[Phil Kalbfell]

I have read this with interest as I have done this! I built a Chappy 2 J with two fans running off two very small RC helicopter tail rotor motors . I use a super capacitor to keep them rotating when braking/power off in the corners.
I first found a couple of very small flat motors BUT the voltage was a a bit high and they ran a little slow. I also found some very cheap tiny RC 1/43 cars with suitable motors.

Why did I do it,simply because the series I was going to race in gave me bonus laps for working aero dynamic devices. The " suction" provided by the motors and fans was non existing! But the bonus laps were helpful.

 

[Carl Jen and Harry]

Hi Andy, I can vouch for them RC wall hugging cars. My father in law bought me and my little boy 2 of em off the guy who invented them (I bet a few people told him not to bother) and they stick to the wall like glue. I might have to take one apart now... have a look at how it works.
Keep with it... a bloody good idea!!!
Carl

 

[Gone Racin]

Graham
The 5th wheel should succeed in driving the fan. If that's good enough then its an idea worth trying.
If the idea is to make it go round corners quicker there's a couple of problems-

The power to drive the 5th wheel has to come from the motor via the tyres. This must use up some of the grip that would otherwise be available for cornering.
The 5th wheel would need some weight on to transfer the power to the fan. If this reduces the weight on the rear tyres it will reduce the grip available for cornering.

So there are good reasons why a 5th wheel car would be slower round corners than a similar car with the fan driven directly from the motor.

CMOTD
The Lotus 79, Williams FW07 (and many other F1 cars) did indeed have shaped venturi sections to help suck the car down.
The Brabham BT46 "fan car" was sucked down to the road by the fan, not venturi sections.

 

[chief32s]

I had wanted to do this when I built My First Thingie. I was going to go the direct drive method, using a second pinion gear driven off the crown (behind the axle), to drive the fan. I was n't concerned that the fan would be at its most effective in the straights when it was least needed and least effective in the corners, To be honest, I didn't think it would have any noticable effect one way or the other, I just wanted to do it for the looks. Alas, I ran out of time. I had considered many of the other solutions now outlined here in this thread, the pc motors in particular. But I had not seen those wall hugging cars back then. Cool.

I think with a well designed chassis and skirt combination (isn't it more like a hovercraft in reverse than inverted wings?), and a fan similar to those wall huggers, you should be able to notice 'some' increase in down force despite the slot. If you included a capacitior, and, as Jon said, some circuitry that applied power to the fan inversely to throttle input, then it might even be effective. I'm sure one of the electrical wizards could come up with a simple circuit.

If you get this working, be sure to post your results, cos I'm a big fan of the fan car and would love to build one.

Watching with interest.

Al

 

[ferraif40]

The Brabham didn't use venturi tunnels because the Brabham used a flat 12 Alfa engine so there wasn't the room that the Williams and Lotus had because they were using the DFV.

 

[conti_rowland]

great that this thread is causing so much excitement.

all what you say about the venturi effect not working for the Alfa V12 is true otherwise I'd have built it like that as ostorero did on their Lotus 79. In fact I have built one of those and that's what I want to race this against!

I'm not sure about those wall hugging cars. From the little I can see in the videos the wheels don't turn or touch the ground/wall. they use totally different technology to do something quite different........

on the why.... and the 'it'll get banned'...... what exactly do you think it'll get banned from? there are no Italian F1 race series and so obviously it'll only be a demonstration car really. But who cares? I can set up a Swedish GP '79 race like Graham's MMM one year maybe and see who comes up with the best one??????

anyway I've been getting on with the build and now have a fully working car without the fan as it hasn't arrived.

I've been doing all the bodywork stuff.....

first I cut 3mm from the centre of the whole car and removed most of the rear bit.......

then that started to look about right

once glued

an early mock up with the front suspension off the original Scalextric

I then rebuilt the back part as it needed better strength over the rear air box and added the guide

and now it looks like this compared to the original drawings and the old car

I'll get some further shots of the internal build once I sort out the fan. I added a bulkhead in front of the chassis holes to 'seal' the area around which I'll put the skirts.

the car now looks much better being narrower, lower and closer to the ground. I've taken a sort of 'avergae' approach since it would be a huge job to get it 100% accurate.

I'm using Ostorero tyres and wheels, the original front suspension mounting and will have to do a new windscreen as the old one clearly wont fit.

Next I'm going to complete the back part of the car.

Cheers for today

Andi

 

[jp_olifer]

These are the projects worth following... when it seems it can't be done and then you find the solution somewhere.
I haven't read all the posts, but it would be possible to use the electronics of a lighting kit to keep the fan motor running even in slow corners.

