Landracing Forum
Tech Information => Steering - Suspension - Rear End => Topic started by: hawkwind on January 01, 2009, 06:31:52 AM
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hello im very interested in gaining as much information as possible about how one goes about designing rear wheel steering , especially anything about the setup thrust SCC used , i believe it was two rear wheels slightly offset and one behind the other,anyone able to assist?
cheers and a happy new year to all :-D
gary
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AHHHH not again, best talk to those who have tried.
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First you will need a ski-billion dollar computer to enable the rear steer to work as good as SST. Normal backyard guys like us have yet to make it work. There is a rule against rear steer for cars, have yet to see an attempt with a bike yet.
The last time Chet Herbet's last car ran the driver climbed out about the two mike mark and said in effect "...this thing is going in the dumpster!!!!"
DW
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Hawk, our first attempt had 2 wheels side by side, wrecked :| Second had them aligned one behind the other in a row, the thought was that would provide a little dampening effect, wrecked :|
The rule that car steering is provided by 2 front wheels is courtesy of the Bockscar streamliner.
More info, the car fronts had a 18 inch track for both attempts. the back in the side by side was about 10 inch track. Wheelbase was about 10 feet.
Try to not do anything too crazy, sure the fastest car in the world steers from the rear but I would re-look at what they had to do to make it work, yes, fish steer from the rear too, but they seem to know what they are doing... :roll:
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Gary;
I asked Andy Green how he ever got used to rear wheel steering and he said "I never did, really." Of course he did a magnificant job driving Thrust SSC anyway.
Regards, Neil Tucson, AZ
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Hi, Gary -
Okay, maybe there's some vehicular dynamic issue here that I'm overlooking, but this topic keeps coming up, so I'm going to ask what I think is an obvious question.
What advantage can one gain through rear wheel steering?
Sounds scary, regardless of how the vehicle is powered, but then my only encounter with RWS is operating a forklift.
Chris
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Thanks for the replies , Im in the process of designing a 3 wheel streamliner ( ok for FIM or DLRA) that could be converted to a 4 wheel streamliner with a minimum of effort , I spose it could be considered similar to the pollywog in wheel layout , I was exploring the option of front wheel drive with fixed wheels and rear wheel steering , further research has shown it( rear steering) to be an extreamly difficult task ,not impossible but near to. I also came across some other types of steering that I have not seen used or tried before in LSR will post these up when i learn more about them for comment,, I did come across a very interesting vehicle (Dymaxion ) and an even more interesting individule buckmaster (bucky) fuller ,only 3 vehicles where ever made ,one is in a museum , another was traced to brooklin in the 60"s and had covered 300,000 miles ,I also noted that the bloodhound is again a trike type wheel arrangement but this time a delta config with front wheel steering, ,and some news today Andy Green visited lake gairdner last week and pronounced it to be the best site bar none he has ever seen and believes that will be the prefered site for the record attempt :-D
cheers
gary
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Andy probably hasn't been on the other side of floating mountain.....
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No matter what kind of unconventional design makes you even think of rear wheel steering, forget it. Now. Forever.
There is no stable position and as soon as you apply any steering input it wants to go that way forever and fast. Over correcting and speed wobbles are the norm.
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The rear wheel steering isn't the tough part, the tough part is finding a driver with experience in handling a 200 mph forklift.
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No matter what kind of unconventional design makes you even think of rear wheel steering, forget it. Now. Forever.
There is no stable position and as soon as you apply any steering input it wants to go that way forever and fast. Over correcting and speed wobbles are the norm.
Ditto.
Big time.
I get asked about this a lot and have come up with a simple exercise for anyone to understand how rear wheel steering is unstable compared to front wheel steering:
1. Take a wrapping paper tube and hold it with your thumb and forefinger about 3" from one end. Let it hang. This is stable. To move the tube to the right, we move our hand to the right and lower part of the tube follows. When we stop moving, the whole tube comes to rest. This is called positive stability.
2. Now hold the tube in the middle. The tube can be at any angle and moving left and right has no stability effect, positive or negative. This is called neutral stability.
