Home

State AgrAbility Projects

AgrAbility Quarterly

Assistive Technology Resources

Assistive Technology Database

Resources

National AgrAbility Workshop (2001 - 2008)

Archive

Contact Us

AgrAbility Site Search

Download PowerPoint Viewer
(Windows only)

Site Translation Help
(Ayuda para traducción de sitios)

Paper No. 018054.
An ASAE Meeting Presentation

Accessibility Modifications to a Ford 4000 Tractor for a Farmer with a Spinal Cord Injury

by

Written for Presentation at the
2001 ASAE/CSAE-SCCR Annual International Meeting
Sacramento, CA USA
July 29-August 1, 2001

The authors are solely responsible for the content of this technical presentation. The technical presentation does not necessarily reflect the official position of ASAE, and its printing and distribution does not constitute an endorsement of views which may be expressed.

Technical presentations are not subject to the formal peer review process by ASAE editorial committees; therefore, they are not to be presented as refereed publications.

Quotation for this work should state that it is from a presentation made by (name of author) at the (listed) ASAE meeting.

EXAMPLE- From Author's Last Name, Initials "Title of presentation.” Presented at the Date and Title of meeting, Paper No. X. ASAE, 2950 Niles Road, St. Joseph, MI 49805-9659 USA

For information about securing permission to reprint or reproduce a technical presentation, please address inquiries to ASAE.

ASAE. 2950 Niles Road, St. Joseph, MI 49805-9659 USA
Voice 616.429.0300 FAX: 616.429.3852 E-Mail: <hq@asae.org>

Accessibility Modifications to a Ford 4000 Tractor for a Farmer with a Spinal Cord Injury

C.L. Wray S.C. Borgelt H.W. Downs K. Funkenbusch

I. Introduction

Farming has been ranked by the National Safety Council as one of the most dangerous
occupations in the United States with over 140,000 disabling injuries occurring each year to farmers (Morris, 1996). Long hours and fatigue, combined with a sense of urgency to complete a given task before the weather changes or the sunlight fades, in an environment that is harsh and dangerous to the human body all contribute to accidents and injuries. For many farmers who are involved in disabling accidents, farming is not just an occupation; it is a way of life they are unwilling to leave behind.

Lashley Garnett, a farmer from Cole County, MO retired from his job as a school administrator with the Jefferson City Public School District to return to the farm that has been in the family for over 150 years. Lashley retired to operate the family farm the way he had always wanted. While building a barn, Mr. Garnett was seriously injured when a self-constructed boom pole fell on his head. The impact of the pole traveled down his spine, crushed the Tl2 vertebra, and caused a spinal cord injury. Mr. Garnett returned to his home, and with the help of the Missouri AgrAbility Project and a lot of determination, is trying to continue farming.

Mr. Garnett owns a Ford 4000 tractor (Fig. 1) that he would like to operate, but was told that it would be expensive and difficult to modify. Being a smaller tractor, no fabricator or machinist could build a lift that would be able to help Lashley get into the tractor seat because of the limited amount of space available on the tractor. In addition, the few commercially available lifts were very expensive and would cost more than the value of the tractor.

Fig. 1. Lashley Garnett's Ford 4000

II. Purpose

The purpose of this project was to design, fabricate and complete the necessary modifications to adapt the Ford 4000 tractor for Lashley Garnett to operate. The project involved the examination of ideas and recommendations of occupational therapy students at the University of Missouri-Columbia, the work of others in the adaptive equipment field including Darrel Whitmarsh of DW Auto and Home Mobility, and the desires of Lashley Garnett. After researching the current technology in this field, considerations and design criteria were established for the lift and the hand controls. After initial modifications were made to the tractor, a lift was designed and fabricated to assist him from his wheelchair into the tractor seat. In addition, the tractor was equipped with hand controls that were designed and fabricated for Lashley and his functional reach. During the process, the OT students were consulted for recommended modifications to satisfy safety and ergonomic issues for a farmer with a spinal cord injury.

III. Considerations and Design Criteria of Lift

Lashley has a Ford 8000 tractor equipped with a wheelchair lift that consisted of a platform that he could wheel onto, and the lift would then raise both him and his wheelchair to height level with the operator seat. He then used a 6 ft. long transfer board to slide from his wheelchair to the seat. Since this lift required a lot of space on the tractor, a lift similar to this could not be considered for the smaller Ford 4000. In addition, the OT students thought the long transfer was unsafe and irritated a pressure sore that Lashley had.

