Compensation, springing or another way?

[Ruston]

Afternoon all,

 

I am currently making drawings to build this loco in 4mm/OO and I am stuck on how to set it up.

 

I thought about setting it up with a knife edge for the leading axle and the rear axles sharing a sub-frame that moves around a pivot at their wheelbase centre, as in the Judith Edge Kitson long boiler locos. The problem is that the motor/gearbox that I want to use takes up the width of the main frames and, ideally, needs to be fixed to the main frames, leaving no space for the subframes.

 

Will a fixed rear axle and sub-frame on the leading two axles still work effectively in terms of traction and electrical pickup?

 

I really don't want to get into springing as it's far too complex to design and build.

Edited May 28, 2018 by Ruston

[N15class]

If you want compensation, use as you say centre pivot on the front and side beams on the rear two. Then the motor unit can still fit and if supported by a wire will stop it rotating but allow it to move with its axle.

Or you can use CSB the clay site will help you with that.

 

If you need to have the motor fixed you can leave the rear axle fixed and then a centre beam. Pivoted in the centre between the two from drivers. This will give you Mike Sharman style compensation.

[wagonman]

Or you can use CSB the clay site will help you with that.

 

 

 

Close – but CLAG would be better!   :-)

[N15class]

Close – but CLAG would be better!   :-)

Damn spell checker.

[Michael Edge]

Afternoon all,

 

I am currently making drawings to build this loco in 4mm/OO and I am stuck on how to set it up.

 

HERCULES-4mm-scaleforweb.jpg

I thought about setting it up with a knife edge for the leading axle and the rear axles sharing a sub-frame that moves around a pivot at their wheelbase centre, as in the Judith Edge Kitson long boiler locos. The problem is that the motor/gearbox that I want to use takes up the width of the main frames and, ideally, needs to be fixed to the main frames, leaving no space for the subframes.

 

Will a fixed rear axle and sub-frame on the leading two axles still work effectively in terms of traction and electrical pickup?

 

I really don't want to get into springing as it's far too complex to design and build.

 

Fixed rear axle will work a lot better than nothing, I've built lots of locos with this half compensation in the past. Central compensation beams leave the loco prone to wobbling in my experience - and also need individual movement for each axle bearing. This is usually done with hornblocks which you probably don't want but you could perhaps use individual swinging arms as I do for single axles.

[Ruston]

Fixed rear axle will work a lot better than nothing, I've built lots of locos with this half compensation in the past. Central compensation beams leave the loco prone to wobbling in my experience - and also need individual movement for each axle bearing. This is usually done with hornblocks which you probably don't want but you could perhaps use individual swinging arms as I do for single axles.

Thanks.

 

Another problem with getting the beams in is that the part of the frame between the front axles, where the pivot needs to go, is very close to where I need a slot in the frames for the motion bracket and a hole for a brake hanger but I think I can make it work by beefing up the frames at that point by going double thickness there.

 

I am going to make provision for a cross member above the rear axle to take a knife edge (actually an adustable screw). With the motor/gearbox being inclined, the top of the axle ought to be exposed, so I may be able to get swinging arms in the frames, I will put holes in the frames, to the rear of the cab steps, for the pivots. If it all fits then fine but if not I'll just fit the rocking beams on the front axles.

[N15class]

I often hang the motion bracket on a flat cross member let into the top of the frames so it can be removed with the cylinders.

[Jeff Smith]

I don't think you can use twin beams with a fixed third axle. Twin beams are good with a rocking third axle or bogie. With twin beams and a fixed third axle there is a danger that one of the fixed wheels will lift when one of the other wheels is forced up or down. You basically have two parallel fixed axes, the fixed axle and the fixed beam pivot. If a wheel on a beam lifts, the wheel on the other end of the beam moves down, this will lift this side of the loco and with it the fixed axle. A central beam will give the same effect but to a lesser extent and I think would be preferable.

[Michael Edge]

Never mind the theory, it does give some benefit in practice - and that comes from very long experience.

[N15class]

Fixed rear axle will work a lot better than nothing, I've built lots of locos with this half compensation in the past. Central compensation beams leave the loco prone to wobbling in my experience - and also need individual movement for each axle bearing. This is usually done with hornblocks which you probably don't want but you could perhaps use individual swinging arms as I do for single axles.

With this system you have make sure the centre of gravity is between the fixed axle and the pivot beam. If it's forward if it the loco will be unsteady.

[Izzy]

I have often used tbc with both fixed and downward floating outer axles. Either works well. Let’s face It, apart from probably P4/S7, or unless you have appallingly laid track, it’s as much about improving electrical pickup as it is road holding. If space for hornblocks, beams etc is at a premium then why not just slot the frames downwards for a bit of axle movement. A little is all you need. All too easy to get hung up over theory and lose sight of simple ways given the myriad options around.

 

Izzy