|
|
Post by the light works on Jul 19, 2018 14:35:30 GMT
I've noticed that it sometimes seems I can turn tighter in reverse than going forwards. this is a bit counterintuitive, but it might be a good topic for a junior mythbusters segment. the critical point on this is that it is about the SAME vehicle with the SAME steering system, not a car vs a forklift. then, if it is true, what about the mechanics of it causes the direction of travel to make a difference?
is the actual turning radius tighter, or does the fact the "rear" of the vehicle is swinging around instead of the "front" allow better maneuvering?
|
|
|
|
Post by GTCGreg on Jul 20, 2018 14:00:02 GMT
I've noticed that it sometimes seems I can turn tighter in reverse than going forwards. this is a bit counterintuitive, but it might be a good topic for a junior mythbusters segment. the critical point on this is that it is about the SAME vehicle with the SAME steering system, not a car vs a forklift. then, if it is true, what about the mechanics of it causes the direction of travel to make a difference? is the actual turning radius tighter, or does the fact the "rear" of the vehicle is swinging around instead of the "front" allow better maneuvering? I think the turning radius, or turning circle as some prefer to call it, is the same for front or rear steering provide it is the same steering system. The only difference is that the end with the steering is better to manage where it is going. For example, when parallel parking, you back in to get the harder to control non-steering rear end in place first, then you can more easily get the front end of the vehicle to go where you need it to go. |
|
|
|
Post by the light works on Jul 20, 2018 14:14:26 GMT
I've noticed that it sometimes seems I can turn tighter in reverse than going forwards. this is a bit counterintuitive, but it might be a good topic for a junior mythbusters segment. the critical point on this is that it is about the SAME vehicle with the SAME steering system, not a car vs a forklift. then, if it is true, what about the mechanics of it causes the direction of travel to make a difference? is the actual turning radius tighter, or does the fact the "rear" of the vehicle is swinging around instead of the "front" allow better maneuvering? I think the turning radius, or turning circle as some prefer to call it, is the same for front or rear steering provide it is the same steering system. The only difference is that the end with the steering is better to manage where it is going. For example, when parallel parking, you back in to get the harder to control non-steering rear end in place first, then you can more easily get the front end of the vehicle to go where you need it to go. but once you learn to drive backwards, it is also easier to do perpendicular parking by backing in. the truth is, that unless you have strange steering geometry (I.E. the steering tires do not track the same, such that one tire scrubs while the other tire directs the turn, and a different tire scrubs depending on whether you are going forwards or backwards) there is no reason why the circle made by the tire tracks would be different. however, there WILL be a difference in the shape of the surface area the test vehicle passes over, depending on whether it is entering the turn with the steering in front or in the rear. this is why forklifts with single axle steering have the steering axle in the rear - because that way it can pivot around the front, and leave the "swing" out in the open area behind it. however, you have given me the idea for an additional test - trying to parallel park a vehicle that can transfer steering from one axle to the other. does that make it easier or harder to park? (steering only one axle at a time) |
|
|
|
Post by GTCGreg on Jul 20, 2018 16:31:44 GMT
however, you have given me the idea for an additional test - trying to parallel park a vehicle that can transfer steering from one axle to the other. does that make it easier or harder to park? (steering only one axle at a time) I would think having that option would make difficult maneuvering much easier, provided the driver has experience using it. |
|
|
|
Post by the light works on Jul 21, 2018 0:45:58 GMT
however, you have given me the idea for an additional test - trying to parallel park a vehicle that can transfer steering from one axle to the other. does that make it easier or harder to park? (steering only one axle at a time) I would think having that option would make difficult maneuvering much easier, provided the driver has experience using it. I know that with boom lift forklifts, selectable two axle steering can give you almost as much maneuverability as the omnidirectional wheels Jamie and adam got could do - though not as smoothly. but that is drifting out of stuff junior mythbusters can do. |
|
|
|
Post by Cybermortis on Jul 21, 2018 11:51:38 GMT
Could it be that it just feels as if you are turning tighter due to the drivers location relative to the turning point? Or possibly the location of the main mass of the car; Most cars have the engine, and hence the majority of its mass, at the front.
This would be easy enough to test by having one or more identical 'cars' with the driving seat in different locations (front, middle, rear).