A search for lifts commercially available for the Ford 4000 was completed, and Lifeessentials was the only company that was found that manufactured a lift that could be installed on this smaller tractor (Lifeessentials, 2000). The Pilot Lift (Fig. 2) consists of a vertical mast with a rotating beam and chair mounted. The beam and chair move up and down the mast with a power screw, and they can be rotated into position for transfers. If this lift were installed on the Ford 4000, the chair would lift Lashley up and over the tire and place him where he can transfer into the operator seat. The price of the lift was over $10,000, which is more than the value of the tractor.

Fig. 2. Pilot lift Manufactured by Lifeessentials

1. The lift would need to take Lashley from a low position to transfer from his wheelchair seat; 22 in. from the ground, to a higher position to transfer to the operator seat 55 in. from the ground. Transferring should only be done across level surfaces.
2. The lift could use a platform, a separate transfer seat, or the tractor operator seat to raise Lashley up to the higher position. The lifting apparatus was constrained to fit the limited space of the tractor.
3. The lift should require minimal tractor modifications, and should not interfere with the operator's vision, the operation of the tractor, or the equipment attached.
4. The lift should be powered by the electrical system of the tractor and should not require the tractor to be running in order for the lift to be operated.
5. The lift should be capable of lifting 300 lb. and should operate at a speed between 4 and 20 ft/min.
6. The lift should have a fail-safe operation that would protect the operator from injury in case of electrical or mechanical failure.
7. The design of the lift and the modifications to the tractor should be easily adapted to other tractors of similar size.
8. The lift and modifications should utilize commonly available materials and tools for fabrication, and be reasonable inexpensive.

IV. Considerations and Design Criteria of Hand Controls

Hand controls were needed for the brakes and the clutch, but not for the differential lock. The hand controls for the Ford 4000 were to operate similarly to the hand controls on his Ford 8000 since he was accustomed to those controls.

The design of hand controls and examples of homebuilt controls were analyzed by "Breaking New Ground" in Plowshares #2 for functional performance (Field, Gaynor, and Willkomm, 1990). While a standard set of hand controls are manufactured for automobiles, a standard set of hand controls is not manufactured for tractors due to the great variations between different models and manufacturers. The article also listed design criteria of hand controls. Following examination of these criteria, speaking with Darrel Whitmarsh, and consulting OT students and professionals, criteria for the Ford 4000 hand controls were compiled:

1. The hand controls should be located in easy reach and actuated without undue strain or fatigue. The maximum force to operate the hand controls should not exceed 30 lbf.
2. The hand controls should be placed where they will not interfere with the hydraulic controls, throttle, etc., with Lashley, or with other tractor operators.
3. The hand controls should not bump or rub against the operator's legs. Sharp or jagged edges should be avoided.
4. The clutch hand control should pull back toward the operator to disengage the clutch, and should lock the clutch in a disengaged position.
5. The brake hand controls should push forward away from the operator to apply the brakes, and should allow independent or equalized braking. If the conventional brake interlock between the two brakes is affected by the addition of hand controls, a new interlock should be included in the hand control design.

V. Initial Modifications To Tractor

Some additions were made to the tractor to update the tractor and make it safer to operate. A Roll Over Protection System (ROPS) donated by Saf- T Cab was installed (Fig. 8). Installing the ROPS before designing and fabricating the lift insured the integrity of the ROPS safety protection for Lashley. Modifying ROPS or installing a lift that would require a modified set of ROPS substantially increases the liability of the engineer and the University, and was avoided. A power take-off (PTO) shield was also designed and installed on the tractor.

While the tractor could be accessed from either side, it was decided to install the lift on the left side of the tractor to avoid the brakes and the hydraulic controls on the right side. To provide more space for a lift, the left rear tire and the fender were moved out. The tire was moved out using the spinouts on the hub and effectively widening the wheelbase, allowing the fender to be mounted further out. Moving the wheel and fender according to the directions in the service manual for this tractor increased the amount of space between the fender and seat by almost five inches. Most tractors are equipped with similar provisions for widening the rear wheel track width.

Since the original seat on the tractor was in poor condition, a new seat donated by K&M Manufacturing replaced it. To provide even more space for the lift, the new seat was offset 2 in. to the right using the multiple mounting holes and bracing the overhung portion. Offsetting the seat 2 in. allowed the necessary clearance for the transfer seat and did not significantly change the operator's position with respect to the steering wheel and fabricated hand controls.

