Slow motion DC motor controller ?

[Jolly 7]

I am looking to build a slow motion controller for a motor and have been thinking of either using an ordinary 12V DC motor or a brushless motor. The speeds I have in mind are a 360 degree rotation adjustable from 1 minute to 10 minutes. Is there a circuit that could be made for this, maybe using a 555 IC or similar ?

[Radio Wrangler]

A stepper motor with a microstepping controller?

Otherwise a faster motor with a gearbox reducer.

What is it driving?

David

[Terry_VK5TM]

Running either motor at such low speeds without some sort of gearing is going to reduce the torque massively.

Either Davids suggestion or gear down the 12v DC motor and reduce the voltage.

[Jolly 7]

Here's the high torque 12V BLDC motor I have in mind. It has four wires, one of which can be used to regulate the speed using a PWM signal. The motor does have some built-in circuitry.
I've been hoping to build a motorised platform for a pocket camera to allow slow-motion 360 degree panoramic recordings.

[Bookman]

Hi,
You may want to check out model boat DC drive motor suppliers and the range of motors and controllers they provide.

[McMurdo]

Is the speed reference done by frequency variation, or pwm-ratio? Either way a little 555 or op-amp circuit should do it, but you need to know the spec of the control signal.

A brushless motor like this should hopefully have good torque control across the speed range, at least industrial-sized ones do, utilising the hall sensors around the windings.

A model boat "winch" servo may well fit the bill, position is controlled by a 1 to 2ms pulse. I use one for my loop antenna rotator. I said a winch servo as they go more than 360 degrees, normal servos only do 60 or so.

[Ed_Dinning]

Hi, if you can get the motor spec sheet they often include applications data on the sheet that should tell you all you need to know.
A gearbox is probably still an essential for smooth movement .
RS do some nice nylon kit ones to go with their sync motor timeswitches.

Ed

[Bookman]

If this was before the 1970s or perhaps sooner you would most probably be looking to use "selsyn" motors for such a requirement. I wonder if those more familiar with the armed forces on this forum would know where miniature selsyn's could be sourced as well as an invertor?

[Julesomega]

You might be interested in my old thread Small geared DC motor

[Jolly 7]

Originally Posted by McMurdo

Is the speed reference done by frequency variation, or pwm-ratio? Either way a little 555 or op-amp circuit should do it, but you need to know the spec of the control signal.

A brushless motor like this should hopefully have good torque control across the speed range, at least industrial-sized ones do, utilising the hall sensors around the windings.

From what I understand from the seller's page, the motor has four wires. There is a white wire that needs to be connected to a 1 to 50 kHz signal to control the speed. The yellow wire is for 'rotational speed output'. The other two wires are the positive and negative terminals.

[woodchips]

Do you want smooth movement, or is the jerky steps from a stepper acceptable?

What about a clockwork motor?

[elanman99]

Originally Posted by Jolly 7

Here's the high torque 12V BLDC motor I have in mind. It has four wires, one of which can be used to regulate the speed using a PWM signal. The motor does have some built-in circuitry.
I've been hoping to build a motorised platform for a pocket camera to allow slow-motion 360 degree panoramic recordings.

I'm sure that motor would be 'suitable', whether it suit your purpose depend on what the purpose is and how you implement it.


You mention compact camera and slow 360 degree recording. Is is recording video continuously whilst its rotating, or is it single still frames at set intervals?


There are not many motors that inherently rotate very slowly and I suspect close to 100% of slow turning tables (or whatever) will involve high ratio reduction gearing. A stepper motor might directly drive your rotating camera but it will do so in discrete small jumps rather than at a constant angular velocity, that would be fine for time lapse as long as you dont want resolution to fractions of a degree.


If using a DC motor then reduction gearing could be a basic as the (small diameter) motor spindle being kept in contact with the edge of a large diameter turntable so working as a friction drive, same job could be done with a belt drive just like gramophone turntables but most belts dont work well on very small pulley diameters.