3. Now place your hand under the tube and try not to move. Without constant correction, the tube falls over. This is static instability. If we constantly make little motions to keep the tube upright, we have created artificial static stability however the system is still unstable without power and constant control input.
4. Now try "turning". To move the tube right, we must move our hand left, then right very quickly. To stop a turn, we have to move our hand out in front of the CG of the tube to stop the momentum, then back very quickly to stabilize the tube in one spot. This is dynamic instability, the situation that Andy Green found himself in.
The Thrust SSC team thought they had tested this by building a Mini Cooper with rear wheel steering. While it demonstrated stability at low speeds, this stability was caused by the damping forces of the steering system and the tires. This damping increases linearly with speed, while the inherent dynamic instability forces increase with the square of the speed.
If they had driven the Mini to 150+ mph, it would have swapped ends just like a forklift or a shopping cart pushed backwards. Try the shopping cart. Easy at walking speed, run with it around some corners and be ready to let go!
Read Andy's account in Noble's book; it is well described and shows a big disconnect between the designers' intent and reality. Andy has been quoted on many occaisions that no one, ever, should make an LSR car with rear wheel steering. Playing with the cardboard tube and shopping carts can help you understand why.
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Blue, what book would that be?
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A question yrs truly asks when somewhat unconventional ideas come up is . . .
"And just what will this do to give you a faster time slip?"
Next time Doug Kruse is at El Mirage with the Ferguson 'liner ask him about his ride with Mickey Thompson on the Long Beach Freeway back when Mickey was examining RWS for Indy!
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Eric! Excellent answer.
If they had driven the Mini to 150+ mph, it would have swapped ends just like a forklift or a shopping cart pushed backwards. Try the shopping cart. Easy at walking speed, run with it around some corners and be ready to let go!
It's much more fun with the forklift! Come on, you haven't lived until you've done a speed wobble with a forklift!
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I always thought lifting the inside front 'round corners kinda spiced up the workday............
Ed
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The late John Beckett built a front wheel drive / rear wheel steer Modified Roadster and attempted to run it at Bonneville in the '90's. It spun twice towing to the starting line. The car spun right off the starting line and SCTA banned the car right then. John did run the car at Maxton to 78 mph...pure white knuckle driving. The rear steering caster was adjusted from 15 degrees positive to 15 degrees negative in 2 to 3 degree increments to no avail. It just never handled correctly.
joe
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"It spun twice towing to the starting line. "
Now that's got to get your attention! And then try to make a run? Got more Buicks than I have!
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It's much more fun with the forklift! Come on, you haven't lived until you've done a speed wobble with a forklift!
ROTFLMAO!!!
Just remember the famous words of the professional: "Do not try this at home..."
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Blue, what book would that be?
Thrust.
It may be out of print, but I bet that Richard printed a bunch of copies before they launched Bloodhound.
Which, BTW, is a front wheel steering car!
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(http://ecx.images-amazon.com/images/I/51BQK2BZ36L._SS500_.jpg)
Thrust Through the Sound Barrier (Hardcover)
http://www.amazon.com/Thrust-Through-Sound-Barrier-Richard/dp/1852252685/ref=ed_oe_h
(http://ecx.images-amazon.com/images/I/41YE5FSCMDL._SS500_.jpg)
Thrust: The Remarkable Story of One Man's Quest for Speed (Paperback)
http://www.amazon.com/Thrust-Remarkable-Story-Quest-Speed/dp/0553812084/ref=sr_1_1?ie=UTF8&s=books&qid=1232550798&sr=1-1
Dave
http://www.roadsters.com/
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Come on, you haven't lived until you've done a speed wobble with a forklift!
Yeah, but it's a long walk back to the foreman's office to request a second set of forklift keys. :roll:
Sure, if nobody gets hurt, everyone laughs it off a week later, but you're stuck with a new nickname -
Flipper.
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I never had to request a second set of keys.
But I have driven in circles with the forklift up on two wheels. :cheers:
Forklift = $10,000 +
Getting caught = Many lost $$$
Curing Boredom = Priceless
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I never had to request a second set of keys.
