Heljan O-gauge class 33, MX699KV motor noise

[pricei]

Hi, I've just converted a Heljan class 33 (one of the first O-gauge versions) to DCC using a Zimo MX699KV decoder. The sound file is ActiveDrive SL from Digitrains. The loco works fine but there's quite a loud 'groaning' noise from the motors at low throttle settings. Having researched the issue, it seems the noise might be caused by back EMF settings? Other forum posts I've seen suggest the noise can be reduced by changing the values in CVs 9, 56 and/or 57.
 
So far, I've changed two CV values:
CV57 (original value 100) changed to 150. This was on the basis that the track voltage from my Digikeijs DR5000 varies between 16 - 18v and I assumed an average value of 17v (hence 150).
CV9 (original value 95) changed to 25. This was derived by trial and error and does reduce the noise a fair bit albeit at the expense of a little more juddering at very low throttle settings.
 
Before I try changing CV56, I was wondering if anybody else has installed an MX699KV in a Heljan 7mm Class 33 and what values they had used for CV9, 56 and 57?
Regards, Ian

[Nigelcliffe]

Zimo manuals available here

http://www.zimo.at/web2010/documents/handbuch.htm

With advice from maker on how to go about finding the appropriate motor control parameters. 

[pricei]

Thanks Nigel. I've already been using the Zimo large-scale decoder manual to help with the changes I've made to date. Page 23 does list a number of manufacturers/motor types but Heljan isn't one of them and I don't know whether the motors Heljan fit in their 7mm locos are normal DC or coreless. My thought was that if somebody already has a class 33/MX699 running well, their CV values would give me a better starting point from which to start tweaking.

[mikeg]

If the 33 is one of the original the noise might be due to cracked gears, this is a known problem and to find out you need to remove the bogie base plates and closely inspect the gears being driven by the worm if they are cracked a black line will be seen in the bottom of one of the teeth.

Hope this helps and you don’t have any cracked but I have several of the diesels and have repaired several but still have some that don’t make a lot of noise and run them slowly so they are quiet.

 

regards mike 

[norman]

Hi Ian

I doubt that a groaning noise is as a result of cracked gears, cracked gears are quite distinctive bit like a clickty click, which gets louder until the gear completely fails and jams the mechanism.

The groaning may well be due to one motor fighting the other if for some reason they are not matched. The decoder must somehow do a balancing act between the two. The two motors are never exactly the same but you would hope that particularly at low speed they are very similar.  Have you tried it on DC without the decoder? Also, have you tried switching the BEMF off, CV58=0?

   

[pricei]

2 hours ago, mikeg said:

If the 33 is one of the original the noise might be due to cracked gears, this is a known problem and to find out you need to remove the bogie base plates and closely inspect the gears being driven by the worm if they are cracked a black line will be seen in the bottom of one of the teeth.

Hope this helps and you don’t have any cracked but I have several of the diesels and have repaired several but still have some that don’t make a lot of noise and run them slowly so they are quiet.

 

regards mike 

The loco was in storage for a while and did have two split gears when I unboxed and checked it recently. I've since replaced all four gears (the double ones next to the worm) with brass versions from Ultrascale and the gear train now works fine. Thanks for the suggestion, though.

Regards Ian

[pricei]

15 hours ago, norman said:

Hi Ian

I doubt that a groaning noise is as a result of cracked gears, cracked gears are quite distinctive bit like a clickty click, which gets louder until the gear completely fails and jams the mechanism.

The groaning may well be due to one motor fighting the other if for some reason they are not matched. The decoder must somehow do a balancing act between the two. The two motors are never exactly the same but you would hope that particularly at low speed they are very similar.  Have you tried it on DC without the decoder? Also, have you tried switching the BEMF off, CV58=0?

   

 

Thanks Norman. I did try the loco under DC before fitting the decoder and there was no groaning noise from the motors. I just tried setting CV58=0 (it was previously set to the default 255) and that did eliminate the noise but made the loco pretty uncontrollable. It needed a high throttle setting to start moving and then it was off at some speed. I guess that indicates the noise is caused by Back EMF and I'm probably going to be faced with a compromise between smooth operation and motor noise. The best I've achieved to date is changing CV9 from 95 to 25. I'm yet to try tweaking CV56 - I guess that's my best next step.

Ian

[34theletterbetweenB&D]

On ‎31‎/‎07‎/‎2020 at 11:53, pricei said:

... My thought was that if somebody already has a class 33/MX699 running well, their CV values would give me a better starting point from which to start tweaking.

This is a fairly frequent thought, but it falls down in two significant respects:

among owners the idea of what constitutes 'running well' varies widely;

sensitivity to the sound output from the motors starts from deaf...

 

This is all before we get to the inevitable variation in manufactured product. Best off working through it to suit yourself is my suggestion.

[Mike Buckner]

Just a thought. Perhaps have 2 decoders, one for each motor, only one with sound. Endeavour to get them Speed matched. Perhaps use one decoder with the Back EMF reduced or turned off.

[Nigelcliffe]

Are there capacitors or inductors in the loco to remove EMF noise (normal for UK RTR locos) ?   Are those making the decoder's job harder, and can you remove them ? 

Capacitors are usually across the motor terminals, just remove.  Inductors are usually in-series with a motor feed, bridge with a wire link. 

[pricei]

On 02/08/2020 at 10:48, Nigelcliffe said:

Are there capacitors or inductors in the loco to remove EMF noise (normal for UK RTR locos) ?   Are those making the decoder's job harder, and can you remove them ? 

Capacitors are usually across the motor terminals, just remove.  Inductors are usually in-series with a motor feed, bridge with a wire link. 

 

There might have been what looks like a capacitor on the old Heljan DC board (sorry, my knowledge of electrical components is limited) but I've dispensed with that board now and both motors are wired directly into the Zimo decoder.

Ian

[pricei]

I followed the guidance in the Zimo manual and tried several different P and I values in CV56 but I couldn't discern any difference in motor noise so I left it at its original value of 33. I also tried a selection of non-zero values in CV58 but that didn't appear to make any difference either. 

 

I've decided to limit my changes to CVs 9 and 57 only as per my original post. They do reduce the noise sufficiently that it can't be heard over the sound file playing which was my main concern. My thanks to everybody that offered help and advice. 

Ian