02-24-2012, 07:36 PM | #101 |
Rock Crawler Join Date: Jun 2011 Location: San Diego
Posts: 698
| 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. |
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02-24-2012, 07:55 PM | #102 | |
I wanna be Dave Join Date: Sep 2005 Location: Houston, TX
Posts: 16,952
| Re: RC Crawler Steering Quote:
BTW, I added a short description of "correct" Ackermann geometry to the first post. | |
02-25-2012, 02:29 PM | #103 |
I wanna be Dave Join Date: Sep 2005 Location: Houston, TX
Posts: 16,952
| Re: RC Crawler Steering |
02-26-2012, 07:41 PM | #104 |
RCC Addict Join Date: Mar 2011 Location: Way out there!
Posts: 1,465
| 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. |
03-12-2012, 01:46 AM | #105 |
Rock Crawler Join Date: Oct 2011 Location: Co,Cork..Ireland
Posts: 579
| Re: RC Crawler Steering
Why haven't they made this post a sticky?
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08-14-2012, 12:21 AM | #106 | |
RCC Addict Join Date: Jan 2012 Location: Sweden
Posts: 1,809
| Re: RC Crawler Steering Quote:
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? | |
08-14-2012, 04:54 AM | #107 | |
I wanna be Dave Join Date: Nov 2010 Location: 07456 N. NJ USofA
Posts: 8,314
| Re: RC Crawler Steering Quote:
It DOES make a difference once you start to steer, but that really changes the relationship of TX steering angle vs. rig steering angle. | |
08-14-2012, 06:20 AM | #108 |
I wanna be Dave Join Date: Sep 2005 Location: Houston, TX
Posts: 16,952
| 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.
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08-14-2012, 06:31 AM | #109 |
RCC Addict Join Date: Jan 2012 Location: Sweden
Posts: 1,809
| 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?
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08-14-2012, 07:09 AM | #110 | |
I wanna be Dave Join Date: Nov 2010 Location: 07456 N. NJ USofA
Posts: 8,314
| Re: RC Crawler Steering Quote:
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. | |
08-14-2012, 08:16 PM | #111 |
Rock Crawler Join Date: Oct 2011 Location: Great Outdoors
Posts: 651
| 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. |
08-15-2012, 05:12 AM | #112 | |
I wanna be Dave Join Date: Nov 2010 Location: 07456 N. NJ USofA
Posts: 8,314
| Re: RC Crawler Steering Quote:
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. | |
08-15-2012, 05:49 AM | #113 |
RCC Addict Join Date: Jan 2012 Location: Sweden
Posts: 1,809
| 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. |
08-15-2012, 06:20 AM | #114 |
I wanna be Dave Join Date: Sep 2005 Location: Houston, TX
Posts: 16,952
| Re: RC Crawler Steering |
08-15-2012, 08:57 AM | #115 |
Rock Crawler Join Date: Oct 2011 Location: Great Outdoors
Posts: 651
| 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.
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08-15-2012, 09:07 AM | #116 |
I wanna be Dave Join Date: Sep 2005 Location: Houston, TX
Posts: 16,952
| Re: RC Crawler Steering
Well of course. There are pros and cons to every setup...
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08-15-2012, 12:33 PM | #117 |
Rock Crawler Join Date: May 2011 Location: SoCal
Posts: 949
| 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? |
09-20-2012, 01:42 PM | #118 |
Newbie Join Date: Jan 2007 Location: Washington DC
Posts: 34
| 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. 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. |
09-20-2012, 04:56 PM | #119 |
RCC Addict Join Date: Nov 2006 Location: Lowell, Arkansas
Posts: 1,307
| Re: RC Crawler Steering
Good work!
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12-07-2013, 04:53 PM | #120 | |
Rock Crawler Join Date: Aug 2013 Location: Central Coast
Posts: 570
| Re: RC Crawler Steering Quote:
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? | |
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