Stepper motor for automatic camera rails

Thread Starter

cvangordon

Joined Mar 28, 2016
31
i want to build an automatic rail system for my camera for macro photography. I have seen a lot of systems using a stepper motor controlled by an arduino which is then controlled with a computer. Not only is all the circuitry too bulky to be carried into the field also using a computer outside with possible rain sounds like a bad idea. Is there a stepper motor system you guys know of that is:
#1. Strong enough to move a camera with a few accessories attached a few milimeters per second
#2. Have a small enough driver board to be housed in a handheld enclosure
#3. Control it all with handheld controller no bigger than an average cellphone
#4. All together be less than 200 bucks
 

philba

Joined Aug 17, 2017
960
I've got exactly what you are asking for. Though, have yet to write it up and the code is not finished. The board itself is 85mm x 50mm. Uses a Teensy 3.2 ($20) and a 2.2" color TFT LCD ($6). It uses an external stepper driver ($15ish). I'm using a 400 steps per rev NEMA 17 stepper ($10-15) and a 250 mm rail (about $100). Misc parts are probably another $15. I have several extra bare PCBs that I was planning on giving away at some point. So, it comes pretty close to your price goal.

The controller uses a rotary encoder with a switch. It has a camera control output and also allows you to plug in a remote shutter switch to directly control the rail and camera. I'm still working out the camera control aspects. My goal is to to use it for focus stacking. The current design is set up for a minimum of 2.5 microns per step. Though with a different lead screw, one could get a lot lower.I'm still working out the user interface which is why the code isn't done. I'm also still tweaking the hardware though the current PCB is pretty good.

You can see two versions in the picture below. I decided the rotary encoder would make for a cleaner interface over the 4 button design. The rail is a kit from Open Builds. I'm not in love with it but it seems to work well. Gotta run, if you have questions, don't hesitate to ask. I'm happy sharing the design and intend to make it open source when done.
P1010020_DxO.jpg P1010018_DxO.jpg
 

Sensacell

Joined Jun 19, 2012
2,518
Closed loop DC servo motors can produce much more output power from a smaller package and do not consume the same standby power that stepper based systems require.

This becomes a huge factor when you go into the field, running batteries.

Stepper drives are simpler at first blush, but they are weak power hogs, by comparison.
 

philba

Joined Aug 17, 2017
960
True on power consumption - do you have an inexpensive source of 12V DC servo motors?

But there are several mitigating points. A typical focus stacking session doesn't last that long. With 5 seconds per shot (mostly settling time) it takes less than 10 minutes for a 100 shot stack. These devices don't need a huge amount of power - typically camera and sliders will weight < 5 lbs. There isn't a lot of holding power needed so a good stepper controller can reduce holding current. The usage sequence is move a small distance (1-100 microns is common), wait for settling, take shot, move a small distance... Total distance traveled in a session is on the order of millimeters. Rewind when done and repeat. Characterizing consumption is on my list of things to do.

I have thought about building a geared motor system with an encoder that would allow micron level positioning. My board has a serial connection breakout that could be used to communicate with a controller. Conceptually, it's fairly easy. Not so sure about actually building it. It's a second or 3rd stage of development.
 

Sensacell

Joined Jun 19, 2012
2,518
Typical holding current for a stepper is 25% of running current.
A open loop stepper running with no load consumes almost the same power as one fully loaded.
This is not entirely true if considering closed loop stepper systems, technology far beyond what we are discussing here...

Without a reasonable current flowing, you lose your position.
DC servo's consume power in direct relation to mechanical output torque. (power)

Nice DC brushed gearhead motors are a bit expensive, but you can find great surplus deals.
The other advantage the servo has is that the acoustic noise is far less.

All the stepper based camera motion systems I ever worked with ran hot, 100's of watts burning constantly.
 

MaxHeadRoom

Joined Jul 18, 2013
19,437
My instruction from stepper motors Manufacturers state that the current in a stepper should be maintained at a constant at the Rated Plate current, from stationary to full RPM, .
At rest, the power can be removed in order for the natural holding torque to hold position.
It is typical to use a higher than rated plate voltage in order to supply the rated plate current as the rpm/inductive reactance of the winding increases.
The drive is responsible for maintaining the plate current.
Max.
 

philba

Joined Aug 17, 2017
960
The stepper I have is about 1A. At 12V that's a far cry from 100s of Watts. Just doing back-o-the-envelope - a 75% efficient boost supply with a 4000 mAH LiPo cell would run for 55 minutes flat out. I'll dial the stepper current down to as low as possible so I'd get considerably longer. Factor in lower holding current will help a lot though I haven't built the model to estimate the actual benefits. Am planning on testing it. I appreciate your comments on power but I don't see this a huge concern.

Typical holding current for a stepper is 25% of running current.
A open loop stepper running with no load consumes almost the same power as one fully loaded.
This is not entirely true if considering closed loop stepper systems, technology far beyond what we are discussing here...

Without a reasonable current flowing, you lose your position.
DC servo's consume power in direct relation to mechanical output torque. (power)

Nice DC brushed gearhead motors are a bit expensive, but you can find great surplus deals.
The other advantage the servo has is that the acoustic noise is far less.

