|10-28-2019 12:08 PM|
I think we were just getting to that with ThinAir back in the day....but were mainly IFS based thoughts. Something you should really understand before designing and building.
Robbie Gordon just showed up with a Portal IFS with inboard brakes. Looked fast. A rear trailing arm bolt failure crashed the truck. Hopefully sorted by the 1000.
2004 thinking. Hopefully there is more agreement today??? Or more posts since. Maybe that is where this discussion should continue???
If portals are going to be the next big thing then it needs to be understood. And possible consequences like too much antisquat= brakeing chatter...???
|10-27-2019 04:01 PM|
|Triaged||It's been a while since I have thought about it but if I remember right it moves the start of the line of action down from the center of the wheel (for normal IRS) towards the contact patch based on the ratio of gear box reduction and portal reduction. With normal geometry you would get more anti-squat. Anti-lift would depend on where the brakes are located.|
|10-27-2019 03:10 PM|
I am guessing that portals would be pro-squat in the rear????? And the only way to effectively control that would be a 4 or 5 bar system to one side.???
|10-27-2019 02:19 PM|
Photobucket even still work? I took this pic at Dakar way back in 2007. No idea if I already posted it in this thread.
|10-16-2019 01:51 PM|
LOL... Luckily I have had great mentors (!!!) to pose questions and listen to...Jeff. Being 5 hours plus from any real wheeling or riding promotes thinking time. Just trying to connect the dots. My life really took off when riding for Husky in 6 days events. Stock bikes wouldn't make it so we would break stuff and make it better or replace it easier. I got to ask simple questions to the likes of Malcolm. "How do you go so fast?" A couple simple tips and I was riding 10% quicker the next day... not necessarily faster. From there, the tech and open to learning was on. Family led to wheeling.
Note: None of us know it all. There is so much that we just don't know that we don't know. Pose good questions and listen. Watch others do their work and try to understand their thinking. Instead of thinking "FOS"...ask why did he say that? If you get the chance, ask or give your experience, then listen. "Wow, that Changed my mind."
We all gained so much from Pirate and individuals. It was an easy place to learn. Now we have to work at it.
Because I have also been "that guy" who has built things three times because of fail or becomes obsolete, I really hate to see someone new to a tech we are familiar with learn the hard way. We all have confidentiality we have to keep, but you can always give the hints to where to look and encourage thinking from maybe a different perspective.
We are so lucky. Cheeeers!
|10-16-2019 10:42 AM|
We can always count on Ben for a worthy contribution to any thread.
Sent from my SM-G892A using Tapatalk
|10-16-2019 10:28 AM|
There you go folks you have just benefited from the best. About 2 million hours of reading, internet searching, conversations, notes on cocktail napkins and listening in when the right people start whispering since about what 1966?
Ben you rock.
|10-15-2019 10:26 PM|
OK, I'll bite. Since this thread was active, I think the Ultra4 guys have been making small improvement steps toward dependability and steering accuracy for faster speeds. HP has pushed dependable gearing to the limits.
On the steering side we are seeing more camber gain geometry in turns. Both IFS and SA. And on the straight axle hydraulic side, the hydraulics are much improved keeping a few on the 4400 podium. Most have designed out the rear steer on articulation prevalent in the early adoption of 4 bars.
Stock anything is now in the past. T400's with sturdy cases and 300m internals, Big brake rotors with 6 puck calipers, $30-50k motors, huge alternators to feed huge and numerous fans, KOH intended and marketed tires, $$$ Shocks, electronics, electronics, electronics, etc, etc. Every system seems to have been incrementally improved.
Not "proven" yet, but Portals are of big interest recently to try and open up the drivetrain gearing dependability, as well as a little more ground clearance.
We will see how portals work out. It seemed like the tech was started in Ultra4 but may be taken to the next level in Trophy Trucks. The Trophy Truck community seems to have more resources and $$$$ to improve on that game. Easily adding $200k to a build. ($16k single speed transfer cases, $32k Differentials, ???$$ Portals, designer time, ....)
So now the innovators are really thinking and I believe Ultra4 will be following the TT lead on drivetrain development for awhile.
Not all innovators are thinking portals. Not all want increased COG. Enter the thinking of 4 gear transfer cases. This opens up running the differentials on the correct side of the gears. Here is one example from Weismann, I believe.
Driveline shock from hitting rocks, landing jumps, ledges, braking, and etc.: There is some new technology being tested in driveshafts to absorb some of that torque. LIke a torsion bar. But that is just like coiling a spring. What will it do on the rebound?? That may have to be another driver learned reaction to the brake or other... Time will tell.
