5 inch 0-4-0 Shunter

Well my motor controller arrived today, got it from Ebay (Chinese) 12 volt rated at 40 amps continuous - 60 amps max for short periods and cost is less then £15.00. Comes with a rotary speed control and a reversing switch.

I connected it up to the four motors and it works (always a bit doubtful with Chinese stuff). As best I can tell at the moment and with no load all four motors appeared to be running about the same. I need to find my digital tacho and then I can check them for sure.

Now, what it will be like under load I have no idea, will it turn faulty or go up in flames I just dont know. I have had the top cover off and it does have some meaty looking components so here,s hoping.

At less than £15 I just had to give it a try, if it fails I will just have to get a better one but the one I have my eye on is over £100 so I,m keeping my fingers crossed.

Ron

Will the axles be connected with a coupling?

Hi Jon

No the axles are independent of each other, each one driven by two motors

Ron

How are you going to guarantee the same output from two motors on one axle ?

Just curious Roy

You cant guarantee the output Roy, they are off the shelf can motors and unless you have a duff motor the two motors output should be within 3 or 4 percent of each other and they will be fine. The motors are driving the same spur gear and will balance out albeit one will be working a little harder. Obviously if you had motors with a difference of 10% or greater then that would become more of an issue.

Ron

Edited By Ron Laden on 15/05/2018 19:08:05

Edited By Ron Laden on 15/05/2018 19:10:01

An interesting little project.

Does it matter, I don't think so, as long as it's something like it will be OK

I don't think it matters either. One of the most famous electric locomotives in the world, Pennsylvania Railroad's GG1 in the USA, used two 385 HP motors per wheel set / axle with a "quill" axle. Motor pinions drove quill gear, quill applied force to modified spokes of each wheel via spring cups on the quill. Only 4620 HP total though, and only lasted from 1930's to 1990's, but hey..... 2 motors each axle might just work for your 0-4-0 project. Pics from various websites below.

Edited By Jeff Dayman on 16/05/2018 04:58:13

That was some loco Jeff, thanks for the pictures. I see from the picture of the motors that they were mounted on the axle as you can see the axle bearings below the motors. This is the way I am mounting my motors, the motor mounting plate has a central bearing which the axle runs through. With the axles having suspension (springs) it was the easiest way I could see to maintain the relationship/position between the motor pinion gears and the drive spur gear which is fixed to the back of the wheels.

I am reasonably confident it should work ok but wouldnt want to count my chickens too soon.

Since I started the design I have changed the gear ratio, due mainly to availability of suitably sized gears at the right price. The ratio is now 6.25 to 1 this should give approx 7 - 8 mph top speed. I have gone with MOD 1.0, I considered finer gears but I thought MOD 1.0 had a little more meat to them without them being too coarse.

There is no clever calculations to any of this its mainly my gut feeling with a bit of "if it looks right it probably is"

I,m getting itchy fingers as I want to get the build started but as I dont have any machining I have to rely on other people for machined parts. I can and will do a lot by hand but at the moment still waiting for chassis parts before I can make a start.

Ron

Edited By Ron Laden on 16/05/2018 09:43:04

Well whilst waiting for chassis parts to arrive I have started on designing the loco body. The main body panels will be from 6mm Birch plywood with some thin sheet aluminium and plastic etc.

Obviously this will not be a scale loco but a sort of look alike, "very loosely" based on a 03/04 type shunter. The size of the body will be no where near scale, thats impossible as having to house the 12 volt leisure battery dictates the sizes.

In fact the driver would have to be 9 feet tall to stand on the foot plate and look out of the windows.. so at best it will be cartoon scale.

Update on the parts I am waiting for is another 2 weeks so will just have to be patient.

Ron

Morning guys,

I am trying to get my head around choosing the correct compression springs for the loco. There will be 4 springs, one sitting vertically above each axle box. The loco and leisure battery will total 28kgs and I would like the 4 springs to be just starting to compress with that load, leaving the rest of the compression to deal with the humps and bumps of the track.

Is it as simple (doubt it) as 4 x 7kg springs or doesnt it work like that, I know nothing about the workings of compression springs...?

p.s. I guess my question is does a spring rated at 7kg support 7kg,s without compressing or is it fully compressed at 7 kg.

Regards

Ron

Edited By Ron Laden on 20/05/2018 09:30:15

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Edited By Redsetter on 20/05/2018 10:50:08

Thanks Tony, I will check the the rating figures to see if the springs are reference mm or cm.

I can well appreciate that this is only a starting point, I have watched a lot of youtube builds and some of them have started with a certain spring and then made 2 or 3 changes before getting it right and a lot of it was just trial and error.

Ron

Just out of interest I located my digital tacho and did a non loaded check on the 4 motors.

The motors are rated at 5167 rpm, the readings came out at 5988, 5997, 6040 and the highest at 6235 rpm.

The motors are running a fair bit faster than the speed quoted in the spec but then I dont know how they test or arrive at that figure.

Three of the motors are very close considering they are just can motors with the fourth one a little higher. They will be running through a 6.25/1 reduction so they should be fine as a set.

Ron

Edited By Ron Laden on 23/05/2018 07:42:46

The total average speed is 5940rpm, it wouldn't take much voltage difference to make the difference to the rated 5167rpm.

Ian S C

As already said four similar motors should would work together as a set without problems.

