Fine movement of 12v motor on pan/tilt head

[rcarbaugh1]

Hi all:
I'm a mostly wood DIY-er and audio engineer, but have not used a soldering iron for much more than audio connectors over the years. I have attached a rudimentary drawing of a circuit.

We bought a pair of motorized pan and tilt heads for remote control of cameras for live streaming. They have a small joystick that sends + and - 0 to 12vdc on two pair cable for the two bi-directional variable speed 12v motors. They work great on wide shots, but are difficult to adjust on tight shots as the joystick is too coarse. Project idea is to compliment the 12v main feeds with a low voltage fine adjustment circuit.

I'm trying to brainstorm a way to send low voltages (.01v to 1v) to the motors as a fine adjustment. Thinking of the design (attached) with two AA batts in series with one motor side connected between the batteries and the other on a wiper of a center-tapped pot. That gets positive and negative to the motor, with a center "off." Aside from wondering what value the pot should be, my biggest concern is that the batteries would always be looking at the resistance of their half of the pot, and would constantly leak current. Getting very controlled low voltage to the motor would be solved, until the batteries drained. A switch to open the circuit could work, of course, but the batteries would still drain significantly when it was activated (standby?), even if the wiper never left the center tap.



Any ideas would be fabulous.

rcarbaugh

 

[Nanren888]

A few different things to check on this one.
So it's just a motor? That is the joystick is velocity, not position? That presumably makes it tricky to accurately position.
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Servos could be an option. Ones that include internal feedback, so they really only need a control signal to tell them not to move, but where to position to.
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As you mention, the load on the battery is a problem. If the resistance of the joystick is low enough to provide enough current to the motor, then it's going to also drain large current form the battery.
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An active stage, using semiconductors, an amplifier, &c would normally be the solution. High resistance joystick, so low current through it, but amplified signal to the motor. Maybe google "H-bridge" or similar to see other ways to do it.
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Should be able to find units available to do this sort of pan, tilt,if you hunt round.

 

[rcarbaugh1]

Thank you for your insights, Nanren888. This device is designed and built and is commercially available. I am withholding the actual name, although I'm sure it would be okay. I purchased a pair of them from a large photo/video store in NYC. It is designed for sweeping camera boom shots like a jib over an audience (generally on a wide lens), so I am using it a little "off label," if you will.

The existing joystick box has a circuit board in it with a few chips. I have no idea what is going on inside, but the output to the motors seems to be ±0-9.75vdc. Your description is accurate, the existing joystick system is supplying varied velocity, not position. With moving talent on stage, there is no need for repeatable positioning, just fine tuning the tight shot of a person at a podium. Accurate position is the whim of the operator. What I am trying to create is an add-on to the existing joystick system, even with four pots need be, to tweak the shot by one degree of rotation or less. The pots would have to send out zero voltage when the operator is satisfied with the position, so they would either manually or by a spring (think zoom toggle on camcorder) return to center/off.

It may be a fool's errand, but I'm determined to make it work somehow.
rcarbaugh

 

[Bluejets]

Most quality units would use stepper motors so you may be limited if that is the case to the min step of the motor or the driver.
Details of the units may reveal more.

 

[davenn]

there is no need for repeatable positioning, just fine tuning the tight shot of a person at a podium. Accurate position is the whim of the operator. What I am trying to create is an add-on to the existing joystick system, even with four pots need be, to tweak the shot by one degree of rotation or less. The pots would have to send out zero voltage when the operator is satisfied with the position, so they would either manually or by a spring (think zoom toggle on camcorder) return to center/off.

almost impossible to do with any ease

as @Bluejets said, they will most likely be stepper motors which are easy to use for fine positioning adjustments

 

[Harald Kapp]

The joystick typically will not operate the motors directly due to the power required which will burn the pots as others have mentioned. Instead the pots will be used to control the motors via the electronics on the circuit board. I'd expect some kind of motor drivers there.
What you can do - if you can do anything at all using the existing circuit(s) - depends on how the potentiometer position is evaluated by the circuit. We would need to have a schematic of the circuit or at least how the potentiometers are connected to the circuit.

I am withholding the actual name,

As long as you are not violating any laws or infringing on somebody's rights it is o.k. to post brand names and even model numbers on this forum. Knowing what we are dealing with greatly speds up our understanding of the problem.
It may be possible to use the existing pot for coarse adjustment and an additional pot for fine adjustment as shown e.g. on this site or this site.

 

[rcarbaugh1]

Hi all:
Thanks for the input to this issue so far. The unit is a TigerTilt by ProAm USA, purchased from B&H Photo. The mfr. has been kind and responsive, but I don’t expect him to hand over the schematics of his proprietary device. I have asked him what motors he is using and what the gear pitch is, but he has not answered as yet. The device is rated for an 8.5 lb camera. He did send me the dimensions of the motor’s gear. See pics below.

