My first ducted fan car!

[bad_karma_2805a1]

So I just placed the order for my ducted fan! A good friend of mine in the Cub Scout Pack and I are each building ducted fan cars to race in the open event. I am super excited. I am naming mine "Thrust PDW" in honor of the Thrust 2 and Thrust SSC land speed record cars. I hope to be able to mold a body that will look something like Thrust 2 to cover up all the parts. I will start posting pics and my progress when the part arrive next week...wish me luck.

This is the car I hope to model mine after...

[Kenny]

Should be a fun project. Be sure to post pics.

[Duane]

I'm eager to hear what parts you and your friend are using. My fan & motor just shipped, and the thin wheels arrived today, but I haven't ordered motor control, battery, charger, and radio receiver yet.

[DKO]

Any updates on this one?

[bad_karma_2805a1]

So the parts cam in yesterday from Maximum-Velocity. I got yelled at because the first thing I did was rip open the box and look for a battery....before I said hi to my wife. She just doesn't get it. But this little baby has some power, with just an old 9v battery I was blowing stuff off the kitchen counter. I put it together like the directions said and dropped some wheels on it. On the hard would floor it was buzzing right along.

Here are all the parts you get...


And if you follow the directions this is what you end up with...



I plan on moving the fan forward, notching the body so that the front kill switch is flush with the wood, and then I am going to start the body work. I am also planning on making a tube to run the length of the body what will keep the air flowing smooth. I will keep you posted.

[bad_karma_2805a1]

I am working on the pics...if you right click and say open in a new tab you can see them.

[gpraceman]

Not everyone has a Facebook account. Can you post them to PhotoBucket or other such photo upload site?

[bad_karma_2805a1]

Hope that works better for ya.

[Duane]

I didn't realize that maximum-velocity sells a ducted-fan kit, and has done so for one and a half years. That's a useful resource.

From the photos, it appears that your duct and fan have a 40mm diam, one of the standard sizes for the smallest pseudo-jets like on the dual-jet A-10 warthogs. That's the same size I've acquired. In the standard derby size rules, there is barely enough track width room for the next-larger duct size of 55mm, but its power would be overkill in this use. Does your fan have 3, 5, or 6 rotors?

Are there any markings on the electric motor that could identify it?

Your battery is directly driving the electric motor with no engine speed-control electronics in between. The motor controls itself and is fed plain, steady direct current. That's uncommon in hobby r/c airplanes & helicopters, but does allow simple on/off switches to start & stop the motor.

In the hobby plane approach, the battery drives an 'electronic speed control' microcomputer, which separately drives the 3 arms of the motor. Gives higher max power and variable power, but the controlling wire is pulse-encoded like with r/c transmitters, and it is very difficult to include a plain on/off switch. If you do switch it on, the controller goes into a safety 'idle speed' mode rather than going to full power. So I was planning to include an r/c radio receiver to drive the motor control, and giving it full throttle remotely after the car is set on the track and before the starting pins drop. Hopefully it won't prematurely climb up over the half-dropped starting pin and lose tracking on the guide rail. The plain direct-current motor is a lot simpler and easier.

It would be good if you could mount your battery outside of the fan's fast exhaust stream. Perhaps you could toss the battery holder, and sink the bulk of the battery into the wooden car body.

When you make an exhaust tube, it is best to make it slightly tapered so that the final opening has less diameter than the fan itself. The ideal exit diameter for maximum thrust at low air speeds, has a cross section that has the same area as the outer section of the fan that is unblocked by motor or fan hub. (In model airplanes flying at 40mph and higher, the exhaust tube is narrowed further to squeeze and accelerate the air further. But this creates back pressure that reduces the total air flow and take-off thrust.) A simple way to make a light-weight exhaust tube is to take a plastic dixie cup, remove the bottom, cut one slit up the side, and then overlap at the slit to create the duct and exit diameters you want.

