community event Occidental College

Join us at #MovableParty 1.0 @ CicLAvia + Oxy’s Founder’s Day

Movable Party @ CicLAvia, April 2013

Join us to celebrate the vibrancy of streets in Los Angeles at MOVABLE PARTY — a bicycle-powered dance party. We will implement our bicycle-powered generator custom designed and built by members of Movable Parts, with the help of students of Occidental College.

Place: MacArthur Park, downtown Los Angeles [corner of Alvarado and 7th]
Time: 11:30am – 2:30pm, Sunday April 21, 2013

This Movable Party will feature the following DJs:

J.Vu (Hungry Beat): indie pop, northern soul

The Attic Bat: global bass music

Music by KOXY

Xandão: global bass

Facebook event link:


We will also be launching our interactive bike-powered DJ system at Occidental College’s Founder’s Day on Saturday April 20th.

Place: next to the Solar Array
Time: 5-6pm, Saturday April 20th

Movable Party is made possible by ASOC Renewable Energy and Sustainability Funds, Center for Digital Learning + Research at Occidental College, Flying Pigeon, Bike Oven, and the Knowhow Shop.

bike mechanics design generator workshop

Video from Workshop #1: Hub Motor + Bike Generator

In this workshop, Josef Taylor, structural engineer of Buro Happold, LLC, took us through the steps of using a hub motor on a bicycle to generate power, while explaining the laws of physics related to electricity. We compared the resultant voltage generated while using various levels of resistance in the circuit.

Arduino Interactivity Sensors

Interruptions and Interrupts

In my earlier post RPMs to BPM, I demoed a fairly simple hall effect circuit that I used to control the playback speed of an audio file in Max. In the video, I wave a magnet in front of the sensor and used the resulting data to trigger a “bang” in max. This method worked fine in my demo as I could not trigger the sensor very quickly. When I hooked the sensor up to the bike, I realized that above a certain rotational speed, the software would “miss” rotations. [I have since switched to using the sensors in the hub motor, but they present the same issues]

2013-04-01 21.30.26

Thus I realized I had a problem. Though the Arduino has no problem catching the incoming sensor data (it typically executes code in the range of microseconds (1 millionth of a second), I was running into trouble passing the data between the Arduino and Max. Without getting too technical, the data transfer speed was too slow.

As someone who tries to be primarily concerned with the realization of creative projects rather than elegant technical solutions, I will admit that I always aim for the simplest solution even if it isn’t the most efficient. Sometimes, as in this case, the simplest solution (handling all of my data calculations in Max) just isn’t going to work. I realized I was going to have to calculate RPMs using the Arduino and then transmit a running tally of the current RPMs to Max (along with data from the Force Sensing Resistors, as seen in this video). I knew that this could pose a large technical problem. I would need to calculate the RPMs by taking the triggers from the Hall effect sensors while at the SAME TIME I would need to be constantly updating the data from the Force Sensing Resistors. Typical Arduino sketches have one function–loop(), which runs over and over while the board is on. Pausing to wait for incoming data from the Hall effect sensors would delay the execution of my code and stop the data being sent to Max–I needed to do two things at once.

Fortunately in the world of open source technology, the solutions to many technical challenges lie online. This great example by Zitron shows how to use hardware interrupts to read in the data from the hall effect sensor outside of the loop() function.


The result is that I can just send a constantly updated stream of RPM data to Max. This turns out to be a much better solution, because if I miss a sensor trigger between the Arduino and MAX, the RPM data will be wrong (sometimes VERY wrong). If I miss one read of RPM data, it’s not a big problem because I am constantly sending the current number of RPMs.

The bigger lesson here is that the easiest solutions are always the best, but sometimes an easy solution just wont work. In that case you have to delve deeper. While you don’t want technical complexity to derail your project, sometimes more complex solutions end up being the most elegant.


Arduino design Interactivity Music Sensors workshop

Video from Workshop #2: Arduino and Sensor Fun!

Movable Party 1.0 // Workshop 2: Sensors, Arduino, & Interactive Media

#MovableParty Workshop 2 was about the design of an interactive system. We placed sensors of various types on the handlebars of one of the bikes with a hub motor. Our workshop leader Steven Kemper mapped the pressure sensor data through Max MSP to demonstrate different effects (parameters of low-pass filter) on a song. The Hall Effect sensor was used to set the tempo of the audio playback. Jack Moreau is our DJ on the handlebars for this round! This workshop took place at Occidental College’s Brown LearnLab. Participants included students from Occidental College and members of The Bike Oven.

bike mechanics generator workshop

Workshop #3: Bike + Hub Motor Assembly

Hub Motor on Bike at the Knowhow Shop
Hub Motor on Bike at the Knowhow Shop

Linda and Joe will be running a workshop on bike and hub motor assembly tomorrow, on Saturday March 23 in the Bike Cage on the campus of Occidental College. Come on by if you are curious about bike mechanics, and want to assist with the mounting of a hub motor and all the necessary electrical components on a bicycle. We will be working with donated bike frames and components from the Bike Oven and Flying Pigeon. Thanks for their generous offerings!

Our goal is to build a second bike for Sunday’s Arduino workshop. Ready to get your hands dirty!

Place: Bike Cage at Oxy [southwest corner of the Rangeview parking garage, come through the gate and turn right]

Time: 1-4 or 5pm, Saturday March 23

Arduino Interactivity Sensors workshop

Workshop #2: Sensors, Arduino, and Interactive Media

Movable Party Workshop #2

Our workshop #2 is happening on Sunday March 24, 2013. Get psyched!

In this workshop, we will introduce the design of the project’s interactive media/music system. In particular, we will explore interactivity and the Arduino microcontroller platform by attaching sensors to the bikes and using the resulting data to control musical output. Specifically, we will be using Hall effect sensors to measure the speed of the rear wheel of the bike, as well as pressure and flex sensors to capture movements of the riders. We will also discuss issues of design and physical computing—using sensors to translate (transduce) action in the physical world into computer data.

Time: Sunday March 24, 2013, 2:30pm
Place: Brown LearnLab, library
The Bike Share will buy some pizzas for us.

The workshop should last 2.5 hours. If you want to get a head start on the workshop, read these two posts by Steve:

This is the beginning of the interactive music design. If you would like to learn about robotics and interactive media design, this is it for you!

design generator workshop

Generator Development

We’ve just received many of the parts for the generator, and will test them out this week! Suddenly all of the planning and fund-raising and cogitating is going to be attached to a couple of bikes with power cables coming out of them. This is a big step, so I suppose it’s time to update everybody on how this thing is going to work.

Hub Motors

We bought our motors from in Vancouver BC. There are more local options, but these come highly recommended, and there is a wealth of information and support at their website. The motors are “brushless DC motors,” which is a bit of a misnomer, as the motor itself runs on (or outputs) three phase AC. In a motor application, that AC comes from a motor controller which converts 12V DC into a variable frequency, variable voltage power signal according to the desired speed and power. Since we’re using the motors backward, taking power out instead of putting it in, we’ll need to make sense of that 3 phase AC.

Nine Continent Rear Hub from
Nine Continent Rear Hub from

The motors come in three different windings, from 6 turns to 8 turns. This is equivalent to using gears of different sizes on your bike; if you supply a given voltage, the 6 turn motor turns faster than the 8 turn motor, but with less torque. What this means to us is that the 8 turn motor will supply our target of 14V at a lower speed, meaning that we can use the low gears we’ll need for hauling cargo. However, it might be too much, and we’ll have to use super low gears to keep our voltage low. We ordered a 7 and an 8 turn motor, and we’ll figure out which one we need once we have the bike in the trainer and a load attached.


A rectifier takes the alternating output of a motor and converts both the positive and negative peaks into positive current, effectively flipping all the troughs into peaks. It works by feeding the alternating current through an arrangement of diodes (which only allow current in one direction, like a check-valve). Ours are packaged in neat little boxes with spade terminals and a must be mounted on a heat sink; the diodes don’t put out a lot of heat, but it’s enough to damage them if they can’t dissipate it.


We’re using the element from a ceramic space heater as a load. This is basically a big resistor; current has to pass through a series of special ceramic blocks that are poor electrical conductors. These heat up, normally to heat the air blown through them. This element is unfortunately a bit too strong, with a resistance of 180 ohms, but since there two elements, we can connect them in parallel, cutting that resistance down to 90 ohms. If I’d been able to find a traditional coil element, we could clamp on anywhere along the coil to adjust the resistance.

For a more visible effect, we picked up three 100Watt light bulbs. These have a resistance of 144ohms apiece, but connected in parallel we’ll get 48 ohms, which is a pretty reasonable load to power.


One of the toys we received is the Watt’s Up meter. This little guy connects in line with our power, allowing us to see just how much power, in volts, amps, and watts (just so you don’t have to compute the product). This means we can finally get a good idea of what a person puts out on our system! This is really exciting.

Alright, see you at the workshop!

community generator partnership workshop

Workshop #1: Generator & Hub Motors

Bikes with Hub Motors

We’re excited to announce the first of our workshop series for Movable Party. In this workshop, we will be fitting the bikes with hub motors and testing their electrical output. We will talk more generally about the laws of physics related to electricity, and compare the results of two different hub motors.

Place: Bike Cage at Oxy [southwest corner of the Rangeview parking garage, come through the gate and turn right]

Time: 5:30pm, Friday March 8

The workshop will last no more than 90 minutes. We will have some pizzas! Please let me know via email [hsuw at oxy dot edu] if you’re coming, so I can make sure that there will be plenty of food for everyone.