Ian

[SiriusHardware]

You could also consider re-purposing an old pop-in microwave turntable (In the early days of microwaves not all microwave ovens had a revolving turntable, so you could buy optional clockwork (?) ones to put in). We had one.

Or, along similar lines, re-use a solar plant turner, intended for keeping houseplants on window sills evenly lit over the course of the day so they don't lean towards the light. These may be better for your purpose as they are more highly geared / turn more slowly.

[Jolly 7]

Originally Posted by woodchips

Do you want smooth movement, or is the jerky steps from a stepper acceptable?

What about a clockwork motor?

I would be aiming for smooth movement as I want to be able to take continuous high quality videos with the camera rotating. In relation to clockwork motors, I have never experimented with one but I think one of my old Panasonic radios uses one of these for its timed auto switch-off mode.

[Jolly 7]

Originally Posted by Julesomega

You might be interested in my old thread Small geared DC motor

Thanks Julian. I'll have a go with what I have and if it doesn't work out I may send you a PM in case you have any of your motors left.

[Jolly 7]

Originally Posted by elanman99

I'm sure that motor would be 'suitable', whether it suit your purpose depend on what the purpose is and how you implement it.


You mention compact camera and slow 360 degree recording. Is is recording video continuously whilst its rotating, or is it single still frames at set intervals.


If using a DC motor then reduction gearing could be a basic as the (small diameter) motor spindle being kept in contact with the edge of a large diameter turntable so working as a friction drive, same job could be done with a belt drive just like gramophone t


Ian

I want to record continuous video. Thanks Ian and everyone else for your replies.

Of a couple of VCR drumheads I've been experimenting with off and on, this particular one, shown mounted on a ply platform, stood apart as being the most suitable. Sadly I burnt its circuitry while trying to drive it, but then I thought could I repurpose it for something else ? After a previous project where I made a pulsed DC motor out of it, this is how it looks at present. My idea is to cut a circular platform out of plywood for the camera and screw it to the top of the motor. I have attached a gear to the shaft of the motor ( in the second picture) and hope to use another motor and gear to turn the VCR drumhead at a slow speed.

Trial and error will tell me if I do actually need to go for one of the more specialized motors. I chose the VCR drumhead because of its fluid motion and greater surface area that should be able to accommodate a camera platform securely.

[Argus25]

Be aware with any precision motor control, be it a head drum or other type:

There are two aspects to the controller or "servo".

There is the average speed of the drum, the feedback servo that controls this sets the frequency of the rotation (rpm) and mostly is designed to keep a stable speed with frictional forces applied. It is actually positive feedback in some cases.

One way it was done in early VCR's was to place a copper coil in series with the motor, to act as a current sensing resistor (with the same temperature coefficient as the wire in the motor) and filter that and feed it back into the + input of the amplifier controlling the motor. As the drag increases, the feedback applies more drive to the motor. If the feedback is too much though, it can oscillate, in that if drag is applied to the drum, it speeds up.

The other method was to use the frequency generator (FG) in a negative feedback loop to keep the average speed stable.

Then there is phase control of the position of the head, a fine adjustment of you like to position the head with respect to a sample pulse, so you know where the head is at any one time and can position it, say at the start of a track on the tape.

Using a head drum as a carrier for a camera could work, but you would need to both frequency and phase control it, if you want the rotational speed a constant value (irrespective of friction & drag) and you want to know where the camera is pointed at any stage of the 360 degree cycle.

[Terry_VK5TM]

I think you'll find he is only using the head drum as the mechanical mounting, having killed the electronics of it already.

[Electronpusher0]

The problem you are trying to solve is very similar to those who want to mount a camera to track the apparent motion of the stars for astrophotography to prevent start trails on long exposure images.
A popular solution is the "Barn Door" camera mount and there are loads of projects published on the net using stepper motors. These range from simple discrete circuits to arduino and raspberry Pi implimentations.
This is a link to an Arduino one
https://fstop138.berrange.com/2014/0...motor-control/
Just google "Barn door camera mount stepper motor schematic"

Peter