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Using DCC for gravity shunting


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I've always been fascinated by the East Kent Light Railway but anyone who knows the line will know that the termini are very basic, especially Canterbury Road, and don't have run rounds. The loco gets to the right end of the train by running into a siding and then the guard gravity shunting the train - usually just a single carriage - past the siding into the platform.

 

My question here is whether it would be feasible to fit a "brake" in a free running carriage which is applied using a servo which is controlled by an on-board decoder.

 

Anyone have any thoughts? Anyone tried it?

 

(I've had a search on rmweb and not found any previous discussion. That's not to say there hasn't been of course)

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Scaling down "inertia" will be very diffecult & will need some serioyus fettling to make it work & conti nue to work.

 

Maybe, fit a motorised bogie to the coach to give the illusion that it is running by gravity ?

 

The loco & coach will have to run as a consist between the stations & then as single units.

 

May work, may be too much faffing around.

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As with the others, I suspect getting the free-wheeling to work may be tricky.  If you can, then the brake should be simple, just a strap around an axle which is pulled tight as the brakes are applied.      

 

Doing the brakes by DCC is OK *if* the coach has reliable pickups.  Which are great if its fitted with them, but if added afterwards are a potential source of friction on the free-wheeling.   Alternative might be battery and some sort of wireless control:  infrared or radio; either requiring pretty minimal control.  

 

 Could use a servo for the brake (though you then need a decoder with servo control outputs, look at Zimo and ESU for those).  Or could just use a small DC motor and stall it briefly - a bit of fine cord would around the motor shaft pulls the brake on, and a small light spring to pull it back to release again.  (See the Preci-models motor kit for opening Kadee couplers as an example of this).

 

Motorised coach doesn't quite cut it for me, too much hassle to have to consist it with a loco, and speed match stuff.   What may work on motorising is a mechanism which can be engaged/disengaged by a servo:  perhaps a large rubber roller pushing an axle around by friction, which can be lifted away from the axle when not needed.  

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I have done this on a few wagons, by motorising the wagon correct loose shunting can be performed. The only difficulty is moving the loco and wagons at the same time -  needs an extra operator! It was shown at a few exhibitions in the past.

 

In the case of your description of the coach, it would probably be easier, as when the coach is gravitating back, the loco would be stationary. You could have on-board uncouplers as well - a real 'hands-off' experience.

 

A motor in the coach could replicate the mass of the coach, it would need to move at about walking pace. When in the train with the loco, it would run as a consist.

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3 hours ago, Nigelcliffe said:

As with the others, I suspect getting the free-wheeling to work may be tricky.  If you can, then the brake should be simple, just a strap around an axle which is pulled tight as the brakes are applied.      

 

Doing the brakes by DCC is OK *if* the coach has reliable pickups.  Which are great if its fitted with them, but if added afterwards are a potential source of friction on the free-wheeling.   Alternative might be battery and some sort of wireless control:  infrared or radio; either requiring pretty minimal control.  

 

 Could use a servo for the brake (though you then need a decoder with servo control outputs, look at Zimo and ESU for those).  Or could just use a small DC motor and stall it briefly - a bit of fine cord would around the motor shaft pulls the brake on, and a small light spring to pull it back to release again.  (See the Preci-models motor kit for opening Kadee couplers as an example of this).

 

Motorised coach doesn't quite cut it for me, too much hassle to have to consist it with a loco, and speed match stuff.   What may work on motorising is a mechanism which can be engaged/disengaged by a servo:  perhaps a large rubber roller pushing an axle around by friction, which can be lifted away from the axle when not needed.  

 

The coach wheels would have to be split axle jobs, any wipers or those DCC Concepts spring like wrap-arounds would introduce too much friction. I have made split axle tender axles for tender pick-up and they worked well. (Incidentally adding tender pick ups makes locos much more reliable)

 

For the brake I envisaged just a light wire - guitar E string springs to mind - pressing onto one of the coach axles. Experimentation required certainly.

 

My first thought was a small motor turning a threaded flywheel which pulls a screw thread. Again, experimentation required. The purpose of this question here was to ask about controlling either that or a servo with an on-board decoder.

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1 hour ago, whart57 said:

 

I've seen this but that's a motor in the coach isn't it?


Yes, it is. I thought you wanted to be able to model a gravity shunt, and was pointing you to a method that had been used to model that. I didn’t realize you were wanting to actually shunt using only gravity for power.

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59 minutes ago, whart57 said:

any wipers or those DCC Concepts spring like wrap-arounds would introduce too much friction.

I would agree regarding the wipers but not with the DCCConcepts spring pickups - I have them on a number of rakes & find they have negligable friction, especially when used with track magic on the acels.

