Motor Speed Controller for 12v Brushed DC Motor (not PM) with speed regulation

I'm just messing with an old motor. It's series wound. Would it be easier, especially to get speed regulation, if I seperatedly energised the field windings?

-- Sue

Yes, that's good. I'm finding it hard though to find anything with speed regulation or a circuit diagram incoproaring that. That seems to be most difficult.

Well, yes, a closed loop controller will (generally) be more "difficult" than an open-loop one.

The circuit in the reference provided is fairly easy to modify to allow for proportional control. The demanded speed is available as an analogue voltage. It should be fairly easy to produce an analogue voltage dependent on actual speed. Using the difference as the input to the PWM waveform generator will give you proportional control.

You can then complicate things, say to reduce overshoot, as needed. Half a dozen op amps, in total, should do it nicely.

However, you really need to have a very good reason for going for an analogue electronics solution, for a problem that lends itself so well to a digital one. I don't know what you have against micro controllers..

-- Sue

>>

I'm on a learning curve here, because I'm not an electronic engineer.

I've learned (AN905) that you cannot achieve precise speed control with series wound brushed DC motors. This is the type of motor that I have.

I believe that I'd have to seperately excite the field windings of my motor to make the motor somewhat equivalent to a PM DC motor.

I don't have anything against micro controllers. I was thinking things might be unecessarily complex if I used one. But, as I say, I'm not an electronic engineer.

One of the advantages of a microcontroller solution is that you can design-in much more complex control algorithms than is practical using analogue electronics. For the experimental, non electronics engineer, digital has many advantages - not least being the ease with which you can change timing constants or even the entire control system without touching the hardware at all.

Speed control is a *control engineering* problem - not an electronics one. The solutions tend to involve lots and lots of mathematics. Which computers, eg microcontrollers, are good at.

-- Sue

** That controller is for permanent magnet motors.

..... Phil

>

It will probably "do the job" for his motor, once the connection changes needed to allow it to be made bi-directional have been done and the field winding has been adequately catered for. The OP is experimenting with speed control, not trying to meet a particular detailed specification (IIUC).

What the brush gear will make of operating in the reverse direction to that for which it was designed is also a factor - but again, the OP is only experimenting.

-- Sue

Remove motor. Remove throttle actuator hand grip device. Remove Power Switch. Remove charging connector. Remove battery pack. Remove motor controller. Remove drive train segments.

Installation:

Adapt and install drive train segments. Adapt and attach motor securely. Mount motor controller. Mount battery pack. Mount Charging connector. Mount Power Switch. Attach throttle actuator hand grip device.

Drive away. 12 mile range... more if you assist. Convert a bike.

Okay, but is it not the case that I'd have to change speed using commands from my PC?

But can I use a micro controller that stands alone, where I can set speed with a potentiometer?

Not necessarily, see below.

In the example that you chose above, an MCP6526 is used to convert the motor current and motor speed analogue inputs and present them to the PIC. The MCP6526 has 4 unused analogue inputs - one of which could connected to the wiper of your speed setting potentiometer.

Alternatively, many PICs have built-in A/D converters, so don't need a device like the MCP6526 at all.

But, why use a pot? They make sense when used with analogue electronics, of course. But, with a digital system, you can use BCD switches, "up/down" buttons + a digital display, etc..

-- Sue

I agree.

There are at least 3 options:

1 Analogue using pot or "up/down" buttons.

2 Digital, control only thru PC.

3 Digital using pot or "up/down" buttons.

Either 1 or 3 would do. Perhaps 3 would be the choice of most.

Actually having a rpm readout would be fantastic. Yes, I'd like that.

But, I've not yet found a kit or a diagram to realise say option 1 or 3. Kits about but hard to find ones with speed regulation. And how many offer rpm readout.

What I'd like ought to be piece of cake with all these sophisticated IC's, but I am out of my depth unless I find a kit or a product.

I percieve that perhaps were in the realm of speed conntroller kit modification.

Tachometer can be a seperate project. No need to be part of the speed controller.

If I did not want speed regulation, it's just a matter of sourcing a kit. But it seems to me that once speed regulation is required there just ain't any kits about. But, perhaps some kits are capable of mofification to cater for speed regulation. But as a techical ecercise that's beyond me.

So, I look for speed controller circuits that incorporate speed regulation. But I don't want to control speed from my PC.

My enquiry is perhaps more suited to a model makers or a robotics person. It needs someome who actually has hands on experience or is is familiar with making speed controllers. Someone with the hardware in posession.

Thanks for the help anyway. Rich