We’re excited about moving our project forward. Come and prepare to get your hands dirty!

Arduino Interactivity Music Sensors


Well, more like RPMs to playback speed. The video below shows how I’ve hooked up the hall effect sensor to Max in order to control playback speed of a sound file.

Movable Party–Hall Effect Playback Speed Demo from Steven Kemper on Vimeo.

Interactive DJ

Moveable Party will feature traditional DJ sets (bicycle-powered of course) as well as interactive DJing that uses sensors attached to bikes to control parameters of sound production/processing. The goal is to design an interface in Max that mimics those found in traditional DJ software. The interactive DJs will be able to map the sensors on the bike to various modes of sound control. For example, the speed of the rear wheel could control playback speed (as in the example above), or tempo of a step sequencer. Pressure sensors mounted on other parts of the bike, for example the handlebars, could be mapped to a variety of different types of processing, including EQ, Delay, Volume (enveloping), etc.

Redirecting the Flow of Power

How many times have you gone to a charge station at an airport only to find that all the plugs are being used? Have many conversations not mediated by a cell phone or other mobile computing devices have you witnessed in public spaces lately? It’s true that people don’t engage with one another in an embodied, face-to-face anymore. But sometimes people come into physical proximity when they need something – electricity. They crowd around charge stations or sit awkwardly in spaces around electrical outlets in order to gain access to electricity.

Charging station in waiting lounge, image CC BY-NC-ND 2.0 by ariffjamili

A group of students – Judy Toretti, Jacob Brancasi, Maria Lamadrid, and Cory Bloor – at Art Center College of Design recognized this social pattern and took it to heart in their design of an interactive media system for a homeless youth organization called Jovenes in east LA. Working with the youth participants, the student designers came up with Conversation Space, an interactive cellphone charging booth that requires at least two individuals to step on a foot pedal in order to activate electrical current. The design calls for a coordinated effort on the part of the users. To achieve the common goal of charging cell phones (and other handheld devices critical to the lifeline of homeless youth), users must engage in a face-to-face social interaction. It could be as much as a conversation, as little as a nod, an eye contact, or a chin-up.

Conversation Space @ Jovenes , design by Judy Toretti & Jacob Brancasi
Conversation Space @ Jovenes

The design of Movable Party is meant to accomplish something similar. Like the foot pedal charging booth, our system attempts to transform people’s interactions by redirecting the flow of electricity. We don’t mean this in a strictly physical sense [don’t ask me explain the physics behind the flow of electrons, ask Joe.] What I’m referring to is a design that yields particular desirable social sequences. This design challenges power consumption, a behavioral norm in most public and urban spaces in this country, and shifts our normative relationship to electrical power from consumptive to generative.

Our efforts aim at creating opportunities to generate, instead of compulsively consuming, power. Pedaling is an exciting, eco-friendly, and embodied practice. At an advocacy event like Ciclavia, collective cycling can instantiate the power of human-scale transportation. Moreoever, pedaling comes with a direct consequence of powering a musical performance within our system. This is a participatory event that involves lots of agents including the cyclists on the generator, DJs who will be spinning records, and bystanders and passersby who may be dancing to the music. The embedded sensors and Arduino microcontrollers will interface the system to fine-tune the interactivity among all the participants.

Through a system that re-routes the flow of energy, we hope to articulate the generative impact of pedaling, a goal that involves the translation of the significance of electricity from the physical into the social and symbolic domain. We want people to congregate in a public space. We want them to realize that the outcome of the event – a musical performance – is contingent upon a collaborative process of generating power.

We can’t take electricity for granted. Electricity is not just a physical resource; it is also a kind of social resource that can be harnessed to bring people together. Electricity can be used to power communication that happens in mediated platforms. But we know that already. We hope on at the Ciclavia event on April 21, we will start to see how electrical power plays a critical role in igniting positive and communal social interactions.

* * *

Incidentally, at the airport before my flight took off from LAX, I went looking for an electrical outlet to charge my laptop.

I shared an electrical outlet in the airport terminal with a lady who struck up a friendly conversation with me. “Is that plug available?”

I said, “of course!”

She and I exchanged stories about the overwhelming presence of mediated communication in our society today. She told me that she just saw a mother and her young son of eight or nine years of age dining somewhere. The mother was on the phone the entire time. The son was left to entertain himself.

“Isn’t that ridiculous that we are so dependent on these devices? What did people use to do before cell phones? I guess they talked to people around them,” she remarked.

I said, “It’s funny that we’re talking about this. I’m working on a project that involves the building of a bike generator to power a music event.” I told her the rest of the project.

A few minutes later, with my laptop charged at 84 percent, I disengaged from the electrical outlet and packed up my gear.

Before I scurried off to board my flight, she smiled and said, “good luck with your project!”

Thank you, lady, whoever you are, for your kind reinforcement of the meaning of our project.