The purpose of this Instructable was to create an interactive bicycle energy demonstration to spark kid's interest in engineering. The project works as follows, as a kid pedals the bicycle faster, he is able to activate more lights on the display board, ultimately spelling out the word CITADEL in blue LED lights. As the rider continues to pedal faster, he is then able to activate the bulldog's eyes as red LED lights. The width of each assembly never exceeds 30 inches to ensure the project is able to fit into classrooms through any standard size doorway. The display board is built on wheels so that it is easily transportable. With all materials and tools available, this project will take roughly 6 to 10 days to complete at an estimated cost of around ~$400 USD if you have to buy all hardware/electrical components as well as the bike.
Tools Used: Power drill, table saw, jigsaw, drill press, sander, tape measure, vice grip, socket wrench set, solder iron, wire crimping tool, 3D printer, various household tools (pliers, scissors, etc.)
12mm Diffused Thin Digitel RGB LED Pixels (Strand of 25) (2)
GDSTIME 5V DC 50mm Fan (2)
5 mm (HTD) Pitch, 15mm wide Single Sided Belt
Kent 20" Boys Ambush Bicycle or any other 20" bike with rear pegs
Large Heatsink - Multiwatt Package (from Sparkfun) (5)
Weathershield 2”x4”x8’ Pressure Treated Lumber Everbilt 1-1/2” (4)
Plywood for Display Board (want light-weight but somewhat durable)
Particle Board for Letters
Square Wood Dowels for Display Board Legs
Corner Brace Value Pack (18564)
Everbilt 2” heavy duty corner brace (2 pack)
Grip-Rite #8 x 2” Screws (Model# PTN2S1)
24V 250W Electric Scooter Motor for belt drive scooters (Item# MOT-24250B)
WIR-110, 16 Gauge Black Power Cable Wire (12 ft)
WIR-110, 16 Gauge Red Power Cable Wire (12 ft)
16-20 Gauge Wire
LM338T/NOPB Linear Voltage Regulator
5 Gang Terminal Block (2)
1.0 Ohm Resistors (5)
5.1 kOhm Resistors (2)
150 Ohm Resistor
100 kOhm Resistor
2200 uF Capacitor
20 kOhm Resistor
200 pF Capacitor
5V Zener Diode
2N2905 Transistor or Equivalent
Jumper Wire Kit
Paint / Paint Brushes
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Step 1: Building the Trainer
Start by cutting a 2x4x8 pieces of wood into two 28" boards, another two boards at 24", and two more at 16". You will need two 2x4x8 boards for this. Cut an additional four boards with 45 degree angles on each end. These two boards should be 10" in length. Using the 16" boards, use a jigsaw to cut notches in the board that are 3" deep and 1 3/4" wide. It is helpful to trace out these dimensions before you make your cut.
Take 2 of the 10" boards and attach them to one of the 16" boards. Stand the 16" board up right and lean the 10" boards against each side of the 16" so that they are flush with the board and the floor. Use screws to fasten the 3 boards together. Repeat this process for the remaining 16" and two 10" boards.
Mark the center 12" mark of both 24" boards and the center of the 16" boards. Line the two marks up together so that the 16" board is upright and flush with the 24" board laying on its side. Drill 2 screws into the 16" to the 24" board and 2 more for each 10" board to the 24" board. Repeat this process with the other 24" board and the 16" board with the 10" boards attached.
Next, mark the center of the board on each of the 28" boards. Make another mark 4" on each side of the 14" mark. There should be 8" between these 2 marks. Line up the 24" boards on these marks with the inside of the board on the mark. Drill 2 screws into each to fasten the 3 boards together. Repeat this with the other 28" board so that all are connected.
Step 2: Building/Attaching Motor Tensioner
Deriving a suitable way to tension the belt was something the team struggled with. We went through a few different ideas before arriving at what is seen above. A metal sliding rail would have been ideal but due to a low budget the team had to settle for a make-shift wooden rail.
Start by created an L shaped figure using 2"x4" blocks. The lower part of the L that he rail will mount to should be approximately 8" long. The upper part approximately 6" tall. Cut another 2"x4" block for the motor mount. The team used a spare, small rectangular wooden post we found to create the rail system. The bottom rail is straddled by two rails mounted to the bottom of the motor block. The key here is to use wood durable enough not to split when being screwed into the 2"x4"s.The team used a drill press to drill a hole all the way through the 2"x4" block the motor is mounted to. Another hole was drilled through the upper portion of the L. A long bolt was run all the way through the system. Be sure to use large washers on either end to distribute the load. The final assembly was mounted to the trainer using L-brackets. A small block of wood was inserted between the rail and the trainer to prevent the system's tendency to bow up when under high tension. It is helpful to have someone holding the assembly in place when mounting it to the trainer to ensure proper alignment with the back tire.
