Coreless Motors - Back EMF - Feedback Controllers - DCC

[RBAGE]

NOTE: Same subject as already posted in non-DCC and DCC sections.

 

I wonder if anyone might be prepared to share their experience and at the same time help me decide how to proceed with motor selection.

 

I build loco kits only to fill the gaps that RTR has not yet ventured into. My latest is Dave Bradwell J39 chassis that I intend to fit into a detailed Bachmann body. 

My strategy is to build the kit as best as my limitations will allow, run it in DC until I am satisfied it's a goodun, then convert to DCC.

I have almost always used Mashima motors for my kits and they tirelessly run my kit built fleet.

 

Some years ago, I bought a number of Portescap motors but hearing tales of woe with their operation on DCC, I have avoided fitting them and these expensive pieces of engineering have languished in the miscellaneous box.

 

Biting the bullet, I have fitted a Portescap to what I was satisfied is a free running chassis. It sounds like a pig on my DC test track. I cannot take this loco forward for DCC sound operation in this condition.

 

I have a number of problems that I am hoping might be resolved:

 1. Is there a problem with running coreless motors on feedback controllers?

 2. What are these problems and do they extend to the squealing pig that has now gone back in the box?

 3. If I have problems related to feedback controllers, are they likely to carry over to DCC? What I'm saying, can I ignore the squealing pig and go ahead and safely fit a sound decoder?

 4. Has anyone experienced problems with coreless motors on DCC operation?

 5. Should I put my Portescaps back into miscellaneous?

 

Any advice would be most gratefully accepted. However, my Portescaps have spent their lives in their boxes because of unconfirmed suggestions that that DCC would destroy these masterpieces so I would like to avoid thirty year old "he said, she said" type of comment. Direct experience would be most valuable. 

 

Thanks in anticipation. 

 

Bob 

[Dave Holt]

Bob.

Nearly all my kit-built locos have Portescap motor/gearboxes, usually the 1616 type.

I always start them running on DC to get the running smoothly as DCC can hide minor mechanical problems. I've only used them with non-feedback controllers on the Pentroller and, currently, a PICtroller.  I have been lead to understand they don't like older DC feedback controllers.

Once satisfied, mechanically, all my completed locos are then DCC fitted. Modern chips run feedback at such a high frequency that even coreless motors can't chatter. With the very low current consumption, I normally use chips intended for Z gauge and have settled on Digitrax DZ126 model. I have also successfully used chips by Lenz and another I can't remember. I settled on the Digitrax simply because they are very small and fully encapsulated, making them easy to install.

All that said, many of my Portescap units are extremely noisy, sounding like a cement mixer and clearly audible in use, even in a large room. Again, I'm told this is because the tooling for the nylon gears wore, causing poor meshing and mechanical generated noise. I don't fit sound, so this only an irritant to me, not a major problem.

Hope that helps.

Dave.

[JeffP]

I'm sure I read somewhere about the very light grease with which Portescaps were lubricated, drying out and causing noisy running.

Could you strip the offending gearbox, clean out and re-lubricate?

Can't hurt.

[RBAGE]

42 minutes ago, JeffP said:

I'm sure I read somewhere about the very light grease with which Portescaps were lubricated, drying out and causing noisy running.

Could you strip the offending gearbox, clean out and re-lubricate?

Can't hurt.

Thanks, I think I'll give that a go.

[kevinlms]

Suggestions in early issues of MRJ included wiring resistors (50 - 80 ohms approx) in parallel, or a small lamp (4-8 watts). The idea in both cases is to swap the feedback.

 

I haven't tried either, as I don't have any Portescap motors.

 

As others have suggested, using better quality DCC decoders would be the best solution. Remember DCC has been around a long time now and modern decoders are much better than early types.

[O-Gauge-Phil]

I would get the mechanical stuff sorted first.  If you look up noisy Portescap on here you will find a few bits.  I assume the chassis runs free.  If you can remove the motor and turn the axle and if all is well then it’s most likely it’s the motor gear. No problem if you can live with the rattle from the gears.  There was someone on here a little while ago with the same problem and somebody recommended a grease, I asked if this had done the job as I have an RG7 just the same but he couldn’t hear any difference.

Coreless motors do not have much back EMF and so on a dc system you have to tailor the controller to your target customer, hence Pentrollers was good for cordless but not a 5 pole motor.  One advantage of dcc is the control can be set up for that motor and that motor alone.  The decoders I use (ESU Zimo) have an auto tune function, the ESU on setup runs the motor at full speed for one yard then calculates the proportional and the integral, Google PID for an explanation.  Zimo has a function that continues to tune the control loop.  So in your case dcc would give excellent low speed running for your rtr and your kit built. My locos can take several hours to travel down my layout, about 16 feet. Think that’s slow enough for anyone.

Good luck .