Everyone is cringing at the coming of an electric or hybrid racer. Right now there is about a 30% loss in HP due to the in-efficiency of all the gearing and slush box transmissions for dependable 4wd. Many thought it would effect the driveline parts manufacturers. But we are finding out that motors have best efficiency ranges also. And they don't like to be stopped instantly either. So for the designers, It might just be another game to understand. (If they can gear down a jet engine...a motor should be a piece of cake)
Sadly, I my opinion and experience as now building an IRS. I don't think it has a great future. You might have better control of the wheel but the grounding out (G-out) of the differential at full bump against terra firma HURTS and severely limits travel. (On the tech side it is really hard to control camber and axle plunge on the droop side of travel. As understood on Side-by-sides.)
|10-14-2019 11:12 AM|
|mcutler1||I would really enjoy seeing this thread come back to life with more looks into the recent go fast designs, straight axle and ifs/irs...anyone still here?|
|10-04-2016 12:11 PM|
|ISDTBower||Thanks Tim. Good Info.|
|09-07-2016 09:57 AM|
man, i haven't logged into Pirate in forever... doesn't mean we don't have some cool shit going on though.
Something to note about the early days of panhard placement. We were all thinking to raise the RC we would place the panhard higher in the chassis since bump steer wasn't on the mind with full hydraulic steering, the consequences were seen in tire jacking. Those huge brackets on the axles acted like a lever that had enough force in corners and off kilt landings to lift the other side of the axle up, or lock suspension up. As fun as it was to see cars corner hard enough to float the inside tire off the ground, it was causing major problems in the pursuit of speed. Today, we are again seeing panhards come into the equation of newer steering ideas, but designing for bump steer is placing components much lower in the chassis.
|08-27-2016 01:46 PM|
All good. I think you are restating the issues that were and still are common to panhard bars. I know there was a big discussion back then about where in the travel, should the panhard be parallel. I think the consensus was at ride height.
Most recreational Jeeps have "steep" panhard bars to parallel the steering link.
Most recreational SA Jeeps that start to "get it" have worked on making that parallel portion as flat as possible.
In any event...We are only talking about an event that happens in probably a second or less. If you are wheeling slow, that event will never happen as the slow valving in the shock will allow the driver side shock to compress and the axle to move sideways per your explanation.
That was probably why almost all rigs that "Get it," build to cope with those extreme millisecond events. Outside of crawl comp, I am pretty sure that most believe that a rig set up to "get it" will perform very well in the rocks. The only hook in that statement is where the CG is on climbing and dropping off of obstacles.....and camber/scuff on turning.
All of this plays well into a SA for recreational and moderate wheeling.
Bottom line: If you are dropping off of, or jumping something and turning left immediately be aware that it is completely different than turning right after that same event....body roll may get you in turning left because of the panhard rod pushing up on the body/frame initiating a possible roll. (Steering gear on US driver side)
Edit: Now things can change when you move to hydraulic/bellcrank steering and a panhard rear. I have not followed that closely, but know that there are reasons for changing the frame side (Driver or passenger) of the panhard rod. I believe it may have to do with the location of the diff...and how far offset it may be. I am not familiar with a thread on that. Now you are talking comp crawling and probably won't find it or the people here in the dez section.
|08-27-2016 12:22 PM|
Also, if you have a steeply-angled panhard at ride height, isn't that going to be more liable to pitch the body during a suspension event?
I'm going to try to explain this thought and I bet I'm going to fail, and maybe it is completely invalid overall ...
... but if the angle of the panhard is steep, as it wants to return to an at-rest state, it is going to push / pull moreso in a direction other than you want it to, fighting the at-rest state moreso than if it was closer to level. Or in another sense, will it not have more resistance fighting the return to rest from a steep angle than it would at a more level angle? By this thinking, if a panhard was level at full stuff, it would be at a steep angle at ride height and therefore the suspension, even worse at full droop. Whereas, if it were level at ride height it would never see such extreme overall angles and would see less steep angles both at full stuff and full droop than the prior example, therefore resisting the return to rest state less as well.
Trying to think of an analogy. If you have a 10' stick of tubing laying flat on the ground that you are trying to push straight across the ground without flipping it end-over-end. If you If you left it laying flat it would be very difficult to flip over as you scooted it across the ground. But if you picked up your end end even a little, the far end is going to want to dig / resist as you push it and as it does, it will fight your efforts and try to flip over. The more you pick it up, the more difficult it will be to continue pushing without flipping.