Step 3: Remove Back Tire From Bicycle and Attach Rear Pegs
To remove the back tire from the bicycle, first deflate the tire. Next remove the nuts holding the bearing in place for the rear wheel. Disconnect the chain from the rear gear. If the bicycle has rear brakes, it may be necessary to remove the rear brake pads. Once the wheel and tire are completely off, use a crowbar to stretch the tire over the side of the wheel. While maintaining the crowbar between the wheel and tire, have someone turn the wheel to slowly pry off the tire. Once complete, follow the steps in reverse order to reinstall the wheel back on the bike. Be sure to put the belt around the wheel before reinstalling. To install the pegs, slide them over the rear axle before reinstalling the fastening nuts.
Step 4: Building the Circuit
The circuit seen in the schematic was obtained from the link provided:
The circuit we built has two functions. The first is to regulate the variable DC voltage input from the motor to a constant 5V DC output used to power the lights. The second is to utilize a voltage divider to reduce the voltage output from the motor to between 0 and 5 volts. This output is then input into the Arduino Uno's analog input port which has a limit of 5V. The Arduino Uno is coded to activate specific lights at a certain voltage. This code is provided below.
The circuit shown in the schematic above is used to distribute the current evenly between 5 linear voltage regulators (lm338). These regulators can not simply be placed in parallel to distribute the load because differences in their internal components causes slightly different outputs from each. The linear regulator which provides the highest output ends up taking the entirety of the load. Utilizing the circuit above stabilizes the outputs and distributes the load evenly. The lights draw a maximum current of around 1.5A configured using the chosen colors (48 blue 2 red). Coding the lights to all be white would create the maximum current drawn (3A). The voltage is regulated down from a maximum of 28V to 5V. This is a 23V difference. 23V x 1.5A = 34.5W of power that must be dissipated as heat. This is why distribution of the load between the regulators is so important to the team. If one regulator was to take all the load, it would exceed its maximum operating temperature.
First, build the circuit on a solder-less breadboard. A rather large capacitor (we used a 2200 uF) will need to be placed across the motor output to decrease its noise. This cleans up the input that the Arduino is receiving and makes the light display more consistent (lights not flashing erratically). However, if you would like to create a seizure producing machine, save $2 and void the capacitor. Next, incorporate the voltage divider circuit. Run a jumper wire from the voltage divider to the Arduino Uno analog input A0. Jumper the Arduino into ground as well. See drawing attached. Further information for wiring the lights can be found at the link below:
Step 5: Testing the Circuit
The equipment seen on the lab bench above is useful but not required to test the circuit. However, you will need some way to turn the output shaft of the DC motor. Ideally, we would have just used the bicycle but since it was still in the mail, we had to find an alternative solution. Make sure you reverse the polarity of the motor (ground (black) wire becomes hot and hot (red) wire becomes ground). Once everything is hooked up, adjust the potentiometer in the circuit until you get an output voltage of 5V. Any standard voltmeter can be used for this. The circuit will need to be under a substantial load to properly adjust the voltage output. The Arduino computer software will need to be downloaded to run the code for the micro-controller. The FastLED library will also need to be installed. Once the software is downloaded and you upload the code to the Arduino, go to the serial monitor in the top right corner and you will be able to observe the voltage input that the Arduino Uno is receiving. Make adjustments to condense the circuit down as far as possible if necessary and test again. Ensure all components function properly before moving forward.
Step 6: Solder the Circuit
In the picture above you might notice that there are two circuit boards built. Originally, the team planned to use 10 lm338 linear voltage regulators but after further testing, determined one circuit with 5 was substantial. However, the board we ended up not needing contained the voltage divider, hence it is still utilized.
Out of personal preference, the team decided to jumper the linear regulators to the circuit board. This allowed us to mount them a little more freely and better support the large heat sinks. Solder all the components from your prototype to your new solder board. We used a permaproto board so that the circuit would be an exact replica when moving it over from the solder-less breadboard. Two 5 gang terminal blocks were utilized to create quick disconnects from the motor and the lights.
Step 7: Build the Display Board
The display board was built in a series of steps.
1) The display board consists of a board and a mount. The display is constructed out of thin wood and mounted to a stand that is 57 1/2 in by 5 ft. the stand is supported by a cross-sectional beam extending at a 45 deg. angle from the back leg to the vertical stand. This was constructed using wood and screws. After the completion of the board and the stand, four wheels were drilled in the mount at each respective corner
2) The display of the letters (C-I-T-A-D-E-L) were constructed separately from the display and mount. The letters were first drawn and then cut out of tiles of particle board that were 8 in x 12 in. The letters are all sized to be 10 in tall, with varying widths. The letters were cut with a band-saw for the exteriors and a jigsaw for the interiors of the letters.
3) After the letters were cut they were attached to the board with liquid nail. This ensured the letters being secured to the board. Next, holes were drilled in the letters using a 12' bit. This would make sure the Lights would be displayed.
4) Next, the display was painted white and the letters (C-I-T-A-D-E-L) were painted baby blue. A blue trim was then added to the frame of the board.
5) The letters (T-H-E) were painted onto the board all at a 4 in height with varying widths.
6) The Bulldog at the bottom of the board was painted onto the board using a mixture of acrylic paint. Holes were drilled through the eyes with a 12mm bit to fit the lights.
7) Finally, the lights were placed in the board and the display board was complete.