Thinking about fans a bit more

Fans driven from the motor mean fan speed is directly proportional to car speed.
On straights where you don't need much if any down force except in breaking what you get is maximum fan speed, maximum air blown and maximum down force.
In corners where you want plenty of down force what you get is low fan speed, not much air blown and not much down force.

The microfan idea might be better. They are often 5v motors, so you need some simple electronics to drop the voltage to 5 v -do this cleverly and the fan will run at full speed when the car is running from anywhere from just over 5v up - probably most of the time. So that means you should be able to get full air flow, and full down force in corners - just where it is most needed.

Also microfans are designed to blow air effectively. Boat propellers are designed to blow water effectively. Water and air are very different, and the best blade shapes for air and water are very different.

But of course that's all just theory, no substitute for trying it.

 

Yeah but the problem is finding a small enough "micro fan". Got a source ?

 

I was going to try this using an old scaley lemans car with a pc fan mounted on the back and my plan was to cut two vents in the chassis either side of the motor and duct them to the fan, this way avoiding the slot.
My other idea was to adapt a lighting kit with the charge capacitor so the fan will pretty much run all the time one it's done a few laps.
This was just my theory so I'll be keeping a close eye on this topic!

Good luck with it and never give up until it's proven not to work!

 

Who cares if it actually works? I mean... really?

The car is scaled down but he atmosphere is not! Therefore anything you do scale wise to the vehicle will not react as it would with the full size car no matter how careful you are with the seals. To be totally effective the fan just might have to be 3 times the size! However the coolness of the fan spinning just like the real car makes up for the lack of performance and I say just build it and never tell me the odds.

 

Maybe these clips can give a hint about the BT46B fan car project.

The small, battery powered fan in these cars provide enough suction power
to keep them running on a wall or in the ceiling for approximately ten minutes.

 

Bonkers or genius?

'Egg' and 'face' spring to mind.

 

Obviously..... I have been concerned about the fan speed thing in the straight and the corners.....

My thoughts were these.......

Idea 1: What I really need is a free wheel ratchet a bit like a bicycle so that in the striaght the motor spins the fan up and then in the corners, when you brake, the fan just keeps on spinning, provided it has sufficient weight / inertia.

answer 1:Where do I buy such a ratchet? I think we're talking watch spring technology here and that's just way beyond my league!!

Idea 2: In the real car the drivers had to completely readapt themselves to the car since they realised that the faster they went in the corners the more downforce there was.

answer 2: My idea is just to try to go real fast in the corners to keep the fan spinning........ bonkers right??

Idea 3: I have found a small enough electrical motor 17mm diameter which I could easily fit in (easier than the propeller actually). It seems to have sufficient flow rate too. But as has been pointed out without the capacitor this suffers the same 0 voltage in the corner problem, and my electronics aren't up to it. Maybe i'll try this if the mechanical system doesn't work.

answer 3: Of course if I made this digital the voltage is always on peak so the fan would always be spinning on max right? Provided I bypassed the chip directly?

Andi

 

Hi Andi
Idea 1 - How big a flywheel do you need to keep the fan going all round a corner? It could be calculated. The answer might well be inconveniently large.

Idea 3 - The 0 volt - fan stops problem should only happen on breaking. Using a 5 volt fan and regulating the voltage down, you'll have full fan speed as long as you apply more than 5 volts in corners (which you probably do).

 

Im not sure how you would wire it up, but could you wire it so it does the opposite to the motor, so it slows down on the straight when you are on full power but speeds up when you slow down?

Or could you have it on maximum power all the time? As you want it to be spinning at the full rate when you start from a standing start to give you traction? I'm assuming it will help grip levels?

I'm watching this build with keen interest!
Regards
Jon

 

Cool project, but why bother with this fan thing?
Chaparral tried dual fans on the 2J - and got banned and outlawed.
Brabham tried a single fan on the BT46B - and got banned and outlawed.

If conti_rowland succeeds in his attempts, however unlikely
that might be regaring scale and physics, he can be pretty sure
that the car will be outlawed and banned equally as fast as the
real 1/1 predecessors/counterparts.

As a side remark: Both Jim Hall, the man behind Chaparral, and
Gordon Murray, the chief designer behind the BT46B, were quite
keen and experienced slot car racers back in the days. But neither
of them tried experimenting with fans on the slot car track...

 

QUOTE Cool project, but why bother with this fan thing?

Why not? If it's of interest, it's of interest.

 

QUOTE (ferraif40 @ 14 Sep 2010, 12:14) <{POST_SNAPBACK}>Im not sure how you would wire it up, but could you wire it so it does the opposite to the motor, so it slows down on the straight when you are on full power but speeds up when you slow down?
Hi Jon
I cannot see how that would work in analogue. Anybody else got any ideas?
You could do that with two digital chips, one for the car motor and one for the fan motor. You'd then have to arrange for the controller for the fan motor to do what ever you wanted it to. Not that simple.

Or could you have it on maximum power all the time?
Easy in digital - feed the car motor via the chip and connect the fan motor to the pick ups with no chip.
I cannot see how that would work in analogue without some sort of energy storage in the car. That's why there's all the discussion about flywheels and capacitors.

I'm assuming it will help grip levels?
Exactly, the idea is to produce a lower air pressure under the car. If you manage that the air pressure on top of the car pushes the tyres down on the track and increases tyre grip for much the same reasons as traction magnets.
The important bit is the pressure differance. The better the gap between the car and track is blocked up the easier it is to generate the pressure differance. That's why there's all the discussion about skirts. This all works great in theory ignoring losses and friction from skirts rubbing on the track etc. In the real world all these problems are real, and reduce the theoretically expected extra grip.

 

The fan needs to run at least as fast as the motor, right? The motor runs in direct proportion to the track passing beneath the car, right? So why not run the fan from the track using a fifth wheel. Simples.

And 'Why bother with this fan thing?'. Cos it's fun, that's why.

By the way, I've just handed Andy his next challenge.

 

Absolutely brilliant idea - I do hope you manage to finish the project.

I think you need to look at the underbody/chassis if you want to achieve full ground effect though. The reason current F1 cars have a flat plate underneath is to limit aerodynamic effects - the early projects such as the Lotus 79, Williams FW07 and your BT46 had shaped venturi sections to help suck the car down. This LINKY should give you some idea of how it was done. The normal flat slot car chassis is not going to do the job.

I did try a half-hearted experiment with an MRRC FW07 many years ago - built the underbody venturi with plastic sheet and fitted working (sort of) spring loaded skirts. It had some potential but, at slow speeds, the springs forced the skirts too far downwards and lifted the guide out of the slot! This was probably due to my own incompetence as a modeller and I would love to see someone make a ground effect slot car work properly.

 

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.

 

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

 

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.

 

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

 

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.

 

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

 

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

 

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.

 

I absolutely love this build!!!

 

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

 

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.