Speed adjustment on a 12 volt motor

[sloz1664]

I have fitted a 12 volt motor to control my observatory dome and have connected a motor controller to govern the speed. Although the motor controller works when connected direct to the motor it will not govern the speed when installed within the circuit.

Power input 12v DC into the controller and the controller output going to J1-1 & J1-2. The A?C input can be ignored.

 

Steve

[wxsatuser]

Does the motor run at all in the circuit?

[sloz1664]

Yes the moter runs in both directions. The circuit works but I cannot control the motor speed.

[symmetal]

The circuitry below the motor is fed with 12V via D13 so needs to be a fixed 12V. If you feed the controller output to J1-1 the relays and opto sensors will get a varying 12V, or chopped 12V if PWM controlled. The relay coils  in particular wouldn't like power switching on and off at the PWM frequency and whatever's in p8055 probably wouldn't either.

You need to intercept the 12V going to the motor only (where the power lines enter the blue box) and put the controller there.

[wimvb]

+1 for @symmetal's reply. If the speed controller also has direction control, the direction switches aren't needed anymore, and could cause trouble in case you use the controller's direction settings.

As a sidenote: the azimuth sensor is connected to 12 V, so is inoperational in your current setup.

[symmetal]

1 hour ago, wimvb said:

As a sidenote: the azimuth sensor is connected to 12 V, so is inoperational in your current setup.

If the motor controller is a PWM one the azimuth sensors will give an output pulse at PWM frequency so p8055 will think the dome is pretending to be a helicopter. 

[sloz1664]

9 hours ago, symmetal said:

The circuitry below the motor is fed with 12V via D13 so needs to be a fixed 12V. If you feed the controller output to J1-1 the relays and opto sensors will get a varying 12V, or chopped 12V if PWM controlled. The relay coils  in particular wouldn't like power switching on and off at the PWM frequency and whatever's in p8055 probably wouldn't either.

You need to intercept the 12V going to the motor only (where the power lines enter the blue box) and put the controller there.

Yes I can see the logic of normal 12v supply to the circuitry. But if I add the motor controller into the circuit where you have mentioned, would that cause an issue with the motor controller + / - input , as the feed from the solenoid can be reversed. To reverse the motor direction

Steve

[sloz1664]

2 hours ago, wimvb said:

+1 for @symmetal's reply. If the speed controller also has direction control, the direction switches aren't needed anymore, and could cause trouble in case you use the controller's direction settings.

As a sidenote: the azimuth sensor is connected to 12 V, so is inoperational in your current setup.

I am using a Bourns Rotary optical encoder , on top of the drive gear, which runs on 5v fed from the Velleman board and restricted to 25 milliamps. The controller has no directional switches.

Steve

[symmetal]

If you insert the speed controller at the point where the red power lines enter the blue box, the + and - 12V are fixed and won't be affected by motor direction as the relay switching occurs after that point. As wimvb said if your controller also has direction change option this could complicate things, but if you set the controller so it only drives the motor in one direction and let the relay switching in the circuit control the actual motor direction it should be ok. I assume you just want the motor to run at a slower speed than it currently is  and that everything else stays the same. 

Edit, just saw your reply to wimvb so no problem with direction on your controller.

[sloz1664]

3 hours ago, symmetal said:

If you insert the speed controller at the point where the red power lines enter the blue box, the + and - 12V are fixed and won't be affected by motor direction as the relay switching occurs after that point. As wimvb said if your controller also has direction change option this could complicate things, but if you set the controller so it only drives the motor in one direction and let the relay switching in the circuit control the actual motor direction it should be ok. I assume you just want the motor to run at a slower speed than it currently is  and that everything else stays the same. 

Edit, just saw your reply to wimvb so no problem with direction on your controller.

Connected as described. Motor moves in both directions but no speed control.

Connect both the circuit & motor controller power to 12v supply.

 

Would the following work:_

If I connected controller output wires as shown as the red & black wires. Would that work?

 

Steve

[Dr_Ju_ju]

No, just applying power will make the motor turn in one direction or the other...   

To vary the rate of movement would require some form of voltage and or current control. This could be done with a PWM (pulse width modulated) circuit, which sends a fast on\off voltage to the motor to make it turn at various speeds, but this relies on the motor being capable of driven this way.

