Cloth Drying Technology

Appropriate Technology: Bicycle Powered Spin Dryer

Comments/Suggestion Section : Feel free to share your ideas on how we can improve the project and website!

Problem Statement

Everywhere in the world humans wear clothing to protect their bodies from different challenges presented by the climates we live in, so washing and drying clothing is a global need. In developed and wealthier countries, washing and drying clothing is typically done using expensive, energy-eating machines. Our goal is to help develop an appropriate technology for people in developing countries. Many quick washing methods already exist, but no real drying method has been effectively brought in.

First Experiments (Hand Wringing, Squeeze Roller, Squish) : Check out some of our early experiments before we started working on the bike powered spin cycle.

Bike Powered Spin Cycle

After realizing that the wringing squeeze rollers and squish method with buckets weren’t very effective, we decided to take a completely different route. We made a new decision matrix based on our discoveries, and the bike powered spin cycle clearly came out on top.

Design Matrix 2.JPG

Some initial materials for our spin dryer

Video 1 of the Spin Dryer in Action:

Our spin dryer design:

  • Five-gallon bucket with holes drilled all around the sides. The bucket has a lid and a round piece of wood inside the bottom of the bucket for added stability. Two wooden fins are screwed inside bucket (opposite of each other) to prevent clothes from merely sliding along the bucket walls.
  • Threaded rod that goes through the bucket vertically. By placing this rod horizontally on a stand the bucket can spin freely on the rod.
  • Extra bike gear cassette screwed on the outside of the bottom of the bucket. An extra bike chain runs from this cassette to the cassette on the back wheel of a bike. It’s quick and easy to attach the chain to the bike’s cassette by popping the back wheel of the bike off.
  • Wooden stand with two notches to put bucket on and take bucket off stand with ease.
  • Additional items not shown in picture: bike, extra bike chain, bike trainer (keeps bike stationary)

Spin Dryer

With the spin dryer, we were able to repeatedly remove about 55% of the water from our two shirts and six rags! On average, wringing by hand only removed about 45% of the water, as seen in previous tests. Wringing by hand took more effort and a longer time. With one person pedaling quickly on the bike and someone else standing on the back of the bucket stand, it took just over half the time to dry the clothes: 1 minute 25 seconds, as opposed to 2 minutes 45 seconds wringing by hand.

Feb. 26th Calculations (Trial 1):
Spin Cycle
(2.6 lbs water removed / 4.7 lbs total water in clothes initially) x 100 = 55% of water removed

March 5th Calculations (Trial 2):
Spin Cycle
(2.4 lbs water removed / 4.3 lbs total water in clothes initially) x 100 = 56% of water removed

How does this compare with the spin cycle on a high energy washing machine? We tested how much water was removed from the same two shirts and six rags starting with the same amount of water in them:

March 5th Calculations
Washing Machine’s Spin Cycle*
(3.1 lbs water removed / 4.3 lbs total water in clothes initially) x 100 = 72% of water removed

*Maytag Commercial High Efficiency Washer (Property of WEB multifamily laundry systems, ENERGY STAR)

While the washing machine clearly removed much more water than our bike powered spin cycle, a typical laundry load in a washing machine is much larger. Usually, less water is removed from these larger loads of laundry. Our bike powered spin cycle fits the scale of the laundry loads in developing countries, and it has pretty high efficiency for being powered by a human.

Screen Shot 2013-03-05 at 8.16.25 AM.png
Getting ready to run some more tests.

Next, we worked on making the whole spin dryer system more stable. The lid of the bucket melted in the center from the heat caused by rapid spinning, so we reinforced it with wood. We cut wooden spacers to put tension between the bike trainer and the wooden bucket stand, and we put bolts in the bucket stand to keep the rod that runs through the bucket steady. We changed out our original threaded rod for a thicker and stronger half-inch rod.

We wanted to eliminate the use of an expensive trainer so we built our own rudimentary bike stand out of wood. Thanks to the Bamboo group ( for letting us look at your design!

