Ackerman Steering with Locked Diffs

[DKNguyen]

Hi everybody. I was wondering if someone who knew more about car steering could help me answer this question. When turning corners on pavement you need both ackerman steering (to compensate for the different geometries of the two steering wheels) and an open differential (to compensate for the differences in speed). If you don't have these then the wheels skid when you turn.

What if you had a steering servo for each steerable wheel (rather than ganged) and a computer to control both to get ackerman steering. Would it be pointless if you didn't have an open differential since the wheels would still skid due to the speed difference? Except that now they have no more side-skid (they only skid along the steering circle rather)? I think it might improve control (and maybe reduce axle stress) but I'm not sure. I know the ackerman is pointless when you're on rocks but I'm talking about pavement.

THanks!

 

[Kamikaze]

Are you planing to crawl on pavement????

 

[DKNguyen]

If that's what the robot encounters, that's what the robot must pass.

 

[_BEN_]

The ackerman effect happens when caster is added to the front axle.

What this causes is the inside rear tire to lift while the vehicle is turning. It is a very simple.

There are two things to increase rear wheel lift:
-Add more caster. But this also increases the amount of camber that is gained while turning the wheels.
-Space the front tires further out on the spindles.

I would research the effects of Caster and the ackerman effet by reading through some Kart articles. My Swiss Hutless would lift the inside tire about 3"~4" without someone in it.

Edit: http://www.sniper.com.au/kartoztech2.htm

 

[DKNguyen]

Is it even possible to add caster with a CLod axle tube?

 

[hotwheels000]

change the length of your links or clock the axle C's/tubes if you have steel ones

 

[YoUnG_vErSiOn]

wow a pavement crawling clod robot, whats next? maybe you should check www.pavementcrawler.com

 

[kawika]

wow a pavement crawling clod robot, whats next? maybe you should check www.pavementcrawler.com

Punk:shock:. I actually tried to follow the link:lol:

 

[YoUnG_vErSiOn]

:lol:

 

[Mnster]

http://www.thundertechracing.com/CDBCS.htm

 

[Coligny]

You do know that ackerman steering is acomplished by simple mechanical geometry arrangement ?

 

[_BEN_]

http://www.thundertechracing.com/CDBCS.htm

That is an interesting product. BUT as long as the steering knuckle pivot point is 90° to the ground there will be no rear tire lift.

Clock the axle to about 85° (If you are running a 4 link just use shorter top links)

 

[Grizzly4x4]

Behind the Axle (BTA) is the best way to correct the Ackerman on a Clod. This actually gives you too much but it's better than the stock setup with the steering arms out front.
Leave the tie rod behind the axle on the rear axle.

Ben, I really wouldn't expect to see any weight jacking or weight transfer in a slow speed crawler.

 

[DKNguyen]

That's a neat product. I still might try and go with double servos though just due to wanting to stick some antenna on the knuckle steering mounts as well and with double servos you get independent antenna that can face in different directions.

 

[JohnRobHolmes]

With locked diffs it wont matter anyway. The inside tire wont be able to turn slower than the outside so you will get skidding.

 

[bigblazerboy]

the new e-maxx have two servos in the front one for each wheel

 

[Jammin57]

the new e-maxx have two servos in the front one for each wheel

the new emaxx has 2 servos that are connected to each other. They are not used for each wheel.

 

[2Slo2Curious]

Behind the Axle (BTA) is the best way to correct the Ackerman on a Clod. This actually gives you too much but it's better than the stock setup with the steering arms out front.
Leave the tie rod behind the axle on the rear axle.

With the steering arms in front of the axles you get the outer wheel to turn with smaller turning radius then the inner wheel which is the opposite of Ackerman steering - not good.

 

[DKNguyen]

If you only had one, ackerman, or differentials, would have better performance in steering?

 

[2Slo2Curious]

With Ackerman and open diff - best for pavement only

With Ackerman and lock diff - best for rock crawling but still perform well on pavement in term of steering control since there is no side-skidding

Without Ackerman (parallel steering arm) - acceptable steering performance on rock (with locked diff) and pavement (with open diff).

With negative Ackerman (stock setup) - worst steering performance for rock and pavement . It may help a little bit if you have open diff but you cannot overcome most of the obstacles. There will be a lot of stress on your steering servo, axle tube and axle C etc. IMHO