RC Crawler Steering

[JeremyH]

Thanks for the description opek....that is pretty much what I have read (minus the specifics about angle for the different applications). However, what I am looking for (and the main reason that I started this thread) is how this applies to our crawlers. Do you have any thoughts on that?

 

[opek]

Slip works not just in the side to side, but in accel and decel. So a good race driver will slip the tires on the braking then keep slipping them the same amount during trail braking, then keep them slipping the same amount during through the apex, then keep them slipping on the way out. Slip angle gives more traction to shitty tires so with some driving styles drivers can move very very fast on shitty tires, but when they buy nice tires they don't really go faster.

When I look at well set up rigs drive they do lots of controlled tire spinning. It seems like if you don't do the spinning you are giving up traction so maybe some ugly toe will give it to you! It seems like a looser sidewall lets the tires shoulder harder. When I touch my boss claws filled with memory foam they don't feel like they will work well, the tread does not shoulder on my finger tips. When I touch my boss claws filled with cotton/polyfill they feel like goop. Turning left to right while climbing loads the treads differently and that probably helps in addition to maybe moving the tire to a new place where there is actually more traction.

It seems like only a small part of what we do is finding extra traction, but it never hurts to know why and how your tires can make extra traction. Slip extends way beyond steering.

 

[Charlie-III]

A few notes/comments for your excellent thread....

"0" Ackerman angle is when the line through the tie rod mounting point & the king pin mounting point are 90* to the axle centerline when viewed from the top & no toe-in/toe-out.
-Something other than "0" ackerman can make one tire turn more than the other which can be helpful since the tire towards the inside of a turn need to turn more than the outside tire (different turn radius).
-Altering the tie rod length to give toe-in or toe out can alter what the tires do during a turn, thus helping or hurting the ackerman angle.

King pin inclination is the angle formed when viewed from the front or rear relative to a vertical line. It seems similar but is different from camber.

Scrub radius can be changed by altering:
-Wheel backset/offset
-King pin inclination
-Wheel width (sometimes, some wheels leave the hex mounting surface constant to the inner or outer beadlock surface and then move the other beadlock surface to change width)

As mentioned, "You fix one thing, you FUBAR another thing." It's all about tradeoffs, there is NO perfect set-up since each driver is different as well as the surface, tires, etc.

Defining "scrub", maybe we need to use:
-"Geometry scrub" based on suspension mounting points vs tire contact patch (as shown in your pictures).
-"Differential scrub" based on our use of lockers (which would relate to tire slip angle)

Any thoughts on this??

As to reading 1:1 books, I have read (several times) Millikan, Kuhn & Smith. All are decent but yes, Millikan is tech heavy.
I used to do some road racing as well as autoX, not really enough time or money to do them now, but it was fun.

I give JeremyH "thumbsup""thumbsup" for a great thread, covering the basics with pictures and then inviting worthwhile discussion.
My comments above are NOT to be considered negative in relation to this thread.8)

 

[West Cork Basher]

Very good post "thumbsup"

But I'd like to know more about Panhard steering ..




I have the side mounted steering set up..as Bender has on his SCX FOFFer . .

Still need to be tweeked ,but I cann't do that untill my new links arrive next week as I'm half way though a FOFFer build...

Sean
..

 

[JeremyH]

I give JeremyH for a great thread, covering the basics with pictures and then inviting worthwhile discussion.

Thanks for the compliments Charlie. "thumbsup"

Very good post "thumbsup"

But I'd like to know more about Panhard steering ..

Thanks!

There are two basic (and most common) ways to setup the steering servo on a crawler.....on the axle or on the chassis.

Mounting the servo on the axle is pretty straight forward. You should not have any problems with bump steer using this method.

Mounting the servo on the chassis is not as easy. Any time the suspension on your crawler cycles, it will also affect your steering. You should notice on your setup that if you push down on the suspension, the tires will turn slightly and when you release it, they will straighten again. This is the reason you want a panhard bar (or track bar). This bar will provide a rigid link between the chassis and the axle and will keep the tires from turning when the suspension cycles. A 5 link setup (4 control arms and one panhard/track bar) is pretty common in 1:1s with solid front axles.

 

[Hardline]

A 5 link setup (4 control arms and one panhard/track bar) is pretty common in 1:1s with solid front axles.

