Noob Help... Auto reversing motorized camera slider for videography project

Thread Starter

rcheez

Joined Sep 20, 2018
6
Hello everyone,

I am a professional videographer working on motorizing an off the shelf slider for cinematic sliding video shots (not timelapse). I have watched dozens of videos on people diy motorizing their sliders with dc motors, pwm speed controllers, and some even adding in contact switches with dpdt relays to automatically reverse direction and I want to give it a go.

Simplest approach... use a drill or a battery powered fan with some fishing wire... Yes it will work, but I need more control, want to set and forget while I perform interviews, and do not have the capital to invest in one of the fancy multi thousand dollar rigs like a Rhino slider. I have a very inexpensive nice slider that has integrated panning control via a control rod in the center of the slider. (http://a.co/d/e71Oobh). At one end I can frame the subject, and the other the same and it will give me a very fluid parallel motion while keeping my subject in frame, such as during an interview. What I want is the ability to do what Parker is doing in this video at 14:16 with the Rhino Slider, (
) by adding in a dc motor with a speed controller that will go back and forth until the battery dies.

He is able to set it up to slide at a controlled speed, and it will automatically go back and forth while he is doing an interview, exactly my use case. (I don't care about the ramping which is an ease in and out toward the end of the slide, just back and forth at a continuous speed).

I am a computer nerd and could easily accomplish this with a little investment and some arduino programming with a stepper motor. With that said, sound is a concern and dc motors are much quieter. I also believe this is possible with straight analog electronics with lower overall cost.

I do not need assistance with the belt, driver design. I need help with the electronic solution.

This guy seems to have what I am looking for here:

However I am troubled by two things, at 5:32 his diagram shows "Carriage needs to be headed toward SW2 when started"
https://drive.google.com/file/d/0B06sUIMWtgdkR09BMGhSRTdoeGc/view
Which seems like some kind of design flaw in the electrical design. I want to be able to turn on my motor and regardless of what direction it is headed, it will automatically switch direction when it comes into contact with either contact switch. Second is that DPDT relay is frickin huge, can I use the smaller ones I find on Amazon rated for the voltage I am targeting? I want to put everything into a nice control box attached to the slider and as small as possible.

I plan to power this at 5v using usb charger battery packs. I could also utilize 18650 batteries (I vape), or 7.4v NP style batteries used in film applications, but have selected motors and parts based on 5v USB power supply (Is amperage a concern?)

These are the parts I am looking at getting to implement this approach.
DPDT Relay: http://a.co/d/fNdzmOA (this looks nothing like the dpdt relay in the sample video, what is the difference, should i care?)
Motor Driver: http://a.co/d/6JG6rAX (has directional switch and integrated off switch +1)
Limit Switches SPDT: http://a.co/d/1USMwRy (Only need two, and this little roller thing looks more reliable than the ones without.)
Finally a motor: http://a.co/d/8o3m5lP (cheap, and comes with a little mounting bracket so I can attach to my frame attachment for the slider)

So the questions I need help with are...
Is there a better wiring solution that the one presented in the second video that does not worry about the carriage direction at the beginning, or is this even a valid concern at all?
Can I use the DPDT relay I selected on Amazon instead of the big ugly one he shows?
Are the Limit switches I found suitable or the wrong thing?
Am I approaching the power supply properly or should I consider going up?
I saw a lot of videos adding a diode into the circuitry to prevent undervoltage spiking from the motor from the PWM modulator, is this a concern with the one I have selected?

Finally, Is there a more elegant approach to what I am trying to do here that I haven't come across yet?
 

Alec_t

Joined Sep 17, 2013
14,280
Welcome to AAC!
I think you need to start by determining what torque the motor will need and what the shaft rotation speed needs to be to get the desired camera motion. That will inform the motor size and maximum current draw (stall current), which in turn will inform the relay contact rating or motor control module rating (if you decided to use a PWM module for smoother control, with speed and reverse controllable too).
You may find that the cost of a PWM module is little different from that of the relay module.
 

