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Brabham BT46B 'fan-car'

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#63 ·
QUOTE (bwaminispeed @ 17 Sep 2010, 10:07) <{POST_SNAPBACK}>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

Good point - gearbox from brain to typing fingers disengaged! Need to flip the crown gear.

EM
 
#64 · (Edited by Moderator)
Won't the car go backwards if you flip the crown gear? Then you can switch the leads and the car will go the right way - but you have the same problem I think? Or maybe I don't understand this miniature engineering stuff!

Why not use two crown gears on the axle, only one engaging with the motor pinion. Cowns like the MB Slot gears, without the centring boss, take up very little axle room. So you could have one turned the other way around driving the fan. Would this work?
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David
 
Discussion starter · #66 ·
for col de torini

this was the link I gave on page two of this thread. See http://uk.rs-online.com/web/search/searchB...t&R=0191856

I really did find a 15mm one somewhere though i've now forgotten.

key word search in google for MINIATURE AXIAL FAN or something along those lines......

cheers

Andi
 
Discussion starter · #68 ·
Discussion starter · #70 · (Edited by Moderator)
nice those, but I don't understand yet if they're static model fans or real? I will check.....

Anyway managed to squeeze in an hour or so over the weekend to get this thing going.......!!!

First I built the static rear fan housing which I decided to also use as the rear location for the fan axle

Then I embarked on the fan. I marked out and then used tin snips to cut 0.25mm sheet which at that scale is strong enough.

The problem I had here was that the tin snips are right handed (as I am) and so the cut distorts the metal to make a fan which would automatically spin clockwise. unfortunately I needed the opposite so I then had to carefully bend each blade back on itself against the swarf edge of the snip - not ideal but after a bit of work I got something that looked like this.

On from there I made up my axle using plastic tube drilled out enough to push fit 3mm dia. brass tube as a bush for the 2mm axle to turn in. I decided to use a plastic scalextric pinion to cut down noise a bit in the gearing (I hate noisy cars).

That all looked like this -

and after assembly like this -



I test blew the fan while holding the bush with tweezers to ensure it ran smoothly and was quite excited when it really buzzed round making quite a high pitched wail.......

After a bit of trimming around etc. I managed to get the centre lines pretty much perfect and the fan roughly round. I made a bit of a mess of the soldering of the fan to the axle so had to spend time filing.............

Anyway the rear of the axle is held by the centre of the fan housing as mentioned and the front is held horizontally by the crowngear 'walls' but I had yet to devise how to restrain it vertically but still allow disassembly.

After a bit of thought and some trial and error I simply glued a bit of 3mm plastic tube to the top and bottom chassis sections which once assembled gently held the axle bush tube.

Well NOW starts the interesting bit. Of course having got the fan in I wanted to see if this thing would indeed suck at all and by how much. SO I got out a bit of old track rigged it up and tentatively squeezed the trigger. It wizzed round and nothing exploded so that was good......

It was a bit slow though and the motor began to heat so the friction was obviously too much. It seems that running the two pinions of the crown in that way does cause friction mainly from the fact that you have the two axles rubbing on both sides of the crowngear slot. I guess if the fan axle could be rigged in a better way this could be eliminated.

I found actually that the whole thing needed quite a lot of slop in it. Initially I made it all too tight but as I loosened it I got better speed and rather less motor heat!

Well I was desperate to see if it would suck........... and, well it sucks all right but that's nothing to do with air!!!!!!!!!!!!!!!!!!! More to do with the American slang!

That's not quite true..... it will hold a piece of paper to its underside....

And from the rear comes a 'blast' of air which you can feel with your hand for about 12cm and with your top lip for about 20cm, so something is deffinately happening.

At this point though I have to put my hands up and say all you doubters are probably right sadly. Obviously there is a fair bit of fine tuning still to do and I do think the home made fan could be hugely improved but the fact is despite wizzing that fan at say 19.000 rpm (the motor is 21.500 rated) and getting a good wind out the back the effect under the car is essentially zero.

