Flywheels in small 4mm shunting locomotives

[DCB]

It seems to me that to get the best of both worlds one needs a heavy flywheel but a torque limiting clutch to protect the gear train if te loco rams a buffer stop or something gets caught in the valve gear.  The cheapest and nastiest loco I ever bought, H0 0-8-0T battery powered loco which came with two wagons and a circle of plastic track for a fiver actually had a spring loaded cam arrangement to act as a torque limiter so its not exactly rocket science. 

[TheGunslinger]

It seems to me that to get the best of both worlds one needs a heavy flywheel but a torque limiting clutch to protect the gear train if te loco rams a buffer stop or something gets caught in the valve gear.  The cheapest and nastiest loco I ever bought, H0 0-8-0T battery powered loco which came with two wagons and a circle of plastic track for a fiver actually had a spring loaded cam arrangement to act as a torque limiter so its not exactly rocket science. 

 

I have a gorgeous USRA 0-8-0 switcher in brass from Lambert, and one of the nice details is a very simple friction clutch on the motor that actuates the reverser lever whenever the motor changes direction. It is however very fiddly and requires fine adjustment. A similar principle could be used to make a larger clutch for the driveline and would probably be workable. The Lambert one is tiny and is only so fiddly because of the limited surface area for friction.

 

Another thing to consider with flywheels (this occurred to me while musing why nobody gears up the flywheel rather than run it straight off the motor shaft) is that spinning up the flywheel is a load on the motor. There is no doubt a balancing act between enough weight to help prevent abrupt stops of the motor, but light enough it isn't overloading and overheating the motor.

 

I did a brief search and found that DC capacitor packs have been discussed in the past and the general consensus was that DC power was just too inefficient, and that you would need a bridge rectifier and PWM module controlling the motor to make efficient use of a capacitor, which is most of the hardware for a DCC decoder.

Edited February 27, 2018 by TheGunslinger

[AndyID]

why nobody gears up the flywheel rather than run it straight off the motor shaft) is that spinning up the flywheel is a load on the motor.

 

Not entirely

http://www.rmweb.co.uk/community/index.php?/topic/116955-high-energy-flywheel/

[hayfield]

Hear, hear!

I would go so far as to say that a keep-alive capacitor of the same physical size as the flywheel will have a greater effect on smooth running than the flywheel will.

So, if you're building a small 0-4-0 shunter, leave out the flywheel and fit as large a capacitor as possible in its stead.

This is because a fully charged capacitor can store much more energy than the flywheel can.

Cheers,

John.

 

Whilst being in the group who like flywheels, my Bemo H0m loco has an electrical inertia system which has an inbuilt electrical system which is very effective

[TheGunslinger]

Not entirely

http://www.rmweb.co.uk/community/index.php?/topic/116955-high-energy-flywheel/

Hmmm, I think you guys were onto something with the magnetic clutch, but I'm surprised nobody tried setting it up with opposing magnets. This would create what is essentially a sprung drive, with progressively increasing resistance to slip as the magnets are forced closer together, but a distinct point where the opposing fields is stronger than any force the loco imparts and it will "slip" no further. It'd be friendly on gearboxes too as all your forces are cushioned.

[AndyID]

Hmmm, I think you guys were onto something with the magnetic clutch, but I'm surprised nobody tried setting it up with opposing magnets. This would create what is essentially a sprung drive, with progressively increasing resistance to slip as the magnets are forced closer together, but a distinct point where the opposing fields is stronger than any force the loco imparts and it will "slip" no further. It'd be friendly on gearboxes too as all your forces are cushioned.

 

I don't think that's going to work as you might expect. I believe the input and output will either be locked together (synchronized) or, if the torque exceeds some value, completely asynchronous with the output oscillating but not rotating. It will behave more like a torque limiter than a progressive friction clutch.

 

It might be possible to use powerful magnets to create some sort of eddy current drive. They only transmit torque when they are slipping but that might not be a problem in a shunter.

Edited March 1, 2018 by AndyID

[TheGunslinger]

I don't think that's going to work as you might expect. I believe the input and output will either be locked together (synchronized) or, if the torque exceeds some value, completely asynchronous with the output oscillating but not rotating. It will behave more like a torque limiter than a progressive friction clutch.

I don't think I explained myself very well. The magnets would be set up in a manner that would prevent them from slipping past one another (preventing the "cogging" problem that was noted when using attracting pairs of magnets) because of strong repulsion force. Heck, you could orient them in a manner that the magnets actually physically touch like teeth on a gear, but the strong repulsion would prevent them ever making contact.

