By installing a seat-lifting device and hand-operated
driving controls, undergraduate engineers at Johns Hopkins
have transformed a tractor to allow people with
disabilities to help maintain the grounds of a southern
Maryland state park.
The project resulted from a request from Donnie
Hammett, ranger and manager of the 596-acre
Greenwell State Park in St.
Mary's County. In keeping with the wishes of the Greenwell
family, which donated part of the property, the park has a
special emphasis on outdoor recreation for people with
disabilities. When some of these users offered to help with
trail maintenance, hayrides and other chores, Hammett
obtained a federal grant to purchase a tractor, then adapt
it for use by people with disabilities.
After buying the vehicle more than a year ago, Hammett
could not find a business willing to make the alterations,
so he sought help from the Baltimore-based
Volunteers for Medical
Engineering. Because of successful collaborations with
Johns Hopkins in the past, the VME referred the tractor
challenge to students in the two-semester Engineering
Design Project course offered by the Whiting School's Department of Mechanical
Engineering. A team of four undergraduates was assigned
to confer with the VME and people with disabilities in
devising and constructing modifications for the tractor.
The students needed to adapt the tractor so that
people who are paraplegic and others who use wheelchairs
could access and operate it. To address the first
challenge, they installed a folding chair and hydraulic
lift system, powered by the tractor's diesel engine, on the
side of the tractor. The user can start the engine with a
remote control, transfer to the lift and raise the seat via
a hand control. At cab level, the operator can fold down a
ramp, grab onto handholds and slide into the driver's
To enable a person who is paraplegic to operate the
tractor, the students modified an electronic video game
controller to serve as a hand-controlled throttle. They
also built a mechanical device that allows the driver to
depress the brake pedal with a hand. In addition, the
controls were set up so that a person without disabilities
can disengage or bypass the hand controls and drive the
tractor in a conventional manner.
The student inventors, all seniors majoring in
mechanical engineering, were Alex Forman, Jon Haslanger,
Emily Nalven and Brian Wolcott. Their modifications cost
A few days before their graduation, the students gave
the customized tractor to Hammett, the park ranger who
commissioned the project. "This is going to offer some
unique opportunities for people in wheelchairs to work as
interns, volunteers or even employees on the park's
trails," he said. "You don't know what an esteem builder
it's going to be."
Hammett added, "We couldn't find anyone in the
commercial sector to take on this tractor project. I think
it was a great learning experience for the students."
The project is not completely finished. The ranger
said he plans to replace the hydraulic system that powers
the lift with an electric motor that will not require the
tractor's engine to be started before the lift can be
activated. He also wants to install sturdier, more
permanent grips in place of the rope handholds placed by
the students. Overall, he was pleased with their work. "I
think it's 85 percent of the way there," Hammett said. "I'm
going to have someone with disabilities riding on that
tractor before the end of the summer."
The students said they enjoyed applying their
engineering education to a real-world project. "It was
rewarding because you could see everything you'd studied
and worked on coming together," Haslanger said.
Added Forman, "A project like this makes everything
else worthwhile. You get to apply everything you've learned
and find out if this is what you really want to do. It's a
Forman, Haslanger and Nalven plan to continue their
studies in graduate school. Wolcott will be working for a
private consulting firm.
The modified tractor was one of nine Johns Hopkins
projects completed this year by undergraduates in the
engineering design course taught by Andrew F. Conn. Each
team of three or four students, working within budgets of
up to $10,000, had to design a device, purchase or
fabricate the parts and assemble the final product.
Corporations, government agencies and nonprofit groups
provided the assignments and funding.