Thread Starter

rcheez

Joined Sep 20, 2018
6
Thank you for the reply! I did look into torque ratings, etc, but have generally found the gear reduction motor I identified to be a common use case in these applications. There is very little resistance on a slider properly balanced, even slightly tilted the weight and torque requirements ahould be well under the capabulities of this motor. I am more worried about underpowering with 5v usb charger battery. So, base on the motor I have selected, are the other components suitable?

Regarding PWM, that is for the speed control, the relay is for the bidirectional switching. I need both to accomplish what I am trying to do. In the video he uses a 3pdt relay, although I have read I need a dpdt latching relay. What is the difference anx what should I look for?
 

Alec_t

Joined Sep 17, 2013
14,280
Regarding PWM, that is for the speed control, the relay is for the bidirectional switching.
I appreciate that, but have you looked for a module which will do both speed and reversal electronically, thus avoiding the relay?
The 6V motor is rated for 3W, so will draw 500mA at its rated load/speed. The stall current could be a couple of Amps or more, so your power supply would have to be able to cope with that.
If the stall current is less than 2A an L298 based module should be usable for motor control.
 
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Thread Starter

rcheez

Joined Sep 20, 2018
6
Yes, the speed controller unit I have identified has an integrated bi-directional switch, but I do not believe it is compatible with the contact switches I am looking at without a seperate relay. I do not know enought about relays to understand the difference between the manual switch on the PWM controller and using a dedicated relay with contact switches. Ideally I would use the PWM controller as is, and it's manual switch to go left/off/right, and the contact switches be dedicated to reversing the carriage direction automatically.
 

Thread Starter

rcheez

Joined Sep 20, 2018
6
Ok, here is a link to another article written up by someone who has done this successfully.

http://cheesycam.com/cheesycam-diy-auto-reverse-polarity-motorized-video-slider-update/

His diagram is attached. (and I realized in my original post, the original person was using a 3pdt relay, while this one uses a DPDT relay, sorry for the confusion)

His DPDT relay is a big block with a mechanical thing toggling back and forth as the contact switches are triggered.
https://www.ebay.com/itm/121034195696
 

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Thread Starter

rcheez

Joined Sep 20, 2018
6
Edit to previous post, the new guy does not have the speed control integrated into his circuit, just controlling speed by motor selection. So original post is essentially what I am trying to do.
 

Alec_t

Joined Sep 17, 2013
14,280
I think, to get all the options (right only, left only, off, toggle left-right, use of a PWM speed controller, and relay latching), you will end up needing a 3-pole relay or a latching type relay, unless you are prepared to build and add a bit of electronics. The PWM complicates the latching arrangement if the relay has only 2 poles and is inherently non-latching.
Do you know if your proposed PWM speed controller uses high-side pulsing or low-side?
 

Thread Starter

rcheez

Joined Sep 20, 2018
6
I am unsure about the high -side pulsing or low side here is the one I am looking at http://a.co/d/5d30Opm (there is a version with the left/right toggle, and one that just has speed and off). How about if I just went with the pwm without the left/right toggle? I want the simplest and most elegant approach to this.

Regarding latching, I just googled it a bit and think I understand the difference. The one that the guy used in his video was really big with a mounting terminal. What should I be looking for here? https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias=aps&field-keywords=dpdt+latching+relay&rh=i:aps,k:dpdt+latching+relay
 

Alec_t

Joined Sep 17, 2013
14,280
One of the reviews for that linked speed controller says it's rated for only 3V, despite what the ad says.
As for the relay, are you handy with a soldering iron and pin connections (cheaper), or do you really need a module with the screw-down connection terminals (more expensive)?
I'm not sure which of those relays (modules) in the link would be best, because only some specs give the DC current rating of the contacts. A dual-coil latching relay would be simplest if you want left-right auto toggle.
How about if I just went with the pwm without the left/right toggle?
In that case you wouldn't need the relay.
Whatever path you choose, you should really add a supressor across the motor, to prolong the life of the reversing switch contacts.
 

Alec_t

Joined Sep 17, 2013
14,280
Here's a basic manual sytem for left, off, right and speed control (no auto toggle) :-
SliderControl(basic).PNG

Edit: The centre-off position of the switch allows for a slight pause, so that the motor doesn't try to reverse instantly (which would be stressful for the mechanism and possibly the camera).
 
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