Need help designing a DC motor controller

[Thorn3]

Hello, I am a mechanical engineer. I am developing a special chair in my spare time. I have no electronics partners to help with the electronics. Can anyone help me to design what I would call a "master controller"? What I need to do, is create a simple controller, to control the speed and direction of 12VDC motors, numbering 14 in all. I am hoping, to be capable of switching any of the motors onto the output bridge individually. Example: Lower leg support UP/DOWN. If I push the UP button, the motor will turn say CW. If I push the DOWN button, the motor will turn CCW. Due to the various locations of the motors, some of the motors need to turn at different speeds than the others. I was thinking, that if a relay was actuated, it would pull the motor, and a resistor onto the controller. The resistor could be the R component of the RC circuit in the controllers oscillator. Maybe? Each motor, could be switched into and away from the one output bridge in this manner, keeping it simple and functional.
I have and use EagleCAD, as well as AutoCAD2000. I can draw PCB's, but cannot efficiently design circuits. Is there anyone who can help me? Max current on any of the motors would be 15amps. All motors are 12VDC.
TIA,
Thorn3

 

[Lewish]

It would be better to control the speed of the motor with PWM so that you don't lose your torque and so you don't have wall toaster size resistor for speed control. A nice microcontroller and power FETs, not relays is the way to go. More reliable, less noise.

 

[Thorn3]

Hello Lewish,

Thank you for responding so quickly. But, this is my problem: I do plan to use a PWM type controller. As the oscillator, I was planning either a 555 or a 4011. In regards to the oscillator RC circuit, I planned to use a group of resistors, not just one, and not a variable. These resistors are switched via a relay into or out of the RC circuit. The same relay, multi-pole, would also switch the appropriate motor onto the outputs of the H-bridge, before the oscillator begins, which would mean a slight delay would have to occure before the oscillator starts, after the relay is actuated. Maybe then a 556? One half to allow the delay after relay actuation, the other as the oscillator to drive the H-bridge.
My goal, is to be capable of driving 14 different motors, at different set speeds, one motor at a time, depending on the button pushed on the control panel. The goal is also to use only one H-bridge. I wish not to have to build 14 different motor controllers. That would be a bit much. But, if I could use just one controller, and switch the different motors in one at a time...this would simplify the system overall. So, to set the speed per motor, place a certain value resister into the RC of the oscillator, using the same multi-pole relay that the motor chosen to be driven is switched onto the outputs of the bridge.
The idea is good for me, because I cannot work with processors. I simply don't know how to program them, nor do I have the appropriate equipment. Also, although I can generate a flow of needed events, creating the circuit to make it happen efficiently is not my specialty. This is why I was hoping that someone could assist me by throwing me a circuit design, that I can then generate a PCB for, then etch and populate the board myself.
Again, thanks Lewish for answering so quickly. Hope this second note clarifies things a bit better as to the overall goal.

 

[nbucska]

Give full spec's <nbucska@pcperipherals.com>

 

[Thorn3]

Thanks nbucska,

I will assemble a complete list of spec's for you and send them out as soon as possible, more than likely this evening (AZ time)Thanks again!