SlotForum banner
Cancel
Create thread New Forums

Brabham BT46B 'fan-car'

Jump to Latest
21 - 40 of 160 Posts
Discussion starter · #22 ·
well this turned out to rock lots of people's boat didn't it?

first, thanks to everyone who have spent time replying and trying to help.

second, i'm deadly serious - i've seen what other guys achieve in terms of scale builds and I really don't think I could match it with the sort of time I have available. I'm much more interested in the physics experiment end of it all!

To answer some points people have made:

- the simple thing to do is surely to make a simple mock up with the fan to test the concept first. The problem here is i'm always too excited to start the project when I haven't got all the bits and the one bit i'm missing is the fan!!!!

- love the calculations about atmospheric pressure - very special. My own calculations went around the concept that if a car travels 10m in 1 second and the slot is 2mmx8mm then how much air do I need to suck before I even overcome the slot problem. My rudimentary calc's showed positive signs on this one.....

- the microfan idea (comupter cooling etc.) was also my first thought. Then I decided that since I know mechanics better than eletronics I didn't want to use something that would draw too much current. I found one at 15mm diameter which would fit perfectly and I might still resort to this if the direct drive fan wont work. See http://uk.rs-online.com/web/search/searchB...t&R=0191856 or for something more special http://uk.rs-online.com/web/search/searchB...t&R=0580506.
these are a bit big but somewhere I found smaller still.....

- it also occured to me to make the fan from a circle cut from sheet - I would use brass so I can solder it direct tot the axle. I'm worried about vibration through lack of accuracy though and inefficiency and bent flat is not the best shape......... What I came up with is this http://www.cornwallmodelboats.co.uk/acatalog/R148-M2.html I reckon if I could turn the outer edge down to 14mm i'd be rocking. Actually i've order a plastic one for now to try before taking the plunge with this expensive item.

- now to the real problem. I agree with everone who said that it is unlikely to make any difference due to the fact that a well sorted production car is more likely to be better. I think that's totally true sadly. Despite Graham's optimism my 'plank' prototype is already 1 sec. (10%) a lap slower than a production class 'C' although most of that is about weight distribution so i'm not being too optimistic but just enjoying the challenge.

- finally skirts. I have my ideas about this to avoid too much friction and where to put them etc. but you'll just have to wait until I get there folks...........

thanks to everyone who answered and yes I know i'm totally bonkers

Andi
 
Discussion starter · #23 · (Edited by Moderator)
oh and by the way sadly the siren whistle wont work. I found a picture of one and the axial fan part is just the far outer edge - wont give sufficient volume flow I don't think........

more ideas welcome..........
 
#24 ·
You may be able to find a suitable fan from a Model Diesel Locomotive of some sort, these usually have cooling fans in the roof, probably O gauge I would think, people do scratchbuild these so there may be parts websites out there somewhere!
 
#26 ·
I have yet to add to the discussion here or anywhere else on the forum but since I want to post some photos of stuff I've built, Im not sure but I think I have to post a certain amount first. So let me start by saying what a great build, although the van wall is more my style. But I believe I have the same affliction, not being able so finish one project before I start a new one. Oh well, more to finish when I retire. BUT, seeing as this is the holy Grail of slot cars,(cars with suspension) I have to say keep up the posting and if there are others out there with some shocking ideas they too should add to this one. Maybe this could be a topic for the scratch building area.
Wbb1978
 
#27 · (Edited by Moderator)
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.
 
#29 ·
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!
 
#30 ·
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.
Image
 
Discussion starter · #33 ·
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
 
#34 ·
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).
 
#35 ·
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
 
#36 ·
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...
 
#38 ·
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.
 
#39 · (Edited by Moderator)
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.
 
#40 ·
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.
 
21 - 40 of 160 Posts
About this Discussion
159 Replies
66 Participants
Last post:
c-vroom
SlotForum
posts
1.4M
members
37K
Since
2002
A forum community dedicated to slot car owners and enthusiasts. Come join the discussion about collections, racing, displays, models, track layouts, styles, reviews, accessories, classifieds, and more!
Full Forum Listing
Explore Our Forums
1:32 scale Cars Tracks & Scenery Scratch building Scalextric Digital (APB, ARC PRO) The Pit Lane