But that only if the 4-link is prettymuch parallel. Link systems using triangulation don't generally use a panhard. A panhard forces the axle to move slightly left or right during cycling because the end of the panhard is travelling in an arc. Triangulated suspensions want to keep the axle centered during cycling. Using both invites binding.

I know nothing of chassis-mounted servos, but since a panhard will mandate some left-right shift during cycling, I wonder if a watt's link would work better. Unlike the panhard, it causes the axle to remain centered during vertical movement.

 

[JeremyH]

That's true. I was referring to factory style 4 links (most of which dont triangulate the links as much as they should to properly locate the axle). Here is a picture of the factory TJ suspension.....you can see how far the uppers are apart:

And they mount to the inside of the chassis. The lowers also have very little triangulation as the mount to the bottom of the chassis rails.

As for the panhard moving the axle, that is also correct. That is why the positioning of the panhard is important. IMO, it is best to keep the panhard parallel to the axle at ride height. This setup will give a slight amount of adjustment during uptravel and a slight amount during downtravel. This might be a bit different on crawlers since ride height on most is full downtravel.

Watts link.....good call, but good luck finding the space to set one up properly on a 1:10 RC....

 

[TexasSP]

Jeremy, thanks for this fantastic write up and to the other contributors!

It just helped me work through a few things I had been pondering and decide the correct measures I need to take to get my desired results.

 

[korn_2956]

Does anyone have a diagram or picture on how to set up a panhard bar like certain angels that are important to have or lenghts of links that are important. I'm new to this and learn by pictures.

 

[korn_2956]

And thanks to everyone on here for all your help. Threads like this make rccrawler the best there is. Thanks.

 

[korn_2956]

Also will the panhard work fine with the stock 3 link on a scx10.

 

[opek]

Does anyone have a diagram or picture on how to set up a panhard bar like certain angels that are important to have or lenghts of links that are important. I'm new to this and learn by pictures.

I'm gonna guess flat and above the axle. Longer keeps the roll axis in check and above the axle is where you want it.

 

[ctrwannabe]

Tons of great info to read about and learn from in here, thanks for taking the time to put it all in one place!! A+ thread.

 

[JeremyH]

Jeremy, thanks for this fantastic write up and to the other contributors!

It just helped me work through a few things I had been pondering and decide the correct measures I need to take to get my desired results.

And thanks to everyone on here for all your help. Threads like this make rccrawler the best there is. Thanks.

Tons of great info to read about and learn from in here, thanks for taking the time to put it all in one place!! A+ thread.

Thanks guys. I'm glad that my ramblings were somewhat coherent. "thumbsup"

 

[JeremyH]

Also will the panhard work fine with the stock 3 link on a scx10.

In theory, it should. But my guess is that if you are going to run an upper link, it should not be dead center in the axle. This is not something I have tried out in practice and I dont have an SCX10 to test. In a panhard suspension setup, the upper link should only be present to eliminate axle wrap.

 

[Charlie-III]

Thanks guys. I'm glad that my ramblings were somewhat coherent. "thumbsup"

Whoaaaa....huh??!!:shock:

:lmao::lmao::lmao::lmao:

8)

 

[JeremyH]

Whoaaaa....huh??!!:shock:

:lmao::lmao::lmao::lmao:

8)

Oh, I didnt mention that I was completely shitfaced when I wrote all of that?!?! :ror: ;-)

 

[Knarly Nerd]

Nice!"thumbsup" Good timing as I complete my BJ4/Berg. Today I sat in puzzlement while staring at my steering possibilities.

I'm diggin' the wheel weights on your super...whose are they?

 

[JeremyH]

I'm diggin' the wheel weights on your super...whose are they?

Mine! :ror:

Seriously, I cut them out of delrin with my dremmel...."thumbsup"

 

[4xFord]

Scrub Radius --- One of the down sides to increasing this is when turning hard on traction less surfaces the likely hood of having the whole rig slide a bit is increased. Instead of the tire being pivoted(less scrub) its being pushed(more scrub) which can easy push the whole rig.

This can also be a plus, when you want to slide the front end away from an up hill gate, and twitch the steering to get a little slide (from gravity) away from the upper gate. I've noticed more scrub makes this manuever easier.

Great thread Jeremy! Almost as good as the skittles battle thread. :ror: