Pinewood Derby's Olden Days
Whether you grew up, are still growing up, or refuse to grow up you have probably seen or build a pinewood derby car in cub scouts, scouts, or independently. In my years of growing up and now continuing to refuse to grow up I have built many of these fun cars. Typically you start with a block of pine wood and four wheels. You are supposed to carve out some fast shape and paint it to look like some hot ride. I have had some wedges, some more shaped like actual cars and some plain ol lead sleds. Gluing Lego people in the drivers seat is always fun too. But this year I want to do something a little more advance. And having just been made a Scout Master, I think its time we had an open "anything goes" class of derby racing.
I have seen a few videos of people putting CO2 cartridges in blocks that explode down the track... sometimes... sometimes the just blast off and away. Sounds fun but maybe next year. I saw others who used slot car gearing and motors to drive themselves to the finish line. Fast and cool but I am not feeling that either. Further investigation showed another option, the Electric Ducted Fan. Have you ever seen one of those RC Jets? A lot of them use small battery powered turbines. This sounded promising. Powerful, fast, and loud! Like a small jet loud. That is what I want to scare the pants of these scouts and their leaders car screams like a hawk down the track. Now lets hope the cub at the bottom with the pillow doesnt bail on his catching duties!
I started off with my block and figured "I can hollow this out and put the fan and a battery in it no problem." Well quickly I learned I would need more electronics then that and my little block would not cut it. We will figure the rest out later. EDF fans come in many sizes typically between 50mm and 90mm in diameter. I wanted smaller though! I wanted to be discrete somewhat about this and not just have a huge fan on the back of a block. trudging the interwebs I discovered a 27mm fan with a lot of push. Score! And ordered. This is a NEEWER EDF off of Amazon for around $22. Even though it shipped out of China it arrived in a little over a week.
I had some more learning to do on how to power this thing though. As you can see in the picture there are three unlabeled wires coming off of it. EDF fans use a PWM (Pulse Width Modulation) brushless motor that can handle high amounts of current and super fast RPM's. In order to get this to the fan we need to have what is called an ESC (Electronic Speed Controller). I read that you want to make sure to overdo your ESC a bit. This tiny motor would not need too much to achieve its max output so I went with a 30A ESC also from NEEWER off of Amazon for around $12. As you can see we have a + and - lead as well as a connector which will have to connect to a receiver that will tell the ESC how much juice to deliver to our fan. On the other side we have three wires which will mate with our fan. I could find no explanation as to how these wires were supposed to be connected to the fan other than trial and error. One site said if you hook it up and it is spinning backwards, just flip two of the three wires and it should reverse the direction of spin. Well that was true advice!
Now to get some sort of throttle signal to our ESC. I dont want to turn this derby car on and have it full blast on the starting line and full blast till I pull off the battery or something. Speaking of battery. We need one. We are going to need a lot of power for our fan. I chose to go with a VENOM 11.1V 20C 2100mah LiPo battery. Our fan is rated this high and will last a good while with the 2100mah size fuel tank we will give it.
The venom battery comes with these connectors which you can solder to the ESC. I also recommend a SPST (Single Pole Single Throw) Switch being wired into the negative line here so that we dont have to pull the battery to shut down our electronics. More on this later.
Alright, we have our fan, our controller for the fan, battery, now we need a way to tell the controller to hit the gas and GO! Luckily I had lying around an old Nitro HPI Savage RC Truck. This thing is hella fun and also breaking the bank. Every time I put $50 dollars in parts into it I get 30 minutes of fun then I do something dumb and rip off a steering knuckle or rip the teeth off of the spur gear or clutch bell. So lets borrow the receiver out of it and its Radio.
Here is what I learned about this radio.The trigger is our throttle and brake all in one channel. Our receiver has 4 channels. We will only need one. The trigger at rest is sending a 50% or centered signal so that the servo knows to be centered. On the Savage this servo opens a carburetor for throttle and on braking reverses direction to clamp the brakes on the transmissions flywheel. When this is connected to the ESC, the ESC is going to take that 50% signal and deliver 50% throttle. So in order for us to stop the fan we have to hit the brakes on our trigger. Imagine my surprise when I turned it on and it blasted off!
Well all of our parts are on the way. I hate waiting...
Follow the links below to see the progress! You can even skip to Race Day to see the final video of the build!
Suggestions, Ideas, or comments welcome.