Monday, October 14, 2013


Because FanKar(t)
(Version 1.0)

For several years I've been fooling around with fan propelled R/C vehicles - FanKar happens to be the latest incarnation. Stemming from June 2012, FanKar has gone through plenty of modifications and several hilariously terrible accidents.

Probably half the people who frequent RC events have seen or driven some form of FanKar. In the beginning it was a "let's see how fast we can make a fan on wheels go." type of thing, but it turned out much more awesome than I expected, and probably a few others too. 

Fankar is fantastic, there are many reasons why. I'll attempt to list a few in the hopes that some of you may understand what it means to FanKar.

1. It's got a power to weight ratio almost exactly equal to a 2013 Formula 1 car.

2. It's got almost no suspension
3. There is almost no engineering forethought into FanKar.
4. The steering system is made almost entirely of plywood with a few brass tubes as bushings.
5. FanKar has been clocked at 87mph (right before it exploded).
6. There are no brakes.

7. The wheels are held on by zip ties
8. There is almost no protection for any of the components
9. The steering servo is nearly too small, and has no servo screw.
10. The steering system is under-defined.

These are a few of the reasons why FanKar is like that cheap abused plane that should've died many flights ago, but you just keep flying it because you love it, and probably don't care if it explodes (which would just add to the hilarity).

Shown above is version 1.0, or the first version that you could drive in a remotely straight line above half throttle. One of the largest issues with these air propulsion RC vehicles is the thrust line compared to the Center of gravity.

Generally with onroad racing cars you want to have the Center of gravity as low as possible to promote quick directional changes - this is true with fankar, it also helps it stay on the ground when you accidentally sideways (which happens a lot). Low CG is a problem when you introduce a thrust source of some kind because generally it will be above the CG.

this creates a moment arm, making the rear wheels "light" with power input....that's not generally great for stability, so I decided the easiest way to fix this was to add a blown rear wing element.

Stealing pages from the F1 Pagebook, I added this piece of foam behind the fan to create rear traction with thrust.
It worked extremely well, the drivability increased to a level it had not been at before; read (you could go to full power in a straight line and keep it there) You could even make slight left and right turns at full power. Wow, exciting! of course now I saw this as an aero project and started to go crazy with CAD. I turned out a few crazy CAD designs which all utilized the blown rear wing technique. Then I decided that I would ruin the "FanKar-ness" of FanKar if I got too technical about it and added a simple top element and endplates/vertical stabilizers. Also present are new black fiberglass rods to control chassis flex torsionally:

This is the part of the story when FanKar's true potential was realized. I dropped about 10 MPH top speed, but the car had incredible grip and was very stable...until it wasn't. It drove how I thought a fan propelled vehicle should drive. The only problem with this configuration was that the foam actually wasn't strong enough to cope with the high velocity airflow provided by the fan over the double element rear wing...I figured this out when all of a sudden the wing departed in similar fashion to this Kimi Raikkonen accident:

(Pretty much the same thing happens to FanKar when the wing comes off)

here's an after picture of the wing with damage from tumbling after separating from the car.
(also present is a thru-fan receiver.)

At this point I got tired of fixing the foam rear wing and decided to build a stronger and more durable setup.

Enter alternative building materials.

The structure was now comprised of 1/16" plywood endplates with carbon tubes supporting the elements on the underside. You can see the lower tube is also attached to a link which connects the wing to the chassis in a way that I can break the glue joint from the lower wing element to the chassis and adjust the angle if I found that it was needed. This wing worked really well, I actually picked up speed and rear downforce over the Depron version, meaning it was a more efficienct setup. It also didn't fail just driving around, which was a plus.

And now for the tragic end to FanKar 1.0 in the form showed above.
I was showing some friends how awesome the latest FanKar was and forgot how to drive it-
coming off of the throttle means you lose all of your rear downforce with this setup. It behaved like the Raikkonen crash above and swapped ends.....right into a parking block at near top speed.
The car had taken off as soon as it went backwards and landed directly on a parking block without bleeding off much speed at all. It broke nearly everything important.

Components that survived:
the wheels minus a few flat spots from the snap turn, the main chassis rails and rear axle, the fan (I don't  know how) and the ESC. Everything else was broken enough that I didn't really want to deal with it and set the project aside. 
Here's another picture of the car after the crash:

The Fankar chassis still lives in the FanKar box and someday I'll get around the implementing a few more ideas once I become interesting in air propulsion vehicles again (which could be soon, because it's almost that time of the year again)

Anyhow, here's another form that the FanKar chassis has seen since it came into being:

it's a ceiling car...and it sucked, literally.

It worked pretty well until the suction battery voltage would trigger the low voltage cutoff in the ESC,....then you better run and hit throttle hold 'cuz it was coming off the ceiling.

now onto an abbreviated CAD portion of this post -
I'll leave a few of these here for thought.

(above) This was designed for a 70mm fan around a set of rules a few buddies and I had come up with.
(below) Rendered here is a 120mm all out racecar designed around the Formula Fan series rules, maybe it will spur some interest and we can see some truly innovative RC car racing?
time will tell, I'll leave you here with these below.


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