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Author Topic: Dapol Prairie Motor Speed  (Read 361 times)

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Offline Dalteth

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Dapol Prairie Motor Speed
« on: September 13, 2020, 08:05:14 PM »
Hi all,

I’ve got a Dapol prairie chassis that was missing it’s motor and I ended up replacing, along with some modifications to suit a new body shell I was repairing.

What I’ve got since I have rewired, is a chassis that runs very well, but far too fast.

Even the smallest amount of power that has other locos crawling, sends this one off at speed.

Electrics aren’t my strong suit, think I’ve forgotten everything I learned in school! So basic explanations much appreciated 🙂


Online Dr Al

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Re: Dapol Prairie Motor Speed
« Reply #1 on: September 13, 2020, 08:12:18 PM »
Normal for these motors - they are 3 pole and very high revving, and all these come from the factory like this.

You need to adopt more fine control of them to get the best out, and this can be done.

Same for the Ivatt tanks, 14xxs and M7s.

Cheers,
Alan
Quote from: Roy L S
If Dr Al is online he may be able to provide a more comprehensive answer.

“We have also arranged things so that almost no one understands science and technology. This is a prescription for disaster. We might get away with it for a while, but sooner or later this combustible mixture of ignorance and power is going to blow up in our faces.”Dr. Carl Sagan

Online ntpntpntp

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Re: Dapol Prairie Motor Speed
« Reply #2 on: September 13, 2020, 08:56:18 PM »
What controller are you using?   As Al says, the early Dapol steamers like this one do seem to suffer from let's just say not the best choice of motor and gear ratio combination.   

I have two 45xx, and they've never impressed me with their running qualities.  On the other hand my little 14xx 0-4-2T is actually surprisingly slow and controllable, though I never need to go beyond about 30-40% on the knob of a simple DC Gaugemaster 100 controller.  I think I've been lucky with that loco and got a good 'un compared to some people's experiences.

It's tricky to do much about it in a small loco.  If there were space inside I'd say maybe try some inverse-parallel diodes to reduce the voltage that the motor sees. That's worked really well to tame some Tomix chassis I've used but I had plenty of space for the string of diodes. A resistor is another option but I've found they tend to heat up more obviously than using a diode's natural voltage drop.

A DCC decoder might tame it, especially one designed for lower voltage motors or which can have the peak output voltage tuned down (not just the PWM duty cycle reduced).  I've just got hold of a couple of CT Electronik decoders designed specifically for 4-5V motors, to use with little TGW chassis.

There is a German company SB-Modelbau that offers differently pitched worms for the motors of some Continental locos and that results in slower running, but nothing suitable for Dapol models as far as I know.

Maybe a different motor such as the coreless offerings now available from Tramfabriek or Micromotor.eu  might give better slow running?  They're not the same dimensions though and would need to work to fit.  I wonder if anyone has tried such a motor in a 45xx?
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!
https://www.ngaugeforum.co.uk/SMFN/index.php?topic=50050.0

Offline Dalteth

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Re: Dapol Prairie Motor Speed
« Reply #3 on: September 13, 2020, 10:49:50 PM »
Thanks gents.

I’ve compared to an ivatt I have, but have never run much, and it is marginally quicker. It is only a bit, so this could be down to the extra weight I took off, a slight variance in manufacture or other small differences.

Sounds like something I’m just going to have to live with!

Offline Dalteth

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Re: Dapol Prairie Motor Speed
« Reply #4 on: September 13, 2020, 10:51:49 PM »
What controller are you using?

It’s only a very basic Graham Farish one, so that could be contributing to the problem.

Offline longbow

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Re: Dapol Prairie Motor Speed
« Reply #5 on: September 14, 2020, 12:10:46 AM »
Fitting DCC certainly transformed my Dapol 45xx.

Offline PLD

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Re: Dapol Prairie Motor Speed
« Reply #6 on: September 14, 2020, 07:49:36 AM »
First question - it is a 12v motor isn't it?? If it is a 6v or 9v motor, it will be getting closer to it's full voltage sooner.

