Go Back   RCCrawler Forums > RCCrawler General Tech > General Crawlers
Loading

Notices

Thread: RC Crawler Steering

Reply
 
LinkBack Thread Tools Display Modes
Old 02-24-2012, 07:36 PM   #101
Rock Crawler
 
Join Date: Jun 2011
Location: San Diego
Posts: 698
Default Re: RC Crawler Steering

I am talking about the AX10 knuckles. I will go make a tie rod and flip and twist and snap a few pictures. I have a habit of remembering things backwards.


The knuckles are exactly as were described. Reverse ackerman when mounted in front and ackerman when mounted BTA. I am a cook.

Last edited by opek; 02-24-2012 at 08:39 PM.
opek is offline   Reply With Quote
Sponsored Links
Old 02-24-2012, 07:55 PM   #102
I wanna be Dave
 
Join Date: Sep 2005
Location: Houston, TX
Posts: 16,952
Default Re: RC Crawler Steering

Quote:
Originally Posted by opek View Post
I am talking about the AX10 knuckles. I will go make a tie rod and flip and twist and snap a few pictures. I have a habit of remembering things backwards.
Ah....ok. Well, that is what I posted a picture of earlier. Granted, it was used on a berg, but that shouldn't matter much.

BTW, I added a short description of "correct" Ackermann geometry to the first post.
JeremyH is offline   Reply With Quote
Old 02-25-2012, 02:29 PM   #103
I wanna be Dave
 
Join Date: Sep 2005
Location: Houston, TX
Posts: 16,952
Default Re: RC Crawler Steering

Quote:
Originally Posted by opek View Post
The knuckles are exactly as were described. Reverse ackerman when mounted in front and ackerman when mounted BTA. I am a cook.
Better you than me...
JeremyH is offline   Reply With Quote
Old 02-26-2012, 07:41 PM   #104
RCC Addict
 
Join Date: Mar 2011
Location: Way out there!
Posts: 1,465
Default Re: RC Crawler Steering

[QUOTE=JeremyH;3589782]Interesting. Did you notice any changes in scrub when you switched from zero ackermann to your current setup?

My side hilling has greatly improved while turning up hill. Before I would run a little toe out to compensate. That killed the side hilling while going straight and seemed to make my rig seek holes.
josh6575 is offline   Reply With Quote
Old 03-12-2012, 01:46 AM   #105
Rock Crawler
 
Join Date: Oct 2011
Location: Co,Cork..Ireland
Posts: 579
Default Re: RC Crawler Steering

Why haven't they made this post a sticky?
West Cork Basher is offline   Reply With Quote
Old 08-14-2012, 12:21 AM   #106
RCC Addict
 
Join Date: Jan 2012
Location: Sweden
Posts: 1,809
Default Re: RC Crawler Steering

Quote:
Originally Posted by JeremyH View Post
Drag Link:
... your drag link should be at a 90* angle with the servo horn and parallel to the axle shafts ...
I totally agree with this. So, why do we see so many rigs with very short drag links? (Servo mounted on a plate next to the knuckle where the drag link is attached. The drag link does not stay even close to parallel with the axle shaft as the servo horn moves!)

For optimum geometry the servo should be mounted on the opposite end of the axle, with the drag link being almost as long as the tie rod. Right?
Olle P is offline   Reply With Quote
Old 08-14-2012, 04:54 AM   #107
I wanna be Dave
 
Join Date: Nov 2010
Location: 07456 N. NJ USofA
Posts: 8,314
Default Re: RC Crawler Steering

Quote:
Originally Posted by Olle P View Post
I totally agree with this. So, why do we see so many rigs with very short drag links? (Servo mounted on a plate next to the knuckle where the drag link is attached. The drag link does not stay even close to parallel with the axle shaft as the servo horn moves!)

For optimum geometry the servo should be mounted on the opposite end of the axle, with the drag link being almost as long as the tie rod. Right?
At "0*" steering, it does not matter where the servo is mounted (close or far) or how long the drag link is.
It DOES make a difference once you start to steer, but that really changes the relationship of TX steering angle vs. rig steering angle.
Charlie-III is offline   Reply With Quote
Old 08-14-2012, 06:20 AM   #108
I wanna be Dave
 
Join Date: Sep 2005
Location: Houston, TX
Posts: 16,952
Default Re: RC Crawler Steering

