Stepper motor or Servo?

[hevans1944]

@Neil-4545 I like the worm-geared motor you picked. You might want to order the stainless steel mounting bracket for it too. And perhaps a flexible shaft coupler between the gear-motor and the horizontal plastic wheel.

 

[Minder]

You may want to look at as much hardwired and relay logic as possible, you can get micro switches which have the repeatably that you require at that rpm, another advantage is that they can all be wired in series which does get tricky to do with S.S. switches where any more than 4 or 5 outputs in series gets tricky to do.
Is the indexing to be done by an automatic sequence or manual?
You may need a timer or two for the indexing off a switch.
M.

 

[BobK]

An optical sensor can be either an interrupter type as people have been talking about, or a reflective one. This type sends out light and looks for a reflection. The only thing needed on the wheel then is dark (or light) patches at the index points. I have not used this type, and they might be somewhat less accurate than an interrupter type.

Bob

 

[Minder]

I have found the slot detector type much more accurate than the retro-reflective which are OK for rpm detection.
But once you get to 17 S.S. sensors then you have to read them all separately without the advantage of series wired that you can achieve with mechanical type, micro switch, reed relay etc.
M.

 

[hevans1944]

I would think you could wire the seventeen sensors in a wired OR fashion so the wheel would stop and brake at each sensor position after a momentary contact closure got it moving, per @Bluejets post #18.

 

[Minder]

Slot sensors are N.C. (conducting) until broken, so normally they would need to be AND'd .
M.

 

[hevans1944]

Slot sensors are N.C. (conducting) until broken, so normally they would need to be AND'd .
M.

Picky, picky. The devil is always in the details. Add an open-collector inverter (or open-collector buffer) as appropriate to how the sensor works and tie all the collectors together for one output. First of the seventeen outputs wired together that goes low stops the motor.

 

[Minder]

Another alternative would be to use small prox detectors such as Honeywell SS400 series in conjunction with a miniature magnet, these are N.O. open collector and could be OR'd, only a couple of $ each.
http://sensing.honeywell.com/honeywell-sensing-ss400-series-product-sheet-009050-3-en.pdf
M.

 

[Neil-4545]

Thanks for taking the time to draw it out Bluejets, that makes it much clearer. I see how the optical sensor controls the relay starts or stops the motor depending upon the position it's in. I take it the relay an incoming connection then 2 (switched) outputs. Actually, I'm thinking of using an Arduino to control everything (with shields?) because I need to start it remotely, via the Internet - so a virtual start button if you will. The big problem with that is learning enough programming code as necessary to do it. Still, should be fun learning! Do you know if I'd need an Ethernet shield or a WiFi shield?
Colin, I'm a complete newbie to your world, so I have to say I don't know what "registrations" is, sorry. But I'm leaning quickly as I go, so would be grateful if you expand a little. I wouldn't want to assemble a device around a motor only to find it's not suitable.

 

[hevans1944]

... I wouldn't want to assemble a device around a motor only to find it's not suitable.

Like so many newbies here, you have described a solution (a worm-gear motor driving a plastic disk) instead of describing what you are trying to do. Please tell us what you are trying to do. What determines the size of the "horizontal hamster wheel" and why does it have to have seventeen discrete positions? Are there compartments or ridges on the "horizontal hamster wheel"? Or perhaps there are seventeen images mounted on the "horizontal hamster wheel"? Why do you want to control it from the Internet? How do you propose to control it from the Internet? How will you know which of the seventeen positions the disk happens to be? Is it necessary to know the disk position to control it from the Internet? Perhaps you will aim a webcam at the wheel? You said there is no load on the disk, but it must weigh something. Are you going to support the disk from the motor shaft? Are you going to support the outer edge of the disk? We can give better advice if we know what you are trying to do rather than offer shotgun suggestions based on incomplete knowledge of the task.

Sketches and drawings are always a big help. They don't have to be "professional" or even complete to get ideas across. Pencil sketches on plain white paper are okay. Draw it, photograph it, upload it.

 

[BobK]

I must be missing something. Why would you need more than one optical sensor?

