Another Newbie trying to not reinvent the wheel!

Hi, I’ve only just discovered the wealth of information amassed by the various contributors and having read, and hopefully digested it, would like to ask the question which eventually follows.
 
I have been aware of “Detritus” for a long time, as a result of being involved in 16mm narrow gauge, and thought that it would be good to try something similar.  Dave Watkins website at [url=http://www.davewatkins.pwp.blueyonder.co.uk/16mm railway/detritus.htm]http://www.davewatkins.pwp.blueyonder.co.uk/16mm%20railway/detritus.htm[/url]
gives a lot of information about a mechanical drive solution, if suitable gears can be sourced.  I initially contemplated this route and found a forward/reverse gearbox made for an HPI Savage which, with work, could be adapted.  These are available in the UK for about £36 from Modelsport.co.uk.
See http://www.rcgroups.com/forums/showthread.php?t=1269548 for details of general arrangement of this gearbox.
 
However, the electrical route looks far more interesting.  My prototype is likely to be an Australian sugar cane loco.  These are relatively large, which I think may be needed to accommodate the volume of the silencer that I would wish to use on the Force 15 engine I have purchased for this project.  I initially planned on using a Graupner Speed 600 as the generator, being unaware of the possible advantages of the brushless motors advocated here.
 
The question is has anyone tried running either a brushed, or brushless, motor at say 3 to 4 times the engine speed?  In my quest for quietness (not silence, as I do want it to sound like an IC engined loco) running the motor at only slightly above its tickover speed would seem to be an advantage.
 
Suitable metal, acetal and delrin 1 module gears are available from Parkside Electronics at sensible prices.  The acetal and delrin gears are all 10mm wide and are used in the majority of 5 and 7.25” gauge battery electric “diesels” in the model engineering world and seem sufficiently robust for use here. 
Possible advantages would include quieter running of say a 54t acetal gear driving a 14t steel pinion and also the approx 4:1 advantage where the electric motor is to be used for starting the IC engine.
Parkside are at http://www.parksiderailways.co.uk/1_module_gears_21.html
 

I’m fortunate in being a model engineer with a well equipped workshop so making one off flywheels, gear cases etc isn’t a problem.  So what do you think?

Hello and welcome to the forum.

Good to see another diesel project manifest itself.

For motor speed question, yes and no!

A DC brushed motor dynamo will not handle very high rpm. Although I have had an 850 Torpedo motor up to about 20,000 rpm briefly with no apparent damage.

A brushless motor depending on size and type will handle much higher rpm especially those designed for use in model aeroplanes.
They don't even seem to get very hot!

However.....you may encounter some stalling problems with trying to run a large electric motor with a glo engine running at slow speed. You may have to juggle a fair bit with gear ratios and look at keeping the glo plug energized.
Glo engines don't really like running at idle for long periods.

You can of course try a very low KV value for the brushless motor. The lower the KV value the less rpm required for voltage output. This may eliminate or reduce the gearing required.

A good chunky brushless motor will start a small glo engine direct.

Good luck.

Carl
Thank you for your welcome and comments.  I am aware of the problems of running glow motors at relatively low revs.  I had already planned to incorporate a heavier flywheel than is common in cars, on the advice of a marine modeller with considerable experience of open water racing, and that provision of power to the plug may also be required.
 
To take this forward I have ordered a brushless motor and gears to try a 3:1 and 4:1 inc of generator speed over engine revs, effectively running the engine well below its max revs.  I have today run the pull start Force 15 for the first time and am impressed by the ease of starting and relatively cool running, admittedly at low “running in” revs.  I will post the results of my gearing trials when it’s all put together.
 
One further question though, I note that your generator outputs directly to you traction motor, with speed control via changes in engine revs.  If an ESC is used between the generator and traction motor, where do the excess volts/amps go when the generator is generating and the loco is stationary?  Is a ballast load, battery, or other means of dissipation of the excess reqd and does the ESC need any form of protection.
I really can appreciate the simplicity of your direct system, but am trying to avoid having an excessively noisy loco considering the locations where it will principally be used.
 

