Hoverboard

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Introduction: Hoverboard

Prototype Hoverboard for children.

This is a fairly quick build of a prototype hoverboard. It’s basically a hovercraft with the forward propulsion provided by your foot like a skateboard, it uses two 65mm Electric Ducted Fans (EDF’s) to provide the lift, these are each driven by a 30 Amp ESC and the battery supply if via two 3 cell Lipo’s.

Step 1: The Main Hull.

There really isn’t much to this project!

The bottom ply is 800mm long by 250mm wide and has the corners cut off at 45 degrees. I cut the corners off to make the corners the same length as the front/back (73.22mm long and down to give corners 103.5mm and front is the same), but it really doesn’t matter as the skirt isn’t mounted on this edge. The skirt is mounted 25mm further in, but I mark this out when I have the top glued to the bottom just in case it’s not central.

The top deck is 900mm long and 350mm wide 9mm (3/8”) plywood. The corners are cut off at 45 degrees 102.5mm in from the edge and 102.5mm down again this is to make the corners the same length as the front section so you only need to cut two different sizes of skirt sections. (Front/corners and sides)

Starting with the bottom I added the 4 sections of ply to make up the battery box. I am going to be honest at this point and say I didn’t take measurements just made it up as I went along. So all the dimensions are approximate (apart from the length, width and height) the battery box end is 100mm wide and the two sides are 200mm long. And the back section starts 100m from the end. All of these pieces of ply are 57mm high, this gives a total height from the top of the top deck to the underside of the bottom of 75mm which is important for the skirt shape. Next you can see in the pictures I have added the section of wood at the back which runs along the centre line of the board this bit was 100 mm long and doesn’t have any holes cut in it. Then I added the two pieces at angles these do have holes in them, but I didn’t measure the bits as I just cut them to size. Then add the 4 bits which run along the sides of the battery box all these bits have holes.

I decided at this point to add a pointed front to the battery box so cut two pieces with angles on to meet at the front sections of the box. Then I added the long bit which runs the whole width of the board with the big cut outs as shown. Then add the remaining bits starting with the long bit which runs along the centre line of the board and as shown in the photo runs over the edge of the board by 50mm which was to help me line up the board top deck, this bit doesn’t have holes in it. Then I added the other bits of ply half way along the pointed section of the battery box, and the front of the battery box, also the angles bits at the front then the two bits which run along the edge of the board. I hope that make sense I think the picture will explain it better.

Once happy with the bottom section I carefully lined up the top deck and marked out where the battery box was, then cut out the rectangle for access to the battery half way in-between the sides of the battery box.

Step 2: The Twin Electric Ducted Fans (EDF's)

Next bit to make before sticking the top deck to the bottom was the fan housing. This bit was designed on a cad program then the plans printed out and stuck to the ply wood before cutting out. The curved section was made using 1/16 inch ply and the front and sides (and middle) are all 9mm. please see the attached PDF for the plan.

You will see in the photos I added a piece of ply wood at the back of the fan housing to allow the curved top ply to be glued down.

You can also see in the photos the pieces of ply I have glued into the corners to mount the fans onto. These were not the best solution. The fans should have been mounted from underneath!

Once the fan unit was made I then positioned it onto the top deck, a line was drawn 15mm in from the edges of the deck to show where the skirt retainer would be, this was used as a guide to where the fan unit was to go. Once I was happy with the position I made sure it was all square then carefully marked the position before cutting out the two rectangular holes for the air to enter the hull.

To mount the fan unit I added two strips of wood to the bottom edge to allow easy fitting and removal.

Step 3: Joining the Top to the Bottom.

This stage was the easy bit just line up the top and bottom and glue and screw into place.

BUT don't forget to add the battery cables for the two lipos! for these i just uses 14 AWG silicone wire with suitable connectors at each end.

And that is basically it for the hull.

Step 4: The Skirt.

The skirt was made using a waterproof fabric I got from the sewing shop. The shape is based on 270 degrees of a 75mm radius circle (that is why it was important to cut all the middle bits 57mm height once you add the 9mm top and bottom decks you get 75mm). This is a fairly basic “BAG” skirt and because the corners are the same length as the front you only have to cut out two different length of fabric. The corners and front can be cut straight from the PDF template (with extra edges for sewing). I also use the template as a gluing guide. The template needs to be printed at 100% and on big paper, in the UK this is A3 size which is double the size of A4 (standard paper size). Check the dimensions on the plan once you have printed it.

So to explain the process, I cut out the templates and draw around the template on top the fabric, I then mark out where the top and bottom lines are. These lines are where the skirt is joined to frames on the top and bottom of the board. I then cut out the fabric section about 10mm extra along the sides to allow for the sewing along the drawn lines. Once I have all the section I generally start with the front and back section and using a glue guide stick the sections together making sure you can still see the drawn line to allow accurate sewing along it. Once all the sections are glued together I then sew along the lines. Then I punched loads of holes 40mm from the bottom edge. These holes were 8mm in diameter and there are 3 in the front/corners and about 23 in the sides.

The skirt is then mounted to the hull using pieces of 9mm ply you can use the PDF plan as a guide to cutting these pieces. The long sections that run down the sides should be cut to gap but if all has gone well these should be 550mm long. I mentioned at the start that the skirt isn’t mounted at the edge of the underside, it needs to be mounted 15mm in from the edge. So with the hoverboard upside down use a square at the edge and measure in 75mm and 90mm, then draw the two lines and use these lines to mount the skirt on. The skirt was then stuck to the hull using double sided tape and then the retaining strips were the screwed down on top again using double sided tape.

Step 5: The Wiring and Arduino Circuit.

So this step is a bit out of sequence. You had to add the power cables before you joined the top deck to the bottom!

Otherwise the wiring for the EDF’s is simple, just join the three wires from the EDF motor to the ESC making sure the motor spins the correct way and then add a battery connector on the power wires. Initially I checked the board worked by driving the ESC’s using a servo tester and this worked well.

Finally I made up the control circuit using an Arduino board and a 10k Ohm POT for the input, and 28 full colour WS2812 LED’s 12 in a ring around the POT are used to show the power level, and two strips of 8 are used on each side to show the battery voltage of each Lipo.

All the LED’s are really just to keep my 7 year old boy happy, if you want to keep it simple just use a servo tester or just a basic Arduino program.

Anyway the whole listing is shown below for clarity.

#include 

int oldAI;
int maxVoltageBits = 1024;
float dividedBits = maxVoltageBits / 11;
int escOne = 2;
int escTwo = 3;
const int LedOutput = 4;
const int rotaryInput = A5;
const int battOne = A4;
const int battTwo = A3;
unsigned long currentTime;
unsigned long timeNow;
unsigned long delayTimeCorrect;

Adafruit_NeoPixel strip = Adafruit_NeoPixel(28, LedOutput, NEO_GRB + NEO_KHZ800);
void setup()
{
  strip.begin();
  pinMode(rotaryInput, INPUT);
  pinMode(LedOutput, OUTPUT);
  pinMode(escOne, OUTPUT);
  pinMode(escTwo, OUTPUT);
  //Serial.begin(115200);
}

void whichPosition(int AI)
{
  uint32_t colouroff = strip.Color(0, 2, 0); // define the colour for OFF.
  uint32_t colouron = strip.Color(30, 0, 0); // define the colour for ON.
  if ((AI > (oldAI + 10)) || (AI < (oldAI - 10)))// see if the value has changed?
  {
    for (int i = 0; i < 12; i++) //12 leds on the ring
    {
      strip.setPixelColor(i, colouroff); // it has changed so set all OFF value.
    }
    strip.show();
    int newAI = round(AI / dividedBits);
    strip.setPixelColor(newAI, colouron);
    strip.show();
  }
  oldAI = AI;
}
void displayBar(int batt, int bar)
{
  uint32_t colouroff = strip.Color(0, 0, 0); // define the colour for OFF.
  uint32_t colouron = strip.Color(0, 10, 30); // define the colour for ON.
  for (int i = bar; i < (bar + 8); i++)
  {
    strip.setPixelColor(i, colouroff);
  }
  strip.show();
  strip.setPixelColor(batt + bar, colouron);
  strip.show();
}
void loop()
{
  currentTime = millis();
  int readSw = analogRead(rotaryInput);
  whichPosition(readSw);
  int readVone = analogRead(battOne);
  if (readVone < 800)
  {
    readVone = 803;
  }
  readVone = map(readVone, 803, 1023, 0, 7);
  int readVtwo = analogRead(battTwo);
  if (readVtwo < 800)
  {
    readVtwo = 803;
  }
  readVtwo = map(readVtwo, 803, 1023, 0, 7);
  displayBar(readVone, 12);
  displayBar(readVtwo, 20);
  digitalWrite(escOne, HIGH);
  digitalWrite(escTwo, HIGH);
  delayMicroseconds(997);
  delayMicroseconds(readSw);
  digitalWrite(escOne, LOW);
  digitalWrite(escTwo, LOW);

  timeNow = millis();
  delayTimeCorrect = timeNow - currentTime;
  delay(20 - delayTimeCorrect);
}

Step 6: Testing and Conclusion.