But I have driven in circles with the forklift up on two wheels. :cheers:
Forklift = $10,000 +
Getting caught = Many lost $$$
Curing Boredom = Priceless
Why is it people like us do these things? :-D :-D
When I was younger it was raining at a former employer (Gale Banks) and we would blast out of the shop at full song on the forklift. As we hit the wet concrete we would turn the wheel hard and see how many donuts we could do. :evil:
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To Hawkwind.
Hey Mate, As you can see from all the other comments, you'd be better off spending your "dreamtime" in another direction. If you're set on doing a front wheel drive liner, (Pollywog style) take a look at Ken Walkey's liner. Thats a pretty successful car, front wheel drive front wheel steer. I know there's some stuff on line about it, just google his name I think you'll find what you need. He also did the trip with us to Gairdner in 95 but had engine problems & didn't run too well.
I seem to remember the 79 F100 4x4 I had when I lived in OZ had a 9" under the front, that would have to be a good candidate for the front of your liner, might have to narrow it up some. You can get used gears right up to 2.47 here in the US. I recently got a set of 2.50's off ebay for $65.00. 4x diesel Blazer's & Suburban's also come with a 2.73 or 2.56 gear, might be a little harder to find one of those down there but. A set of 2.50 gears & some 29" Mickey Thompson front runners are enough to get you into the 240mph range with enough horses. I hear Lynchy went over 300, good one.
Speeking of rear steer, a few yrs ago at Bville I was heading back to the pit after a memorable trip to the green dunny when I spied a kinda-ruff yellow T roadster with a 9" in the front with no steering, that got my attension! I wandered around the back & found it had a ford twin I-beam under there, HOLY... In true Kiwi/Ozzie form I suggested he might want to turn the diff upsidedown & turn the seat around. He didn't take it well. I never have seen the car again, I'm pickin it didn't work too well.
Have you ever backed ya car up at about 50mph mate?? Gets ugly doesn't it. Sid.
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Twin I beam ford trucks wanted to wander around when on the right end of the vehicle. :-D
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That's a fact!
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I don't know if this was ever mentioned. But 2008 Rule book page 37 states the definition of an automobile. Nuf Said. Don't like it? find an organization that allows what you want to do or buy the time to porve it.
As for the Beckett roadster; at the time I was the chairman of the roadster committee and inspected the car with many other people. You all knew what happened by reading what's been said here. I knew there was a reason for not allowing it; I just could not find it. While towing home rereading the "book" I found that definition. I would have saved a lot of trouble along with the weeping and knashing of teeth had I found it the day of inspection. It still may have been allow to try a run anyway.
This book and what's written it has taken 60 years to evolve; many wise men have contributed to it. That definition of an automobile has been in for over 40 years...Again Nuf Said.............................................................................................JD
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Your attention is well directed while driving in reverse on the Freeway. People in the next lane try to get your attention when the only place u need to look is in the rearview mirrors. It's a azz puckering deal when u have to negotiate the off ramp. It's also best to loop on the off ramp and head into traffic going the right way.
68 MPH is the best I have ever seen and it was in a Buick. A Cadillac went 67 but the rev limiter takes over. It's possible to "nurse a few extra "mph" by being very gentle on the throttle at the high end. If u just mash the pedal to the floor, the rapid engine speed increase wakes up the rev limiter.
You need to keep your knees together and use them as the steering dampner on your hands or the car gets squirrly. Use all three mirrors. It's unstable when you rotate your body and try to look out the back while cruzin' in reverse.
I haven't done it for a few years. I quit when Toyota's computer took over. Top speed was only 35 MH and then the car just slowed down, controlled by the computer. Throttle position had no effect.
Well, there's one more thing for my wife to find out about. That's why she doesn't go to the races with me.
FREUD
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Freud
It's replies like yours that have made you a legend!
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Your attention is well directed while driving in reverse on the Freeway. People in the next lane try to get your attention when the only place u need to look is in the rearview mirrors. It's a azz puckering deal when u have to negotiate the off ramp. It's also best to loop on the off ramp and head into traffic going the right way.
68 MPH is the best I have ever seen and it was in a Buick. A Cadillac went 67 but the rev limiter takes over. It's possible to "nurse a few extra "mph" by being very gentle on the throttle at the high end. If u just mash the pedal to the floor, the rapid engine speed increase wakes up the rev limiter.
