Monday, November 24, 2014

Build Project: Headlight for a Tricycle


Headlight for a Tricycle

This is a headlight I built for my son's tricycle.  It is designed to fit a fisher-price plastic tricycle, but you can tweak the designs (in openSCAD) to mount it on any kind of tricycle you like.  It is perfect for riding in the dark, and my son absolutely loves it.

If you want a cost-effective way to put a light on your own kid's tricycle, you should probably just duct tape a flashlight to the steering wheel and be done with it.  On the other hand, if you are looking for an over-the-top solution that lights up a whole damn room, costs you more than thirty bucks in parts, and is incredibly difficult to assemble, please keep reading.


Step 1: Print the Parts

Printing with supports and raft.

Using a 3D printer, print each of the parts, which can be found on the thingverse as STL files.  If you want to customize it to fit your own needs, all of the SCAD files are included as well.  You will need to print the following parts:

  • Trike_Headlight_mount
  • Trike_Headlight_base
  • Trike_Headlight_1
  • Trike_H_battcase
  • Trike_H_battlid
  • Trike_H_bracket

I printed Trike_Headlight_1, Trike_Headlight_mount, and Trike_H_bracket in black, and everything else in white.  I used ABS plastic on a Flashforge Creator printer, and I printed all the parts with supports, rafts, three shells, and a 30% infill.

Step 2: Install the Base

This just gives you a glad surface to mount the light on.

The base has a flat top, and a concave spherical underside to fit over the center of the handlebars.  It has three screw holes in the front, two in the back, and three on the top.  You may need to open these screw holes up (I did it by hand with a drill bit) depending on your printer, and you probably want to drill into the trike while you are at it. Also, in order to get the base flush with the tricycle, I had to sand down the printed part quite a bit.

The underside of the base.

Once the base is ready, screw it into the tricycle with three 3mm screws in the front, and two in the back.  The three holes at the top will be used to attach the mount later on.

Step 3: Assemble and Mount the Battery Pack

The battery pack and the switch.

I used six 9V batteries in series (so 54V total), which takes up a lot of space, so I designed a battery pack to go in the back of the trike, along with a switch.

Start by attaching the battery case to the back of the tricycle using the four screw holes on the bottom.  Connect the batteries together in series and connect them to the switch, which goes in the square hole at one end of the case.  When you are done, thread both ends through the circular wire hole near the switch hole, and screw on the lid.
I used this switch.
These connectors are easy to find.
Battery pack, complete (without the lid).

Step 4: Assemble the Electronics in the Light

For this build, I used 12 high brightness white LEDs assembled in series, six 9V batteries, and 20K ohms of resistance.  This is the LED pack I used, but you can build your own any way you like.

I soldered all the LEDs together in series on the base plate and added the resistors.  The kit I used actually had the + and - backwards on the LEDs, but that's not a difficult fix.  The resistors can be included here or in the battery pack (I included them in the battery back near the switch).
The LEDs
The Baseplate
Me soldering the LEDs onto the baseplate. I burned my middle finger with the soldering iron shortly after this was taken.

Step 5: Prepare the Light

Line the inside of the Trike_Headlight_1 part with aluminum foil.  This will help ensure most of the light generated will come out the front of the light instead of being absorbed.  I used a thin coat of acetone (which dissolves the ABS plastic) to stick the aluminum foil to the inside of the chamber.
Good Enough.
Slip the baseplate and the LEDs in through the hole at the base of the part and secure it (I used two screws).  You can slip the wires through this same hole, or you can drill another hole wherever it it most convenient (I put one in the bottom).  Place a fresnel lens in the slit at the front of the chamber, and cover all holes using duct tape or electrical tape (so the light does not get out).
These lenses are fun toys for kids too.

Step 6: Attach the Mount

Place the Trike_Headlight_mount part on top of the base, with the supports facing the back of the tricycle.  Using the three screw holes across the center, attach the two pieces securely.  I also coated the top of the base and the bottom of the mount with a thin layer of acetone, so they would fuse together for an extra-strong hold.
You could probably attach it with just acetone but I still used the screws.
Glue a thin piece of silicone, latex, rubber, or something similar to the inside of the brackets and the inside of the cylindrical hole on the back of the mount.  This will allow you to adjust the angle of the headlight with enough resistance to hold its position as well.
I accidentally broke the ends off the bracket but that is fine.

Step 7: Final Assembly

Place the headlight (with the electronics already assembled) into the mount and screw on the brackets to hold it in place.  Connect the wires from the headlight to the battery pack, leaving enough slack in the wire to turn the steering wheel.  I drilled a hole in the neck of the tricycle, and fed the wire to the battery pack along the bottom of the body.
Completed headlight, back view.

Now you can test it out.  It should provide a relatively dispersed light, very powerful, but not so powerful that it would blind people or cars in the dark.  After the assembly, I tool a walk with my 3-year-old son at night, and it worked wonderfully.  It was very cute to watch him pedal around with the headlight in the dark, almost as if he was riding a little motorcycle.
Completed headlight, front view.  The light is brighter than it appears in this photo.

If you build your own, or tweak the design, please let me know how you like it.