The concept of this project is to be able to harness energy from an every day or usual activity, to be used in an every day energy need, which is usually electricity.
I do not own a bike , but I love skateboarding, try to do it as much as I can and use it as a mean to go from place to place… it was the selected every day activity since it requires a somewhat big physical effort and it could be used to produce electricity..
The electric needs around me and in my house are not that many:
avg of 97.667 kWh a month according to ConEd
Other than my laptop, and cell phone I do not use many other house hold appliances.
Put out the idea of making toasts….but did not quite like it.
So… power up and charge the cell phone or ipod using the USB interface seemed like a good project and challenge.
A stepper motor was chosen to be used, since I had it already, and a characterization of it out put was made using a oscilloscope, it gave a no load output of 20 + volt at a fairly slow speed, with no mechanical advantage. A bridge rectifier was used to do an LED test.
At first, it seemed difficult to mount a motor and something to move the shaft with. At first, mounting it on the wood seemed the most obvious place for the motor to be in contact with one of the wheels. But a skateboards’ elements move a lot and change angles radically for it to change direction, so this seemed quite difficult from the mechanism point of view.
So then, an idea about using a stick with the motor attached to it, and use the stick while riding was given some thought: I even found a good size branch in prospect part, took it to ITP and got it all nicely sanded and presentable, it became a very nice walking stick. I walked and skated with the stick for two days trying to imagine the best way to mount the motor, but it did not feel right at all. By this point, I thought about using shake flashlights (solenoid and magnet) mechanisms mounted on the walking stick, since the walking movement makes it go back and forth in a pendulum like movement. You also press on it, to help you on your walking needs (more if you are hurt or limping or using a walking stick for mountain climbing).
All this, plus the self powered backpack and the nPower PEG showed in class got me to think that it would be possible to incorporate this ideas in a well designed hiking stick that can be shock absorbent (like the ones on mountain bikes) and be able to light a camping LED flashlight.
But back to skate boarding….
So.. the only part of the skateboard that stays put in relation to the wheels are the trucks (or axis) on which the wheels are fixed and provide the turning mechanism. I did not thought about this in the first place because I did not think it would fit or that there would be a place for to motor to be mounted on, and because it is a place that takes a lot of beating.
But, finally I decided to try it and found out that, YES, it did fit and there was an appropriate mounting place that was just perfect for the motors shaft to go in contact with the wheel.
It must be noted that the specs of my skateboard are not “standard”. Firs of all, it is considered a longboard
(Loaded Tan Tien), and has wider trucks (randall 180 mm) and bigger wheels (abec 11 grippins 70mm), which is a typical setting for a longboard and not for a “standard street, trick, skateboard”, which are awesome for other type of skating .
So it was decided. It was going to be mounted on the truck.
First a LED test was made inside ITP to see if the mounting worked:
Then was taken outside to Broadway, where it broke:
A rubber band was used in order to make the turning shaft be in better contact with the wheel all the time, but the rubber band was cut with small street debris.
So this proved the mounting would have to be made so that it would protect the motor. I tried to make a metal mounting harness, but it was not very effective due to the skateboard truck shape and the reduced space. It also did not provide enough friction for the wheel to move the turning shaft, so the rubber bands still had to be used.
It was then decided to go ahead with the tape mounting for the rest of the project, and to “protect” the rubber bands with extra heavy duty tape.
Still the mounting system is very fragile, the motor is too close to the ground so riding has to be done carefully.
A circuit was designed, and it was corrected with the help of ITP resident Ariel Nevarez and the final word from ITP teacher Eric Rosenthal. The circuit uses a bridge rectifier a 1000uf 50v capacitor, a 5v voltage regulator and two 10f 2.5v capacitors to store energy.
For the USB connection, a bypass of one data cable had to be done, so the white data cable was attached with the Vcc cable in order for the charging state to be activated on the phone. Just the vcc and ground cables were not enough for the charging mode to start on the phone. This was discovered by trial and error, if the hacked USB cable was connected to the phone charger, on one end the vcc and green data cable had
to be together and on the other end the vcc and the white data cable had to be together.
On the final setup, just the vcc and white cable had to be together and attached to the Vcc output of the designed circuit.
Grooves where cut on the acrylic plastic turning shaft for a better grip with the wheel, as well as a secure screw so that the shaft would not turn without turning the motors metal shaft or fall.
The longboard that I have also helped the mounting and wiring since it has got a cut through design for a drop through mounting of the trucks. This and the geometrical shape of the board allowed me to mount everything without interfering with the foot placement while riding.
The final mounting process is shown below.
A video of contact between the turning shaft and the wheel, more tension from rubber bands and better positioning of the motor was done after this test (it would also have helped to make the hole on the inside of the acrylic rod, perfectly centered, but it got really close to perfect):
Videos of real riding and monitoring of the charging process are here:
test while waiting for the N train, with no cell phone mounted:
Riding down hill on crown heights Brooklyn , 4-th avenue in Manhattan and arriving home at night:
The circuit and the mounting worked, the phone switched from idle to a charging mode when connected, but
the power produced was not enough to be stored and then used, it worked better while riding, but still then the energy produced over time was small, and a very long distance ride in good downhill speed will have to be done.
The voltage on the circuit dropped to 4.2 +- if you did not maintained a high +- speed, and the specs of the charger said it had to be 4.8v.
Improvement on the circuit would have to be made by adding a third 10f 2.5v capacitor in series, and a lm317 variable voltage regulator in order to be able to obtain more energy over time. This are going to be made. Some small rechargeable batteries could be added to help the purpose.
Improvements would have to be made in order to protect the motor used, by using another type of motor that would be smaller, in order to obstruct the riding less.Another one would be to find a suitable motor with an output as good as this one or better, but smaller, in order to be mounted to make contact on the inside or side of the wheel
I enjoyed the project, I think it was successful. Watching the charge mode turn on when riding was a nice feeling. Also, while it did not affect dramatically the riding experience, you could feel the riding was slower and over time the extra effort was noted. It also made you appreciate the physical effort being made in order to provide a daily power “need”.
I enjoyed skating and the possibility of a practical energy use for it.
Small talks with people on the train and on the streets were encouraging for the purpose of the project. So the improvements on the circuit will be made and possible solutions for mounting and size and weight will be thought through.
Another idea that came up while this development was that of making tail light for skateboards, in a way that can be universally attached to any truck and grip the inside or side of the wheels. This would require a smaller motor to generate energy and it would not have to be stored or power complicated electronics, just be used while riding and light up 4 or 5 bright LEDs.