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Stepper motor controller

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Dear All

Can anyone suggest a circuit for this small stepper motor controller I want to build. I'm sorry for not knowing the correct nomenclature so I hope this description will suffice. I'm sure this type of system crops up in industrial machine control very frequently. It's possible someone might know of a kit out there.

I want to build a small stepper motor controller which will consist of a small hand held enclosure with a knob. Inside will be I suppose some kind of encoder. The encoder and associated circuit will send signals via a cable to a small stepper motor so that the rotational direction and arc of movement of the motor exactly matches that of the control knob. The whole thing will need to run from a small DC battery pack maybe 6v possibly built into the controller enclosure.

The application I have in mind is a focus control for a video-camera. The stepper motor will turn the focus ring of the camera lens via a gear or small drive belt exactly matching the movements of the control knob. Such systems are just becoming commercially available but are horrendously expensive. It seems to me this shouts DIY quite loudly.

Thanks in advance.

Trevor
 
With some clever mechanical design you might be able to use a small hobby servo driven by a 555 timer. Not sure if this is an add on or a bottoms up design so I may be way off base.
 
Do you have a link to a commercial one?
Is this simply a remote focus system?
Do the knob and ring have to match exactly or just repeat consistently. I.E. could 270 degrees of pot movement equate to 180 degrees of focus movement or visa versa?

Mike.
 
This sounds more like a servo motor situation than a stepper. Servos get a pulse value sent to them that determines its final position. With a stepper, you have to synch both the controller and stepper to a zero position and try to keep them in synch with an encoder.
But a typical servo has an inherent zero position. You send it a 1.5mS pulse and it goes to its zero position. You keep sending it this pulse every 20mS and it "locks in" to that position. Send a narrower pulse, down to 1 mS, and it starts to turn to a position from zero. Send a wider pulse up to 2 mS and it goes the other way. Either way, it has internal stops you have to respect. Modified servos can be made to turn continuously one way or the other, 360 degrees. You need to determine what strength in ounces the servo needs to arrive at the servo's ability to hold the device it is attached to in place.

Once again, I recommend this all-in-one motor controller from BasicMicro(.com), the $25 Nano Driver Board:
**broken link removed**
The simple USB programmer is just another $15. Once you finish programming, you can use this device to do serial communications with a PC or other serial device. This is a total controller solution for $40.
The best feature of this driver board is its ability to work with so many motor types. It can do servos, simple DC motors, and steppers. It has a PIC 16F88 onboard with a bootloader. This is the Nano18 processor. It has a free powerful BASIC, run from a Window's GUI IDE called Studio. This allows you to create powerful control programs that go beyond a mere hand controller, but could be that simple. Demo code for different motor types is available at the BasicMicro(.com) site and in the forums there and at the Lynxmotion robotics forums. Your handheld box could just be a potentiometer wired to one of the unused stepper pins, the driver board and programmer, a power-on LED and a 6V battery holder.
Beyond the PIC's straight control of servos, the other more powerful driver chips onboard are the ULN2803, the L293 and four MOSFETs. The 2803 allows stepper and DC motor control at 500mA per channel; the L293 is a simple half-bridge controller capable of 1Amp per leg; and the FETs will handle 9 Amps EACH! This one board will handle just about any motor situation you care to mention. And if you don't use the stepper motor pins, they are available for analog and digital input/output.
Take care.
kenjj
 
With some clever mechanical design you might be able to use a small hobby servo driven by a 555 timer. Not sure if this is an add on or a bottoms up design so I may be way off base.

Thanks for the reply.
Bottom up, I think, but I'm afraid my strong point isn't design. I am very good at construction but would need a circuit to follow. The mechanical side would be withing my abilities.

Trevor
 
Do you have a link to a commercial one?
Is this simply a remote focus system?
Do the knob and ring have to match exactly or just repeat consistently. I.E. could 270 degrees of pot movement equate to 180 degrees of focus movement or visa versa?

Mike.

Hi Mike

Yes, a remote focus system. Here's a link to a video presentation of a pre-production system from a German company. It doesn't look like a highly complex system electronically.

INTUIT FOCUS - (FFHF.01.) follow focus unit demo on Vimeo

I've heard estimates of the pricing around 2000 euros but that has not been confirmed. Hardware aimed at videographers using DSLRs is astronomical, even for simple rods and clamps for the support systems, so it wouldn't surprise me if this was in the ball park.

I think consistent and precise repeatability is what's needed. The ratio of turns of the pot to turns of the ring can be controlled with gearing.

Thanks again.

Trevor
 
Hi Ken

Many thanks for the detailed reply. I'll check out the links you recommend. It sounds promising. In my reply to Mike, I've pasted a link to video of a commercial system from Germany which is what I have in mind.

Many thanks again.

Trevor

This sounds more like a servo motor situation than a stepper. Servos get a pulse value sent to them that determines its final position. With a stepper, you have to synch both the controller and stepper to a zero position and try to keep them in synch with an encoder.
But a typical servo has an inherent zero position. You send it a 1.5mS pulse and it goes to its zero position. You keep sending it this pulse every 20mS and it "locks in" to that position. Send a narrower pulse, down to 1 mS, and it starts to turn to a position from zero. Send a wider pulse up to 2 mS and it goes the other way. Either way, it has internal stops you have to respect. Modified servos can be made to turn continuously one way or the other, 360 degrees. You need to determine what strength in ounces the servo needs to arrive at the servo's ability to hold the device it is attached to in place.

Once again, I recommend this all-in-one motor controller from BasicMicro(.com), the $25 Nano Driver Board:
**broken link removed**
The simple USB programmer is just another $15. Once you finish programming, you can use this device to do serial communications with a PC or other serial device. This is a total controller solution for $40.
The best feature of this driver board is its ability to work with so many motor types. It can do servos, simple DC motors, and steppers. It has a PIC 16F88 onboard with a bootloader. This is the Nano18 processor. It has a free powerful BASIC, run from a Window's GUI IDE called Studio. This allows you to create powerful control programs that go beyond a mere hand controller, but could be that simple. Demo code for different motor types is available at the BasicMicro(.com) site and in the forums there and at the Lynxmotion robotics forums. Your handheld box could just be a potentiometer wired to one of the unused stepper pins, the driver board and programmer, a power-on LED and a 6V battery holder.
Beyond the PIC's straight control of servos, the other more powerful driver chips onboard are the ULN2803, the L293 and four MOSFETs. The 2803 allows stepper and DC motor control at 500mA per channel; the L293 is a simple half-bridge controller capable of 1Amp per leg; and the FETs will handle 9 Amps EACH! This one board will handle just about any motor situation you care to mention. And if you don't use the stepper motor pins, they are available for analog and digital input/output.
Take care.
kenjj
 
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