So as the two videos show the hoverboard was very effective at lifting a large weight! however the balance of the board was essential, if you positioned your foot to far left or right then the board struggled to lift.

As a prototype it worked very well and is a very good demonstration of pressure force and area equation. Where the Force that can be lifted (weight) is equal to pressure (caused by the fans) * area (under the skirt).

A limiting factor was the surface the board was on, and i believe the only reason it was able to take my weight was because i was in my shed which has a laminated floor.

A larger area would help and so would a more powerful fan (more volume).

Calculations

Hopefully i will get this correct........

My weight = 74 Kg or 725 Newtons. (weight-force)

Area under skirt is the same as the top deck area = 0.9 * 0.35 -(2 * 0.1025 * 0.1025) = 0.294 M2

Hence the pressure under the board had to be at least 2466 Pascal's or 24.66 millibar. (0.357 PSI)

This goes to show how little pressure (acting over a large area) can lift such a heavy weight! The normal person can blow between 1-2 PSI however you wouldn't have the volume!

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34 Comments

I'm curious as to how this will hover over water

Nice one.

Is there a parts list? What size LiPos did you use? What is ESC an abbreviation for? Doesn't the third wire from the motor give a rev. count output? If I'm right, did you use these data? Any views on construction using Pb acid batteries - heavy I know but light comared to the masses you've shown can be supported?

J

So the main parts are the Electric Ducted fans (EDF's) and the Electronic Speed Controllers (ESC's) the Brushless motor used in edf unit is basically a 3 phase motor so there are 3 wires connected to it supply the rotating magnetic field. you then connect a 3 cell lipo which is classed as 11.1 volts but when fully charged is 12.6 Volts, so a 12 Volt Pb would also work. However be mindful of the current drawn as the EDF's are running at nearly 100% so the Lipo's will only give a few minutes (i didn't measure and i am using small capacity ones at the moment)

No revs measured but the ESC are given a pulse to control the speed. normally the pulse would come from a receiver as part of a radio controlled plane, but in my case i made up a circuit so give out the pulses depending on the pot on the front.

Could you provide a parts (and source) list please?

Also a circuit would be helpful.

I'm not sure about your description of the fans as "basicly a 3 phase motor"; this would only be applicable to AC and would require 4 wires - the three phases plus a ground.

J

I will sort out a parts list for you, the two main bits are listed below in reply to ecruz11..

As for brushless motors.... they can be wired up with the 3 sets of windings in delta OR the 3 sets of windings in Star with the common connection left floating... The ESC does the clever bit switching on and off the 3 sets of windings to create a rotating magnetic field.

Cheap EDF from BigDotUncleStore, 3800KV. $23.99 for one set.
(Two sets needed)

https://hobbyking.com/en_us/turnigy-plush-30amp-sp...

ESC is a hobbyking 30A Plush. (Two needed)

http://www.bigdotunclestore.com/product_detail.php...

Servo tester. Which will drive both the fans. And avoid
having to use the Arduino board.

https://hobbyking.com/en_us/hobbykingtm-servo-tester.html

9mm (3/8”) plywood. Brought a couple of boards 1220 * 607mm
but you may get away with just one bit?

http://www.homebase.co.uk/en/homebaseuk/hardwood-plywood-1220-x-607-x-9mm-407069

Fabric I can’t give you a link to as it was from my local
fabric shop and purchased of the roll. (oh and they don’t have a website
anyway!) 1 * 2 meters cut from a roll, must be strong and water tight.

Screws to hold the bits together and glue.

Very clean build! I'd like to know how you figured out how large of a fan to use, plus how much volume/flow was required for the task at hand. I am a bit heavier, which then causes the math to go haywire, with bigger batteries, and so on. Does anyone have a spreadsheet with formulas to work out the math for this? If someone can explain the flow calculations, then I could possibly create the worksheet myself.

Flow in from fans must be greater than exhaust flow out under board (and backwash through the fan itself, but how many liters/sec are necessary to keep it all going?

This was a bit of guess work. i have been making model hovercrafts for a while and i use these fans for both lift and forward. One of the tests i did with the hovercraft was to see how much weight it could lift.. and with just one fan and an area of 0.2 meters squared it would lift a car battery. so i used that as a bench mark and made the area bigger and doubled the air flow with two fans.

But if anyone has any information on air flows then that may also help me out on the next project!

I aspire to be this kind of dad.

You and me both brother! I saw that kid on there and I said to myself, my wife would hate this! I can't wait to figure out how to make one for my guy! Lo, the balancing act of husband and awesome Dad.