VI. Design and Operation of I-beam Lift Concept

With the initial modifications completed on the tractor, an adequate amount of space for the lift was made available, and attention was then focused on designing the lift (Fig. 3). Lashley insisted on a lift that would consist of a chair rolling up and down a beam. The chair was attached to a chain that was powered by a gear-motor. While the amount of space available on the tractor would be adequate, careful placement of the beam was necessary in order to move the transfer seat from a location next to the operator seat down to his wheelchair without rubbing on the fender, tire, engine, or other parts of the tractor. It was determined from visual inspection that the structural beam should be placed at an approximate angle of 30 degrees from the horizontal and 5 degrees in the vertical direction, placing the bottom of the beam directly behind the front wheel to reduce the possibility of damaging the lower end of the beam on obstacles.

 
Fig.3. Concept of Lift

I-beam Selection and Mounting

In selecting the main structural member for the lift to travel, an H-beam was preferred with its straight-flanged webs that would make designing a carriage easier. However, an I-beam was more readily available, especially in the small sizes considered. Considering the nature of this project, and the desire to limit the materials used to those readily available, an S3x5.7 I-beam was selected.

A static deflection analysis was performed on the I-beam to ensure that it would have enough strength and promote Lashley's confidence as the lift was used. Even with adequate strength of the lift and component, the operator might fear a lift failure if a noticeable deflection of any component would occur. The deflection of the beam would be less than 1/64 in. with a 300 lb. load supported in the middle of the 5 ft. length of I-beam.

The lower end of the I-beam was supported by a section of 4 in. wide x 5/8 in. thick flat bar designed to mount on the loader bucket mounts and placed the I-beam 20 in. away from the engine and directly behind the front tire (Fig. 4). The lower mount had a ground clearance of 16 in. and placed the lower end of the I-beam at the correct height for the transfer seat. The static deflection of the mount was mathematically determined to be less than ½ in. with a 300 lb. load supported on the end of the I-beam.

Fig. 4: Lower Mount of Lift Attached to Tractor

The upper mount placed the I-beam directly in front of the ROPS without interfering with it, and was made from 1-1/2 in. square tubing and another section of 4 in. wide x 5/8 in. flat bar (Fig. 5). The upper mount also placed the I-beam in the correct path to prevent the transfer chair from hitting the tire or the fender, and placed the transfer seat next to and level with the operator seat. The deflection of the mount with a 300 lb load was determined to be less than ¼ in.

Fig. 5: Upper Mount of Lift Attached to Axle

Rolling Carriage and Transfer Seat

A carriage that would roll up and down the I-beam with the seat attached was designed as an assembly fabricated from a section of 4 in. x 6 in. rectangular tubing with a side removed and ½ in. plate attached to locate the cam follower bearings (Fig. 6). McGill part # FCF 1-1/2 and part # CFC 3/4 were chosen as the bearings that would support the carriage on the I-beam. These bearings have dynamic load ratings of 690 lbf and 1660 lbf respectively, which would be sufficient for this application. Note the four 1-1/2 in. bearings have a flange that will locate the carriage laterally on top of the I-beam. The two smaller bearings have crowned surfaces that will help mate to the flanged webs, and are adjustable with the ½ in. plates they were mounted to. They provide the necessary support to keep the carriage against the I-beam and to prevent the seat from tipping side-to-side. In addition, a mount for the chain to attach to the carriage was welded to the outside adjustable plate that would hold the chain inside the web of the I-beam for protection.

Fig. 6. Cam Follower Bearings Used in Carriage Assembley

A plastic boat seat with removable vinyl cushions was used for the transfer seat (Fig. 7). The seat required a flat base to be mounted and includes a swivel mechanism that allows the seat to be locked into a fixed position. Since the I-beam would be mounted at approximately a 30- degree angle from the horizontal, a bracket was welded to the carriage that would make a level and flat base to mount the seat where it would lock in the position that would be easy for Lashley to transfer. The folding seatback was rigidly bolted, and a seatbelt added. The OT students replaced the cushioning with a material that they determined to be optimum with proper feet supports designed to swivel with the seat. They were fabricated using ¾ in. square tubing and sheet metal with traction tape and Velcro straps to properly support Lashley's legs, keeping them from hanging or catching on anything as he travels up and down the I-beam.

