the magnet on the gear just need time to mount the sensor in headstock. Try this link for pictures of what I am dealing with http://www.lathes.co.uk/atlas6inch/page7.html
 
Please don't take this as an attack because I don't mean it that way. But what is it you are doing with your lathe that requires you to know the exact RPM?
 
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