Monday, 14 March 2011

Ackermann Steering

The Ackermann steering principal was invented by the German ( no surprise there!) Carriage Company Lankensperger in 1817 and then patented by their agent Rudolph Ackermann in England. Why this system was worked out and applied to a horse and cart, I really have no idea. But the basic principal is that when steering wheels turn, the inner wheel should scribe an arc of a smaller radius than the outer. To achieve this, the steering arms are angled inwards and by projecting a line backwards from both arms, the point where they meet should be dead centre of the rear axle. This creates a differential and causes the inner wheel to turn slightly more than the wheel on the outside. I have endeavoured to produce a unit to fit a slot car chassis. In particular the PCS 32 chassis although I guess it will fit a Slot Classic unit in just the same way. The unit is produced using the trusty photo etching method and is made from .55mm brass. It comprises four parts as shown. The main cross piece which is folded in two planes to form a channel section and carries the four "wishbones". Two uprights are fitted into .55mm holes in the ends of the wishbones, with the whole piece being held together by the tie bar. A tab at each end of the tie bar is bent over to keep everything as one.
The uprights need to have the axle "bearings" soldered in and these will be made up from two 3mm lenghths of 3mm o/d brass tube. The stub axles are being made up from steel.

The complete unit moves very freely. An important point in any trail steer unit, but there is no slack, with the whole piece being quite a precision item.
How it performs, I have yet to find out, but if it works half as good as it looks, i'll be very pleased.

Friday, 4 March 2011

Small parts.

The GT is now starting to appear as I want it to. The art that was put into the original car is not easy to replicate. All the major styling points can be included, but without that arty ingredient the model will look almost but not quite there. I've been messing around with this one for getting on for five years now, so I guess it's about time it was finished. As it's my personal favourite of all the DB Astons, there'll be an extra bit of finnessing. The photo above shows the patterns for the rear lamp lenses. I was introduced to pearwood some months ago, but never really did anything with it. But the delights of pearwood are now obvious. It carves easily and has a close and very consistent grain giving a finish way above anything else i've used. The lenses themselves are approximately 7.5 mm high by a shade over 2 mm wide. There is a horizontal cut around halfway up that hopefully will take photo etched trim piece. The particular small part may be pushing things a bit far. We'll see how it turns out.
The glazing formers shown above were made from pearwood too. These have had only handwork with 320 grade wet and dry apart from the single cutline at the B post point. The part on the extreme left is the second of the two tail lamp lenses. The final shaping and detailing takes place before the piece is cut off and trimmed. My next step is to experiment with clear casting resins adding a touch of red pigment. This particular process is very wasteful of materials as the smallest amount of resin I can mix accurately is 25ml. Of this i'll probably use 0.001% and throw the rest away.

The shot above shows just how the GT is now looking. Sometimes when I look at it and see something that just isn't right, I can't quite work out why or where. With everything in place around the front and looking very balanced, from one or two angles it still didn't do it for me. I found it eventually and added 1 mm to the top of the screen extending the headrail forward. The difference is quite amazing.