b20btec

iTrader: (11)

Thanks for making a "BOM" list! Good news is I got some of those parts laying around and can substitute with something else.

patorz31

The old Custom Works Dominator dirt oval car had the servo in front of the blukhead. Their solution is pictured below.



They have bellcranks mounted vertically. Might be something to consider.

heretic

Sorry wtcc, forgot to answer. Maybe you can use something like this?

http://cmchobbies.co.za/shop/image/c...a1-600x600.jpg

You know what they say... "smart people have all the luck".

wtcc

iTrader: (2)

Awesome! Thanks for this cool input.
I will look how to implement this for my FF.

30Tooth

iTrader: (1)

If all else fails consider a linear rack

Papi

Problem with vertical belcranks is, that they will always make some bump steer, because of height change in inner link mounts.

What about ABC Gambado solution? It might work. Or you can mount low-profile servo vertically, it shouldn't affect CG that much.

thomsva

I like the direct steering arrangement! Less moving parts and less slop. As discussed eariler, bumpsteer can be minimized by making the arms horisontal. You could add shims to raise the outer ends of the steering arms higher.
A long servo arm can be a good thing. The height difference between center and full lock is smaller when the arm is long. A longer arm also makes the steering faster (but weaker).

A possible way to adjust ackermann would be shimming the whole servo forward/backward.

patorz31

Weaker should not be a problem. With a front steer system the force needed to turn the tires is less. There was a big debate on this in full scale circle track racing years ago when no one wanted to run power steering. The best way it was explained to me was " It's easier to pull a stick on the ground then push it..."
Makes sense there will be less force needed to pull the loaded outside front in the turn then to push it against the force of the turn.

Papi

But single arm also pull steering rods closer together, as it rotates. Although it can be reduced by making it longer, it's still not as good as double steering arms.

Also, with steering arms rotating around vertical axle, not only will reduce height change, but also introduce front/rear movement of centre, which can be used to tune ackermann more precisely without change in bump steer. Which is needed, as in case of front steering you need angled steering rods at straight and parallel (perpendicular to longitudinal axle of car) in full lock

MatsNorway

If it works, it works. Compare lap times first. Then the design if your behind.

wtcc

iTrader: (2)

I really appreciate this discussion.
Looking at this from the available space between gear box and bumper a 1/12 sized servo would be perfect. But the height should be lower. Are there low profile 1/12 servos?



Tomorrow is shakedown day. I soldered the motor cables, added a flat sensor cable and changed the colorful steering servo cable with a black one. The plastic rocker arms were replaced by the beautiful blue aluminium ones. The M410ULT is also ready. With color, sticker and wing it weights in at 68g. Now the whole car is down to 1014g

wtcc

iTrader: (2)

Back from a successful first trainingsday with the KR-MF chassis.
All new prototype parts hold up very well. I was a little afraid that the new "gearbox" would cause trouble, because of its reduced stiffness in comparison to aluminium, but no it did a fantastic job holding all gears at perfect distance. The 10.5t motor was too much for this small high grip indoor circuit. I reduced its power to 70% to achieve a nice balance between speed and front-tire-killing. The body helped a lot to reduce roll. Yet, in some situations using half the curb let to a barrel roll move which always was landed perfectly on all four tires. I am sure my springs are to hard. I started with 2.5-2.8 in front and the car didn't look good on track. The switch to 2.3-2.6 was much better, but I think even softer would be better. Something like 11lbs springs should do a better job.
Apart from this typical lw-car-problem everything was smooth. Again I had not even a loose screw.


FF cars are funny:

Airwave

iTrader: (1)

Honestly I wouldn't be a Tamiya engineer looking at this picture... I don't know what I would be feeling at this moment lol

Do you plan to do something for the rear rocker? They don't seem to work in a proper plane...

wtcc

iTrader: (2)

I know the angles look suboptimal, but fact is that they work properly. The rear of the car is stuck. Right now I ran 2.6 springs, which is quite hard for the light rear and two degrees of toe in.
What would you recommend me to do? Should I build angled bases for the arms?

Airwave

iTrader: (1)

If it is working... That's just the last point you get make better.

If by stuck you mean that the rear wheels are glued to the asphalt, I think you can go for less toe, or try to transfer your inboard toe to outboard toe. The behaviour can be different but it can also make the rear slide a little...