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Seems to me the way to do a gravity shunt by gravity is to have a gradient around 1 in 75 and a servo applying the brakes.   Probably an arm bearing on an axle would do it.   Powering the stock is basically cheating, though an old Kitmaster power bogie would get the job done, couple of well placed isolators and maybe a capacitor somewhere in circuit on the isolated section to give a soft stop and it could be done with decent DC, a Morley or a H&M Autotransformer "Variable Voltage" controller, anythihg but a resistance controller basically or the coaches would accelerate as the loco powers down

With an actual gradient on board batteries would work as would track pick up to power a servo motor to apply and pick up the brakes. Near frictionless pick up is not hard, brass pin point bearing cups with split axle Bachmann wheels for both side pick up or Lima wheels for one side of each bogie and they should roll on about 1 in 75 exactly like non pickup fitted stock.   The left / right steering of a R/C car would work well for brake application

Uncoupling is a doddle with Kadees but again a servo powered coupling which drops the eye and lifts the hook on tension locks would get the job done.  The real tricky bit is Fly shunting where the loco pulls the stock before uncoupling and pulling ahead with the stock going into one road and the loco into an other

 

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GoWest did a slip coach on the Hornby forum. Uncoupled and braked remotely. There was a link to a video showing it in action on his 00 live steam layout.

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11 hours ago, pH said:


Yes, it is. I thought you wanted to be able to model a gravity shunt, and was pointing you to a method that had been used to model that. I didn’t realize you were wanting to actually shunt using only gravity for power.

 

Sorry, perhaps I should have made that clear.

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2 hours ago, DavidCBroad said:

Seems to me the way to do a gravity shunt by gravity is to have a gradient around 1 in 75 and a servo applying the brakes.  

With an actual gradient on board batteries would work as would track pick up to power a servo motor to apply and pick up the brakes. Near frictionless pick up is not hard, brass pin point bearing cups with split axle Bachmann wheels for both side pick up or Lima wheels for one side of each bogie and they should roll on about 1 in 75 exactly like non pickup fitted stock.   The left / right steering of a R/C car would work well for brake application

Uncoupling is a doddle with Kadees but again a servo powered coupling which drops the eye and lifts the hook on tension locks would get the job done.  The real tricky bit is Fly shunting where the loco pulls the stock before uncoupling and pulling ahead with the stock going into one road and the loco into an other

 

 

I was thinking of something more like 1 in 40, that might be a bit more reliable.

 

Fly shunting is not envisaged, the modus operandi on the EKR was to stop, uncouple, run the loco into a siding, let the carriage(s) run down the slope.

 

Assuming track power is available, how would you use DCC to control the servo?

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28 minutes ago, whart57 said:

 

Assuming track power is available, how would you use DCC to control the servo?

 

Needs a decoder.  Could be an "accessory decoder "(turnouts/signals) or a "loco decoder".    The loco decoder option is probably more flexible. 

I know my way around Zimo decoders, but ESU can do similar-ish things.    All Zimo's have the ability to operate a couple of servo motors, though with most you have to add a handful of components to control voltages/currents (in the Zimo manuals), so a "basic" MX617 with a few parts added to solder-pads on the decoder will do all of this.    Once installed, the servo could respond to a function key press, or could respond to throttle speed/direction (using the "live steam" control options in the decoder) - those are all choices you can make.   

 

Would need experiments to see if a two position brake (on/off) from a function key gave acceptable braking behaviour, or if it was too sharp.  The alternative of throttle position could give more fine control of movement.  

 

 

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Many suggestions** seem to relay on 100% pick up so it's possible that the coach will not brake.

 

As the OP wants prototypical operation would it be an idea to have the brake default to on & held off via the DCC signal.

 

Or, what about buying a small cheap R/C vehicle & cannabalising it ?

 

** Forget mine - i was way off.

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If the coach stop position is reasonably fixed, could you make the brake external with dummy check rails that can move slightly on a servo or solenoid and spring, to apply light pressure to the inside of the wheel flanges in the appropriate stopping area.

 

That should allow a controlled stop, based on the spring pressure?

 

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13 hours ago, RobjUK said:

If the coach stop position is reasonably fixed, could you make the brake external with dummy check rails that can move slightly on a servo or solenoid and spring, to apply light pressure to the inside of the wheel flanges in the appropriate stopping area.

 

That should allow a controlled stop, based on the spring pressure?

 

 

There are mechanical ways of actuating the brake, another idea I had was a wire that lifted rather like a traditional uncoupling ramp. And then with the powerful tiny magnets available these days there is real potential using magnetism. However as DCC is now well established I wanted to investigate the potential of computerised control.

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