If it is a lower voltage motor, the answer is a resistor in series with the motor, and this can be used to tame fast revving 12v motor also.

The other solution is self-control. Just because the controller goes up to 11 doesn't mean you have to!
« Last Edit: September 18, 2020, 12:11:55 AM by PLD »

Offline longbow

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Re: Dapol Prairie Motor Speed
« Reply #7 on: September 14, 2020, 08:12:19 AM »
Many of these early Dapol tank locos have two-speeds - stalled and scalded cat - and no amount of throttle self-control will cure it. 

Offline JanW

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Re: Dapol Prairie Motor Speed
« Reply #8 on: September 14, 2020, 09:10:22 AM »
A resistor in series with the motor is never a good solution, although I know it is done quite often.
It will make starting more difficult, first no response and then it leaps off.
You're better off with a good controller with fine control in the lower speed range.

Jan

Offline Dalteth

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Re: Dapol Prairie Motor Speed
« Reply #9 on: September 16, 2020, 05:21:31 PM »
Thanks all for the replies.

I decided to do a comparison with my Dapol ivatt I have. The current chassis is certainly quicker.

I’d like to experiment with adding a resistor because as it is, it’s virtually comical the speed it goes!

Can anyone point me in the direction of an idiots guide to what resistor I might need and where to fit it into the wiring...?

Online Dr Al

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Re: Dapol Prairie Motor Speed
« Reply #10 on: September 16, 2020, 05:30:14 PM »
Can anyone point me in the direction of an idiots guide to what resistor I might need and where to fit it into the wiring...?

Better to fit a diode array, this will drop the voltage in a better manner (~0.7V per diode used).

Cheers,
Alan
Quote from: Roy L S
If Dr Al is online he may be able to provide a more comprehensive answer.

“We have also arranged things so that almost no one understands science and technology. This is a prescription for disaster. We might get away with it for a while, but sooner or later this combustible mixture of ignorance and power is going to blow up in our faces.”Dr. Carl Sagan

Online ntpntpntp

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Re: Dapol Prairie Motor Speed
« Reply #11 on: September 16, 2020, 05:57:21 PM »
I agree a string of inverse-parallel diodes works better, just a question of finding enough space!

Here's where I fitted 4 SMD diodes in each direction for a Tomytec chassis to drop almost 3V





These two methods are equivalent, just that splitting into two strings was better for the space so I used the lower diagram



The diodes were something like 99p for 100  :)
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!
https://www.ngaugeforum.co.uk/SMFN/index.php?topic=50050.0

Offline Chris Morris

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Re: Dapol Prairie Motor Speed
« Reply #12 on: September 16, 2020, 06:36:37 PM »
The right controller will get good performance out of a Dapol Prairie. This in itself can cause its own issues. I use a H&M Walkabout feedback controller for the Dapol Prairie but of course this is no good for the Farish 64xx.

Working doesn't seem to be the perfect thing for me so I'll continue to play.
Steve Marriott / Ronnie Lane

Offline Dalteth

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Re: Dapol Prairie Motor Speed
« Reply #13 on: September 16, 2020, 08:03:49 PM »
The diodes were something like 99p for 100  :)

Perfect, I’ve picked up a bunch so will see how I get on!

The right controller will get good performance out of a Dapol Prairie. This in itself can cause its own issues. I use a H&M Walkabout feedback controller for the Dapol Prairie but of course this is no good for the Farish 64xx.

A better controller has long been on ‘the list’ maybe this will provide the prompt to sort myself out!

Offline V72

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Re: Dapol Prairie Motor Speed
« Reply #14 on: September 17, 2020, 10:08:05 PM »
I run a Dapol Prairie on a Branch Line layout in alternation with a Farish 94xx Pannier. The controller is a basic Farish c. 1986. The Prairie runs perfectly smoothly at a scale speed of 30 mph at about 15% rotation of the controller dial, whereas, 40% rotation is needed to achieve the same speed with the Pannier (both on the same 5 coach train).
It is absolutely no problem to adjust the controller to the right setting for each of these locos.

 

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