Will these Motors/Potentiometers Work for Me?

The motors look OK, but the lower of the two pot values offered is 500K - which is way too high compared with the current requirement of the motors - they'd need about 500mA at no-load, rising to over 5A at stall (taking the data for the nearest similar motor I could find on the Johnson website).

I think you'd be better going for a single motor & a split supply, with a control setup configured to reverse it. Also, if there's any chance of stalling the motor, you'd need very high power pots to take the current without burning out. Have you considered a DC speed controller?

Sorry I'm waffling a bit, but I really don't see your arrangement working as drawn.

What's the difference between a pot and a dc speed controller?

Also what does it mean to stall the motors?

A pot is just a variable resistor. A speed controller has some active electronics to control the motor voltage and current. Here's an example. Ready-made ones tend to be a bit pricey (especially reversible ones), but you may find something affordable at a hobby store (as used for controlling model cars etc). Try a google search for "model speed controller". If you're feeling brave, you could build your own - there are plenty of circuit designs around.

A stalled motor is one that's trying to drive - but is mechanically prevented due to too much load/drive system jammed/end of travel etc. The current a DC motor uses for a given voltage goes up as the load increases, typically a stalled motor will be drawing over 10 times the no-load current.

Good luck,

John

Thanks John, for the definitions.

The only object that this system would rotate would be a small digital video camera--slowly and precisely at variable rates. I would be torquing it down with pulleys or gears a great deal because the motors run apparently around 5000 rpm. Because of this I don't think stalling is anything to consider. Seeing now that it is such a light duty job, do you still think a pot is insufficient? If you think a pot would do, what sort of specs should I look for to go with this motor?

If you want precise control, I'd suggest a PWM (pulse width modulation) motor control. You can make your own from a 555 timer with some supporting pieces you can get at Radio Shack. There are loads of plans available on the internet.

Typically, a relatively expensive pot is required to control a motor directly, and even then the control is imprecise: getting both low speed and high torque is difficult. Not impossible, but more difficult than with a motor controller. Only one motor should be necessary, and a single pot could be rigged to give zero speed at mid revolution and forward and reverse on either side of mid.

I wonder if some of the home-style video surveillance systems (available at Office Depot etc) might have an available camera position controller off-the-shelf.

This guy doesn't know the difference between a pot and a motor drive. Don't suggest to make his own drive. It's way above him.

The only way he will get something like this operating is by teaming up with an electronic technician or engineer or spen the next few years burning components until he knows enough to succeed.

You may be right re his skill level, although if he has some manual dexterity and a good set of plans...

A couple ready made alternatives:

http://www.bhphotovideo.com/c/product/502557-REG/Vidpro_EBRA_121R_EBRA_121R_Automatic_Motorized_Pan.html

http://www.adorama.com/VDMPH.html

This one seems identical to the adorama, but specifies pan and tilt (I assume the adorama just left tilt out of the ad):

http://www.huntsphotoandvideo.com/detail_page.cfm?productid=MP101&adid=GoogleSitemap

You'll probably get away with something like this:

To get a decent controllable current into the motor over the range of the pot (say the motor's going to need 1A @ 12V with your load), you'll need a pot of about 50Ω (47Ω - often written 47R - is a 'preferred value').

The power dissipated by the 47R pot with 24V across it is given by

V²/R = 24 x 24 / 47 ≈ 12.5 W.

That's with the pot balanced (no current through the motor). As you move the wiper towards either end, more current starts to go through one arm or other of the pot winding, so you'll have the 12.5 W plus the power due to the motor current. With the wiper half way between the centre and one end (motor at about half speed), that'll mean adding about 6²/12 = 3W.

[BTW - when pots get up to this sort of power, they're generally called rheostats].

As Blink said in #7, such a pot is not cheap. I found this 47R 25W rheostat on the RS site for about £25, but you may find a cheapo somewhere on the web.

Remember your power supply will need to be able to give at least 1.5A on both the +12V and -12V outputs.

Have you looked at using stepper or servo motor? one motor would be all you need with the right controller.

Search the web for motors/controllers......

Depending on the load you are wanting to move, some of these might work.

I would opt for a twin pot ( same common axle but with two resistive elements ) then you could mount the joystick directly to it without the need for extra guff! Then I would connect them to the electronic motor control suggested by johnjohn!

Using two motors and two pots like that introduces the certainty of either a "dead spot" or a "spot" where both motors are driving in contention. If the dead spot is acceptable, then, as others have said you still need to introduce some other means of amplification.