Lotus Shark: Ackermann percentage

[MiniCooper1460]

Hello,

I have a question about Ackermann percentage calculated by Lotus Shark.

I have read the software help and I have understood 100% Ackermann is full Ackermann.

Before I use the software, I have done the traditional drawing to establish angle at which steering arm should be mounted to obtain full Ackerman but with this configuration Lotus Shark gives only 45% Ackermann.

I have defined the angle of steering arms drawing lines along the arms from the trackrod ends, via the kingpin axis to intersect at the centre of the rear axle line (this approch is valid because the rack and pinion lie on a straight line joing the two trackrod ends each other).

I have used some software template and Ackermann percentage is very different from traditional drawing method.

Can you help me? Where is the mistake?

Best Regards
M.R.

[MiniCooper1460]

Hello,

I have a question about Ackermann percentage calculated by Lotus Shark.

I have read the software help and I have understood 100% Ackermann is full Ackermann.

Before I use the software, I have done the traditional drawing to establish angle at which steering arm should be mounted to obtain full Ackerman but with this configuration Lotus Shark gives only 45% Ackermann.

I have defined the angle of steering arms drawing lines along the arms from the trackrod ends, via the kingpin axis to intersect at the centre of the rear axle line (this approch is valid because the rack and pinion lie on a straight line joing the two trackrod ends each other).

I have used some software template and Ackermann percentage is very different from traditional drawing method.

Can you help me? Where is the mistake?

Best Regards
M.R.

[STRETCH]

I've never had any luck getting ackermann out of Lotus. I have approximately 100% setup in our steering geometry and the graph tells me its got -2900%... so I just ignore it! Your calcs seem bang on, so just trust the traditional method of working it out.

[MiniCooper1460]

Thank you for your answer Stretch.

I have send an email to Lotus about the problem and this is their answer:
<span class="ev_code_BLUE">With regard to your 'traditional' drawing method. You will note from the theory section of our help file that we do not use steering arms to identify Ackermann. The method used within Shark refers directly to the wheels and their relative steer angles. This is because Ackermann definitions are about steering angles on lock rather than any mechanism related property.</span>

I have also noticed the old software versions had some bugs about Ackermann calculation which should be corrected with new version, but I think the problem is still present.

M.R.

[ben]

The big problem with the "traditional" method is that it's not actually for the type of steering system most race cars run. It doesn't factor in the angle change between the rack and the track rod.

In the end you want a different steer angle between the inside and outside wheels, so surely measuring the two angles and comparing them is the best way to assess Ackermann?

Ben