[bad_karma_2805a1]

Well, at this stage I had hoped to have pictures for you all to see, but sadly things haven't been going very smoothly. I am on the fourth revision of the body sides. The fan's intake is just a little wider then then base of the car. So I had to notch the balsa wood in the final lay out of the sides. I will post pics tomorrow for sure on the final sides I am going with and ALL the wood I have removed from the base.

So far I have; recessed the front kill switch into the wood and that works fine, moves the fan forward as far as it can go, tried a couple of different tubes on the end of the fan, and cut a bunch of bodies.

Today I am removing the last of the wood from the base (which will allow me to sink the battery and its trimmed down connector into the base), cutting the final tube for the fan, drilling the new wheel holes in the back, and then tacking it all together.

I need some filler material that is SUPER LIGHT...any ideas? I have to try and keep this thing at 5oz, I need to change that rule next year.

SIDE NOTE! I am also working on two cars for my kids. I will post pics for them tomorrow too, one is a copy of a design my oldest had seen on here and my youngest is making something like a cross between the Batmobile and a LeMans car.

[Darin McGrew]

I need some filler material that is SUPER LIGHT...any ideas?

At the craft store, they have a "modeling compound" that is very light. I forget its name. It should be near the polymer clay, modeling clay, pottery clay, and similar products.

The other approach would be to leave it hollow, covered by a thin film of some sort. I've heard some folks say that packing tape works, but you can get other materials that are designed for RC airplanes and similar projects.

[Kenny]

I need some filler material that is SUPER LIGHT...any ideas?

I use a couple products in my aircraft building that might be useful to you

1) Micro Balloons. http://www.hobbylinc.com/htm/top/toptopr1090.htm" target="_blank

2) Hobby Lite: http://www.hobbylinc.com/htm/hca/hcahcar3401.htm" target="_blank

There are a couple other prospects similar too. I'm not endorsing this company, they just popped up first for me. You should be able to find either of these, and others, at any reputable RC Hobby Shop in your area.

We're sensitive to weight, strength, and ability to finish on the aircraft. These products perform well on all accounts when working with Balsa. Other products are better if you're working with light ply, or harder woods.

Hope this helps,

K

[bad_karma_2805a1]

Okay, time for an update. So I have been so busy at work that the three cars I have to work on have fallen behind. This Saturday is weigh in and I am still aways from being done. Both of my kid's cars are ready for final sanding, sealing, and primer. Mine is in the final layout stages, today I am drilling holes for the axels and then starting to assemble it.

I needed to lose some weight so I brought it in and tossed on on the mill.


Having gotten it trimmed down here is the semi finished body. I need to add fins, a cockpit on top and some finishing touches to the front.


So tonight I hope to have that done and a coat of primer on it. Here is the other fan car in the open race. My friend Bill took the basic car and used some card stock to give it a body.


I will let you all know how things go tonight.

[bad_karma_2805a1]

One note on the body style...the double step design of the Thrust 2 car just did not work. The height to length ratios are totally off on this car, so I just went to a single step design. I think once the wheels and the fin is added on it will look good. Also I tried a necked down tube and just couldn't get it to seem like it was making a difference. So I went with a straight tube.

Sadly while the battery is sunken into the body it still protrudes into the exhaust tube. Not sure this will make a huge difference seeing that in its out of the box lay out the battery is right behind the fan.

[bad_karma_2805a1]

So last night was a very busy night. Final sanding, sealing, primering (is primering a word lol), and then a little more sanding. Then I got to work on my car. So with the body panels finally attached it was time to work on the fins. I have to say that all in all I am pretty happy with how they turned out. I cut them out of balsa wood and then shaped the edges by hand. Man you can really remove some wood if you aren't careful.



So after sanding and test fitting i thought I would lay all the parts on the scale and see how it was. Now mind you for some reason the person (me!) who came up with the class specs left the open race at 5oz. So I was very happy when I tossed it on the scales and it was 4.9oz.



Tonight it gets primed and painted and we work on the axles and wheels. I will have more pics tomorrow.