It may be better to use a stepper motor, which can then be driven via a pololu drive chip for both direction & speed (think 3D printing)

 

[symmetal]

The drawing 

3 hours ago, sloz1664 said:

If that's just a relay base shown, then as Julian says it would just drive the motor in one direction or the other depending if the relay is energised or not. How does the output signal of your Bourns optical encoder get used in your arrangement. The encoder will output pulses the frequency of which vary with motor speed, and possibly another output will indicate motor direction, or a second stream of pulses at 90 deg phase shift to the first set  which can be used to determine the motor's direction. These signals would be processed by your controller as part of a feedback loop. What type of output does the speed controller have to alter the motors speed? Can you give a picture or diagram of the speed controller you're using. Do you want a motor that runs at a constant known speed independent of the load rather than a variable speed motor?

[sloz1664]

33 minutes ago, symmetal said:

The drawing 

If that's just a relay base shown, then as Julian says it would just drive the motor in one direction or the other depending if the relay is energised or not. How does the output signal of your Bourns optical encoder get used in your arrangement. The encoder will output pulses the frequency of which vary with motor speed, and possibly another output will indicate motor direction, or a second stream of pulses at 90 deg phase shift to the first set  which can be used to determine the motor's direction. These signals would be processed by your controller as part of a feedback loop. What type of output does the speed controller have to alter the motors speed? Can you give a picture or diagram of the speed controller you're using. Do you want a motor that runs at a constant known speed independent of the load rather than a variable speed motor?

OK, I have a 12v windscreen wiper motor to drive the Dome rotation. The motor has enough grunt to turn the Dome with ease. The downside is it completes one revolution in 40 seconds. I need to slow the motor down so it completes a revolution in around 60 seconds. The software/hardware controls the rotation clockwise & anti-clockwise. The Bourns encoder counts the revolutions of the drive wheel so software knows where it is on the 360 degree circumference. There is also a "home position" controlled by a magnetic latch should you heed to reset.

All of the software/hardware works and the Dome rotates fine, but travelling at 9.5 metres a minute and a start that Usain Bolt would envious of. I would like to try to slow it down.

The controller is PWM DC Motor Speed Controller.

Steve

[saac]

Steve, I appreciate that you are probably looking for an electrical solution first but if that is not possible with the particular controller what about using gearing to step down the rotation speed.

 

Jim

[symmetal]

Ah! right Steve, that's clearer now. You said earlier it works when you connect the motor directly to the pwm controller output. In your relay picture I assume the relay is relay K2 in your original diagram.

8 hours ago, sloz1664 said:

In that case if the output of your speed controller is used as the 12V & Ground as you suggested then it should work although you won't have the on/off switching of relay K1. When you inserted the controller where the red wires enter the blue box and it didn't work, I assume you cut the wires from j1-1 and j1-2 where they enter the blue box  and replaced them with the controller output. In that case the motor should be totally isolated from the original circuit and work as you want. Perhaps the dome isn't wired exactly as the circuit and there is still a fixed 12V getting to the motor which would override your controller output. Measure the voltage of your controller output when it's wired in the circuit and see if the 12V varies at all when you adjust it. If it doesn't then there must be a separate 12V getting to your motor circuit somehow. Disconnecting the 12V going to J1-1 & J1-2, does the motor speed vary correctly when you adjust your controller.

[Gina]

11 hours ago, saac said:

Steve, I appreciate that you are probably looking for an electrical solution first but if that is not possible with the particular controller what about using gearing to step down the rotation speed.

 

Jim

Just what I was thinking.

[sloz1664]

Cracked it, cracked it, cracked it. The motor power to the DPDT Soleniod was fed by a small solenoid switch initiated by the Velleman board. I connected the Motor into this feed and bingo.....Motor Control.

Thanks guys for your help, very much appreciated. 

All the best and clear skies to all.

Steve

[symmetal]

Glad you got it all working Steve. 

[sloz1664]

Thanks symmetal,

All I need to do now is sync the mount to the Dome 

 

Steve

[Gina]

Don't you mean sync the dome to the mount?  That mount is what points the scope at the sky object.  Glad you got your motor control working