I need to move a stepper a step (or a solenoid).

[steve-o]

I repair industrial stepper drives here at work. (That's what I do for a living)
I've never seen a stepper motor that can be moved 90 degrees by energizing the windings like you're describing.

A DC motor would be easy. Just put mechanical (rubber) stops at 90 degrees and reverse the polarity of your power supply to the motor. A single resistor would be good to limit the current. If the motor gets hot, Increase the resistance. What voltage(s) do you have available for this 'modulator' circuit? I can then try to recommend a resistor.

[carmangary]

I need to change the beam 90 degrees so the mirror needs to be at 45 degrees to the beam when it is in front of it. But even still, that doesn't mean the stepper needs to move that far. It just needs to be out of the beam path to begin with and then 45 degrees in the path at the stop. But, depending on the length of the mirror, a 1 degree change could potentially place the mirror completely in the beam path... and if it was already at 44 degrees when out of the path then the 1 degree change is all that is required. That's why I am shooting for something with 20 degree step or anywhere in that ballpark.

I can see what you are saying with the motors, though. I suppose I could probably do that easily as long as I use a +/- P/S. It is an option.

[The_Doctor]

I don't get it... if you need two beam path states, and highly repeatable accuracy, you need the mirror fixed on a mount that can be translated, not rotated. I think you were nearer the mark with that solenoid. Steve's relay idea is nice, but you'd have to look at a LOT of relays to figure out which was going to be the best. Worth it though, a neat discovery of that kind might be highly useful to many here for the same purpose. The out-of-beam position doesn't matter so long as it IS out of beam, and the in-beam position must be precise and repeatable. While it does include some rotation in the adapted relay idea, that's just incidental, it's the two fixed states alone that matter.


Edit: nm, I re-read, I see you did get that point..

[mixedgas]

this will have a MFE R4-165 in in it, a nice big actuator like used in pro beamtables. Its basically a galvo with tangent correction for the long pen arm , but it will be just fine for your purposes.

http://cgi.ebay.com/MFE-Chart-Graph-...QQcmdZViewItem

you have to be careful, not all chart recorders have actuators, but since MFE made the whole thing, you can be sure that one does. MFE did switch to digital printing in their later years , but I'm sure that one has a analog pen motor.


Steve Roberts

[mixedgas]

The other way, besides a actuator or maybe a model airplane servo

is to use a stepper and a microprocessor such as a pic, or atmel 2051

You'd need to find a older stepper with big steps, you put a arm on it and mechanical stops, you set the micro to drive the four coils (you need a unipolar, not bipolar) motor in 1,2,3,4 sequnce until it slams against the stop. To reverse the motion you drive the coils in 4,3,2,1. position feedback is not needed, you simply send the commands enough times that your sure the motor has hit the stops.

this is the basis of the STP-5 actuator sold in Europe for beam tables.

if your doing this on a goofing off basis, a model airplane servo costs about 12$ and needs regulated 5 volts to power it at about 100-200 ma. The command is sent to the servo using pulses about every 20 to 40 milliseconds.
a 1 millisecond pulse is full left, a 2 millisecond pulse is full right, 1.5 milliseconds gets you centered. Its 10 times slower then the actuator, and about half as slow as a stepper.

a good circuit to control a servo is here: http://www.uoguelph.ca/~antoon/circ/archive/servo1.htm

however that chart recorder I mentioned in a pervious post on ebay has two R4s in it, all you need are 12V and a switch, and to make a little arm to hold your mirror. The R4's mounting brackets are already in the chart recorder

when I get around to posting to the gallery, I can include pictures of all three, need a password though. I want to post some circuits I've done over the years, and I can post at89c2051 code for the stepper.

Steve

[dave]

hehe, someones a 8031 user Atmel make some nice chippies.. I have been using avr's for a while, in both assembly and c. Just trying to find an excuse to have a play round with the ARM's.

Welcome aboard btw