 

There is potential for the flywheel to oscillate, bouncing from one repelling pair back to another, but that would only happen if the drive end was completely stopped, and the torque required to reverse the flywheel's direction of rotation was less than the torque required to drive the loco wheels i.e. hit a buffer stop.

 

Here's a diagram I threw together.

[AndyID]

The magnets would be set up in a manner that would prevent them from slipping past one another

 

In which case you might as well replace the magnets with a torsion shaft (some sort of spring). The point about a clutch is it does allow the input and output to rotate at different speeds while still transmitting torque. I may be confused (that's not unusual) but isn't that what you are trying to achieve?

[DCB]

Just wondering about a small circular super neo magnet on the out put shaft and a larger super neo ring on the input shaft with a small clearance between,  Its late, it probably won't work, I'll order some from China and play with them when they arrive in July.

[TheGunslinger]

In which case you might as well replace the magnets with a torsion shaft (some sort of spring). The point about a clutch is it does allow the input and output to rotate at different speeds while still transmitting torque. I may be confused (that's not unusual) but isn't that what you are trying to achieve?

 

Essentially trying to cushion the torque forces on the gearbox that would be created by spinning up a flywheel two or thee times faster than the motor shaft. You could use a spring or torsion shaft but they're prone to physical wear and they aren't very precise at a miniature scale. My original idea involved less magnets that would give you more "free play" between magnet interactions, allowing the input and output to spin at different speeds (albeit only momentarily). 

 

You could pull that assembly further apart so the two only interact with magnetic fields and make it a true clutch, however we may end up with "cogging" vibration again as the magnets pass one another and you have a momentary alignment of attracting poles. I've got a bunch of 3mm neodymium magnets, might have a play and see what kind of interactions we get.

Edited March 2, 2018 by TheGunslinger

[Ruston]

Just where are you going to fit all this stuff in a small shunting loco? I have trouble designing things to fit a motor and gearbox in, let alone all these fancy clutches and magnetic flywheels.

[TheGunslinger]

Depends on the loco. Most of my ideas are based around upgrading an existing flywheel.

[Ruston]

Depends on the loco. Most of my ideas are based around upgrading an existing flywheel.

Then how would your get one in this, for example?

 

You can just about get a fag paper between the flywheel and the back of the engine compartment and the sides. This is what I mean by small shunting locomotives. The loco is about 4 inches long, so there simply isn't the space for fannying around with magnetic clutches. This is one of my larger locos!

[AndyID]

Then how would your get one in this, for example?

 

DE2-003.jpg

You can just about get a fag paper between the flywheel and the back of the engine compartment and the sides. This is what I mean by small shunting locomotives. The loco is about 4 inches long, so there simply isn't the space for fannying around with magnetic clutches. This is one of my larger locos!

Plenty of room in the cab.

 

Running shoes on, and he's off!

[TheGunslinger]

Then how would your get one in this, for example?

For starters, this why I don't like chassis where the gearbox is on the front drivers. You've got open space in the nose which is going unused. Perfect if you want to slip a DCC chip in there though.

 

That is quite a large motor in there, which may be overkill if you're only using this as a shunter; it isn't meant to go fast, and even lots of torque may just cause wheelslip. Does the current flywheel help with power loss?

[itsthegman]

Then how would your get one in this, for example?

 

DE2-003.jpg

You can just about get a fag paper between the flywheel and the back of the engine compartment and the sides. This is what I mean by small shunting locomotives. The loco is about 4 inches long, so there simply isn't the space for fannying around with magnetic clutches. This is one of my larger locos!

Is that 4mm as it looks a large motor?.

 

G.

[Regularity]

For starters, this why I don't like chassis where the gearbox is on the front drivers.

The alternative being what? Driving the middle axle which means there is little space for the motor, let alone a gearbox, or the rear axle, which means with the gearbox in the cab, or a drive extender, which will simply reverse the current order of gearbox-motor-flywheel, which whilst creating more space, would not create enough for a clutch and a significant flywheel, possibly creating some balance issues into the bargain?

You've got open space in the nose which is going unused.

 

That open space is balanced by the open space in the cab. Most of the mass in this example is over the wheels, keeping the centre of gravity where it needs to be.

 

In answer to the OP, a simple solid flywheel will help smooth out any cogging, and add a little bit of inertia, which is all he wanted to know.

[Ruston]

For starters, this why I don't like chassis where the gearbox is on the front drivers. You've got open space in the nose which is going unused. Perfect if you want to slip a DCC chip in there though.

 

That is quite a large motor in there, which may be overkill if you're only using this as a shunter; it isn't meant to go fast, and even lots of torque may just cause wheelslip. Does the current flywheel help with power loss?