 

Edited April 14, 2020 by O-Gauge-Phil

[RBAGE]

34 minutes ago, O-Gauge-Phil said:

I would get the mechanical stuff sorted first.  If you look up noisy Portescap on here you will find a few bits.  I assume the chassis runs free.  If you can remove the motor and turn the axle and if all is well then it’s most likely it’s the motor gear. No problem if you can live with the rattle from the gears.  There was someone on here a little while ago with the same problem and somebody recommended a grease, I asked if this had done the job as I have an RG7 just the same but he couldn’t hear any difference.

Coreless motors do not have much back EMF and so on a dc system you have to tailor the controller to your target customer, hence Pentrollers was good for cordless but not a 5 pole motor.  One advantage of dcc is the control can be set up for that motor and that motor alone.  The decoders I use (ESU Zimo) have an auto tune function, the ESU on setup runs the motor at full speed for one yard then calculates the proportional and the integral, Google PID for an explanation.  Zimo has a function that continues to tune the control loop.  So in your case dcc would give excellent low speed running for your rtr and your kit built. My locos can take several hours to travel down my layout, about 16 feet. Think that’s slow enough for anyone.

Good luck .

 

Thanks. I will have a go at cleaning the gearbox. It has been idle for a very long time so that could be the problem.

[jim.snowdon]

On 13 April 2020 at 14:55, RBAGE said:

NOTE: Same subject as already posted in non-DCC and DCC sections.

 

I wonder if anyone might be prepared to share their experience and at the same time help me decide how to proceed with motor selection.

 

I build loco kits only to fill the gaps that RTR has not yet ventured into. My latest is Dave Bradwell J39 chassis that I intend to fit into a detailed Bachmann body. 

My strategy is to build the kit as best as my limitations will allow, run it in DC until I am satisfied it's a goodun, then convert to DCC.

I have almost always used Mashima motors for my kits and they tirelessly run my kit built fleet.

 

Some years ago, I bought a number of Portescap motors but hearing tales of woe with their operation on DCC, I have avoided fitting them and these expensive pieces of engineering have languished in the miscellaneous box.

 

Biting the bullet, I have fitted a Portescap to what I was satisfied is a free running chassis. It sounds like a pig on my DC test track. I cannot take this loco forward for DCC sound operation in this condition.

 

I have a number of problems that I am hoping might be resolved:

 1. Is there a problem with running coreless motors on feedback controllers?

 2. What are these problems and do they extend to the squealing pig that has now gone back in the box?

 3. If I have problems related to feedback controllers, are they likely to carry over to DCC? What I'm saying, can I ignore the squealing pig and go ahead and safely fit a sound decoder?

 4. Has anyone experienced problems with coreless motors on DCC operation?

 5. Should I put my Portescaps back into miscellaneous?

 

Any advice would be most gratefully accepted. However, my Portescaps have spent their lives in their boxes because of unconfirmed suggestions that that DCC would destroy these masterpieces so I would like to avoid thirty year old "he said, she said" type of comment. Direct experience would be most valuable. 

 

Thanks in anticipation. 

 

Bob 

Back in the days when I modelled in EM (which is when Portescaps were very new) I did use some, and did experience some issues with feedback controllers. I had the same issues later with a Portescap RG7. The problem was not heating, but a tendency for jerky running, most noticeably at lower speeds. The issue, as far as I could conclude, boiled down to the much faster response of the coreless motor to changes in the input voltage. If the loco momentarily lost contact, the feedback controller would sense the drop in the back emf (and coreless motors generate back emf just the same as any other motor, just more efficiently) and increase the output voltage to try and compensate. The problem is that as soon as contact was resumed, the motor would accelerate smartly until the controller recovered. The underlying issue is that the coreless motor has a much faster time constant than a traditional iron cored motor (by design) and will react to changes that the cored motor will simply damp out by virtue of its slow reaction times.

 

Jim

[O-Gauge-Phil]

Just now, jim.snowdon said:

Back in the days when I modelled in EM (which is when Portescaps were very new) I did use some, and did experience some issues with feedback controllers. I had the same issues later with a Portescap RG7. The problem was not heating, but a tendency for jerky running, most noticeably at lower speeds. The issue, as far as I could conclude, boiled down to the much faster response of the coreless motor to changes in the input voltage. If the loco momentarily lost contact, the feedback controller would sense the drop in the back emf (and coreless motors generate back emf just the same as any other motor, just more efficiently) and increase the output voltage to try and compensate. The problem is that as soon as contact was resumed, the motor would accelerate smartly until the controller recovered. The underlying issue is that the coreless motor has a much faster time constant than a traditional iron cored motor (by design) and will react to changes that the cored motor will simply damp out by virtue of its slow reaction times.

 

Jim

Totally agree.  This is what the P. I. sorts out in the decoder. The P is how responsive it is and the I is the time it takes to respond to  changes.  With the stay alive you don't get any glitches either.

 

All the best.  

Phil

Edited April 15, 2020 by O-Gauge-Phil

[snitzl]

Some years ago, I looked into the workings of the Pentroller which was designed by Stuart Hines for use with Portescap Coreless motors. I include a link to this blog in the hope that some may find it useful.

 

Pentroller Blog.

 

Regards Pete