Good luck

 

[zagato]

I agree with the above sentiments. It's definately worth having a go and there MUST be some effect, even if it's very slight. A few years ago I built a very basic wind tunnel with the idea of measuring the downforce created by the wings on a particular F1 car. I can't remember which car it was now, but the basic idea was to blow air through the tunnel using an old hair dryer. The heating element was taken out, so that the air was cold and the flow unrestricted. Inside the tunnel I placed the car on a set of digital scales that would weight in grams. The hair dryer was switched on and the weight of the car was noted before and after. Believe it or not, there was a weight increase with the blower on. So Conti, keep it it my friend, it's worth the effort.

G.

 

[dreinecke]

I absolutely love this build!!!

 

[conti_rowland]

I was a bit rushed with my posting last night as I wanted to add the photos of the body build but to respond to a few other points.....

5th wheel
Graham, I know where you're going with the 5th wheel thing but have to agree that this would almost certainly create more friction and drag in the system than my idea to drive off the crownwheel.

Also since slot track is never 100% flat (we don't use routed board here in Italy) I doubt that it would work very well in practice.

Finally it wouldn't give an advantage in the corners since as soon as the car moved sideways the efficacy of the 5th wheel would be minimal......

Electrical fan
I'm going forward with my geared fan for now but if that doesn't work might well consider this. What i'm worried about is that the capacitor can keep 4 LED's on for a few seconds or make the 'Turbo Flash' delay feature from the '80's but could it run a 5 or whatever volt motor with fan? Remember also that if there is suction the fan itself will be sucking against a 'partial' vacum so it will create quite a bit of drag itself! this is true for mechanical or electrical but i'm worried that in the electrical case it'll absorb power......

Lot's of people have offered ideas on this but i'd love if someone could actually do some electronic design calculations to see what sort of power consumption this would have and what sort of capacitor / circuitry would be necessary??

Finally on this one if i'm going to beat the Group 'C' Ninco car I reckon i'm going to need every bit of voltage I can have to push the car forward without also running fans??

Cornering speed
it seems to me on reflection that the car is never really 'still' in a corner. if you look at how a car drives with a magnet underneath it has slightly less acceleration on the striaght and maybe less top speed but more than makes up for that in the corners. In fact with magnets you really don't need to slow that much in the corners and that is what i'm hoping to achieve. If the car sucks the cornering speed will go up and the fan speed will therefore stay good. its a positive feedback loop (although not a very steep one maybe!).

Weight
now the build is coming together I thought i'd see how heavy this beast is. I weighed my Porsche 956 Ninco and it is 66g. So far my build (with driver and other bits I added last night is 64g so i'm doing much better than I thought.
By the time i've added the fan with axle, windscreen, roll bar, paint etc. i'll probably be a few grammes over but i'm feeling quite happy about this. there are areas I could drill for lightness if it does start to get too much.
I was worried since those Ostorero rears are huge and heavy which gives the car quite a big rear weight bias. I don't know yet if that'll be positive or negative but it certainly means the handling will be totally different to the group 'C'.

Wind tunnels
Love the thing about the wind tunnel Zagato, that's something i'd love to explore myself. I know that on scale 1/12 RC cars wings deffinately have an affect as I expermiented 20 years or so ago but was never sure about 1/32 slot. I mean air is always a medium so there must be some drag (otherwise those tiny electrical fans wouldn't work anyway right!!!!) but exactly how air behaves at such tiny scales is hard to know.

I still believe the idea can work but the real problem is whether I can build something sufficiently accurate for ME to make it work.

And FINALLY for today....

If it does even slightly work I reckon all of you interested in this topic should build one and we'll have an F1 race ONLY for these cars with rules on motors, tyres etc. That way we can't get banned but would have plenty of fun!

Andi

 

[Deslotted]

Looking Good So far.
at the end of the day if theres zero ground effect, it's still a very nice car and definately different.

Any classic F1 build is a good one I reckon.

Good stuff Andi.

 

[Gone Racin]

Hi Andi

You ask for some calculations on keeping a fan motor running.
OK lets assume you use a 5volt fan and have a regulator circuit that takes a constant current from the capacitor when the fan is powered by the capacitor.
Then the capacitance in farads = (constant current to fan in amps) x (the time the fan keeps running in seconds) / (capacitor voltage at start - capacitor voltage at end)

So for example - The spec for the fan you suggested in an earlier post says it takes 160 mA: assume the capacitor starts charged at 12 v and ends at say 7 v: to keep the fan running for 0.2 seconds (which should be enough to get through the breaking phase) that give a capacitor of 0.16 x 0.2 / 5 = 0.0064 farads (or 6400 micro farads)

Quickly looking at suppliers catalogues there is a 6800 microfarad 16 v electrolytic capacitor 16mm dia x 30mm long. If you only wanted to keep that fan running for 0.1 seconds a 3300 microfarad 16 v electrolytic capacitor 13mm dia x 25mm long would do. Spending more time in catalogues might reveal some physically smaller capacitors.

