Pan/Tilt Head need help designing circuit

[DirtyLude]

How heavy is this? A lot of these are going brushless now.

If you search for brushless gimbal, there are tons of brushless gimbles that can be turned into pan tilt. Cheap controllers on e-bay based on SinpleBGC. Basecam has a guide to making a wireless control. It's definitely not analog, though and the DIY cheap stuff is for smaller rigs, DSLR at the largest. It gets expensive when you get bigger.

 

[Donny_97]

I do not know if the positional feedback is necessary, but the professional pan and tilt heads don't have it, if I'm correct.

A joystick linked to a speed and ramp control, then to the motors would be enough I think, since you will be controlling it just loosely while eyeballing the position via a monitor, and minimal movement of the motors won't be a problem, it will be steady enough I think.

How heavy is this? A lot of these are going brushless now.

If you search for brushless gimbal, there are tons of brushless gimbles that can be turned into pan tilt. Cheap controllers on e-bay based on SinpleBGC. Basecam has a guide to making a wireless control. It's definitely not analog, though and the DIY cheap stuff is for smaller rigs, DSLR at the largest. It gets expensive when you get bigger.

Thank you for your reply, it will be around 2-4 kg's.. But the material I have around here is strong enough to hold the gear I will be using.. And I will be using a Nikon DSLR with a fairly small lens on it, but a Sony HVR-1000E as well, which is a bit bigger..

It needs to be "simple" and working, so I am all in for the dirty way of doing things... (if you know what I mean..... :/ )

I will use ballbearings for both axis, so if I put the camera on, perfectly balanced, the motor doesn't have to handle a lot of weight, right?

 

[Donny_97]

Also, those gimbals are pretty high on the price...

And my main question now is: if I go analog, with 12 volt DC motors (I might get some steppers), how do I control them with a joystick, speed control knob and ramp knob? And what should be the circuit for one? (I am willing to buy a motor driver to spare myself building one..)

 

[alec_t]

Will you be recording sound along with the images? I ask because motor/gearing noise would have to be considered if you were and might dictate motor type.
I've been roughing out an analogue circuit design for PWM control of DC motors using a 2-axis resistive joystick . Do you have any particular joystick in mind? If so, what value potentiometers does it use? Or does it have some other position transducers?

 

[Donny_97]

Will you be recording sound along with the images? I ask because motor/gearing noise would have to be considered if you were and might dictate motor type.
I've been roughing out an analogue circuit design for PWM control of DC motors using a 2-axis resistive joystick . Do you have any particular joystick in mind? If so, what value potentiometers does it use? Or does it have some other position transducers?

The sound might be recorded on the camera sometimes, most of the time with an external boom mic. But minimal sound is always great.

And I do not have a specific joystick in mind! So I'm open for all suggestions!

 

[large_ghostman]

The sound might be recorded on the camera sometimes, most of the time with an external boom mic. But minimal sound is always great.

And I do not have a specific joystick in mind! So I'm open for all suggestions!

Which country are you in? and which Nikon camera are you using? I ask about the camera as i have use of the D7000 and D810. if your using the D800 or D810 I know from experience that the sound from a stepper motor is picked up easily with the on camera Mic. I have given up trying to get video to work on the D810 and will try using the D7000, I am new to the video side but joysticks if your in the UK I might be able to help you with

 

[alec_t]

A microcontroller-based system might be simplest (at least in terms of hardware), but here's a conceptual panning solution doing things the analogue way :-

You would need to duplicate that circuit for the tilt control.
As you can see, it ain't trivial .
Here's how the PWM-controlled motor current (and hence speed) would vary as the joystick pot is moved from its neutral (spring-centred) position to either extreme:-

Circuit explanation:
I have assumed the PanPot is a 10kΩ one with a wiper which can move over a range of 0.4 to 0.6 of the pot value.
U1 is a hex CMOS inverter IC, U2 is a quad opamp IC. The simulated motor has a 3Ω coil resistance and 4mH inductance (your mileage will vary).
U2a gives an output which varies in proportion to the PanPot wiper displacement from the central position. U2b amplifies this output.
U1c/U1d/R4/R7 form a Schmitt trigger which, with R8 and C3, makes an oscillator of ~1kHz. The pulse width of the oscillations is controlled by a voltage obtained by weighting the output d of U2b, using Trim1 a Trim2 as summing resistors, to give a PWM output f.
U2c is configured as a classic square-wave oscillator and drives a voltage doubler to give a ~24V output h.
U1a, U1b, with a small amount of positive feedback via R1, provide complementary direction signals b and c according to which side of centre the Panpot wiper is displaced. These signals switch level-shifters Q1, Q2 which are high-side drivers for N-FETs M1, M3 of an H-bridge M1-M4. The direction signals also enable/disable (via diodes D5 andD6) the PWM signal f which drives the low-side N-FETs M2, M4 via buffers U1e, U1f. Although these CMOS buffers can provide only limited current they should be able to cope, in view of the low PWM frequency and consequent very low duty cycle; but if in doubt they could be replaced by push-pull BJT buffers.
Here's the asc file if anyone wants to play:

 

[Donny_97]

A microcontroller-based system might be simplest (at least in terms of hardware), but here's a conceptual panning solution doing things the analogue way :-
View attachment 99260
You would need to duplicate that circuit for the tilt control.
As you can see, it ain't trivial .
Here's how the PWM-controlled motor current (and hence speed) would vary as the joystick pot is moved from its neutral (spring-centred) position to either extreme:-
View attachment 99261
Circuit explanation:
I have assumed the PanPot is a 10kΩ one with a wiper which can move over a range of 0.4 to 0.6 of the pot value.
U1 is a hex CMOS inverter IC, U2 is a quad opamp IC. The simulated motor has a 3Ω coil resistance and 4mH inductance (your mileage will vary).
U2a gives an output which varies in proportion to the PanPot wiper displacement from the central position. U2b amplifies this output.
U1c/U1d/R4/R7 form a Schmitt trigger which, with R8 and C3, makes an oscillator of ~1kHz. The pulse width of the oscillations is controlled by a voltage obtained by weighting the output d of U2b, using Trim1 a Trim2 as summing resistors, to give a PWM output f.
U2c is configured as a classic square-wave oscillator and drives a voltage doubler to give a ~24V output h.
U1a, U1b, with a small amount of positive feedback via R1, provide complementary direction signals b and c according to which side of centre the Panpot wiper is displaced. These signals switch level-shifters Q1, Q2 which are high-side drivers for N-FETs M1, M3 of an H-bridge M1-M4. The direction signals also enable/disable (via diodes D5 andD6) the PWM signal f which drives the low-side N-FETs M2, M4 via buffers U1e, U1f. Although these CMOS buffers can provide only limited current they should be able to cope, in view of the low PWM frequency and consequent very low duty cycle; but if in doubt they could be replaced by push-pull BJT buffers.
Here's the asc file if anyone wants to play:

Thank you so much for this design alec_t! This is really helpful! If I can find somebody who can put this together for me in the Netherlands, it'd be amazing.
Could the micro controller way be a little simpler than this you think? I am very curious.

 

[alec_t]

Could the micro controller way be a little simpler than this you think?

Definitely, circuit-wise. How are your programming skills?

 

[Donny_97]

Definitely, circuit-wise. How are your programming skills?

My programming skills are decent, if you are talking about Arduino, it won't be a problem, I can learn the language. (not to sound like I am the best, because I am not.)

 

[alec_t]

An Arduino should certainly be able to do the job. You'd need to sense the joystick position with an analogue input pin and convert position to a PWM signal and direction signal on two digital output pins. As for the programming, that's not my forte, but I understand there's plenty of PWM code floating around the web.

 

[Donny_97]

An Arduino should certainly be able to do the job. You'd need to sense the joystick position with an analogue input pin and convert position to a PWM signal and direction signal on two digital output pins. As for the programming, that's not my forte, but I understand there's plenty of PWM code floating around the web.

Thank you so much! That I could figure out myself - I assume.
Do you maybe have any specific motors in mind for this use? Or a specific joystick, because I had this one in mind: **broken link removed** , and the further you push the stick, the faster it goes. That would be the ideal situation.

And do you think one L289n motor driver would be enough? I am thinking about 12 volt DC motors, maybe 100 or 300 RPM, I should also figure out the gear ratio. Should I maybe contact the guys over at servocity for those questions?

 

[alec_t]

The joystick looks good. The linked site also has some geared motors which may do the job if they have enough torque and speed.
Did you mean L298n? I'm not seeing much of relevance for L289n.

 

[tomizett]

At the risk of throwing more possibilities into the mix, you could go half-way and drive a stepper-motor control module from a voltage-controlled oscillator. The joystick would control the speed of the oscillator, which would in turn move the motor one (micro)step on each cycle.
This would be simpler (in terms of number of parts used) than building a controller from scratch, although probably not as simple as using a microcontroller.

I've also been trying to design a minimal closed-loop speed controller for DC motors. I think it will probably turn out more complex then you would be interested in building, but I'll publish the results here if it works out.