There are several chips in the joystick box, so presumably there is a motor controller between the 12v supply and the joystick. Unmodified, the joystick sends up to ±10v down the four lines to the motors. He sent me a modified joystick box with a button which cuts the max voltage down to ±3v. That mod makes the joystick range easier for smooth pans on a wide lens. However, I tested it and the motor does not move at all until the voltage passes 1v (measured at the joystick, which is 70’ from the motor on Cat6 cable doubled up —two conductors per line for max current xfer). When it moves, even the lowest speed is too fast to make the minute adjustments smoothly.

So, I’m thinking about a crash course in Arduino and replacing the motors with a stepper motor that can do really low rpm (gearbox?) but still have a range that can move the final gear to the rated 8.5 rpm. I’d like to program the speed on a parabolic curve so the low speed area is tapered for more control.

Right now, there are two visible gears, the motor one around 1/2” and the one attached to the camera platform is about 3”. I don’t have ready access to the unit. I’m figuring the gear ratio is about 8:1. The top rated speed of the camera movement (8.5 rpm) puts the motor gear around 65 rpm.

Next step for me is to identify the type of motor that is on the unit, so I can assess what I need for a replacement.

Question: If I do set up a new motor (probably stepper) with a new joystick, controller, etc., how far can that joystick be from the motor? The remote controls now are on 70’ of cable. Is that possible with an Arduino and stepper motors?

Sorry for the length of this reply, but I’m such a newbie to the microcontroller possibilities.

Here are some pics:


Thank you.
rcarbaugh

 

[rcarbaugh1]

Thank you for your responses. All helpful. The beauty of a forum like this is the depth of its members, and their willingness to offer solutions. If you have not surmised, I am a complete noobie to the Arduino type of control, working with a somewhat flawed but fully functional commercial pan/tilt device. I am not unrealistic about physics, however. On a zoomed-in lens, I need to be able to do very controlled minute adjustments of less than 1°. The motor starts abruptly at 1.04v, and that starting speed is too fast to make smooth adjustments to re-frame or follow a moving subject.

At this point, I am searching for options. In my setup now, the supplied joystick box and 12v power supply are 70’ from the device and its motors. While there are some chips in the joystick box, as far as I can tell from the mfr the cables to the motor are straight DC, ±10v. I just got the motors’ specs:

• Voltage 12VDC
• No Load Current 0.32 A max
• No Load Speed 65 rpm
• Rated Current 0.8 A max
• Rated Speed 52 rpm
• Rated Torque 0.3 Nm (0.22 lbs/ft)
• Rated Input 9 W
• Rated Output 4.5 W

Apparently, if I change those motors to steppers the power supply and motor controller (at least) need to be near the motors. It is unclear to me if that means there is any possibility of the joystick being 75’ away, or if the joystick, Arduino, motor controller, power supply all need to be together and within a few feet of the motors.

Is there any reasonably inexpensive scenario where the joystick can be at a distance from the motors? If that answer is a hard “no,” then I will probably have to “punt” this whole programming exercise and try to solve the issue with a different kind of DC motor that starts at a slower speed.

Radio control? Perhaps an RC car controller could be set up. We are in NYC, which is a RF jungle, but who knows?

Suggestions anyone?

Thank you
rcarbaugh

 

[rcarbaugh1]

Here’s a thought: If the Arduino-Motor Control-Power Supply have to be near the stepper motor, can I use the existing remote joystick ±10v (optional ±3.5v) to a pin on the Arduino? Can the Arduino be programmed to read variable voltage?

Thanks.
rcarbaugh

 

[Alec_t]

I have no idea what is going on inside, but the output to the motors seems to be ±0-9.75vdc.

That suggests the supply to the motor is PWM (Pulse Width Modulated), with reversible polarity, to provide speed control.

 

[bertus]

Hello,

Some time ago quasar made a bidirectional PWM speed control.
See that attached PDF's for more info.

Bertus

 

[Bluejets]

Can the Arduino be programmed to read variable voltage?

Not negative going, no.

 

[Alec_t]

What I am trying to create is an add-on to the existing joystick system

That may pose a problem if the existing controller does indeed use PWM for speed control. Depending on the controller's characteristics, conflict can arise between any PWM add-on and the controller's own PWM. Do you have a 'scope to check if PWM is currently being used?

 

[rcarbaugh1]

Re: detecting PWM, I don’t have a scope. The mfr told me that he farmed out the joystick electronics programming, but he would probably know whether it was. Asking now.