Connecting a pair of motor controllers.

[Ron LadenParticipant @ronladen17547]

Posted by AdrianR on 05/06/2019 08:37:18:

Ron

Here is a link to 100K linear pots

Thanks for the link Adrian, though I dont think any of the ones shown are switched. The reason I am looking for a switched type is that is the type fitted to the controllers and they switch the controller on/off. What I have found with the 0-4-0 which uses one of these controllers is that throttling back to minium stops the drive and the loco free wheels but switching the pot off gives some electronic braking which is quite significant and worth having.

If I cant find a switched dual type I could always fit a switch along side the throttle for braking purposes unless of course there is another way of achieving it.

regards

Ron

[duncan webster 1Participant @duncanwebster1]

You could use a voltage comparator to monitor the volts from one of the pots to operate a relay, but it's getting a bit complicated. Or have a cam on the spindle to operate a microswitch

[Clive FosterParticipant @clivefoster55965]

Given that many, even low priced, controllers will take a speed reference input its worth looking at the cost of providing effective output speed detection for the motors and using that to control them via single reference.

The continuing march off China Inc and the ever decreasing costs of electronics has made many "best solutions" that used to be considered far too expensive affordable. Indeed its often more expensive to do things the old, simple way, than the modern complicated, integrated electronics way.

Clive

[duncan webster 1Participant @duncanwebster1]

Posted by Neil Wyatt on 04/06/2019 16:26:32:

Using one high-power controller will ensure both motors can balance (if one slips it will generate more back-emf diverting power to the other motor, and if one motor stalls it will 'steal' power from the other – an ideal situation).

Neil

I don't think this is quite right, for motors in parallel anyway. If one motor slips it will certainly develop more back EMF and so draw less current, but I don't think that affects the other motor(s). A battery can provide very high current, and control is done on pulse wave modulation, so apart from any voltage drop in the wires (which should be very low) the non slipping motor shouldn't notice, which is probably good. Having motors in series is a different ball game. Then if one motor slips and draws less current it also reduces the current in its series pair, which is not what you want.

Clive's suggestion of traction control will be an interesting read when he's done it, it's certainly possible.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Ron Laden on 05/06/2019 09:48:05:

Posted by AdrianR on 05/06/2019 08:37:18:

Ron

Here is a link to 100K linear pots

Thanks for the link Adrian, though I dont think any of the ones shown are switched. The reason I am looking for a switched type is that is the type fitted to the controllers and they switch the controller on/off. What I have found with the 0-4-0 which uses one of these controllers is that throttling back to minium stops the drive and the loco free wheels but switching the pot off gives some electronic braking which is quite significant and worth having.

If I cant find a switched dual type I could always fit a switch along side the throttle for braking purposes unless of course there is another way of achieving it.

regards

Ron

Within reason the actual value of the pots may not matter much. They're being used to derive a control voltage. If you can't get 100k, 47k, 150k, 220k or even 470k will probably work. I'd try anything between 10k and 470k.

If it were my problem, I'd investigate the controllers to see if one pot could control both. Very likely it could, but I'm guessing you don't have the background or equipment needed to confirm. In which case safer not to risk it!

Although there are good reasons why working two motors off a dual pot might not work properly, I'd be very inclined to try it and see. Although motors and electronics can be delicate, there are circumstances were rough and ready is good enough. There's a good chance it will behave. If not ask again. I don't think there's any risk of damaging the motors or magic smoke. (Famous last words…)

Dave

[Ian PParticipant @ianp]

Most of the replies so far have concentrated (quite correctly) on Ron's original query about coupling two controllers electronically. I wonder though what why or what the two motors are driving and whether they have to run at identical speed or whether they have to be fully synchronised.

If two controllers are being used to drive plain DC motors driving separate wheels on the same vehicle then using one potentiometer to control both obviously makes sense. How the two speed control inputs are linked can only really be determined when one has full knowledge of the speed controller circuitry. Many controllers use a potentiometer to derive a variable analogue voltage (often 0-5V or 0-10V) to feed the speed input of the controller. Whilst one potentiometer (wiper) could easily be connected to two separate controllers there are some possible pitfalls.

One wiper to two inputs is fine, the two grounds (or 0V) must to be tied together as well which is fine, however if the two controllers are fed from a single power source careful attention may be needed to prevent duplicated ground connections introducing extraneous signals because of any voltage drops in any high current wiring.

One slightly confusing point is that Ron mentions 'switching the pot off' giving some braking action. Potentiometers are not themselves devices than can be switched off so presumably he is referring to a combined pot/switch. Knowledge of the controller circuit then become essential if one is to advise on connecting them in tandem.

