The Slotcar Outhouse

A 'no bull' site for 1:32 slot car racing. Home of the 'Slotcar Legends'

The 'Wixwacing' patent scratchbuilt steering unit.

How DO they do that??
Post Reply
wixwacing
Marshal!!!
Posts: 1871
Joined: Thu Jul 10, 2008 9:22 am

The 'Wixwacing' patent scratchbuilt steering unit.

Post by wixwacing »

A job that I have been dancing around for some time is the Ferrari TR59 Resilient Resin body conversion. I say dancing around as it has been on the bench for a while now and other projects have come and gone. So what’s the problem? No problem really ! I’ just raised the pole a bit for this one and I have been in mental training ever since trying to clear it.! I decided this model was going to have another innovation on it and in a wild reckless moment I promised myself (and other people!!) that this one was going to have working steering! I should really keep my mouth shut, but sometimes, after a couple of drinks (strictly non alcoholic mind you, kids!) you (I) do silly things. No matter, the cat was out of the bag and the horse had bolted??!!??



Image



I won’t go into massive detail as that will be reserved for the finished article, yes, you heard right! But I will just ‘dance about a bit’ for the inquisitive. I decided to recreate the amazing principle of true Ackerman steering in a slotcar because most slotcars are still suffering from a couple of serious problems. Firstly, with the trend towards four wheel contact we enter the realms of wheel speed differential on the front. This is when two wheels are fixed solidly to the same axle. In a bend and an especially tight one at that, the front wheels bind. This is caused by the inside wheel turning a tighter and shorter path than the outer wheel for the same distance travelled by the model. The ‘Wixle’ (see elsewhere on the board) is a classic solution. Both wheels are on the same axis but decoupled from each other to remove the differential problem. This is one problem solved.



Image



The next problem is that of tyre sideslip in tight corners. It’s fine to have decoupled the front wheels to allow different rotation rates but in tight corners, because of the nature of the front end set up, the front tyres try to drag sideways as part of the turning manoeuvre. The only option is to hang the back out round the bend so the tyres are facing the arc of direction of travel. Hairy stuff and difficult to get right bend after bend, lap after lap! What is required is for the wheels to point in the direction of travel, this way you get a model which has enhanced stability because it is sitting on all wheels. Differential compensation, because the wheels are decoupled from each other, and zero side slip!!



Image



Steering is not a new concept in slotcars. (Check out earlier thread, this forum) It has been around almost since day one and in the early to mid sixties companies like Airfix, MRRC and VIP sold models with what was then a novelty at the time. Spanish Scalextric (SCX) made some serious steering models which worked well. The models didn’t really need it as they had huge tracks and light model weight. Ninco, too made some classic GP cars but since then things have dried up a bit.



Image



Not every model needs steering, it is a peculiarity of a culmination of factors. If you are racing large sweeping tracks with models that have very wide axle widths say from 55 mm and over, all you need is a bit of weight down low and let the rest rip. Steering comes into its own on the more technical circuits. Those tracks that have drivers infields and tight bends. This is where the curse of the fixed axle comes into play.

Scenario:

You are racing a mid to narrow sedan or classic sports car model on a technical circuit and the model is great down the straights but some of the tighter bends cause the model to baulk. The model can require exceptional throttle operation or it just slows noticeably?? Removing the front tyres so the model is travelling ‘a la tripod’ you see it immediately overcome the sharp/tight corner problems and make uninterrupted progress around the tighter parts of the track. The only problem is that now, because the front wheels aren’t in contact with the track, the model becomes a little more unstable and tends to tip and tilt if pushed too hard around these bends. You have lost the stability offered by front wheel contact.



Image



There are several alternatives. Apply nail polish to the front tyres, this will need to be done after every meeting (it wears off!). Sand the front tyres’ tread area into a radius so that there is minimal tyre contact (75% effective and will also need repeat sandings) Fit a hard compound to the front and listen to it hammer its way round the track! The only other alternative is to add weight and plenty of it, down low. This will reduce the model’s useable acceleration and decrease its breaking ability. The solution is steering. Four wheel contact stability, no extra ballast and useful braking distances without the corner traumas.



Image



The model I am making is an exercise in scratchbuilding if the truth were known. The model it is going on may never race in anger but the exercise itself could be classed as the MK1 and later versions may well occur! I have tried to mimic the Ackerman principle in that not only do the wheels steer into a corner but the inner wheel should ideally turn a tighter radius than the outer which has further to go! Another feature is that the front wheels should have a slight toe in measurement. This will help the wheels self centre in a straight line (along with the castor angle). Toe out will cause the model to weave from side to side.



Image



The next set back in scale modelling I have tried to overcome is that of King pin inclination. A wheel should ideally sit centred over the steering swivels and turn on an imaginary point below the track surface. This is where the KPI and camber angle meet. The wheel will then ‘turn on a sixpence’ instead of travelling around a steering swivel, much like nearly all previous slotcar models have. The benefit of this in a slotcar is that you can get the wheel to pivot in it’s wheel well and not foul the front and rear well and wheel arch as it turns.



Image



I have made the pivot points in the PCB chassis. The hubs are made from brass tube which is a snug fit over the wheel bosses. The tube has a 1/16th pivot top and bottom drilled and soldered in place. These pivots sit inside the inner wheel rim when in place. The top swivel is a strip of brass again going over the hub inside the outer edge of the wheel rim. This allows the wheel to turn in a very small arc. The tie rod is some music wire with the ends bent at 90 degrees. These clip into two fabricated steering arms also soldered to the swivel hub.



Image



The tie rod has a hollow tube section soldered to it at its centre. The guide has had a pin bored and glued into its front edge. The tube which carries the guide is a little longer than normal and over this I have slipped a yoke which attaches the guide pin to the tie rod pin. The yoke has a small ring placed over it and spot soldered in place. The system works very well and I am in the process of refining the yoke and tie rod pin. This will need to be moved forward to reduce the leverage and decrease the steering movement in comparison to the guide position.



Image



The front wheels work well inside the arches and the only mod here will be a sanding of the outer edges to give me the final clearance I am looking for. The arches will also get a final sanding too before I set about finishing the body. I am very pleased to have got this far and I am going to take it for its maiden voyage this coming Friday at the Red Teams home track. With this final hurdle overcome I look forward to finishing the model.

With the advent of Fly experimenting with steering on their new Classic F1 model, I foresee a resurgence of classic models with steering. Technology dictates that it is no longer in the ‘too hard’ basket and the simplicity with which it can now be moulded ensures that it is only a matter of time.
Image

When I'm not racing slotcars,
I'm out in the back yard, burning food!!

When I win, it's because of my talent, not my car or my controller!
Post Reply
cron