XRAY - Model racing cars

T3-2011

Just getting back to RC cars thanks to my 9yr old son (it’s the best excuse I could find to tell the wife).
Having a background in engineering and motor-racing I have some issues with some of the assertions/beliefs I have seen as being taken as gospel.


Anti-Roll Bars
The design of the AR is poor, it seems one targeted more for convenience and looks than function.
The spec of the material used is not appropriate for the task in this application.

The task of the ARB (in simple terms) is to transfer some amount of the suspension movement from one side to the other.

So let’s look at the T3’11 with the shocks and springs in place, and to make the point really clearly we will use the 1.6mm bar.
Now try compressing the suspension on one side with your hand and watch the other side to see what happens.
Exactly ! Almost nothing happens, at best you may have seen a twitch and that was it.
Ah, you say the springs are too hard, ok - so try the 2.4C on the front and you’ll still find nothing happens.

Ok, so the observation is clear, so what’s wrong.

Well the design here uses the 1.6mm spring steel as an arm extending back from the AR cross bar back to the drop link (it’s all one piece of metal suitable bent after all).
Compress the suspension on one side again and take a good look at the arm and how much curvature is now visible. The curvature is alot worse for the 1.2mm bar.
Well if the arm is bending it cann’t be transfering force to the other side, so the more it bends the less force it transfers.

So if we were to persist with this design, the bar would need to be in the order of 3mm thick before it would show any signs of working correctly.

As for the rear, it would need to be thicker still as the rear arm length is about 15% longer than the front.

Compare the T3’11 design to a typical race car design.


In most competition race car designs the arms are very unlikely to bend, and the adjustment comes from the mounting position of the drop link on the arm and a small amount of twist in the bar itself.


Conclusion
The current design is next to useless, for it to work with the current design of anti-roll bars, the bars would need to be much thicker, or the length of the arm much shorter.
eg
Diameter = 3-4mm or Arm length = 10-15mm and this may need to be matched with new spring rates (probably softer).



look forward to comments.

Ok, so while I can understand the initial thought process by which you are going. However your forgetting one critical part of this. The reason 1:1 car engineers insist on having a rigid chassis is because they use shocks, springs and suspension to control cornering and dampening. The biggest difference in RC cars is the shock technology is very different and we don't have shock potentiometers and data systems to set up our rc cars. So what we lack in adjustability in shocks we make up for with softening the chassis so the difference in grip between the front and the rear is limited.

to demonstrate the difference, try racing a T1 car with the 2.0/2.5 bars. The car is shite with the big anti swaybars installed. So before you pass judgment on the swaybars test them on track.

Two things that would be nice:would be a ball raced center swaybar mount, and adjustable end links(read turnbuckle). I am a second year engineering student and IMO there are only about 4 areas the car needs work on for forward traction, Ball raced swaybar mounts, adjustable end links and better shocks. But given the cost / benefit ratio of developing effective solutions would add say 15-25% to the cost of the kit. A gear diff will improve the service life of the diff, you may lose some corner speed but it can be compensated for. Ball bearing swaybar mounts, minimal gains vs the grip you would get and with 2012 worlds having a VERY light minimum weight I think the weight offset wouldn't be worth it. Shocks, well if the stock shocks aren't to your liking, with a little tinkering you can bolt on tamiya shocks and be happy.

Summary, go drive the car. Throw some swaybar changes at it and spring changes. If the car is in the window to begin with you will be suprised at how much a 0.1mm - 0.2mm swaybar change makes on track.

Come on dude, when you have a (automotive) engineering background you should be able to understand why the car uses these thin bars?.

Same thing goes for the springs right?
For example on a formula type car with medium ground effects we run 1200 LB/Inch springs but in RC we usually don't run anything stiffer as 30 LB/Inch. This is a 40 times difference.
When you would do the same comparison on the ARB's you will probably find the same difference.

In 1/10 nitro cars we do run 2.6mm ARB's, but these cars are around 200-300 grams heavier and have a CoG which is quite a bit higher and less centralized.

If you think that 1.6 anti roll bar is useless becuase it it too thin, try one run without anti roll bar and than mount it back for next run and you will see that bar is not useless. Event better would be to test it in high traction conditions when you will be not able to drive one corner without bar because you will traction rolling

Anyway, thanks for theory