I think one reason is that I'm realising at this scale ever joint is probably leaking. I taped over obvious holes and that made a difference but all cracks and seams probably need to be closed somehow which is difficult if you need internal access.

The second and most important reason is probably the scale thing. I'm guessing that I haven't done anything really wrong I'm just losing a bit to efficiency but even if I sort that I guess air does behave differently at this scale as discussed before and a fan of that size just can't create a real pressure difference that you could notice in a car of that weight travelling that fast.

There's another thing too - when I lubricated the whole thing after I ran it I noticed that the oil was coming out of all the glue seams so the glue is porous and that means air must also be crossing every seam!!! This also doesn't bode well for when I come to try to spray it as the joints are now full of oil!!??

Well I was a bit demotivated but as I can't actually run the deep guides they use here on my antique Scaly track I'll have to wait for Tuesday night and my freend Walter Merulli's to check the actual performance of this thing I thought I'd finish off by fitting the skirts.

They are made from cut and folded black insulating tape and seem to work well......

that's all folks from this rather demotivated slotist
 

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#71 · (Edited by Moderator)
Andi, this is great stuff, one of the most interesting threads for a long time on here. Getting the fan to work and suck a piece of paper is a fan-tastic result
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. If you could reduce the weight of the body, perhaps try a vacform I'm sure it would work even better.
 
#72 ·
Great thread
Image
. I have promised myself that one day I would made a version of the fan car (probably from the Altaya BT46) but I do not plan to have it actually sucking the car to the track!!

One thought that I had that might have already been mentioned (so forgive me if it has), is that it would be more efficient if the area of "ground efect" did not include the track slot. There are loads of gaps on plastic tracks between the rails where air can flow and even a routed track will have a hole at each end of the car (i.e. the groove). Would it be better to have two ground effect areas on each side of the rails that will have fewer track "leaks"?

Does that make sense? I'll get my coat!

Cheers,
Philip
 
Discussion starter · #73 ·
thanks Marlon and Philip for your responses and positive comments.

I think the vac form idea is interesting. At one point I thought of making something from foamboard since its rigid, very light and easyily cut. Just as a mock up you understand to check the concept.

Certainly making everything real light would make the effect much more useful/noticeable!

On the two areas for the skirts i did indeed profer that as an idea at the beginning but then just got on with the single area.

I think that the double area would help but more on the straight rather than the corner I guess as the car starts to slide one or other area would hit the slot.

If I get energy and time i might try something......

Andi
 
#74 ·
Andi,
Mate that is totally awesome, super impressive and a very neat job.

I liked the idea of a fan car with a spinning fan from the start, but must admit I was one of the sceptics when it came to actually producing a ground effect.

The simple fact that it will hold a piece of paper to the car, is proof that you have not only achieved a super looking car with a spinning fan but there is actually suction and therefore groundeffect, it may be minimal and probably not enough to make a lot of difference but it's at least there.

That is the coolest slotcar ever and the coolest thread on this forum
Judging by the amount of hits this thread has had in a short time, i'm not alone thinking that.

Youve got everyone talking about it, the classic GP nuts, the techheads and the racers who are always after an Edge.
You sir, are without doubt, in my mind an inspiration.

Keep up the good work.
Image
 
#75 ·
Very nicely done sir !

Don't be dis-heartened by the lack of immediate results performance-wise; you've got it working (!) and now you get to refine it.

Plugging any gaps and opening up the bottom more may help, tweaking the angle of the blades and putting a smaller pinion on the fan drive shaft would likely change things also...

Let us know how your testing goes.

And again, that's a pretty cool build !

S.
 
#77 ·
I'm completely gobsmacked! That is just the coolest! BRILLIANT!!!
 
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#78 · (Edited by Moderator)
Love it....
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To get a nicely detailed slot car of this iconic racer is fantastic, but to actually get the true concept of the car working in a slot car ... incredible.
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Please don't give up on this project, it's a incredible read so far and you just have to finish this car.

I'll get my order in for one of these before the rush starts ... in the mean time I'll get an extra arm & leg ready as payment for when that day comes.
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