Fig. 7. Transfer Seat Used on Lift

Gear-motor and Chain Transmission

The gear-motor donated by DW Auto was a one hp DC motor with an attached right angle 40: I worm gear drive. The worm gear drive would not allow a load to over-run the motor, and would keep the carriage from traveling down the I-beam if the power was disconnected from the motor. Attached to the output shaft was a sprocket for a #40 chain with 11 teeth, which would make the traveling speed of the chair 22 feet per minute, a little on the fast side. Replacing the 11-tooth sprocket with a sprocket of 8 or 9 teeth was considered, but due to the diameter of the output shaft, smaller sprockets were not available. Knowing that the I-beam would be installed at approximately a 30-degree angle to the horizontal, the horsepower requirement of the motor would be 0.2 hp assuming an efficiency of 50% for the gear drive. This gear motor was salvaged from an older Ricon van lift, and while this gear-motor is not optimum for this application, it was adequate and available, so it was used. A smaller motor (hp) with a higher worm gear reduction would have been preferred. The mount for the motor was fabricated from 3/8 in. thick plate and designed to properly position the drive sprocket (Fig. 5).

A 13 tooth idler gear and a bracket at the lower end of the I-beam were designed to allow tension adjustment of the chain, and a skid-plate/guard was attached to protect the sprocket and chain from severe damage (Fig. 8). The bracket was made from 5/8 in. flat plate and tapped for the two 5/8 in. mounting bolts to secure the bracket through slotted holes cut in the I-beam. The idler gear revolves around a ½ in. cold rolled steel shaft and an oil-lite bushing. A simple flat washer is used as a thrust bearing. Since the idler bearing will only provide tension, and will not support the load of the carriage, this was recommended for a simple durable design and for the limited speed the gear will rotate.

Fig. 8. Design of Idler Pulley and Bracket on I-Beam

Wiring and Controls

In wiring the donated gear motor, the wiring schematic for the van lift that it was salvaged from was followed with a few modifications. The wiring schematic indicates 4-gauge wire running from the battery of the vehicle to a circuit breaker, and 6-gauge wire from the circuit breaker to each of two solenoids and then to the motor. Two continuous duty dual contact solenoids were implemented to switch the polarity of the contacts to the motor, and a simple wiring diagram (Fig. 9) shows how they are wired to provide this.

Fig. 9. Simple Wiring Diagram Illustrating the Use of Two Solenoids

While the schematic of the van lift also illustrated limit switches being used to stop the motor at the end of each cycle, Darrel suggested using a self-resetting circuit breaker and large rubber bumpers to stop the carriage at each end of the I-beam (Fig. 10). The large rubber bumpers are the frame bumpers originally designed for the frame of a van to cushion the impact of the axle housing on the frame if the suspension ever "bottomed out". He suggested using the bumpers and the circuit breaker in order to eliminate the wiring associated with the limit switches that may get tangled in the brush. He also felt that Lashley would be able to release the toggle switch before the bumpers safely stopped the carriage.

Fig. 10. Rubber Bumpers to Safely Stop Carriage

Darrel suggested sizing the circuit breaker by testing and use the smallest circuit breaker that would not open the circuit under normal operation. A donated wiring box was used to house the two solenoids, and supplied the umbilical remote control and toggle switch to activate the solenoids (Fig. 25). The remote control and toggle switch were salvaged from another van lift that he had removed.

Fig. 11. Umbilical Control Box and Toggle Switch

Operation

With the transfer seat in its lower position, and against the rubber bumper at the bottom of the 1- beam, the seat is level with Lashley's wheel chair. Lashley can transfer from his wheel chair to the transfer seat by lifting himself up and over into the transfer seat and then put his feet into the feet supports on the transfer seat. After fastening the seatbelt on the transfer seat, he can reach over and move his wheelchair away from the transfer seat for more room. He then uses the toggle switch to begin raising the transfer seat.

After ascending halfway, and before making contact with the fender or any part of the tractor, Lashley can stop the ascension by releasing the toggle switch. The locking lever on the seat can be released to allow the transfer seat to swivel clockwise and orient the seat to continue ascending back into position. The seat is free to swivel as the toggle switch is used again to raise the seat to the upper position and against the rubber bumper.

Lashley transfers himself by undoing his seatbelt and lifting himself up and over into the operator seat that is adjacent to the transfer seat. He manually moves his feet into position and fastens the seatbelt on the operator seat. The transfer seat can remain in its upper position since it does not interfere with Lashley's vision, it is away from any brush or weeds while the tractor is moving, and is not in the way of Lashley's legs. After the tractor is started, the tractor is steered to pull away from the wheelchair and Lashley can use the tractor. Nina, Lashley's wife, is generally available to assist Lashley in transferring, and can also help with moving the wheelchair out of the way and moving the wheel chair back into position when Lashley is ready to dismount the tractor. The descending process is just a reverse of the ascending process.