It's not particularly useful to measure no-load rpm as this is an unusual condition in practice. (It might happen if the shunter derailed!)

DC Motors operate under a range of conditions between trying to start from stopped (or stalled) and no load. The characteristics of a motor - torque, power and rpm - vary across it's operating range and are best expressed as a graph. It's more common, but less helpful, for makers to give figures for torque and power at one particular speed, usually the one at which the motor is most efficient. They may also indicate that the motor only meets those figures intermittently - don't run motors like that continuously, they need time to cool off between bursts of work.

Torque, power and rpm aren't related intuitively. You might expect maximum torque and power to occur at maximum speed. Nope!

Torque is the measure of a motors ability to apply a turning force. It is usually highest when the motor is stalled, and drops to almost nothing at full speed. Power is the rate at which the motor can do work over time. Normally the power output of a motor peaks somewhere between zero and max rpm.

These graphs are from 'Understanding D.C. Motor Characteristics' - worth a read if you're interested in theory. The graphs simplify the relationships by showing them as a straight line. A real motor's characteristics would be a curve of roughly the same shape. The shape of the curve might indicate one motor to be more suitable for an application than another but that's grown-up design.

Note High Torque occurs at Low Speed, and that power output in this condition is Low. As the excess input power has to go somewhere it appears as heat. A motor stalled for too long is likely to burn-out.

Next graph shows that both torque and power output are also Low at maximum speed, putting a limit on the maximum speed to which the shunter can be pushed.

So, ideally, an electric motor should be operated somewhere in the middle, where torque and speed combine to produce maximum power. Where necessary a gearbox is used to ensure this happy condition.

The good news is that:

• Four motors of the same make and size will have similar characteristics that, on average, will allow them to work together well. This is very different to fitting four different motors and hoping for the best. It's important that the motors match as a set, which yours do.
• In practice, only enough torque is needed to start the loaded shunter. Once moving, the motors will tend to move towards the sweet spot where they deliver maximum power/efficiency. (Quite likely this will be near your intended cruising speed because you calculated how to convert motor speed to axle speed)
• As the shunter isn't a race car, the motors you have available should comfortably support its intended purpose.

My only worry would be if the shunter was operated like a real shunter, that is continually start/stopping heavy loads in a marshalling yard. In that case the design would need beefing up, for example with gearing down and fan cooling the motors.

Bottom line, it should work as you have it.

Dave

Edited By SillyOldDuffer on 23/05/2018 10:42:18

Spring rate is typically the force to compress a spring by one inch (for values in pounds) or 1mm (for values in kg)

With a 7kg load a 1kg spring rate will give a 'sag' of 7mm, which is probably about right.

Assuming that in normal use the weight transfer you might expect is for 75% of the weight to be shifted forwards or aft as you go over a bump, brake or accelerate hard. That would put 10.5 kg over one each of set of wheels and 3.5kg on each of the other two wheels.

The springs at one end would compress by another 3.5mm and expand by 3.5mm at the other.

This seems to be in the right ball-park for 5" gauge but may be a bit too soft, but 1kg or 2kg rate springs could be a good start.

If the springs are too hard the loco may struggle to keep good adhesion or risk derailing. If it is too soft, it will bounce all over the place and may 'surge' back and forth when pulling hard.

You may find you need to experiment, I had to fit slightly stronger springs to my shunter.

Neil

Thank you Ian, Dave and Neil that is a lot of interesting information and certainly made things a lot clearer.

Dave, although the model will have a shunter type body it wont be operated as one. The track it will run on is elevated with no points and no sidings. This is my first scratch build and the aim is to produce a small run around loco which hopefully is capable of pulling myself and our two young grand daughters. The shunter type body is mainly due to it being quite easy to produce and with a bit of detail it should look half decent.

I appreciate that testing the motors with no-load doesnt really show much but I was interested how close they were and also to check that none were faulty.

Neil, thanks for the spring info, I have some springs but I think they may be a bit on the light side. Once I get the chassis built (still waiting for parts) I will be able to try the springs and go from there. I guess there is going to be some trial and error experimenting here.

Regards

Ron

Edited By Ron Laden on 23/05/2018 14:45:27

One of the problems with producing a 5 inch single battery 0-4-0 or 0-6-0 loco is the dimensions of the battery which dictates the size of the loco body. My 12V - 75 amp leisure battery measures 260 mm long x 175 mm wide x 225 mm high. The length is not generally a problem but the width is and the height even more so. I guess thats why most of the small single battery loco,s you see are square boxy diesel types as the body can be modelled to something like the correct dimensions around the battery.

This is the way I have been thinking but yesterday I wondered if a lookalike steam type loco would be possible. I looked at the dimensions of one or two pannier types but there is no way you can get any where near correct dimensions when considering housing the battery.

So below is a rough sketch of what I came up with, its a millions miles from anything scale or realistic and looks more like something from the Thomas the Tank shed. The broken line around the centre is the area needed for the battery. I tried to visualise it finished and I think it could be fun. Seeing as my two main passengers will be our two great grand daughters, I think it could go down quite well with them. I have not decided on it and it may still be a diesel type but its food for thought.

Scale guys look away now...

Maybe worth a thought to put your battery in a scale wagon coupled behind the locomotive. That would enable a more scale steam outline for the locomotive if you want it. Weights (like lead or steel plates or shot) could be added to the locomotive to help with adhesion in the absence of the battery.