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Electric motors

Electric motors for 08 shunter

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Roger Holebrook20/09/2014 12:52:54
8 forum posts

I have under construction an 08 shunter to the 1980's design. The main drawing shows 4No. car wiper motors plus gearing and a subsidiary drawing shows 4 No. conventional mounted axle motors and several alternative gear ratios.

I am trying to achieve approx. 500 watts and be capable of an average speed of 10 mph. My problem is finding motors of approx. 120 watts of either 12 or 24 volts, and with a no-load speed in excess of 6500 rpm and capable of fitting between the wheels. I have looked at the websites of most major manufacturers, e.g. Buhler/Johnson/Mabuchi etc., (some sites are really hard going) but not found anything that fits the criteria.

There are many motors (of Chinese origin) on the market but they have an average of 2400 rpm no-load speed.

I would like to avoid the use of wiper motors as in many cases the specification is unknown and I'm told the central mounting can flex causing the pinion to become disengaged.

If my maths are correct and based on a wheel diameter of 4.75 inches over the tread and an arbitrary motor speed of 2000 rpm, for the purpose of calculation, I have tabulated below the track speeds of the given gear ratios on the drawings.

Gear ration/speed for Charlatan Loco:

(2000rpm is an arbitrary speed for calculation)

Motor Wheel diam Pinion Driven Speed(mph)

2000 4.75 in 14 108 3.65 mph

Gear ratios shown on supplementary plan for M.O.D.

(and alternative motor mounting)

2000 4.75 in 15 80 5.28 mph

2000 4.75 in 12 85 3.98 mph

2000 4.75 in 10 90 3.13 mph

As you can see, the track speed on average is only slightly more than 3 mph, hence the need for a higher speed motor.

The only motor I can find that comes anywhere near the specification I think I am going to need and is currently available is the one sold by MFA/Component shop but even that one is only 80 watts and I can see no physical room to squeeze in a fifth motor. I will try to give below the link to that motor.


So, if anyone knows of suitable motors and suppliers or even an alternative I would be grateful to hear from you.


Bob Brown 120/09/2014 16:43:52
995 forum posts
125 photos

I have a 5" class 08 shunter with three 150 watt motors which originates here **LINK**

They do sell the motors separately and on mine are more than fast enough for our raised track, not sure what mine does but I follow another member round and he was doing 6 mph average on the loop so I must been doing a similar speed. It will go faster but the bends limit the speed as I did not want to take a trip into the undergrowth and it will still pull two loaded carriages.

The motors need to have the torque to start the engine and the ones in your link I think are far too small.


Edited By Bob Brown 1 on 20/09/2014 16:45:47

Neil Wyatt20/09/2014 17:03:02
17093 forum posts
690 photos
76 articles

I think you will find that most hefty low-voltage DC electric motors will run at about 3000 rpm. Surely this is an advantage as you have to gear down anyway?

My little 3 1/2 gauge shunter has a single motor rescued and re-bearinged from a boat shower unit. It is rated 12 volts, 80 watts. I think it manages to pull me at about 2-3 mph but I have two pinions so I can change the drive ratio for tracks with bigger gradients.

The motor is similar to the 5A one here: except it is rated 7.5A. As you can see it is MUCH bigger than the ones you linked to and it quite capable of moving off from stationary, which I think the small motors would fail to do.

For a bigger loco, I'm looking at things like golf-cart motors.


Ian S C21/09/2014 10:39:06
7468 forum posts
230 photos

Roger, an old style Lucas windscreen wiper motor (wound stator) will stand at least 50%, and probably a good bit more over voltage, and seems to be mechanically quite robust, I'v been using one for probably 10 years for traversing the table of my vertical milling machine, the power supply is around 17 volts. It does get quite warm after 1/2 an hour of hard work, but you can still hold your hand on it. Sorry don't know the Wattage.

You could well look at Model Engineer, starting at 17 March 1989, Going Electric by Rex Nicholls,  he explains the conversion of an old automotive DC generator to use it as an electric motor to drive his 0-4-0, 5" gauge locomotive

Ian S C

Edited By Ian S C on 21/09/2014 10:54:46

Roger Holebrook21/09/2014 12:34:08
8 forum posts

Thank you all for your speedy response to my problem.

Bob - The motors you show the link to appear to be the 3000 rpm sold by LEMAC (Leith Electrical) and would with the right gear ratio seem to be the way forward.

Neil - I will look at the golf-cart motors and see if I can fit them as axle mounted between the wheels. There is a firm called Petrol-Scooter that sells a good range.

Ian - The Charlatan was originally designed to run on Lucas 78550 windscreen wiper motors. I have used a tachometer to check their speed and they give a no-load speed of 3500 rpm.

I have considered running 12 v motors at 24 volts but the thought makes me nervous.!

Many thanks for your input, you have given me lots to think about.


Michael Gilligan21/09/2014 13:16:23
14781 forum posts
635 photos
Posted by Roger Holebrook on 21/09/2014 12:34:08:

I have considered running 12 v motors at 24 volts but the thought makes me nervous.!



Locomotives are not really 'my thing', but may I just offer one observation ...

PWM [Pulse Width Modulation] controllers are a pretty safe way of running DC motors at higher than their nominal voltage ... They bring the great benefit that the peak voltage is high, but the mean voltage can be as low a you like.

The instantaneous torque is related to the peak voltage, but motor heating is related to the mean voltage. [That's a gross simplification, and I'm quite sure some of our theorists will want to elaborate upon it.]



Note: There was some rather unproductive discussion about PWM, on another thread; but I'm talking about very simple controllers intended specifically for driving DC motors in this way.

Edited By Michael Gilligan on 21/09/2014 13:17:05

Michael Gilligan24/09/2014 10:33:47
14781 forum posts
635 photos

Posted by Michael Gilligan on 21/09/2014 13:16:23:

[That's a gross simplification, and I'm quite sure some of our theorists will want to elaborate upon it.]


Mmm ... I am rather surprised to see no contribution from our electrical/electronc experts.


Roger Holebrook24/09/2014 10:49:58
8 forum posts

Michael - Thank you for your help, I have to confess I'm a little out of my depth here so I'll have to look into this and try to get some expert guidance.

Many thanks Roger

Bob Youldon24/09/2014 16:02:50
183 forum posts
20 photos

Hello Roger,

It's no good asking me, all I can add, is if you require to that bit quicker then it'll have to be an 09! Many years ago I had the pleasure? of a trip in excess of 40 miles down the main line in one of those.


Bob Youldon

Michael Gilligan24/09/2014 17:57:09
14781 forum posts
635 photos


This should get you started on what PWM is all about .

My link is to the "driving motors" page ... have a quick look at that, then hop back to page_1 and read through [it's pretty easy going].


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