So unless I've made a mistake in the calculations (always possible) that's quite a big capacitor to fit in an F1.

You say you are worried that in the electrical system will absorb power.
Charging the capacitor and running the separate fan motor will absorb power.
Spinning up a flywheel and a mechanically driven fan will also absorb power.
The capacitor / fan motor will take it's power from the track power in parallel with the motor, so depending on the adequacy of the power supply and the track wiring, this may make very little differance to your motor power.
The flywheel / mechanically driven fan will take power from the motor so will reduce the power available for driving the wheels. (Of course you could always get round this by using a more powerful motor)

 

[conti_rowland]

Thanks gone racing, your calc's certainly help focus my mind. It was pretty much as I imagined really and yes 13mm x 25mm is pretty big and I'm guessing you'd need a few other components to make it all work too (resiters and such like), plus something to reduce the voltage from 12 to 5 or whatever in the first place to drive the fan motor.......

Suddenly all looking pretty cluttered inside the car. In an area where I'm trying to keep air flow clean so as to get max sucking power!

Plus all the extra weight.......

I still think the mechanical approach is more elegant if it can be made to work. plus that's how the original was. There was a system of gears and clutches that drove the fan from the engine apparently.

Anyway the propeller still hasn't arrived so I've been pushing on with the build so I'm ready when it does.

Last night I rebuilt the air box sides slightly higher, completed the engine cover, added the wing and the roll bar. I did the roll bar in brass after my experience with the Ostorero resin one. First drive I turned it over and smashed the rioll bar so I had to cut out and add one in brass!

I like that the motor can vent exactly where the original engine took air - a neat parallel. I'll cover that with some fine mesh eventually.

I've also removed the old decals so its nearly ready to rock.

Oh and I took some photos inside so you can see the bulkhead and fixings. The bulkhead is placed level with where the front skirt will cross the body in the area where the original car (and mine) have the straight side protrusions to make the underpan square. The only thing that crosses the bulkhead are the two wires and I made the cut outs for these very tight on the wires so they effectively seal.

The body does have some leakage and I may need to deal with this later but want to see if that's necessary before I work out how to do it. A little bit of grease may be sufficient for now.

If the propeller arrives today I might have it running by Monday!!!! If not I may end up making one from flat brass anyway as I'm getting too excited to wait.......

Andi

 

[vfr750]

Is there any way you could rig drive from the contrate gear to the back of the car to drive fan blades? possibly using a pinion on an old armature shaft.

Cheers

John

 

[conti_rowland]

yes that's exactly what i'm going to do, except i'll be using 2mm brass tube instead of armature axle so I can solder to it......... and it's lighter........

only problem I have is that the axle will turn in the opposite direction to the motor and so i've a 50/50 chance that the propeller will turn the wrong way!

cheers

Andi

 

[Ecurie Martini]

After you have the basic engineering done, you can play with gear ratios - the largest crown gear that you can fit + a motor pinion selected to give you the desired ratio + the smallest fan drive pinion that you can find will yield the highest fan speed. If the fan blows the wrong way, turn it around.

EM

 

[conti_rowland]

not sure turning a fan round makes it blow the other way if the axle is alway turning in the original direction???????????????? one of those logic things my head has difficulty getting straight in my mind!!!

the trick would have been to make the car so i could switch the crown gear from side to side thus reversing the rotation direction of the fan by swapping the crown gear and the braid/motor polarity.

it so easy to think of these things afterwards..........

no post today so i'll be making the fan tomorrow!

wish me luck

Andi

 

[Ecurie Martini]

QUOTE (conti_rowland @ 17 Sep 2010, 08:42) <{POST_SNAPBACK}>not sure turning a fan round makes it blow the other way if the axle is alway turning in the original direction???????????????? one of those logic things my head has difficulty getting straight in my mind!!!

Andi

Think about a standard fan - desk type or window fan - turn it on and stand in front of it - air blowing towards you - pick it up and turn it around - blowing away from you.

EM

 

[bwaminispeed]

QUOTE If the fan blows the wrong way, turn it around.
Turning a fan blade 180 degrees does Not make the air blow the other way if it is still rotating in the same direction.

When you turn a household fan around, you are also turning the motor around, thus, the fan is now rotating in the opposite direction relative to it's previous state. If you leave the fan itself the same direction, and, only take the fan blade off and put it on backwards, the air will still blow the same way.

If the fan blades are airfoil shape, all that happens is that you lose efficiency

 

[MAF]

Andi, this is a great thread, you're making a really nice job of this project

. Thanks for sharing and can't wait for the updates.