Maybe I are dumb?
|08-27-2016 12:04 PM|
BUT My black buggy from years past had an "overbound" 4-link'ed front with panhard in the front. ( 4 parallel links, two of the joints at the axle were rubber bushings.) I LOVED steep downhill ledges in that rig. It was perfectly stable and I often chided my buddies into trying steep drop offs where they were uncomfortable because I was so comfortable. That rig the panhard was relatively level at ride height with a high front roll center. (Only about 2" below the COG.) The rear was 4-linked with as high a roll center as I could get, but still lower than the front with the panhard.
Anyway, not quite sure where I am going with that story other than to say that I do not feel that panhard does not necessarily mean built-in instability going downhill. Granted, that wasn't a go-fast rig by any means, but I don't think most people are going fast down these ledges you refer to either. I guess I'm just looking for the differences in formula where panhards create problems vs where they don't, if such a thing exists.
Also, what did you mean by "steep as most rigs still are?" I feel like most rigs are not steep today and have generally not been so in the past. And I thought what you had been describing in this thread was to be steep?
|08-27-2016 01:48 AM|
I'll let the link gods help you here (And you may have to wake them up with a PM) but maybe some more info on front or rear. If front because of mechanical steering linkage. etc.
On Panhard rods: A few years before this thread started I was sweeping the floor for comp crawler Jeff Mello. He had moved from leafs to 3links plus panhard in the front. We didn't have the money for hydro yet. The panhard bar was pretty steep as most are still today. Soon he had a couple unexplained endo's while dropping off of obstacles. That was when we started looking at video frame by frame. Finally we saw that the panhard bar was actually pushing the car into a roll over. When the axle drooped out the panhard rod went to it's extreme angle. Whne the axle hit the ground, the passenger side would collapse easily on the shock but the driver side (Steering box side) hesitated because the panhard bar was actually pogo sticking that side up...initiating the roll. Flattening that panhard bar helped but was still un-nerving. The front panhard remained popular because the hydraulic steering with the 4bar was almost worse for "get'in it". I was sweeping the floor to learn and started to look for other solutions to steering. Jesse Haines also explored that and we spent a couple days looking at different desert set-ups. With the upgrades in the last year or so to hydraulic steering, that and 4 bar seems the way to go if legal or not interested in IFS.
I knew that the way we run the dunes that it would flip me on the first run. The only real solution is IFS or triangulated 4 bar for go fast when drooping and articulating at the same time. Watch your axle steer, we weren't looking at that as it is easy to driver correct in the front. (Not so in the back as like a fork lift)
I know that there are some torque forces going on as guys can lift the driver front by brake standing on pavement.
|08-26-2016 02:20 PM|
Back in the day people generally built panhards, high, flat, and long at ride height. My general understanding was that this was to achieve a high roll center that would generally result in not a lot of body roll. (I've learned from this thread that was only the case because a smaller proportion of overall forces were being directed through the suspension.) In fact, high roll center was one reason people chose to go with 3-links in the first place. The panhard was generally long and flat at ride height to minimize lateral movement and roughly equalize from side to side.
This thread seems to have established that roll center isn't so important, at least not so important as to justify some of the extremely tall axle brackets we have seen on so many rigs. (They look so cool!) It also seems to have established that the panhard being flat at ride height has some disadvantages. Maybe I missed it, but what were they?
I also see a disadvantage to having a panhard level at compression or droop. The amount that the shocks will move will be greater and the overall amount that the axle will move laterally will also be greater compared to an equal length panhard that was level at ride height. This is just my internal logic, but it would seem to me that having your axle jack laterally to either side less would be better for handling.
Someone tell me what I'm missing ...
|11-19-2012 09:49 AM|
Everyone knows jumping on pavement would be fun
All kidding aside, I think the amount of time at each extreme is a factor BUT this chassis is also going to be running only a 12" stroke shock so the percentage of travel it will be using will he higher. Using even 3" of uptravel is 50% available and will in pretty heavily into the change of roll axis, AD, etc.
Does anyone have any decent numbers on what is too much roll axis slope in the negative direction? I am right about -2 degrees static but it progressively gains to full bump. I guess this would add understeer as it goes into bump.....good or bad?
It looks like Anti-Dive/Anti-lift is fairly independent of Roll axis. With a few different mounting holes that is easy to tune if I have the space. Adding AD/AL is pretty easy, but having less than 50% at ride height is going to be a little hard with the space available.
