Revolution better at slower speeds than train engineer??

[astarr78]

I want to thank everyone for their comments.  They were all helpful. 

 I may be buidling a bridge soon ( in 1/4 scale) but have no desire to buy one :)

[Greg Elmassian]

wow, you make so many controversial points, I must I don't have the energy or free time to rebut them.

Since you are deaf I guess it does not matter to you that no one uses low frequency PWM anymore in quality products.... the motor literally "sings".

Your mention of the 2n3055 surely brings back memories of circuits I used to build as a kid. That definitely used to be the standard power transistor...

Anyway, the poor guy starting this thread wanted to know about the revolution, not how to build circuits himself... if he considering a revolution, then he needs a lot more than just the circuit above.

By the way, how come this code snippet keeps popping up with your pseudonym?

http://codepad.org/QwsbUEi6

Greg

[cabbage]

Oh Dear  Mr Elmassian....

quote:

The guy is asking about the revolution and you turn back the electronic evolutionary clock about 10 years?

unquote:

No Mr Elmassian -I have simply pointed out a suitable circuit that is easy to build, the electronics of it are a personal taste and yes -it does use darlington pairs -but then so does the screen driver of my Blackberry Curve.

quote:

so you want a PWM circuit in the audio range so it not only does not work as well as current technology, but also makes the motor "Sing" due to the audible frequency?

unquote:

The age of the circuit does not affect the usage -as to audible frequency -audible frequency of what? Elephants, Whales -or Dogs? Being deaf I have problems with "audible frequencies" despite the fact that I am quite an accomplished guitarist -I have never heard an unamplified  note that I have played... Oh -the amplifier I use is based on Parallel single ended Class "A" design using KT66 valves (tubes) It uses "Radio Frequency" heating as would be common in the 1950's and is rated at 9 Watts for 150 watts input. It is my own design as well (I designed it at age 15).

You may find out all about it here: http://www.cabbagepatchrailway.co.uk/amp.html

quote:

Since this is a remote control system, even if the sine wave chopping would be superior (it is not except in the case of 10 year old motors), how much more expensive to make a sine wave chopper? goodbye to the FETS, and hello to analog transistors, more cost, size and heat?

unquote:

Well Mr Elmassian -I that is a very strange thing for you to say.... I am using Buhle and Matsushita made models in my locos (I think that last one I bought was May 2012) with an upgraded circuit using TIP3055 as my output transistor (this costs me £0.55p each) as opposed to the International Rectifiers IRF620 HEXFET which did cost me £6.35p each and I needed two of them. The use of a sine wave rather than a square wave does to my eye produce a smoother take up of the loco. This is the circuit I normally use the IRF620 in:

As you can see I use a NAND as a driver. Is the modified Amos Circuit cheaper than using the HEXFET circuit -oh yes! If the circuit does the job, the parts are cheaper and easier to build and to find -then why not use it?

Your Respectfully

R.Brades B.Ed B.Sc M.Sc M.I.A.A.P. Ph.D. (Not the name on my company letter head)

Post Scriptumn: what sort of bridge would you like me to sell him -Diode,"H", "Wein" or possibly "Seller" or given your obvious problems -"The Bridge of SIGHS"... 

[grandpopswalt]

I'm not sure I follow how the number of poles influences slow speed operation in a DC motor.  I'd guess that the inductance of the armature winding and frequency of the applied pulses would have a greater influence on low RPM operation.

[Greg Elmassian]

The guy is asking about the revolution and you turn back the electronic evolutionary clock about 10 years?

so you want a PWM circuit in the audio range so it not only does not work as well as current technology, but also makes the motor "Sing" due to the audible frequency?

Since this is a remote control system, even if the sine wave chopping would be superior (it is not except in the case of 10 year old motors), how much more expensive to make a sine wave chopper? goodbye to the FETS, and hello to analog transistors, more cost, size and heat?

Really cabbage?

The poor OP... maybe you are also going to sell him a bridge?

SMFH

Greg Elmassian (my real name)

[cabbage]

The main problem with very slow startup may not be the controller -but may actually be the electric motor that the loco is using. The minimum number of "poles" that a motor must have for use with a Pulsed Width Modulated system is normally regarded as FIVE. SEVEN poles is probably the best number as the amount of "core" that can be fitted to a motor within the confines of your loading gauge would fall below what would be practical... High pole motors generate less torque than small pole motors because of this. 

What I would suggest is that you find a friendly electronics "knerd" and have him build you a Pulsed Width AMPLITUDE Modulated power supply. This works by "slicing" a sine wave rather than a square wave. Thus the loco receives a rising voltage -rather than a constant voltage.  The design by Roger Amos is almost the "de facto" standard design and can be found in his book "Model Railway Electronics" -it is Chapter 6 that you need to examine. As stated the design uses the EU norm of 100Hz -but the design can be altered very simply to have a variable input frequency.

My sons "Hornby" layout uses four that alters the rate from 100hz to 8.5Khz and modulates 5 amperes by simple duplication of the output stage. After he had built the PCBS I checked them over and a then wired them to the mains for him (he was 10 at the time).

regards

ralph

[Greg Elmassian]

No, both devices use PWM in the same way, so no technological differences. I tested the Revolution and found I was not happy with the low speed control, i.e. start speed, I could not set it low enough to make it crawl as well as other systems. I use DCC, where you can more finely control the starting "voltage". You are actually setting the minimum pulse width.

But as an inexpensive starter remote control system without sound, the Revolution is hard to beat on price. As soon as you add sound to the equation, the advantage pretty much goes away.

Greg

[astarr78]

I am runnung a 2 rail O scale RR with DC, drawing usually elss than 1 amp but as much as 2.5.  I am using a Crest Engineer on the PWM setting and love the low speed start up, effect it has on full brightness lights and smoke generation.  But I would like the locos to start moving at a crawl, even slower than the crest engineer.  Is there any reason to think that the revolution 57000 would achieve that? 

I would be using the receiver as a stationary trackside device with the out put leads going to the track rather than the receiver mounted in a loco mounted.    

Thanks for listening