How to find an Ackerman Steering Gear Ratio

[Elvis Lumnica]

Hi guys, so I am designing a steering system and would like a desired ratio of 1:1. If anyone knows an equation or can even guide me through the process of how to find the number of teeth needed to satisfy the desired ratio, it would be appreciated! Thanks in advance.

 

[GregLocock]

You want the steering wheel to turn as much as the road wheels? That's going to need some pretty mighty shoulders. You need to work out how many millimetres the rack moves if you steer the road wheel by 1 degree, and then find the pitch of your steering rack.

The number you are looking for is called the C factor of the rack, and is typically quoted in mm per revolution of the steering wheel. I'm used to seeing numbers of the order of 50 mm/rev on power assisted cars, and 20 on manual steering cars.

The overall ratio of steering wheel angle to roadwheel steer angle is called the steering ratio, 20 or so for power assisted cars, 50 for manuals, 1-2 for go-karts at a guess.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[cibachrome]

OK, Elvis, since I'm originally from Buffalo, I will chime in.

First of all, clarify your steering system needs. When you say 'Ackerman', do you mean 'Ackermann Steering' (2 Ns) for the condition in which each wheel is aligned with the geometric path of the inner and outer turn circles? That's generally referred to as '100% Ackermann'. So the wheel to wheel ratio is a geometric consideration. When you say 'ratio of 1:1', that could be construed as 'parallel' steering, where each steered wheel turns exactly the same amount. If you really mean you want an overall steering ratio of 1:1 (Steering wheel rev to road wheel rev), then all you need to have, for a rack & pinion gear, is a pinion gear that is the same radius as the steer arm, since that's all the overall ratio really is.

For your Baja cars, measurements of tire cornering properties (in sand, no less), could enlighten you with the need for either a +Ackermann or -Ackermann steering geometry in order to maximize the side bite of your front tires. That amounts to progressive toe-in or toe-out as the wheels are steered.

FYI:

https://bajatutor.net/calculations-anti-ackermann-steering-mechanism/