Olle, yep, just like Charlie said, you'll see the benefit of keeping the torque applied to the knuckles from the servo with a longer drag link when your tires are clocked to one side or the other.
JeremyH is offline   Reply With Quote
Old 08-14-2012, 06:31 AM   #109
RCC Addict
 
Join Date: Jan 2012
Location: Sweden
Posts: 1,809
Default Re: RC Crawler Steering

So, if I'm correct that a longer drag link is better, why so many extremely short drag links? What's the benefit(s) of a short drag link?
Olle P is offline   Reply With Quote
Old 08-14-2012, 07:09 AM   #110
I wanna be Dave
 
Join Date: Nov 2010
Location: 07456 N. NJ USofA
Posts: 8,314
Default Re: RC Crawler Steering

Quote:
Originally Posted by Olle P View Post
So, if I'm correct that a longer drag link is better, why so many extremely short drag links? What's the benefit(s) of a short drag link?
Most use a short link to keep it from getting hung up on rocks. Other than that, I see no reason to do it (maybe it's a few grams lighter?).
My 2.2 Bully uses a loooong link that goes across the front of the rig, my XR-10 uses a shorter link, but the servo is "flipped" so the servo output shaft is away from the knuckle, this helps the geometry a bit.
Charlie-III is offline   Reply With Quote
Old 08-14-2012, 08:16 PM   #111
Rock Crawler
 
Join Date: Oct 2011
Location: Great Outdoors
Posts: 651
Default Re: RC Crawler Steering

In my typically contrary manner, I disagree with most of this. The servo will generally have the least mechanical advantage with the link coming off the horn at 90 degrees. It gives the most turning per horn rotation, but that also means least leverage. A draglink angle other than 90 degrees will provide more steering torque coming off center. That may or may not be a good thing, but the point is the geometry is more complex than you guys are allowing for. It's all about mechanical advantage, which changes for any number of factors during steering.

I think a good argument could be made that the draglink should start off lower at the horn, not 90 degrees. It will pass thru 90 degrees as you steer and wind up on the upper side. Just talking the effect of angles here, not the also important lever lengths.
Hardline is offline   Reply With Quote
Old 08-15-2012, 05:12 AM   #112
I wanna be Dave
 
Join Date: Nov 2010
Location: 07456 N. NJ USofA
Posts: 8,314
Default Re: RC Crawler Steering

Quote:
Originally Posted by Hardline View Post
In my typically contrary manner, I disagree with most of this. The servo will generally have the least mechanical advantage with the link coming off the horn at 90 degrees. It gives the most turning per horn rotation, but that also means least leverage. A draglink angle other than 90 degrees will provide more steering torque coming off center. That may or may not be a good thing, but the point is the geometry is more complex than you guys are allowing for. It's all about mechanical advantage, which changes for any number of factors during steering.

I think a good argument could be made that the draglink should start off lower at the horn, not 90 degrees. It will pass thru 90 degrees as you steer and wind up on the upper side. Just talking the effect of angles here, not the also important lever lengths.
I usually have my link slightly "low" at "0" so it goes through parallel during turning.
As to the rest of your post, I might agree with it, if (and only if) we were looking for travel in one direction. Since we swing the servo arm both ways I think what a few of us do is a better solution.

Since there are both ways used, I believe it really comes down to what you like.
Charlie-III is offline   Reply With Quote
Old 08-15-2012, 05:49 AM   #113
RCC Addict
 
Join Date: Jan 2012
Location: Sweden
Posts: 1,809
Default Re: RC Crawler Steering

From a geometry point of view the ideal, assuming zero ackerman, is to have:
- the servo arm tha same length as the knuckle arm.
- the servo axle parallel to the king pins.
- the drag link parallel to the tie rod, or simply have the tie rod double as drag link.

This way the knuckles turn exactly the same speed and angle as the servo axle.
Olle P is offline   Reply With Quote
Old 08-15-2012, 06:20 AM   #114
I wanna be Dave
 
Join Date: Sep 2005
Location: Houston, TX
Posts: 16,952
Default Re: RC Crawler Steering

Quote:
Originally Posted by Olle P View Post
- the drag link parallel to the tie rod, or simply have the tie rod double as drag link.
IMO, it is best to have a separate drag link.
JeremyH is offline   Reply With Quote
Old 08-15-2012, 08:57 AM   #115
Rock Crawler
 
Join Date: Oct 2011
Location: Great Outdoors
Posts: 651
Default Re: RC Crawler Steering

