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[chrispp]

Hi all, have a problem I can't seem to sort out, I am trying to add the following to my Marie Felling.
Basically 2 MFA 850 motors, 2 Mtronics ESC, a P92 power Board, p44 Twin Switcher, P29 SteamWhistle, P56 Steam Engine Sim and P97 Amp Mixer. I have wired the system and have an issue where through the speaker you can hear the motors ? They are fitted with supressors. Only one of the motors and ESC are connected to the P56
The steam whistle is connected to the P44 switcher, I intend to add a 12v light system to the switcher as well.


Both the P29 and P56 are connected to the P97, I get the hiss and puff, puff but also the engine motor sound, I have tried different esc and the same issue


Anyone got any ideas?


Thanks


Chris

[inertia]

Chris
This covers the situation I think - although I wouldn't use 850 motors in a tug (too fast and current-hungry).

Jean-Pierre
With hindsight I think that the problem was due to the fact that the two steam sound units both use an FM radio chip (TDA7000) to generate white noise for the steam "hiss" effect. Unfortunately these tiny radio receivers were also picking up the RFI from the very large motor in your model and sending it to the speaker; call it a design flaw if you wish, but one of the very few that Craig Talbot ever made. I dare say that some more experimenting with screened cables and shielding might have reduced it to an acceptable level but I doubt if it would ever have completely eliminated it.
To be honest both units were designed almost twenty years ago and we inherited them from Craig. I would happily have taken them off the market. P56 in particular is a pain to assemble and sourcing the long-obsolete FM radio and amplifier chips became increasingly difficult, but they continued to be popular, and you were the only customer who ever had such extreme problems with them.
The smaller P64 Steam Engine sound doesn't have the same chip so doesn't suffer the same problem, although there isn't that "hiss" when the engine is idling.
The newer P100 sound system uses digital samples of a real steam engine and steam whistle rather than a electronically synthesized sounds, so it wouldn't be affected by RFI from the motor.

Hope this answers the question although it doesn't solve the basic problem, which seems to be pretty much stuck without changing some of the items on the list.
Dave M

[malcolmfrary]

Any interfering signal has to come from somewhere, and has to have a path from its origin to where it isn't wanted.  Figuring out the path and how to interrupt it while leaving the wanted bits working is the problem.

Twisting pairs of wires helps cancel radio fields.  This applies both to wiring going to the motors (reducing transmission) and to leads powering or otherwise connecting to the "receiver".  It has been a problem going back to the start of semiconductor amplifiers that speaker leads can pick up radio frequency signals - the semiconductors in the amplifier then detect this, converting it into audio frequency, and amplify it so that you can hear it better.  So speaker leads are best as twisted pairs as well.
Apart from unwanted signals appearing through the air, a poor ground line connection can give all sorts of unpredictable results, especially where large currents are involved.
Does the "motor sound" follow the speed of the motors by increasing in pitch as the motor speeds up, or is it a constant tone at varying volume?

[chrispp]

Any interfering signal has to come from somewhere, and has to have a path from its origin to where it isn't wanted.  Figuring out the path and how to interrupt it while leaving the wanted bits working is the problem.

Twisting pairs of wires helps cancel radio fields.  This applies both to wiring going to the motors (reducing transmission) and to leads powering or otherwise connecting to the "receiver".  It has been a problem going back to the start of semiconductor amplifiers that speaker leads can pick up radio frequency signals - the semiconductors in the amplifier then detect this, converting it into audio frequency, and amplify it so that you can hear it better.  So speaker leads are best as twisted pairs as well.
Apart from unwanted signals appearing through the air, a poor ground line connection can give all sorts of unpredictable results, especially where large currents are involved.
Does the "motor sound" follow the speed of the motors by increasing in pitch as the motor speeds up, or is it a constant tone at varying volume?

Hi thanks very much for the replys, very useful. With regard to the motor sound, yes it increases as the motors speed up. I'll try downsizing the 850's with a couple of decaperms I have but really wanted to keep the 850's as there fitted etc, any further thoughts are gratefully appreciated


Thanks


Chris

[malcolmfrary]

With regard to the motor sound, yes it increases as the motors speed up.

Therefore, it is coming from the motors and/or their wiring, but, since nothing else is misbehaving, it isn't getting back into the system via the radio aerial.  This pretty much leaves the "other wiring", and it is likely to be induction at audio frequency rather than radio interference.  The twisting of the wires mentioned earlier and maybe a bit of re-siting should help reduce the tendency to pick up unwanted signals.