Bob

 

[Neil-4545]

I appreciate that my overall plan has not been revealed hevans, and there is a genuine reason for that. If this means you are no longer willing to take part, then I completely understand and thank you for your input thus far. Admittedly it makes it that bit more difficult, but to give any more details about what it is and why, would disclose personal family information to anyone in the world that cares to read it. I hope you understand and can accept it. I guess I'll have to take what I've learned from you good people, build something and learn from my errors.

 

[hevans1944]

I must be missing something. Why would you need more than one optical sensor?

Bob

Oops! I missed this. One sensor, seventeen vanes of course.

I used to work on a wafer holder that had twenty-five positions for four-inch diameter wafers. This was custom-designed and manufactured by a company that has since gone out of that business. But before they cast their design in concrete, I insisted they provide a means of identifying where the wafer wheel was and auto-magically allow me to specify how many wafer positions to step through (any number from 1 to 25). Their solution was to mount an aluminum disk about eighteen inches in diameter to the shaft connected to the wafer carrier wheel. They machined a series of concentric slots positioned radially from the center, six slots for each wafer position. The presence or absence of a slot at each wafer position defined a BCD code from 00 to 25. They illuminated the slots with a set of seven infrared LEDs on one side of the disk and received the infrared light with seven infrared photo-diodes mounted on the other side. A small counter-sunk pin-hole on the edge of the disk defined each wafer position. At the "home" or 00 position there were three pin-holes, two on either side of the "home" position, to allow the wafer carrier to be accelerated to warp speed and rotated to the "home" position after the requisite number of wafers had been indexed. These two auxiliary pin-holes were used to tell the machine when to drop back from warp speed and proceed on impulse power (or maybe thruster power, to keep with the Star Trek analogy). Anyway, it used a gear-box connected to a two-speed reversible motor to turn the wafer carrier. It was spinning maybe two hundred pounds of aluminum wafer carrier, so stopping that puppy in its tracks was not trivial. But it finally worked! There was just a bit of over-travel from when the photo-diode was illuminated and when the wheel stopped. This was "taken care of" by slots that allowed the indexing disk to be rotated slightly with respect to the wafer carrier shaft. After a lot of "trial and error" we got it to index with sufficient accuracy to do ion implantation on the wafers. One small problem popped up several months after this contraption was delivered and installed as the end-station on our tandem particle accelerator: the BCD encoders began failing intermittently. Long story short: the manufacturer had saved a few pennies by wiring all the infrared LEDs in parallel and using a single resistor for current limiting! They must have hand-selected to match the forward operating voltage of all seven infrared LEDs. As the LEDs aged, their forward voltages changed and eventually one or more quit providing enough illumination to turn on their associated photo-diodes. Simple solution: put current-limiting resistors in series with each infrared LED. Getting all seven of those emitter/photo-diode pairs optically aligned with the slots and the pin-holes was an entirely different matter. Point is: an emitter and a pin-hole in front of the photo-diode works for precise position detection.

 

[Bluejets]

Thanks for taking the time to draw it out Bluejets, that makes it much clearer. I see how the optical sensor controls the relay starts or stops the motor depending upon the position it's in. I take it the relay an incoming connection then 2 (switched) outputs. Actually, I'm thinking of using an Arduino to control everything (with shields?) because I need to start it remotely, via the Internet - so a virtual start button if you will. The big problem with that is learning enough programming code as necessary to do it. Still, should be fun learning! Do you know if I'd need an Ethernet shield or a WiFi shield?
Colin, I'm a complete newbie to your world, so I have to say I don't know what "registrations" is, sorry. But I'm leaning quickly as I go, so would be grateful if you expand a little. I wouldn't want to assemble a device around a motor only to find it's not suitable.

Relay I showed was a double pole if that's what you are referring to.
As far as controlling with the Arduino, a relay can be driven from an Arduino output via a transistor or a small mosfet quite simply.
Output of it would then replace the "start button". There are other ways but this is simple.
The programming for that part would be straightforward being an output that would come on for maybe 1/2 second or so each time it was required to move the disc.
The wifi or ethernet is just another section of the code required.
Once you do some Arduino coding you will see that most is relatively easy and there is plenty of help on the Arduino forum.
Just they prefer you to try at least to write your code and then help is readily available.
Remember to start one thing at a time and once each bit works, try to combine them.
Good luck with it and remember to walk before you run.