Echoraiserthe ultrasonic power assisted lifting cart
Group 11: David L. Chen, William Cheung, Neil NguyenME102 Mechatronics Design • Professor H. Kazerooni • May 7th, 2007
Echoraiser • me.berkeley.edu/ME102/Echoraiser • Berkeley Engineering
INTRODUCTION
Purpose
It is hard to lift and carry heavy objects at home improvement stores, especially when you have
sustained an injury or have limited mobility. Current shopping carts are great, and assist greatly,
but it is often difficult to maneuver objects into the cart bed. Furthermore, though stores will
assist patrons in loading their cars, there is no aid during the shopping experience: patrons are
left moving around heavy objects themselves.
Though key stake holders include partially injured and older workers, pregnant women and
young families, and people with limited mobility, we aimed to make a product that would benefit
all patrons of home improvement stores, regardless of their strength and ability.
We believe Echoraiser achieves this goal, improving the shopping experience greatly, allowing
patrons to automatically lift and lower their cart payloads to facilitate easier movement of heavy
and unwieldy goods in home improvement stores.
Echoraiser • me.berkeley.edu/ME102/Echoraiser • Berkeley Engineering
What It Does
Since most energy is wasted lifting and lowering heavy objects due to the change in potential en-
ergy, Echoraiser assists by lifting and lowering the payload bay, moving with your hand to your
desired height to make it easier for users to load and unload the carts. It has three modes:
6-12cm
range
Hold: At 8 centimeters, Echoraiser holds the position of the platform steady.
12-40cm
range
Lift: From 12-40 centimeters, Echoraiser lifts the platform
3-6cm
range
Lower: From 3-6 centimeters, Echoraiser lowers the platform.
Echoraiser • me.berkeley.edu/ME102/Echoraiser • Berkeley Engineering
Echoraiser modes of operation:
Key Stakeholders
Women and young families are increasingly driving sales at home improvement stores. Accord-
ing to the San Jose Business Journal, “Women initiate 80 percent of all home improvement pro-
jects and represent half of Lowe's customer base, according to the company. Compared to a year
earlier, women characterized themselves as intermediate or advanced as opposed to beginners,
says Lowe's. Ninety-four percent of all female homeowners have completed a home improve-
ment project on their own at least once...” Furthermore, construction workers are high-risk in-
dividuals who put their bodies at risk every day. These users demand products that help them in
their work and help to prevent injuries over time. Echoraiser is a reliable and intuitive product
that can give accessibility to users that may find it difficult to get help otherwise, and facilitates a
more positive shopping experience.
Echoraiser • me.berkeley.edu/ME102/Echoraiser • Berkeley Engineering
Young families
Older
workers
women injuries
HOW IT WORKS
Overview
The ultrasonic sensor detects how far away your hand is, which activates the motor on a high
PWM duty cycle, upwards direction if it is to be raised, and a lower PWM duty cycle, downwards
if the platform is to be lowered, since lowering requires less effort. The motor turns the miter
bevel gears and aluminum collar, which makes the ball screw spin and ball nut rise and fall.
Echoraiser was engineered for high performance, reliability, and ease of use. We achieved these
elements by using steel support rods, a high grade ball screw, and an aluminum plate, mounted
to a wood frame and secure motor housing and hardened steel bevel gears. The schematic below
shows the basic setup:
Echoraiser schematic
Echoraiser • me.berkeley.edu/ME102/Echoraiser • Berkeley Engineering
Original Design and Changes
As with most engineering projects, the design of the product evolved through many iterations.
Before beginning the building process, we sketched out our ideas. Key elements of the original
“UPcart” stayed the same: a payload bay would rise and fall according to user input driven by a
motor housed on the bottom of the four-wheeled cart. However, other elements, such as the hy-
draulically actuated scissor lifting system and range sensors were deemed too complicated for
our proof of concept, and the control panel was removed, replaced with a more intuitive “hand
waving” solution, explained in the next section. Most importantly, the ball screw dictated that we
needed to mount this screw through the center of the top plate, to minimize the torque moment
and ensure that the plate lifted smoothly for the proof of concept usability study. This will be re-
placed by hydraulic actuated scissor lifting mechanism in future iterations, for a more useful cart.
Original Design
After sourcing parts and beginning the build, part and cost constraints dictated the final design
for our prototype Echoraiser. Working with a limited budget, we contacted San Jose Ball Screw
and Actuator Company, Metal Super Markets, and Bearing Engineering Company to source
scrap parts that they were willing to give to our project. Although the parts were generously do-
nated or discounted, they were often parts that did not exactly fit our original design spec. Thus,
we often had to change our design to best utilize our resources. The following section details key
parts and the challenges we faced.
Echoraiser • me.berkeley.edu/ME102/Echoraiser • Berkeley Engineering
Key Parts and Challenges
ultrasonic sensor
motor coupling and gears
motor
We originally wanted to go with a piezoelectric sensor that would sense small changes in the force on the top aluminum plate and automatically assist the user, augmenting the up-ward or downward force expended on the plate. However, we found this approach non-transparent, and decided to use an ultrasonic distance sensor instead, so users would be able to decide cart height without doing any lifting themselves. Fur-thermore, users would no longer need to bend all the way down to adjust the height.
We needed a coupler to join the keyed motor shaft to the miter bevel gears. This coupler was fairly difficult to ma-chine. Initially, we machined a slot in the coupling that fit the motor’s keyed shaft exactly. However, we were unable to mill a precise enough coupler, and ended up with two wobbling couplers. We overcame this challenge by boring the cou-pling to force fit the shaft and tapping two set screws across the protruding key. This process took 20 minutes, versus the 2-3 hour machining time for the original part.