All the stepper based camera motion systems I ever worked with ran hot, 100's of watts burning constantly.
 
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Thread Starter

cvangordon

Joined Mar 28, 2016
31
So since you do macro photography you should understand this:

i wanted to try a different technique for focus stacking. So as you probably know when you close down your aperture a lot and then use a flash to iluminate your subject your flash then becomes your shutter speed meaning you can freeze the shot in perfect clarity even if you are moving during the shot.

Since that is the case i think it should be possible to use a stoboscopic effect on the flash while synched with the shutter speed to take several shots in a second while the camera is moving to get several points of focus. Not the 100 shots that are done on some stacks but 3 or 4 for sure.

I have not tested this though... so my question is could you test this theory for me? I would love to know if it can still indeed produce a sharp stacked shot
 

philba

Joined Aug 17, 2017
960
I'm not set up right now so it won't happen anytime soon. Your idea is solid, though. The problem with steppers is they induce a fair amount of vibration. The cameras I use have both lens and in-body stabilization so they are more immune to the vibrations - I don't use flash for macro. That said, if your flash is fast enough, it will overcome almost any movement. I think the biggest problem for your idea is flash cycle time. Easy enough to program the rail controller to a specific speed that syncs up with the flash cycle time. I wonder if there is a clean way to sense the ready light on the flash. I know I could create a sensor that would "clip" onto the flash to see the ready light. Kind of ugly, though.

The stepper vibration is why I have looked (and am still looking) at a geared continuous drive - it will be significantly smoother. This is much more important for video.
 

Thread Starter

cvangordon

Joined Mar 28, 2016
31
I've got exactly what you are asking for. Though, have yet to write it up and the code is not finished. The board itself is 85mm x 50mm. Uses a Teensy 3.2 ($20) and a 2.2" color TFT LCD ($6). It uses an external stepper driver ($15ish). I'm using a 400 steps per rev NEMA 17 stepper ($10-15) and a 250 mm rail (about $100). Misc parts are probably another $15. I have several extra bare PCBs that I was planning on giving away at some point. So, it comes pretty close to your price goal.

The controller uses a rotary encoder with a switch. It has a camera control output and also allows you to plug in a remote shutter switch to directly control the rail and camera. I'm still working out the camera control aspects. My goal is to to use it for focus stacking. The current design is set up for a minimum of 2.5 microns per step. Though with a different lead screw, one could get a lot lower.I'm still working out the user interface which is why the code isn't done. I'm also still tweaking the hardware though the current PCB is pretty good.

You can see two versions in the picture below. I decided the rotary encoder would make for a cleaner interface over the 4 button design. The rail is a kit from Open Builds. I'm not in love with it but it seems to work well. Gotta run, if you have questions, don't hesitate to ask. I'm happy sharing the design and intend to make it open source when done.
View attachment 144371 View attachment 144372
So i am kind of thinking about doing a system like yours here because im thinking i might need more versatility from my own system. I was wondering about the coding you used for the LCD and buttons. I shoot with a manual lense ao my system wont be communicating with the camera focus system but will probably be linked to the shutter. Im trying to find a good guide for building a stepper motor system that has buttons that let me set "forward", "reverse", "speed", and "run time" so far ive only seen more complicated set ups that use the cameras auto focus system to tell the rails how far to move.
 

be80be

Joined Jul 5, 2008
1,961
wondering about the coding you used for the LCD and buttons

He said he's not coded the user interface.

I would go gear motor like Max posted you want slow moving sound's like steppers love to run fast and do get very hot slow stepping.
 

philba

Joined Aug 17, 2017
960
I disagree on motor choice. A photo stack session lasts but a few minutes with at least a few minutes in between. A stepper is easy and very precise. This why all the comercial focus rails use steppers.

As to button and LCD interfaces, I have a lot written and would be happy to share. I'm in Costa Rica right now but will be back in a few days. PM me and we can figure out how to help you.
 

DNA Robotics

Joined Jun 13, 2014
515
Stepmotor Driver 3.5A Sale: $19.95
Just set the direction and send step pulses.
Everything is adjustable including amps.
Go as fast or slow as you want.

INPUT: 9-40CDC (24 Nominal)
OUTPUT: Selectable up to 3.5A max.
STEP: Full & 1/2, 1/4, 1/8, 1/16, 1/32 Microstep
Full bridge driver for 4 or 6 wire hybrid stepmotors.
Automatic drop to Hold current with no Step Input.
Switch Selectable output current. .5A-3.5A
Over temperature & current Protected.
Under Voltage Shutdown
Opto isolated Step, Direction & Enable Inputs. (+5V Level)
 

philba

Joined Aug 17, 2017
960
Sorry I'm late on this. just flew back last night.

Do you know what stepper chip is in it? I'm guessing it's a Toshiba TB6600 or perhaps the TB6560. On the 6600, a lot of the implementations don't correctly do auto release holding current which means you have to be sure to drop the enable line. Not the end of the world if you are writing the code to drive the stepper.

Also, you can buy similar/clones of that driver for less off ebay/aliX.
 
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