Front suspension

[Cessna]

Hi All

Just playing around with some ideas, if you were going to build a one-off 3 wheeler with a similar layout to the Cursor, and wanted a simple solution to the front suspension, what approach would you take, Rascal front end?

Regards
Cessna

[Bob Purton]

Hi Cessna. The now defunked Tritek company who produced replica Messerschmitts and Isetta's as I recall used Rascal front end stuff on there Isetta so I guess that would be a solution. Also readily available!

[marcus]

Do you mean Rascal as in Bedford Rascal Mini van? Or is there a scooter of that name

[g-o-g-g-o]

hi
  the rascal (van) has 10 inch tyres at the front, whereas the cursor has 8 inch tyres at the front allowing it to ride much lower, you do not say what engine you are to put in your "Cursor" lookalike and will it have a single seat (like most of the Cursor's) or two seats. The Cursor had a steering wheel with 2.6 turns from lock to lock with a rack and pinion steering because it was very light at the front. The size of the engine is important because of the stopping power of the vehicle. You had to look at 5 cars ahead with the Cursor because of it's poor brakes that was with a 50cc engine. Has you car got any door's because my Cursor did not have any and it was difficult to get in and out of without standing on the seat - which was OK in dry weather but if it was raining!!! I hope this helps you on desiining your car - otherwise you can buy a French "Sans Permis" car and save yourself a lot of work.

[Cessna]

Hi All

Thanks for the comments, as I said really only some sketches and ideas on a note pad, from my enquires it seems 10" wheels would be sensible for ride, and clearly good brakes, which I hope would be achieved by twin disc's up front (and possibly one behind dependant on engine/power train used) and light weight construction. Just to share the design thoughts I have on the pad:

1) Monoque chassis/body shell constructed by stitch-ply composite techniques (this would simplify construction and reduce the amount of sub-frame fabrication)
2) Off the self front suspension, possibly Rascal van, or maybe Triumph Herald double wishbone
3) Modern power train, approx 10-15 BHP, belt drive to provide maxium engine efficency
4) Exhaust gas heat exchanger to provide cabin heat and demist facility
5) Crumple zones in front and sides of body shell formed by foam blocks bonded to ply shell profile and skinned with GRP.
6) Body design similar to American Vortex, UK Nova kit cars, using many flat surfaces to aid construction (not bad for aerodyamics either!)
7) Sliding canopy design to gain access to cockpit (brought up with Gliders, light aircraft, and they seems to work well, but with seat protection, or step in areas)
Electric reversing motor driving directly on rear wheel, as per caravan manouvering systems.
9) Capable of staying up with rural commuting traffic 45-50 MPH.
10) Low profile (whilst staying withing Lighting and Construction & Use regulations for low drag and cross wind capability.


This may go nowhere, but the professionally available Micro cars do not offer the fuel economy I am looking for, for example the Axiam seems to only provide 48mph (based on independant reports), and the Smart car can do this in style (so can the Ka, or even  Nissan Micra) at far less cost. Would like to see 100 MPG if possible.

Regards
Cessna

[Smart51]

I am currently making a modern 3 wheeled micro car.  I'm using mini front wheels brakes and uprights but fabricating my own suspension.  It has not been all that easy so a rascal front end may be a good idea.

I'm using a 250cc piaggio scooter engine that makes 22 BHP.  The top speed will be 70 - 80 MPH which makes for a good cruising speed of about 50 MPH.  My calculations suggest 90 - 93 MPG in the "official" fuel consumption tests which often equates to 80 - 85 MPG in the real world.  To get 100 MPG you will have to be very light and very aerodynamic.  About which.  Flat panels don't equate to good aerodynamics.  You need compound curves in a teardrop shape.

It's worth you noting that the MSVA scheme for registering 3 wheeled vehicles on the road in the UK ends in March 2009.  It will be replaced with the IVA scheme, about which little is known.  It is suspected that the test will be tougher and will remove many of the loop holes associated with MSVA.  You might either want to work quite quickly, or take your time until more is known about IVA.

I'd like to know how you plan to do the electric reverse.  That's something I haven't given thought to yet.  In either case, let us see your drawings!

[Cessna]

Hi
Good to hear about your project, once I get to drawing stage I'll let you know, with regards to flat panels, I know compound curves are best (it's why mother nature uses them!) but you can achieve workable compromises with flat surfaces and single curvatures as long as you are careful with the approaching airflow incident angle. Clearly you do not want the airflow to become detached from the surface and stall which creats a lot of turbulence and wasted energy. Good examples of this approach are the Bede BD4 and Whitman Tailwind both racing aircraft with "simple" fuselage dsesigns.