You need to keep your knees together and use them as the steering dampner on your hands or the car gets squirrly. Use all three mirrors. It's unstable when you rotate your body and try to look out the back while cruzin' in reverse.
I haven't done it for a few years. I quit when Toyota's computer took over. Top speed was only 35 MH and then the car just slowed down, controlled by the computer. Throttle position had no effect.
Well, there's one more thing for my wife to find out about. That's why she doesn't go to the races with me.
FREUD
I want to start a racing series. This sounds like a blast......
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It would probably be a race of the laptops.
I think the electronics now control everything.
You'd have to go back a few years to get "good racing stock."
FREUD
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A/PIR Production In Reverse. :-D
Tom G.
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I forgot a VERY important part of "reverse."
One thing is the right side mirror. The inscription that says "objects are closer than they appear" is really important. If you plan an extended drive in reverse you need to sit and change gaze from one side to the other. The different image sizes are difficult to adjust to and location can be a problem. Bott dots and lane lines help as a guide to staying in your own lane. That mirror deal is tough. The center mirror and the drivers side mirror give a like perspective but the passengers side is a buggar.
Another thing is heat build up. Vesco asked me to take a fire bottle to the 7 mile marker and I started out in reverse. This was a Cadillac Seville. On the way to the Salt I had backed thru a construction zone for 3 miles and had no problem but the speed was only 35. (Flaggers freak out) At 3 miles the engine temp started up and continued to climb. I was only going 50 and I figured it would last. At 3 1/2 miles red lights came on. Shortly after that all the warning lights came on and the car lost it's snot. The efi and ignition were struggling and the CB antenna lost some of it's angle. Speed was reducing and the engine started to knock. I lost my balls and looped it and headed into the air. It took almost 3 miles for the instrument panel to lose it's flashing lights but the old girl settled down and was once again ready to haul blue haired ladies in luxury.
I had another problem with the Caddie. I wanted to remove some insulators from the remaining telephone poles but had no way to reach them. I went to one of the diesel truck crews and borrowed an extension ladder. The only way I could haul it was to put the rear windows down and slide it thru. These windows only went half way down, think luxury car and don't blow the blue hair, so the ladder was supported by glass. I stopped at Vesco's pit to borrow a wrench to remove the insulator mounting bolts. Vesco saw the unique hauling position of the ladder, jumped on the front bumper, ran up the hood, jumped on the roof and used the ladder as a diving board. BLEW BOTH WINDOWS OUT. No problem.
When I took the car back to the rental place in SLC I drove up, removed my luggage and walked in the office. Yes, it's full and here's the mileage. The clerk hollered at the lot lizard. " Hey, get that Cad washed up. There's a client waitin for it." I told him that he would have to take the car out of service because the back windows wouldn't go up. No problem.
FULL COVERAGE was worth it that time.
FREUD
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I have had no experience in a cross wind.
You are on your own in those conditions.
The speedos work fine in reverse, they do not remove miles from the 'odometer, and a
GPS doesn't care which direction you are going.
Everybody gives unlimited mileage anyhow.
FREUD
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I used to think I was pretty good backing up fast, 20mph, for long distances, 200 yards, but I can say I be a beginner by your standards. :cry:
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Never tried it on the freeway, but here in Okanogan County, well Ed gave a pretty good description of it so no point in going there again. I only use the left mirror except for turns. The really tricky part is knowing when the turn is coming up. I've had a few close calls when it seems like other vehicles appear to come out of nowhere. We have to find things to amuse ourselves here on the reservation.
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Long story,short. Truck driver buddy delivered a piece of equipment to a co. in Canada. They were at the end of a dirt 2-track w/ no turn-around area. Had to back out w/ 53` low-boy trailer. 7 MILES. Yikes. J.B.
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The last time Chet Herbet's last car ran the driver climbed out about the two mike mark and said in effect "...this thing is going in the dumpster!!!!"
DW
Spike Gorr was the driver on that second pass... and that's almost verbatum what he said! I crewed on that car all weekend, and was in one of the chase cars... I've never seen Spike's eyes so wide as when he climbed out. Spike did say the car was later cut up.