Although we initially designed the gears to mesh at 90 de-grees, the gears given to us by Bearing Engineering were 15 degrees off, and we had to mount the motor at a 15 degree angle in order to have the gears mesh correctly. Further-more, we did not want to machine the thin, load-bearing col-lar piece down further from 1/2 inch, and had to bore out the gears to this diameter. Luckily, only the gear teeth were hardened steel, and the gears machined without a problem.
Though ball screw we used was rated for almost 500 pounds, motors capable of transmitting such high torque were ridicu-lously large. We came up with a compromise of a motor that could lift 100 pounds for our proof of concept, something that will change in the next iteration of Echoraiser, when we utilize hydraulic actuators and decrease the size significantly.
Echoraiser • me.berkeley.edu/ME102/Echoraiser • Berkeley Engineering
ball screw and bearing collar
ball nut and aluminum plate coupling
DSP and breadboard
The ball screw donated by San Jose Ball Screw and Actuator company was the first part we obtained and gave us a strong foundation around which to build the rest of the cart. We had to find a way to attach the ballscrew to the bottom plate and mesh with the gears and motor, ensuring an efficient transfer of energy from the spinning motor to the rising top plate. We machined a ball screw and bearing collar on the lathe and tapped set screws to ensure a secure fit, attaching it on the bottom to a bearing secured by another set screw. Although the bearing we found was not a thrust bearing, Ralph Baca at Bearing Engineering company assured us that this bearing would support at least 40% of rated axial weight, and rated at 500 pounds, we figured that a 200 pound rating would be more than sufficient for our load bearing needs. This ended up being easy and cheap to implement, and smoother than comparably priced thrust bearing installations.
Ballscrew/ball nut combinations generally are able to transfer almost 95% of rotating energy into lifting energy. During transport, however, the ball nut slipped off the ball screw and we lost several bearings. Although we continued testing with some missing bearings, the motor was still able to transfer energy, although with decreased efficiency, and we sourced a few bearings from Gordon in the machine shop to get the ball nut back to its highest efficiency. We needed the ball nut to couple with the aluminum plate, and machined a collar on the Monarch lathe with custom tap threads to mesh with the ball nut.
The DSP and breadboard mounting posed a few challenges for our group. We mounted the DSP on the base plate of our cart to ensure that wiring would be short and efficient. How-ever, we worried that objects slipping off the and around the lifting cart may pull off wires or damage the DSP and bread-board. Originally, we had a wooden cover, but were not able to see the signals from the DSP. Thus, we constructed a clear box out of acrylic to make a strong cover that would allow us to continue monitoring the DSP. A second challenge that we encountered was that the DSP power input protruded past the acrylic base plate and we needed to notch the base plate. Instead, we simply flipped the DSP over so that the power plug was on the inside and we did not need to widen or mod-ify base plate, and kept all wires neatly exiting only one side of the breadboard/DSP.
Echoraiser • me.berkeley.edu/ME102/Echoraiser • Berkeley Engineering
Bill Of Materials! ! ! ! ! Notes!! Price
12” x 18” 1/4” aluminum plate $50.12
Ultrasonic Sensor $29.95
Ball Screw and Nut Donated $140.00
Gears Discounted $15,00
Axial Bearing Discounted $10.00
Motor Provided ($50?)
6” of 3” diameter aluminum stock rod Provided ($5?)
2” of 1” diameter aluminum stock rod Provided ($5?)
4 x cart wheels and casters 4 x 5.89 each = $23.56
Wood Provided ($10?)
Fasteners Provided ($10?)
Total Spent (Including Donations)! ! ! ! 128.63 (348.63)
Echoraiser • me.berkeley.edu/ME102/Echoraiser • Berkeley Engineering
Why Echoraiser
Competitive Advantage
The Echoraiser is an intuitive and reliable product that can make it easier for people to shop and
move around at home improvement stores. Its simple and robust design would be easy to scale
and support, and would be a very useful aid to all shoppers. During our inventor’s open house,
reaction to the product was very positive, and people ranging in age from 10 to 70 years old were
immediately familiar with the controls and able to control cart height adeptly. Many responded
that it was an interesting product and that it would be a useful aid if it were available.
Our “Magic!” Echoraiser cart was a product that people wanted to try and enjoyed using. We
feel that our project not only achieved success as a product to improve the livelihood of reduced
mobility individuals, but would also be useful to the general public. Furthermore, these carts
would enable home improvement stores to differentiate themselves in terms of a shopping expe-
rience, and would add value to any goods sold within these stores. As such, the Echoraiser is a
low-cost, pragmatic, and marketable product that can immediately add value to any home im-
provement store.
The Team
David Chen is a ME Junior at UC Berkeley. Working with RSSP Marketing, David has experi-
ence in web and graphic design and provides web support for numerous UC Berkeley Housing
Department websites. In addition to his interest in web development, David is also interested in
aeronautic and aerospace design and plans to pursue a career in these fields.
William Cheung is a ME Senior at UC Berkeley, and directs Berkeley Innovation, the campus
product design group, in addition to the Undergraduate Finance Association and the Berkeley
Venture Group. He is deeply interested in Product Design and is working at Pay By Touch as a
Enrollment Product Design Intern this summer.
Neil (Nghia) Nguyen is a ME Junior at UC Berkeley. Neil is currently working as an Academic
Services Asistant at Unit 3 dormitory and also as a Academic Coach at Berkeley High School.
Neil has a special interests in robotics and mechatronics design and plans to have a special study/
research section in Japan during Spring 2008. For summer 2007, Neil will be working for the
Good Samaritan Medical Ministry, a non-profit medical organiztion that provides free medical
care for the poor of selected remote villages.
Echoraiser • me.berkeley.edu/ME102/Echoraiser • Berkeley Engineering