Actually, I don't think anyone has a handle on the "best" and it doesn't matter. What does matter is whether it works well or it doesn't. As long as it works well, "best" is irrelevant. Many configurations can be made to work well.
Hardline is offline   Reply With Quote
Old 08-15-2012, 09:07 AM   #116
I wanna be Dave
 
Join Date: Sep 2005
Location: Houston, TX
Posts: 16,952
Default Re: RC Crawler Steering

Well of course. There are pros and cons to every setup...
JeremyH is offline   Reply With Quote
Old 08-15-2012, 12:33 PM   #117
WAM
Rock Crawler
 
Join Date: May 2011
Location: SoCal
Posts: 949
Default Re: RC Crawler Steering

Rereading the previous topic, Goodness of Ackerman, got me to rethinking it. While zero or positive ('good') ackerman have the advantage of less or no scrub if one had an open diff -- we don't have open diffs. So scrub is inevitable regardless of ackerman. So much so, that I wonder if ackerman-related scrub is inconsequential?

On the other hand, negative ackerman (reverse?) has the advantage of steering the outside wheel in further once the inside wheel has stopped because of contact with springs or links. So the "average" steering angle is increased. Yeah, with scrub but we were going to get a bunch of that anyway.

So 'bad' ackerman is better than 'good' ackerman for our purposes?
WAM is offline   Reply With Quote
Old 09-20-2012, 01:42 PM   #118
Newbie
 
Join Date: Jan 2007
Location: Washington DC
Posts: 34
Default Re: RC Crawler Steering

Jeremy has been so helpful with my questions I thought I would post up a diagram of how steer arm placement impacts steer angle.

Name:  ackerman 2.jpg
Views: 6881
Size:  79.3 KB

For the crawler community I am thinking that maximum steer angle at each wheel is the most desireable goal, or maximizing steer angle with a given steering package. Since I don't have any crawling experience I'll leave that judgement up to you guys.

So with parallel steer you get the same steer at each wheel in each direction. If you have front steer and you push the OTRB (outer tie rod ball) outside of the kingpin axis then the inside wheel will steer more than the outside wheel for a given tie rod displacement. Move inside the kingpin axis and the inside wheel will steer less than the outside for a give tie rod displacement.

If you are BTA then the opposite is true. Inside the kingpin axis and you get ackerman and outside you lose it. If you draw these out from the top view it the positions will follow what Jeremy drew a few pages back.

From a package perspective. If your front steer inside tire hits the spring and the outside is no where near the universal's limit, then move the OTRB in to "speed up" the outer wheel. If your outside wheel is limited by a knuckle weight (for example) and the inside wheel has room to move, the OTRB needs to go out. You can see from the diagram that the path of the tie rod can vary as well, so you can think about that if you are bumping into the axle housing at some point. Hope this helps.
runs_wscissors is offline   Reply With Quote
Old 09-20-2012, 04:56 PM   #119
RCC Addict
 
Join Date: Nov 2006
Location: Lowell, Arkansas
Posts: 1,307
Default Re: RC Crawler Steering

Good work!
Manning is offline   Reply With Quote
Old 12-07-2013, 04:53 PM   #120
Rock Crawler
 
Join Date: Aug 2013
Location: Central Coast
Posts: 570
Default Re: RC Crawler Steering

Quote:
Originally Posted by josh6575 View Post
post #84 nailed ackerman. I can't beleive that the only crawler that comes from the factory with a correct acerman set up is the xr-10. All others are not even zero. They are going the wrong direction. When would it ever be a good Idea for the inside wheel to not turn as sharp as the outside wheel. Check out the almost corrected bully ackerman.
Bumping this great thread back up!

But wouldn't the wraith also be a 0* ackermann setup from the factory since the tierod/steering arm intersection is in line with the kingpin when the wheels are straight?
Crawl Space is offline   Reply With Quote
Reply



RC Crawler Steering - Similar Threads
Thread Thread Starter Forum Replies Last Post
my crawler has very little steering 350oshin Axial SCX-10 21 09-08-2011 01:52 AM
My first crawler, 4 wheel steering Slowsteve Axial Wraith 2 08-01-2011 01:37 PM
How can i make my crawler king have 4 Wheel steering??? HPI sleeper HPI Wheely King 8 12-15-2010 06:37 PM
why does the steering on my clod crawler suck?? chino Tamiya Clod Buster 8 12-29-2006 11:23 AM
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -6. The time now is 08:59 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO ©2011, Crawlability, Inc.
Copyright 2004-2014 RCCrawler.com