Mike

I understand what you are trying to do. If you can get your glo plug engine to run smoothly at idle with enough torque then that is a start. Does the force 15 carb have 2 mixture setting screws (high end and low end) and an idle speed setting. If so you may be able to fine tune the mixture so it will run richer and slower.
You can get higher spec carbs for certain engines.

If you use an ESC - and the technology is changing all the time, you will probably need at least 5 volts input for the esc to work. Most of the ones I have used are about this.

The 'excess' current doesn't go anywhere and doesn't need to.  If you want you could put some sort of indicator on the output of the esc such as a filament bulb to tell you that electricity is indeed flowing.

It would be same if you connected a battery to supply the esc.
The load will draw as much current as it needs if it is available. If it's not the esc will shut down.

My generators don't output electricity directly to the traction motor. It is rectified first. You will need to do that if you use 3 phase BLDC motors but not for a standard DC motor dynamo.
You may want to consider some optional smoothing via a capacitor and some fusing to protect against short circuit and some reverse polarity protection such as a diode. Most escs are very sensitive to that.

I have heard of some issues when running alternators open circuit especially on cars and boats but I haven't experienced any open circuit problems in my models.

Hi Mike,

I'm surprised that you thought electrical would be more interesting    I'm into my 3rd year of building a mechanical and it's been very interesting.  I'll soon be at the stage to run the chassis again, as the final drive has been finally worked out and fitted.

My loco is running an OS 26 FS car motor, and at the lowest sustainable revs has heaps of torque.  So much so that however hard I pressed down on the chassis and held it back, the wheels would just slip without the engine revs changing much.  My loco will be run at idle speed only.

Best wishes,
Dave,

Carl / Dave
 
With ref to your comments/queries.  The motor has two setting screws and a slow running adjustment, all of which I am starting to come to terms with.  The carb is a slide pattern and is very quick acting, might be good in a car, but a trad barrel carb might be more applicable here.  This is something I may try as I have one on an old marine engine.  The initial settings suggested by the manufacturer are very rich, making it very easy to flood, these I have now started to lean out.  They don’t however give any idea as to what normal running settings should be.  A tank now lasts much longer and the motor seems to run relatively cleanly at low revs.
 
When I started out on this project I envisaged going the mechanical route, to the extent that I had already purchased a HPI Savage forward/reverse gearbox for something like “Detritus”.  I can, however, see advantages in the IC motor/generator/traction motor route and I intend to try this first.  One principle advantage may be electric starting.
 
I think an ESC will be involved and I had already picked up on the need for rectifiers and also planned to include fuses etc.  Are there accepted ways of smoothing using capacitors and are these as necessary when a brushless motor is used as the generator?
 
I can also see pros & cons to clutches and plan to try without to start with.  The advantage is a direct drive from elec motor to IC eng allowing electric starting, downside is it’s harder to start an IC driving a generator without a clutch to disengage it using the pullstart and it will also inc the load on the pullstart.
 
I accept your comment regarding an electrical “load” not being reqd when the loco is stationary, my query was based on the analogy of a water pump, where a pressure release valve would be reqd to prevent overloading the IC motor.As I said at the start I am anxious not to reinvent any “wheels”, but coming from a rail engineering background (Civils) and practising model engineering, its easy to become bogged down in how its done full size, what works at 5” gauge and completely miss the simplicity reqd for smaller gauges.
 
Regards and thanks

In practice Mike I have personally found that capacitor smoothing hasn't made a great difference with or without using an esc.

You won't overload the motor by 'supplying' too much current to it. You will overload the motor if you supply too much voltage to it.

Imagine using a 12 volt battery that has a capacity of 5 amps to supply a 12 volt motor that draws 1 amp. It doesn't make any difference to the motor if you change the battery for a 50 amp one. The motor will still draw 1 amp.

I have started a glo plug engine with a BLDC motor and with the pull start connected. It doesn't make any difference to the load. So you can eliminate a clutch and keep the pull start.

The electrics for using the BLDC as a starter need some consideration.

The excellent mechanical engineering that Dave has produced is far beyond my time and expertise but a simple mechanical transmission has always been an aim of mine.