Ian P

[Ron LadenParticipant @ronladen17547]

Thanks guys,

It would be good if the two controllers could be connected to a single potentiometer but whilst not knowing the controller circuitry I can appreciate the advice of using a dual pot to keep things seperate and safe.

Ian, yes the controllers come wired with a combined pot/switch.

Ron

 

Edited By Ron Laden on 05/06/2019 11:30:18

[Robert Atkinson 2Participant @robertatkinson2]

From the photo this appears to be a basic PWM controller probably a sawtooth oscillator, variable voltage (from pot)and comparator. While two could be modified to run from one pot I don't think a simple parallel connection is advised.
There are two reversing relays and depending how they are wired they probably provide dynamic braking (also using the MOSFET source drain diode and battery) when the control switch is off. A separate double pole "off" switch or a pair of microswitches operated by a cam on the throttle control would be easier than trying to find a dual gang, 100K linear pot with a double pole switch. I found a 50K, which might be OK but it's a single pole switch so needs investigation or a relay and it looks pretty poor quality.

**LINK**

A professional modular pot and switch would be expensive.

You could try hacking one of these

**LINK**
and one of these

**LINK**

together. I.e put the switch of the single onto the double.

Where are you located? Maybe someone come and have a look at the controllers.

Robert G8RPI.

[Brian OldfordParticipant @brianoldford70365]

Posted by Ron Laden on 05/06/2019 11:19:14:

Thanks guys,

It would be good if the two controllers could be connected to a single potentiometer but whilst not knowing the controller circuitry I can appreciate the advice of using a dual pot to keep things seperate and safe.

Ian, yes the controllers come wired with a combined pot/switch.

Ron

Edited By Ron Laden on 05/06/2019 11:30:18

I would have thought by now you would have reverse engineered the PCB and published a full schematic by now so we could opine further.

[Neil WyattModerator @neilwyatt]

Posted by duncan webster on 05/06/2019 10:26:18:

Posted by Neil Wyatt on 04/06/2019 16:26:32:

Using one high-power controller will ensure both motors can balance (if one slips it will generate more back-emf diverting power to the other motor, and if one motor stalls it will 'steal' power from the other – an ideal situation).

Neil

I don't think this is quite right, for motors in parallel anyway. If one motor slips it will certainly develop more back EMF and so draw less current, but I don't think that affects the other motor(s). A battery can provide very high current, and control is done on pulse wave modulation, so apart from any voltage drop in the wires (which should be very low) the non slipping motor shouldn't notice, which is probably good. Having motors in series is a different ball game. Then if one motor slips and draws less current it also reduces the current in its series pair, which is not what you want.

Clive's suggestion of traction control will be an interesting read when he's done it, it's certainly possible.

Loose explanation by me, but unless the controlled is regulated output voltage one slipping will allow the controller output to rise slightly sending more to the other motor, but how much, will, as you suggest, depend on the internal resistance of the battery and controller. Paralleling does make it harder for one motor to slip , again as you say much better than series.

[Ron LadenParticipant @ronladen17547]

Posted by Brian Oldford on 05/06/2019 19:14:54:

Posted by Ron Laden on 05/06/2019 11:19:14:

Thanks guys,

It would be good if the two controllers could be connected to a single potentiometer but whilst not knowing the controller circuitry I can appreciate the advice of using a dual pot to keep things seperate and safe.

Ian, yes the controllers come wired with a combined pot/switch.

Ron

Edited By Ron Laden on 05/06/2019 11:30:18

I would have thought by now you would have reverse engineered the PCB and published a full schematic by now so we could opine further.

If it was a mechanical device I may have some idea but electronics…? I probably have a better understanding of the Russian language and that is about zero…

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Shepherd on 04/06/2019 16:07:08:

Ron Have you considered … connecting the shafts with gears so that …

In the circumstances, Ron … I'm with John

[Although I would probably couple the two existing shafts with a toothed belt.]

It could be a simple mechanical engineering job.

MichaelG.

.

There is, of course, a risk that the controllers and/or the motors are not as well matched as you hope, but it's certainly worth a try.

.

Edited to remove a formatting problem

Edited By Michael Gilligan on 06/06/2019 08:46:27

[Ron LadenParticipant @ronladen17547]

In the circumstances, Ron … I'm with John

[Although I would probably couple the two existing shafts with a toothed belt.]

It could be a simple mechanical engineering job.

MichaelG.

.

There is, of course, a risk that the controllers and/or the motors are not as well matched as you hope, but it's certainly worth a try.

.

Edited to remove a formatting problem

Edited By Michael Gilligan on 06/06/2019 08:46:27

Hi Michael, I have considered John,s suggestion (thanks John) but if as suggested a dual pot would be within 5% or better then that would be ok. Finding a switched dual pot seems difficult but I could add some mechanics as Duncan suggested using a cam to operate a DP switch or pair of micro switches.

