Rotary-encoder or stepper-motor for POV?

Hei I am starting to build a POV and need to know what is better: Rotary encoder or stepper-motor Pros and Cons? Other options?

I will build either globe or propeller type POV but I have to see costs and complexity of the build first. Ultimate goal is to have touch-screen POV. was first thinking of attaching photocells besides the LED's but I have now now more ideas...

plz. help..

Well I would think a stepper motor would be a simpler method as it’s open loop control, your program would always now where the shaft is. A motor turning a rotary encoder is a feedback method of control so while maybe more precise it does require a lot more code I would think.

I’ve never attempted a POV display so I’m just shooting from the hip as normal. :wink:

Lefty

Hmm, Was thinking along the same lines.. I need to know where the leds are, So I will probaby go for steppers, but I must probably watch code size too, I will need lots of feedback code to have touch-screen capabilities.

Just thought of somethng tangly :( ... I want My Arduino not to be centrefuging with lights and detector (coze it will be controlling my plate column destiller and also a spectrograph (sortof just, the make one, 5 leds)). So there will obviously be a lot of wires that must not tangle with the rotation. How is that solved on other PoV designs?

serial to parallel shift registers, you could control 16 led's with 2 wires

ie:http://www.instructables.com/id/S344OQCG1ZGOSIB/

or daisy chain them together for more

but note, shift registers like I am using in the above instructable are logic level devices and can not handle a significant amount of current directly passing tru it... (hence all the transistors in the schematic) its just a signal chip, but other designs are made to include the signal part and the driver part in one package

I want My Arduino not to be centrefuging with lights and detector

Why not, you could then name your project the Spinduino. ;)

Lefty

'Coz I just wanted a cool spinning led display with feedback capabilities (touch-sensor display) to control the parameters of the still and spectrometer. its a lot of wires, temp on each plate, boiler temp, feed pump, reflux pump, reflux temp etc... Hard to do when my Arduino Mega is spinning 8-) too many wires the other way. So only leds (with sensor feedback photocells) are spinning and blinking.

You probably can't spin a stepper motor fast enough for good POV, and since it's open loop you DON'T know where it is at all times.

Most POVs use an index detector and timing. Pretty easy because you get the current motor speed and a known point in rotation.

so maybe strong el-motor, ir-Led and photocell then to count rpm is best? or hall effect and magnet.?

D.

so maybe strong el-motor, ir-Led and photocell then to count rpm is best? or hall effect and magnet.?

Yea, something like that. Most POV displays I've seen didn't require to know where the motor was at any given instant, but rather just one 'sync' pulse per revolution. If the motor can be made to run at a fixed RPM and you have a sync signal then the timing to output display signals can just be done with internal software timers. Not saying it's a simple software task, but I've seen them done sense microprocessor first came around in the 70s.

Lefty

Was thinking about the wire mess, found hypothetical solution i think…

Centre axle is double to some extent from top and maybe half vay down, stationary axle holder tube of plastic has thin copper or alu rings inside, as many as electrical wires out are. wires attached through drilled holes. LED and sensor mechanism rotates with the motor axle, wires are fastend to springy contactors on axle. its the same solution as is used in motors… sort of. Need at least few analog wires out from sensor elements even if I use shift-registers for the LEDs.
:stuck_out_tongue:

D.

You can have the circuitry (microcontroller etc) on the propeller, so you end up with only 2 wires (power, ground) going through the rotor.

@florinc No I can't, Arduino Mega is buzzy controlling other things... See previous posts, I do not wnt to buy more Arduinos, although it is tempting to have a very small Arduino to do just the display and sensor inputs and interfacing to one of the serial of my mega. Will see later, it boils to money and time, every time.

D.

Years ago (April 96) I used slip rings to light LEDs that were controlled by a computer. The rings were put on a plastic rod and spring fingers went on the part that was moved. I used small sections of brass tube on the plastic rod and cut groves in them to fit the wires. In all I had 9 connections like this. here is a diagram:-

This is what it looked like:-

I’d be very careful of running analogue sensor inputs through slip-rings - they’re notoriously noisy.

POVs do a pretty good impersonation of a flywheel, so a single Hall-effect or opto should give you a reasonable sync reference.

@Grumpy_Mike Cool, it was almost as I thought it.. Thanx for pics

@AWOL THink I can live with noise in the end it will only be on or off signal (is there finger on the plexi screen in front of the LED?)

Maybe I can make a circuit to take the output from photodiodes and give digital on/off signal when threshold is reached, to be on the rotor Should make it more stable.

It is not as I am going to use IR-range finder to interact in 3-D with the screen :)

I am looking to build 4-6 lines screen (Like 4 line LCD) that I can interact with. So I have to use small surface mounted LCDs for the pixels 7-8 pr. line but I was thinking the detector does not have to be so accurate and is to be of normal size (1 pr. line). Mounted on propeller inside clear box or globe (only needs to be clear shield in front of it to protect my fingers)

Definetly needs to control the leds with matrix, perhaps serial interface Will see later (it needs to be small too) the hardware constricts the size to certain minimum so I will have to chose the simplest design possible, I will probably think about this project for some time now. ;)

David.