Will try to find you some details re reversing motors/gears

Kind regards
Cessna

[Smart51]

Just to let you know, I've done a few calcs.  10 BHP, in my car at least, would give a flat out speed of 55 MPH.  12 BHP = 61 MPH and 15 BHP = 67 MPH.  That would be at 7000 or 8000 RPM, wherever peak power is made too.  Its probably not a good idea to run your engine like this, so i'd be tempted (was tempted) to get something a bit bigger. 

As  rule of thumb, don't tun your engine above half power for any length of time.  At lower speeds, 39 MPH = 5 BHP, 43 MPH = 6 BHP and 50 MPH = 8 BHP.  Pick a cruising speed and choose an engine power twice the figures quoted above.

[Cessna]

Hi

Many thanks for the info, re reversing haven't look at the "kit" yet, and it may be far to heavy, but I was considering modifying a Caravan Mover, see web site  www.powrwheel.com, I believe guys in the States are doing something similar with the Vortex.

Kind regards
Cessna (aka Adrian)

[AndrewG]

3) Modern power train, approx 10-15 BHP, belt drive to provide maxium engine efficency

At this power, I presume you are looking at variator-type belt drives to provide the gearing - such as are used on nearly all modern scooters.  The down side of these is their awful transmission efficiency - if you can get a belt-drive microcar to do 100mpg, it would do 120mpg with a conventional gearbox.  Just look at the cooling arrangements of most scooter belt systems as that is where the lost power is going.

If you can get a manual gearbox, you will make your economy goal much more achievable.

Andrew

[Smart51]

I thought CVT efficiency was supposed to be pretty good at around 95%?
You're suggesting more like 80%. Is that right?

Edit to say, I've just looked at the manufacturers data sheet for my engine and have worked out that the power at the rear wheel is 78% at 6500 RPM (peak torque) rising to 89% at 8250 RPM (peak power).  The reduction gear, wheel bearing, disc brake drag and tyre rolling resistance will all be bundled in with that, along with the CVT losses.  Never the less, it is worse than I thought, and it could be worse still at lower revs.

[marcus]

I made a friction drive reverser for my old velorex, a car starter motor driving through an old angle-grinder's bevel gear head then onto a spigot covered with a length of tough radiator hose. Pulling a lever brought the assembly into contact with the back wheel and turned on the power. It worked fine on level ground (keeping the engine revving) but the hose never lasted more than for a few minutes of use. In the kit car world there are various gear boxes available, including Quaife (spelling?!) designed to work with bike engines to provide reverse gear. They are not cheap, but work reasonably well.

[Cessna]

Hi All

Thanks for the ideas, I was looking at the front suspension on a Rascal van which is quite compact but still requires a small McPherson strut, when a passer by suggested the torsion bar set up from a VW beetle. The track on the Beetle would be too wide for my design project and I was thinking about the practicalities of shortening torsion rods when I had this idea.

Why not use either small indespension units or a torsion axle from a trailer, mount a lever damper above and have a vertical link between the two suspension arms carrying the stub axle and providing steering? In essence a modern duplication of the VW set up.

This would require limited enginneering and the suspension units could be well matched to the load, however there are draw back, for a start lever dampers are not as good as telescopic units, sure there must be other draw backs, what do you think?

Regards
Adrian

[inacoma]

Hi

Going a bit off track here, but using new techno. info and 1.5 million of funding, runs on compressed gas.

BMW is one of the car giants inversting in this project

I wonder if any ideas are cheap enough to incorporate.

Link :-  http://news.bbc.co.uk/1/hi/technology/4930794.stm

John

 

[Cessna]

Hi John

I feel I have gone full circle with you talking about the BMW/Bath University Clever car concept, as you will see from the earlier postings I already run a BMW C1, and was very interested when they announced the clever, however this rapidly became dissappointment. The clever seems to be very complicated, almost because the engineering is available, there is an old Russian saying "better is the enemy of good enough" and as far as I am concerned I see no advantage in a very narrow track, using tilting for stability. The Clever car is not a motor bike!, it won't be used to weave in and out of traffic, so why complicate things (however complicated suspension and engine management will ensure good dealer revenue from servicing!).

A simple three wheel design (two at the front) low weight good aerodynamics and a sensible cockpit would provide a very usable product, would require little or no additional R&D and could be available now saving the planet! (not one manufacturer has taken up Bob Curls little Dophin which looks almost perfect!)

As far as natural gas goes for fuel, it will reduce polution, but ulimately any fossil fuel will need to be banned as burning any of them (Oil, Coal, Natural Gas) will release previously locked up carbon, and add to green house gas emission. But before its too late we will have woken up and started to use renwables and carbon neutral fuels such as bio-diesel (hopefully).

Well thats my "rant about the world over"!, the good news is I think I have found a type of windscreen to use in my dream car.

Take care

Adrian