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Re: Driver surfaces ? Brass or NS ?
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Tom Knowles
¿ªÔÆÌåÓýMark, It occurs to me you may have a
bad HH motor if the problem is not traction related. Do I
correctly understand its a traction problem? We may be able to
quantify your problem:
An interesting generalization that may translate into understanding your problem, is on rating a full size steam engine. I think it can translate to model engines (without traction tires). It's "factor of adhesion", expressed as a percentage. If an engine has specified a factor of adhesion, it is usually on the order of 25%. So if the engine weighs 100,000 lbs, then expect no more than? 25,000 lbs of "drawbar pull" (sometimes called Tractive effort, or "TE") from it. This was measured by Dynamometer cars in the old days, with other computations complicating the use of the car and its results! ?I have experimented a bit with model TE, and found though the margin for error is greater since we're dealing with smaller numbers and less accurate systems to measure it, the numbers translate. If the engine weighs 16 0z, expect 4 oz TE. To measure this, I have used a postal scale, set on its side and zeroed for that position to verify this. Being a static measurement, its crude, but informative.? One could measure the voltage and current during the session, but until anything moves, HP cannot be computed. If the engine slips in the test, then TE will be lower at that point since sliding friction is less than stopped friction. Incidentally, that is partly why steam engines at low speed have difficulty starting/accelerating sometimes, the pulses of power from each stroke unevenly apply force to the adhesion, a momentary overcoming of the adhesion will cause the wheel to slip. Electric power is smooother, and the high current required by as motor at stall translates to "force". This is an excellent situation for getting started and should be the case with electric driven model steamers. Try making a test track, set level, and employ some sort of measuring system to compare both your L's and the H and see what happens.....can you do this in DC and measure the voltage and current? Another way may be to simply raise one end of the test track and see what grade the engines will pull before slipping. If the H9 slips early, then I think you're still looking at traction problems. I would love to have a working dynamometer car that could radio out the results of all the parameters of a dynamic test in scale, but have lost too many brain cells to carry out that project at this age.. It may already be available in DCC if we knew how to read out the motor's back emf and load from the decoders that have this feature. Anyway, I think you are in the right forum to figure this out, bear with us! Tom Knowles NOTE NEW ADDRESS: tomk@...On 1/6/2013 12:44 PM, twilight022765 wrote: ? |