manual control of a victor?

[Al Skierkiewicz]

Originally Posted by Adam Y.

Does it affect anything that the motor is an analog device and needs an analog signal (PWM)?? It's pulse position modulation for the incoming signal not pulse width modulation. Pulse width modulation is the signal that controsl the motor.

Adam,
That's kind of the beautiful things about this control. It is a digital signal, running from +12 to ground, that is converted to an average mechanical power with no real active circuitry. The motor does all the conversion with a little help from physics (conservation of momentum) and a little from electrical (inductance) etc.
The control signal and the output of the controller are both PWM. Pulse position signal uses the same size pulse but varies it's position in relation to a reference. In PWM the pulse width varies over the time of a single cycle but the cycle length doesn't vary. That makes it sort of self clocking in that for the most part there is a start and end to the pulse cycle. (about 2 kHz) The output PWM is not an amplified version of the input. The input pulse width varies over 255 steps where the value (width) of 127 represents no motor current at all. A "0" will make the output turn on to full 12 volts (no PWM) and a 255 will do the same but reverse the leads (+12 becomes common and common becomes +12 to the motor) which reverses the direction of the motor.

[DonRotolo]

Originally Posted by Rickertsen2

The control signal is very simple. All you need to do is supply it with the necessary voltage on the power lines and a 1-2 ms pulse periodically on the signal line. 1ms corresponds to full rev while 1.5ms is neutral and 2 is full forward.

That is correct for an R/C servo, but incorrect for a Victor or similar PWM motor control.

For a PWM motor control, the duty cycle of the signal varies from 0% to 100%, corresponding to full reverse and full forward, respectively, with 50% being neutral.

[EDIT:] I stand corrected, the Victor uses standard R/C type PWM control, which operates as described in the quote above. The circuit I have won't work here, but there was a circuit in SERVO (or maybe Nuts & Volts?) earlier this year that had such a circuit using a 556. When I find that I will post a reference to it. [/EDIT:]

I have a circuit somewhere that does exactly what he wants, uses a single 555 and a few passive components, and varies from about 3% ro 97% duty cycle. I'll post it when I find it.

Don

[sciguy125]

Originally Posted by Don Rotolo

That is correct for an R/C servo, but incorrect for a Victor or similar PWM motor control.

For a PWM motor control, the duty cycle of the signal varies from 0% to 100%, corresponding to full reverse and full forward, respectively, with 50% being neutral.

You're thinking of the output of said motor controller. The original poster was looking for a device to connect to the Victor input. This uses the same signal as R/C servos.

However, I recently finished a PIC based motor controller (for true motor control PWM). If anyone wants it, I'll send them the code. As for hardware, you just need a 12F683 (or similar) and the appropriate "glue" components to connect it to an h-bridge. I've got code to read a pot and the R/C PWM signal.

[DonRotolo]

Originally Posted by neilcooper

I was wondering if it would be possible to make a circuit that would control a victor with a pot from full reverse to full forward? If possible using a 555 timer?

As promised, here is the circuit that produces variable width pulses (1 to 2 uSec) at about 60 Hz. This is fairly simple to build, components are not very critical, Radio Shack sells all of the parts. All of the resistors are 1/4 watt 10% or 5% tolerance, the capacitors 1 uF and above are electrolytic or tantalum, the small caps are ceramic monolithic (ar whatever is on hand).

I have included a way of converting some higher voltage (e.g. 12 volts) down to 5 volts using a 7805 regulator, along with the pinout of the Victor PWM signal inputs. Remember, black is ground and white (or yellow) is the PWM signal.

This will drive a Victor or any R/C servo from nearly full reverse to full forward, depending on the setting of the 1 k Ohm potentiometer. Note that there are some PWM motor controllers that do NOT use R/C type PWM inputs; this will not work with those.

Have fun

Don