With regard to matched motors/controllers I did a simple test this morning, driving all four motors from one controller.

Using a digital tacho I found that two of the motors are quite close within 2-3% of each other with a third motor approx 4% slower and the fourth 5% faster. The slowest to fastest motor are within 9-10%, this is all with the motors unloaded of course. I am quite happy with that, the four smaller motors I have in the 0-4-0 are only good to within 10% and they have proved to be fine with no issues on the track.

I then connected the two better matched motors to the second controller and got very similar figures to the first controller, approx 1% difference so that is very promising.

Ron

[Ian PParticipant @ianp]

Ron, I have quickly read through this whole thread and unless I missed it did not learn what the project is and why it needs two motors linked together?

Are they driving a common load, so coupled together mechanically?

If motor reversing and braking are involved then things are definitely more complicated than just gearing two potentiometers together,

Ian P

[Ron LadenParticipant @ronladen17547]

Posted by Ron Laden on 04/06/2019 08:01:31:

The idea of using 2 controllers is for the 5 inch class 22 loco I am designing/building. Its a twin bogie loco and I am using 2 x 24 volt/150 watt motors on each bogie, 4 motors in total. The controllers I am considering are the budget (Chinese) type, they are PWM ctrls rated at 10-55 volt, 40 amp continuous, 60 amp max. I am running one of these ctrls in the 0-4-0 shunter and to date it works very well, 10-15 amp in general running with 28 amp max when working hard.

I am estimating that the class 22 would be in the 20-30 amp region with 45-50 amp max or thereabouts. If the budget controller is as rated (I dont know) then a single ctrl should do the job but it would be near its top end. I thought a pair, one driving each bogie would halve the load and make things easier on the controllers and that is where my thinking came from. I could pay over £200 for a ctrl which would cope easily plus have some loco bells and whistles but if a pair of budget type will do the job at 1/10th the cost then that is an attractive option.

Brian, as I mentioned my electronics understanding is not too good so can you explain an Arduino, I have no idea what that is.

Ron

Edited By Ron Laden on 04/06/2019 08:02:16

Hi Ian,

My above post shows what I am intending for the two controllers, the only thing I havnt mentioned is that each pair of motors will be wired parallel to their controller.

Ron

[duncan webster 1Participant @duncanwebster1]

For driving a loco, all the motors will rotate at the same speed no matter what, they are connected via the rails. The only issue is will each pair receive the same input voltage, or to be pedantic the same mark space ratio, and so deliver the same torque. I would argue that within 10% or so it doesn't matter. I think the best route is a ganged pot with a cam operated microswitch(es), simpler than belt drives and doesn't rely on the bearings in the pots. However, what does the switch do? If it is to provide braking then it seems like an all or nothing arrangement. If it just turns the whole thing off, then a simple manual switch will suffice

[Robert Atkinson 2Participant @robertatkinson2]

Ron said

"Using a digital tacho I found that two of the motors are quite close within 2-3% of each other with a third motor approx 4% slower and the fourth 5% faster. The slowest to fastest motor are within 9-10%, this is all with the motors unloaded of course. I am quite happy with that, the four smaller motors I have in the 0-4-0 are only good to within 10% and they have proved to be fine with no issues on the track."

An off-load test is not representative at all. The speed is dependent on the voltage (supply x %PWM) and load. With no external load the actual load on the motors is just the bearings and brushes and these are very variable between motors. This probably accounts for most of the speed difference you are seeing. When loaded the resistance of the motor and connecting wires will help share the load between the paralleled motors. To help this, make the parallel connection at the controller, not the motors. This means running two pairs of wires from the controller, one pair to each motor. Ideally the wires should be of similar length other wise the motor with the shorter wire will take more of the load.

Robert G8RPI.

[Ron LadenParticipant @ronladen17547]

I have found a 100 amp (60 continuous) controller and at £25 sent off for one, its one of the Chinese ones, a larger version of the one I use on the 0-4-0 and so far that has proved to be very reliable and excellent value for money. How this larger version will perform remains to be seen but fingers crossed it will be similar to the smaller version. It is obviously simpler to run one controller but good to know I can run twin controllers should I need to.

A picture below of the controller internals but as I mentioned previously electronics is lost on me.

Edited By Ron Laden on 29/08/2019 10:28:38

[Michael GilliganParticipant @michaelgilligan61133]

That looks jolly good value, Ron

I would just recommend adding some grommets and strain relief to those wires though.

MichaelG.

[Ron LadenParticipant @ronladen17547]

Thanks Michael thats a good idea, I do have a selection of grommets plus I can add something to prevent any pull on the pcb connectors.

Ron

[Author]

Posts