The front axle also travels rearward upon compression but not much. This should help the front end from getting stuck or having the pogo feeling when trying to bump up a ledge while climbing?
|11-19-2012 09:11 AM|
|11-18-2012 09:14 PM|
|11-18-2012 09:05 PM|
|David D||There's some good questions in there, and I look forward to the answers, but I am in no way qualified to answer them. My only question is with the limited amount of time that the vehicle will see full droop/bump at speed, is it worth worrying about?|
|11-16-2012 11:01 AM|
I have a new design project going. I have read this thread a few times now and seed some more info.
This vehicle is going to be an all around thing. Front mounted engine, 12" travel shocks, 6up/6down, 40" tires, etc. Front suspension is a 3-link + panhard as illustrated in the following screen captures....
Static ride height.
I tried to attain some rearward 'wheel recession' from ride height. Nice flat control arms helped that. This chassis sits pretty dang low overall for 40s with about 18-19" at ride height. Front axle roll axis is tuned for slight understeer. Anti-Dive was tuned to be fairly neutral at close to 50% ( I had to start somewhere?). That should be able to be tuned with a few additional frame side upper mounting points.....going up or down is pretty possible.
This chassis will be running a conventional steering box, so I am stuck with a panhard I think. I can't really see any way to raise the roll center without going WAY into a negative roll axis. The roll center is only about 13" away from the spring CoG ( which is a pretty big guess at this point with the CAD models )
Now for the fun stuff.......what the heck happens when things start moving around??!?!??!
Here is the suspension at full bump. I didn't go through the headache of keeping the link length constant just yet. I just dropped everything to full bump. I hope the calculator, in the 3-link version, can automate this. With the arms being approx 30" long I didn't see the need to get that precise yet.
-The roll axis goes WAY negative....just about 10 degrees. So as the suspension compresses it is going to ??????. My guess would be that it is going to understeer much more. The axle is going to almost anti-steer right? At full bump and trying to corner it is going to take a lot more steering input right?
-anti-dive goes NEGATIVE? Basically this means that at static height approx 50% of the CoG brake transfer force is going into the springs/shocks. As it approaches full bump the spring/shock is going to see more and more of the transfer force due to braking. When it goes negative the suspension is basically going to see a small multiplication of that weight transfer braking force to the front suspension?
-I need someone to explain anti-lift to me more? And how having a negative number at full compression will affect things? My understanding is that the suspension might fight itself slightly when getting on the power at full bump....like adding rebound damping?
-Roll center. At static there is 12" between it and the roll center. At full bump this decreases to approx 10". The roll center basically drops below the axle tube I think? The panhard is envisioned to do this...it is forward mounted similar to the older Tri-County Gear design. This is basically a packaging consideration. The frame end of the track bar shouldn't be lower than the pumkin at full bump. Having a normal steering box is a total headache.
I guess most of my questions revolve around static and full bump....
Here is the suspension at full droop.....
-The roll axis slope goes positive to just over 6 degrees. I am worried that this will make the chassis a little twitchy when the tires are first contacting the ground? Roll oversteer I guess is the term?
-The roll center goes up, but the separation between the CoG and the roll center also goes to 14" approx from 12" at static height.
-Anti-Dive goes up to 93%. I am wondering how this will effect the suspension if I where to have to brake right as the vehicle is coming back onto the ground? Basically, I worry that the suspension might get a little 'stuck' at this point?
I am working on the rear suspension now, but wanted to get the questions flowing.....
Thanks for any help.
|10-06-2012 01:33 AM|
|10-03-2012 01:39 PM|
|Weasel||I'm not going to argue this, do whatever you want. Might help to find a vehicle dynamics book and read it.|
|10-02-2012 11:03 PM|
|10-02-2012 03:34 PM|
Link don't add roll resistance unless you have some kind of binding on your joints. The only thing that can add resistance is a spring or some kind. A bushing would be a spring although I don't really know what kind of rate it would add to the overall system. I would tend to think it would be small but you would have to do some work to determine the exact effect. Roll resistance or Roll Moment is a function of RC height and spring separation on each end of the vehicle.
As for the number that's not exact right. Are the CG the same, link lengths, link placements, wheel travel, spring rates, etc? usually no. Can we be stupid and throw out scenarios that obviously will give problems? Yeah but what's the point it doesn't prove anything. Can we get some basic assumption from one test rig? Sure but the only way to really evolve and confirm the assumptions is to do more testing with a baseline vehicle. As you change one function you start either moving closer or further from your desired effect. I guess if all your concerned with is copying AS values then that would work but won't tell you what the trends for the rest of the system. AS is one characteristic and probably not really all that important, imho.
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