Technical

First of all I would like to say what a great time I had at Doncaster on Saturday, where I met many of you and ran my Silver Link with 5 Greasley Teak Coaches, I took along. Shame I could not get my rake of 6 plus Dynamometer car in but having fitted corridor interconnectors they would not fit in the Hornby boxes.

While taking to Maurice, he said something that as far as I was concerned placed a final piece in a jigsaw regarding regulator servo motor torque drop off on some Locos.

I have found that my older (more run) loco tends to have reduced torque towards the end of a run. Normally I always run on simmer only and power is continually explosive on this setting. Reason is to reduce risk of staining the top of Loco body together with allowing complete cool down after a run and 3 layers of aluminium foil in addition to the provided heat insulation.

Downside of running on simmer especially with the Live steam controller is that the resistor in the live steam controller is higher than the Hornby unit to give finer control. On simmer this factor is amplified, on a new loco allowed to cool down completely between runs and always run on simmer from new no problem.

Well that outlines the issues, why does this happen? Maurice made a few comments Saturday and I immediately worked out what could be happening.

Factor one, a magnet when heat cycled tends to loose it's magnetism.

Factor two, a magnet when heated up temporarily suffers reduced magnetism when it cools most magnetism is regained but not necessarily all of it.

If a loco is run on a high heat setting especially superheat heat builds up and as the run progress reaches the servo motor magnet excessively raising its temperature, this is massively exacerbated by not allowing the loco to cool right down after each run.

This treatment causes the magnet to loose some of it's magnetism progressively.

The problem will get worse as the run progresses because the magnet, with already reduced magnetism, is being heated up.

A new Loco run on simmer, allowed to cool between runs will have enough magnetism not to be affected enough to reduce control on the live steam controller. However a Loco allowed to overheat and cycled in this manner, described before, will suffer reduced ambient magnetism so at the start of a run may appear OK but then will suffer poor response later on in the run as the heat reaches the servo motor magnets magnetism.

At it's worst the response will be affected with the Hornby Controller on simmer and then even on the normal running position.

To re-magnetise the servo motor magnet could alleviate this problem.

Other causes could be a stiff linkage, which gets stiffer as it heats up. I have not really ever considered this a likely cause and until Maurice commented on the effect of temperature and heat cycling on magnets I did not think of this.

To buy a loco new is important and then only run on simmer at all times keeping the heat build up as low as possible. An abused Loco is on a slippery downward spiral.

Can the club source replacement magnets?

I may be well out in my reasoning but welcome comment. I am an electrical engineer, the study of permanent magnets is more metallurgy. I did not cover this in my degree course in electrical and electronic engineering, which was 50 years ago.