 

You may not like chassis where the gearbox is on the front drivers but if the kit, or even the layout of the prototype, dictates it should be so then you don't have much choice. That is far from being a large motor; the body is 12x16mm and 20mm long. Why you think the size of the motor is related to the speed of the locomotive?

 

Wheelslip really isn't an issue unless there is more weight hung behind the loco than it can pull but then that applies to every model loco ever made.

 

You haven't answered how you would propose to fit one of your magnetic flywheel/clutch devices...

Edited March 3, 2018 by Ruston

[AndyID]

 

Or am I missing the point? Is there some other advantage to a flywheel on a shunting loco because a lot of people seem to fit them and I guess they must know something that I don't.

 

So why did you bother fitting a flywheel in that shunter, or are you just trying to wind us up?

[bertiedog]

It smooths out the starting jerk, and the overun to halt, shunting engines are high gear ratio, speed slow, so need aid to run over the frogs, and dirty track with the addition of motor smoothness whilst running

Shunting engines are closely observed in operation, and need the predictable performance to cover the coupling operation. DCC can do with a decent mechanism standard.

With RTR the fact it has a flywheel fitted does not g/tee that it will function better than  on a flywheel free one., DCC will never cure a bad design of either type.

Stephen

[DCB]

Then how would your get one in this, for example?

 

You can just about get a fag paper between the flywheel and the back of the engine compartment and the sides. This is what I mean by small shunting locomotives. The loco is about 4 inches long, so there simply isn't the space for fannying around with magnetic clutches. This is one of my larger locos!

With a coarse worm and small flywheel you don't need any torque limiting clutch.  A bevel drive or a fine worm like a Romford 60 :1 and a sudden stop can cause damage to the gear train or gearbox if you have a etched motor mount or severe damage to valve gear.  Where you need a clutch is bigger locos, I quite fancy a Q1 0-8-0T or getting my Ks  42XX with H/D Ringfield motor running again. It broke its coupling rod when something jammed,  I think a toque limiting clutch should be between the worm wheel or final drive gear on a bevel system and the axle. 2 spring loaded balls bearing on flats on the axle?

 

Edit

 

Took a while to figure out but putting a couple of flats on the axle and then drilling holes in a Romford or H/D drive gear where the screw usually goes so a ball bearing or two fit down with small springs, maybe a collar to give more spring length and to keep the springs in place an outer collar or band with a hole in it which when the springs are in turns and is secured by a set screw.   This should let the gear slip if there is too much torque applied like when you ram the buffers . Hopefully fine tuning of springs bearings and flats should get a reasonable compromise.  see pic

Edited March 5, 2018 by DavidCBroad

[Ruston]

So why did you bother fitting a flywheel in that shunter, or are you just trying to wind us up?

No, i am not trying to wind anyone up. I fitted the flywheel because lots of other people fit flywheels to small 4mm scale shunting locos and I thought I'd give it a try. It doesn't appear to have made any difference and that's why I started this topic, which seems to have gone off course into some kind of wonderland.

[AndyID]

No, i am not trying to wind anyone up. I fitted the flywheel because lots of other people fit flywheels to small 4mm scale shunting locos and I thought I'd give it a try. It doesn't appear to have made any difference and that's why I started this topic, which seems to have gone off course into some kind of wonderland.

That tends to happen a lot on RMweb

 

In so far as it stores kinetic energy your flywheel absolutely is making a difference but under ideal operating conditions (no intermittent electrical connection to the motor) you won't see any difference.

 

If you want to quantify the effect you can run your locomotive on to a dead section of track and measure how far it goes. Then repeat the test without the flywheel.

 

Obviously all other conditions should be equal and you'd want to repeat a series of tests at different speeds, etc.

[TheGunslinger]

Why you think the size of the motor is related to the speed of the locomotive?

 

Because in the case of DC electric motors, the diameter of the armature directly correlates with the RPM produced under load.

 

 

That is far from being a large motor; the body is 12x16mm and 20mm long.

 

Considering I'm running a brass USRA 0-8-0 off a motor 2/3 that size (10mm diameter 15mm long cylindrical body), yeah, it's pretty big for what you need it to do. The problem is OO scale modellers are living in the dark ages thinking the carbon brushed, rubberized "fridge magnet", 3-pole electric motors in their RTR locomotives are the pinnacle of technology when somebody bothers to make them coreless or skew wound. In such a tiny shunter a motor for a large N scale diesel would work just fine.

 

I bought some Mabuchi electric motors with 6 poles and rare earth magnets that are about the same size as your shunter's motor, and they are monstrously powerful.

[Regularity]

I bought some Mabuchi electric motors with 6 poles and rare earth magnets that are about the same size as your shunter's motor, and they are monstrously powerful.

Was that a one-off, or are they available to everyone?