Fantasy Car

[Luniz]

Originally posted by Kevin Hayward:

I don't think there has a team yet that has shown how easily a composte car can be put together if the focus was on speed of build and simplicity of manufacturing.

Kev

Kev, have you ever seen the Oxford Brookes car? It's a folded/riveted/glued Aluminium sheet and honeycomb panel design, and they have told me that they built it with three people in less than a week. Simplicity of manufacturing and easily achievable accuracy were their main goals as far as I can remember...
If you are on facebook, search for them and browse through their galleries, they have published a ton of pics!

[Moreboost]

WA 2011 car with a Ka-racing's engine and 8" tyres

The catch - good luck finding off the shelf tyres

[Kevin Hayward]

Luniz,

ECU did it before Oxford Brookes, and even they weren't the first. The ECU chassis takes a couple of guys a week to build and each year has got a little quicker. Still think it can be done even easier if you changed suspension types to avoid needing any sort of chassis accuracy.

Kev

[Markus]

Originally posted by Moreboost:
WA 2011 car with a Ka-racing's engine and 8" tyres

The catch - good luck finding off the shelf tyres

Tires are easy to find. Fitting everything into the corner is more work but doable.

[mech5496]

?,

2005 is waaay to old for me in these forums, I was still in high school back then. Thanks for pointing that very thread out. On the "huge steel tube" of yours, one thing that worries me is local bending stiffness on the suspesnion mounting points of A-Arms. On the other hand it should have and outstanding torsional stiffness. But the actual chassis section loaded in torsion is extremely short and most of it is the cockpit area, which should be cut open and therefore not great for torsion (cockpit perimeter ribs can do a fair bit of work). The sidewalls see out-of plane bending (from A-Arms) and thin sections don't really like out-of-plane bending. Things would be significally better with a beam setup though....

[DannytheRadomski]

As long as its an ATS, why not skip suspension? Or do something like torsion bars or leaf springs? Could you use the flex of the chassis as suspension?

[nowhere fast]

Danny, rule T6.1 states: “The car must be equipped with a fully operational suspension system with shock absorbers, front and rear, with usable wheel travel of at least 50.8 mm (2 inches), 25.4 mm (1 inch) jounce and 25.4 mm (1 inch) rebound, with driver seated.” Meaning that the car must have suspension, and it’s unlikely that chassis flex would be considered a fully operational suspension system. However, I still think there is a way that the suspension could be simplified further.

For some time now I have had the idea of a ‘bulldozer inspired’ suspension. The typical FSAE car has a 4 degree of freedom suspension system (heave, roll, pitch, warp), bulldozers only have a single degree of freedom suspension system (only warp, although I’m simplifying things a bit here). You only need 1 DOF to keep 4 wheels in contact with uneven ground, so why add more if you’re aiming for simplicity?

A car with only a warp DOF would not need suspension springs, as the cross weights would simply balance themselves. The geometry of the suspension arrangement would determine the lateral load transfer distribution (e.g. for a rearward distribution the front wheels would travel further during a warp movement than the rear wheels).

The car would likely be cited as being in breach of the intent of rule T6.1, but I think it meets the rule as it is written. Each wheel could have the required travel relative to the chassis, and there are no restrictions given on the travel of the wheels relative to each other.

This suspension could be achieved by using beam axles front and rear which are attached to the chassis on longitudinal pivots through the car centreline. The front and rear axles could then be coupled in a few different ways. One way would be to have pull-rods at each wheel which act on bellcranks, the two bellcranks on each side of the car would then be coupled by a longitudinal pushrod or cable between them. LLTD can be adjusted with different pickups on the bellcranks. The suspension would technically be over constrained with a longitudinal connection down the left and right sides, so it would be necessary to provide some compliance somewhere or maybe just connecting one side would be a better idea.

A simpler way would be to replace the pull-rods and bellcranks with wire rope and pulleys. Changing the longitudinal position of the pulleys or changing the position of where the wire rope connects on the outboard side would change the LLTD. By attaching the front outboard end of each cable to the upright away from the steering axis, the cross weights will change when the wheels are steered, which may allow a spool or live axle rear to be used (I haven’t thought too hard about this, it may over constrain the system).

Alternative suspension types to the centre pivot beam axles could be used by coupling the left and right sides in a similar way to how the front and rear were coupled, but I think the beam axle is the simplest option.

Dampers are required by the rules, but the warp mode may need damping anyway. Deflection of the tyres may allow the axles to roll in opposite directions to each other while it is travelling over flat ground. Damping should help keep this deflection of the tyres in check. Conventional dampers are not ideal because of the gas spring rate, and asymmetric damping properties. A through rod or rotary damper (motorcycle steering damper perhaps?) would be better choices. You could also make some kind of friction dampers or use the damping properties of an elastomer or rubber, as suggested by Kevin and Z, in order to satisfy the rules while keeping things low tech.

For those that aren’t familiar, suspended bulldozers have two longitudinal beams called track frames which the track and rollers etc. mount to on the left and right sides. These track frames are mounted to the main chassis on a pivot with a lateral axis somewhere towards the rear of the machine. The front of the left and right track frames are then coupled together by an equaliser bar which is free to pivot about an axis which lies on the centreline of the bulldozer chassis. When the front of one track frame moves up, the other moves down.
The recent UWA car is similar in some ways. Replace the ‘w’ springs with pivots, and the u-bar with a pivot, and you have your bulldozer style suspension.

[mech5496]

MWhat you described is actually Z's twinbeam interconnected setup, only Z setup allows pitch/heave motion. Bulldozer style susension would be even simpler to build, but I'm quite sure it will be deemed illegal.The scrutineers like to check suspension travel by jumping up and down on the chassis. In that case, bulldozer setup would not pass...

[Z]

Nathan,

You may not be aware of it, but I have been flogging that horse since the last century (PM me and I can send you a year 2000 SAE paper).

Don't expect any results soon. Citroen used a similar suspension on its 2CV, designed in late 1930s. Farm tractors (and bulldozers, and ride-on-mowers, and +++) have used similar since the first steam traction engines rattled out of their sheds in the early 1800s. Wooden carts have had soft twist-mode (= soft warp) since, well..., forever...

It is really only motorsports people that can't figure it out. For example, it took UWA's 2012 team of students "a couple of hours", using drawings and an actual car, to explain it to Claude, the motorsport expert.

Z

[nowhere fast]

Harry,

I agree that it probably wouldn’t be allowed to run. However, you could place a brick underneath one wheel and the other 3 would remain in contact with the ground, while most conventional cars would lift a wheel in this circumstance. You could repeat this for the other wheels to demonstrate that they all meet the travel requirement.

Z,

Back when I was in a team I saw a sketch of a z-bar concept you posted on here. It didn’t occur to me that the arrangement I proposed above is essentially the same as the z-bar concept, but with the spring elements replaced with rigid elements to lock the heave, pitch, and roll modes. I have also seen some of your more recent posts on the topic, so I am certainly aware of your stance.