Bike Stand 2.jpgBike Stand.jpg

By screwing the new bike stand and our bucket stand to one large piece of plywood, we stabilized the whole mechanism even more. We also took the tire off of the back bike wheel so we could move the extra chain (attached to the bucket) up to the highest gear on the bike’s cassette. This greatly increased our spin dryer’s efficiency. We ran four tests on March 12th, removing 55%, 56%, and 59% of the water on the first three. But with the increased power from putting the extra chain on a larger gear we successfully removed 64% of the water during our last test!

March 12th Calculations (Trial 4):
(3.07 lbs water removed / 4.77 lbs total water in clothes initially) x 100 = 64.36%

Video 2:

Acceleration Data
Radius of Bucket
r = 5.25 inches = 0.1334 m

Pedaling at 108 rpm
Biggest front chain ring/Second smallest cog on rear wheel = 48/17
Biggest cog on rear wheel/Smallest cog on bucket cassette = 28/14
108 rpm (48/17) (28/14) = 609.8 rpm for the bucket

w = angular velocity
w = (rev/min)(2π rad/rev) = (2π rad/min)(1 min/60 sec) = # of radians/second
w = 609.8 rpm (2π rad/rev)(1 min/60 sec) = 63.9 rad/sec

a = (w^2)r = m/sec^2
a = (63.9)^2 (.1334 m) = 544 m/sec^2

544/9.8 m/sec^2 = 55 G’s

How does this compare with the spin cycle on a high energy washing machine?
Depending on make and model, hard-mount washers pull anywhere between 50 and 250 G’s.

The maximum rpm for last year’s vertical bucket spin dryer design with ropes was only 360 rpm, which resulted in a much lower acceleration.


Our group was split across the two different lab sections, so communication was our biggest challenge as a group. We tried to touch base the day before lab, but we never really knew exactly how much each group would accomplish in lab. Sometimes, one section of lab wouldn’t have the appropriate materials needed, while the other lab section has access to these materials. We continually tried to plan ahead better, and we used email and Google Drive to keep communication open across the two lab sections. After several repeated issues, we finally had a group discussion to clarify everyone’s expectations and ensure that we were all happy with the progress of our project. We also made sure everyone had each other’s contact info. As a follow-up to this discussion, the five of us met up during the second section of lab on Feb. 26th so we could all have half an hour working together.

One benefit of being separated across two lab sections was that we had separate ideas generated in each section that gave rise to even more possibilities than if we were all in one section choosing one thing to do each day. We had six designated lab hours a week to work on our project instead of just three, which lets us try out more options while still making progress toward a goal. This was very useful in our learning process, and enabled us to take advantage of divergence and convergence.

Where can this project go now? What are the next options?

Since our last decision matrix, we realized we should compare our spin dryer design not only with hand wringing but also with the spin cycle on electric washers. We really enjoyed working with bike power and we know bikes are pretty accessible in developing countries, so we thought of some more dryer ideas that could use a bike.

Updated Decision Matrix:

Criteria Cost Wear and Tear on Clothing Building Difficulty Time to Dry Percentage of Water Removed
Weight 10% 15% 5% 22.5% 22.5%
Bike Spin Cycle w/out extra chain 9 8 6 7 6
Bike Spin Cycle w/extra chain 8 8 4 9 8
Portable Bike-mounted dryer 8 6 3 8 7
Solar Dryer 3 10 3 5 6
Hand Wringing 10 6 10 7 7
Electric Spin Cycle 0 10 0 9 9
Physical Effort Quantity of Clothing Number of People Required Total Out of 100
10% 10% 5% 100%
Bike Spin Cycle w/out extra chain 5 9 9 7.175 71.75
Bike Spin Cycle w/ extra chain 5 9 9 7.875 78.75
Portable Bike-mounted dryer 4 9 9 6.03 60.3
Solar Dryer 9 10 10 5.825 58.25
Hand Wringing 4 1 9 6.5 65
Electric Spin Cycle 9 10 10 7.95 79.5

Our method was the bike spin cycle w/ extra chain.

