Friday, October 17, 2008

A Graham Farish chassis conversion to DCC experiment

An N guage chassis can be a right bother to convert to digital.  Certainly my 91 and 08 chassis are both troublesome.  This is beacuse the body is live and linked permanently to the motor. Looking at my 91 last night (to become the other funkey), I took it apart to see how I could convert it.  the bogies pick up and feed a brass strip underneath the motor and directly to the chassis block.  Both brushes of the motor directly touch either the strip or the block via a brass 'hat' which has a spring inside (to spring the brush up to the motor) and is kept in place by a keeper plate, itself rivetted to either the block or that brass strip.  

So, in order to convert it to digital I need to break the link between the pickups and the brushes...easier said than done when they are integral.

This is where the 'digi hat' comes in.  First you insolate the hat by replacing it with a plastic (not brass) one.  Then you place heat shrink around the keeper to isolate that from the spring. Finally, you solder directly to the spring, which sits inside the hat.  Confused?  see below...  Here are the hats, brass on left and new insulated one on right.

That fits into the heavy chassis block like so...

and the spring that sits inside the hat and has a wire soldered to it - that wire then goes to the decoder.  The isolated keeper device is then placed back over the spring to keep it in position.
On some models it is possible to do away with the soldering to the spring and the keeper plate thingy and use an insulated clip which sits on top of the hat to keep the spring tight against the brush.  This will be fine for my 08s but not for the 91 as the clip doesn't fit (chassis block much wider)!

Then you can solder the wires from the clip/spring to the decoder and the red/black wires to the pickups and it's converted.  

we'll see how it works in a few weeks after I've picked up some of these from Warley.



Tom said...

Colin, thanks for posting this, i'd wondered how the digihat had worked for a while. good to see it in pictures, make it a little clearer.

On another note, i fitted a zimo mx620 decoder to my Roco tender loco the other day, DCC is definitely the future!!!! Going to have to try and get a sound decoder at Swanley!!

Rob said...

Thanks as well, this helped me in an installation.