I actually like this for a Jr Mythbusters idea. It's simple, easy and safe to test and if they want to have the kids do a build the only part they couldn't do themselves would be fitting an engine. They might even be able to let the kids take the cars home after filming.
|
|
|
|
Post by the light works on Jul 21, 2018 14:51:47 GMT
Could it be that it just feels as if you are turning tighter due to the drivers location relative to the turning point? Or possibly the location of the main mass of the car; Most cars have the engine, and hence the majority of its mass, at the front. This would be easy enough to test by having one or more identical 'cars' with the driving seat in different locations (front, middle, rear). I actually like this for a Jr Mythbusters idea. It's simple, easy and safe to test and if they want to have the kids do a build the only part they couldn't do themselves would be fitting an engine. They might even be able to let the kids take the cars home after filming. I hadn't considered the driver's position as a factor. I wonder if they could make a go-cart designed so they could move the driver's position and convert it from front to rear steering just by releasing pins and resetting. I was kind of hoping it could be done with a go-cart, so the kids could do the driving. the initial tests I see are to do circles in forward and reverse with washable paint on the tires, and then with paint on the inside and outside corners of the vehicle. then there could be various maneuvering tests. if you built the car with adjustable steering geometry, you could test whether asymmetrical geometry makes a difference, as well. |
|
|
|
Post by Cybermortis on Jul 21, 2018 16:10:26 GMT
A soapbox car might be a slightly better way to go, as it would be something the kids could help put together and be designed from the outset with rails to allow the seat to be moved; Or three different carts with the seats in different positions.
Cost-wise soapbox cars would be a lot cheaper, and an electric motor would probably be safer for the kids to work with than the petrol engines go-carts typically use. The work needed negates the possibility of hiring one, and the cost of even a cheap second hand version in poor condition is likely to be higher than the base cost of the materials needed to build something from scratch.
Having looked at the basic designs I also suspect that go-carts would be a nightmare to try and modify. Shifting the seat isn't just a case of moving the seat but also the steering and control links. It also doesn't look to me that the compact design of go-carts would allow the seat to be moved enough to get a good set of data; The seats are already moved as far back as they can be without also moving the engine and the length of the frame wouldn't allow much in the way of forward placement.
This could also be a case of 'can try at home', where the kids are asked to come up with a base design that they can then post online for others to copy.
|
|
|
|
Post by the light works on Jul 21, 2018 16:26:15 GMT
A soapbox car might be a slightly better way to go, as it would be something the kids could help put together and be designed from the outset with rails to allow the seat to be moved; Or three different carts with the seats in different positions. Cost-wise soapbox cars would be a lot cheaper, and an electric motor would probably be safer for the kids to work with than the petrol engines go-carts typically use. The work needed negates the possibility of hiring one, and the cost of even a cheap second hand version in poor condition is likely to be higher than the base cost of the materials needed to build something from scratch. Having looked at the basic designs I also suspect that go-carts would be a nightmare to try and modify. Shifting the seat isn't just a case of moving the seat but also the steering and control links. It also doesn't look to me that the compact design of go-carts would allow the seat to be moved enough to get a good set of data; The seats are already moved as far back as they can be without also moving the engine and the length of the frame wouldn't allow much in the way of forward placement. This could also be a case of 'can try at home', where the kids are asked to come up with a base design that they can then post online for others to copy. here, a soapbox car is a gravity powered straight line racer, while I was using go-cart to refer to a self propelled vehicle. an electric cart would have some definite advantages, and that would leave just finding a way to make a steering linkage that could be easily adjusted to move the seating position and direction of travel. it would be important to have the steering designed to have mechanical limits on the steering angle, of course. |
|
|
|
Post by c64 on Aug 22, 2018 20:18:39 GMT
The turning radius is perfectly the same. What is different is how the "front", the end of the car facing into the direction you drive behaves. When the front wheels are turned, the front end swings more to the side. When the rear wheels are turned, the front end pivots more around a virtual vertical axis. One of the first things the Wright Brothers had learned about flying is that using the tail rudder to turn the airplane is very uncomfortable and confusing. Commercial airliners never use the rudder except when they have to because crosswinds must be compensated in order to land on a runway. During the flight, the airplane is turned by the ailerons only. So driving a vehicle with rear steering is very confusing and feels very rough until you become used to it. There is a simple test everybody can do safely on an empty parking lot. Park your car in any spot and then turn the steering wheel all the way into one direction. Then put the car in reverse and move it as far as it is safe. Stop, put it into drive and drive forwards again. Your vehicle will hit the very same spot where you have started. If there was a difference, the vehicle wouldn't hit the same spot again. But you are not alone, even my first driving instructor (for just a day) claimed just that what you had asked is true. He also claimed that hitting the clutch will make the car go faster  And by the way: RWD cars often have a tighter turning circle than FWD because of the drive shafts can't bend more than 50°..60° or they will latch up. Only a few FWD cars can break even or are better than the average RWD. Some FWD cars have a different turning circle radius left/right. It depends on where the drive shafts leave the gearbox and the angle to the wheel centers and the length of the shafts. Most transverse engine cars are designed for optimum parallel parking so you can turn the steering wheel more left than right until the steering hits an endstop. The reason is that the engine sits on the right hand side and the gearbox on the left hand side. The inner wheel of the turn needs to pivot further than the outer wheel. Since the actual differential has to sit under the engine, the left drive shaft is longer allowing to pivot the wheel further before the drive shaft latches up. |
|