Ideas for improving our method:

  • Make a better bike stand out of wood. Perfect the design and make it easier to pedal while using the wooden stand.
  • Figure out an alternative method of attaching/stabilizing the bike stand and bucket stand. We used plywood, but there might be better methods out there.

Ideas for future classes:

  • Bike Spin Cycle w/out extra chain = pushing the bike wheel right up against the bucket mechanism. This eliminates the extra cost of buying an extra chain and cassette, but it might cut down on efficiency.
  • Portable Bike-mounted dryer = finding some way to attach the bucket to the bike so that the dryer can be used while biking around. This eliminates the need for a bike trainer to keep the bike stationary, but it would require other extra parts to attach the bucket to the bike.
  • Solar Dryer = solar methods of drying clothing. This could be pretty costly, but it might be worth looking into for future groups in Pete’s class. Maybe bike power could still be harnessed somehow? (Potential idea:

After our final day of lab.


Our group really enjoyed the process of discovering an effective way to dry clothes and continually improving on our bike-powered spin dryer design. We are all happy to have been so successful, ultimately removing 64% of the water from our clothes. This is almost as effective as the spin cycle on a washing machine. We had a great time working together as a group and getting to know each other better. Everyone brought unique talents to the project, and we all learned new things from each other. It was also great interacting with other groups and seeing everyone’s projects change throughout our ten weeks in lab. This class was fun and a great learn-by-doing experience. We hope future classes will take our design and try to improve on it even more, or try out some of our other design ideas from our latest decision matrix.

This class changed our perspectives on the design process. We learned that design isn’t just about the end goal. Even though we wanted to build something to effectively dry clothes, we had the freedom to try out multiple methods before converging to one path. We also got to engage in a process of self inquiry. In attempting to come up with a sustainable method for drying clothes in developing countries, we started to think of ways to live more sustainably ourselves. We all decided to try an intervention in our own lives to be more sustainable consumers by changing our diets. Some of us gave up red meat while others tried to be completely vegan. It was difficult, but the diet changes showed us that there are many small ways to live more sustainably. It’s easy to get stuck in our old habits, but making a change can benefit us as well as our environment. We hope people in developing countries also take advantage of making changes to better their lives, too. Maybe bike-powered spin dryers will be the way of the future!

Group Members:

Oliver Adams

I am a 4th year Liberal Arts and Engineering Studies Major (LAES) concentrating in Manufacturing Engineering and Film/Television and Theater. I enjoy working with my hands building stuff so this class is a great fit for me. I enjoy working with my group and exploring our inner workings.

Oren Ben-Joseph

Currently a fourth year Business Information Systems student at Cal Poly with a passion to learn about this ever-changing world around us. I took 391 last quarter and it spurned my interest in appropriate technologies and other factors of global development. I am excited to work on developing a working product in a hands on lab, fulfilling the Cal Poly learning style.

Nichol-B Jerabek

I am a fifth year Business major, double minoring in Packaging and Communications. I’m the president of Cal Poly’s Road Cycling Team and have been racing and working around bikes for the past eleven years. The only even semi technical experience I have would be working with LEGO’s as a kid or building an automated spice rack in highschool. I was really excited to jump into this class and finally get some hands on experience in school. Working with bikes is just an added plus!

Annamarie Kepple

I am a sixth year Industrial Engineering major with a minor in Business. I will be graduating at the end of this quarter (Winter 2013). I love line dancing, baking, and wine tasting. I initially took this class for extra units, but have been having a lot of fun in it. The amount of hands-on work is engaging, the articles we read for homework interest me, and I really enjoy Pete’s enthusiasm.

Cristy Lopez

I’m a 3rd year English major with a dance minor, and I will be graduating in Spring 2013. For my senior project, I am writing the beginning of a science fiction novel. As part of the dance minor, I’m involved with winter and spring dance performances, and I choreographed a tap dance for the Spring Dance Show last year. I love working together with people to accomplish a goal and build relationships. This class is challenging me to step outside of my comfort zone with a design project, and it’s also just another great opportunity to meet new people and build relationships within our group.