VII. Design and Operation Of Hand Controls

A set of hand controls were designed to operate the brakes and meet the design criteria previously established. Two levers were designed and fabricated from ½ in. solid square bar stock to extend from the individual brake pedals to a position where Lashley could easily reach and operate the brake pedals through a full range of travel. The levers were attached to the brake pedals using adjustable brackets (Fig. 12 and 13). The two levers have two handles fabricated from 1-1/4 in. pipe 4-1/2 in. long to form a T at the top, allowing Lashley to apply either brake independently or both brakes simultaneously. The pipe handles were covered with rubber grips to promote operator comfort and increases the surface area on which to push.

The large mechanical advantage of the extended levers allows the brakes to be applied easily using only arm strength. The original brake springs were replaced with stiffer springs to account for the additional weight on the brake pedals and to give a better feel to the brake handles. In addition, the conventional brake interlock on the pedals was not compromised by the addition of the hand controls.

Fig. 12. Adjustable Brake Brackets Attached to Brake Pedals

Fig. 13. Hand Brakes Installed on Tractor

A hand clutch lever that operates similarly to the hand clutch on Lashley's other tractor was also designed with linkages and a spring that would pull over-center. To equip this Ford 4000 with a hand clutch, a bracket was fabricated and bolted to the clutch pedal to attach a 7/16 in. push rod with rod ends (Fig. 14). The other end of the push rod attaches to a handle that rotates on a base mounted on the left side of the tractor under the steering wheel and within Lashley's reach (Fig. 16). The handle was designed and fabricated to most easily accommodate actuation with Lashley in a seated position, and a spring was attached on the handle in a position to pull over- center in both the straight up position and the straight back position. The over center spring will keep the clutch handle up and will be strong enough to keep the clutch pushed in when the lever is pulled straight back. The clutch pedal requires 30 degrees of rotation to fully disengage the clutch, and the clutch handle rotates 90 degrees to do the same (Fig. 16). The increased travel improves the feel of the clutch by helping it feel less sensitive.

Fig. 14. Push Rod Attached Clutch Pedal

Fig. 15. Push Rod Actuated by Handle and Over-center Spring

Fig. 16. FBD Illustrating Mechanical Advantage

VIII. Ergonomic Seating and Positioning Modifications

The OT students evaluated the seating and positioning of Lashley in the operator seat. The new seat did not offer enough trunk support for his level of injury and recommended moving the seat forward 3 in. relative to the backrest and tilting it up 1 in. in the front to provide more support under his legs and tilt him back into the seat to allow the backrest and the armrests to provide more support. To do this, a wedge shaped bracket was designed and fabricated from ¼ in thick steel plate. The design of the K&M seat accommodated modifications easily with flat bases where the seat and backrests mount.

The OT students also recommended installing the seat belt the operator seat at a 45-degree angle near the corner of the seat and the backrest. With the seatbelt in this location, Lashley would be held into the seat and would still be able to elevate his body routinely for pressure relief. A set of brackets to mount the seatbelts was designed and fabricated from 1/8 in. thick steel plate and positioned in the comer of the seat framework that would move with the seat suspension (Fig. 34). If the brackets were designed to mount to a solid part of the tractor or seat, constant tension would not be held on the seatbelts when the suspension moved.

The final ergonomic recommendation made by the OT students was to elevate the floorboard of the tractor to support Lashley's feet and hold his knees and hips at 90-degree angles. Keeping his joints at 90 degrees would promote trunk support, distribute his weight across a larger area, and minimize fatigue and injury. Modifying the existing floorboards on the tractor would be considerable, so a set of floorboard risers were designed from 4 in. x 6 in. rectangular tubing that would mount to the floorboards and not interfere with the pedals. The floorboard risers were topped off with traction tape, and held in place with ¼ in. bolts tack welded to the inside of the beam to ease installation and removal (fig. 17).

Fig. 17. Floorboard Risers

IX. Summary and Conclusions

This project pooled the resources of the Missouri AgrAbility Project, the Department of Occupational Therapy, the Department of Biological and Agricultural Engineering, and members of the community including DW Auto & Home Mobility to make the necessary modifications to safely and adequately make a tractor accessible to an operator with a spinal cord injury. This tractor, in particular, is often difficult to modify. All of the materials used in the construction of the lift are readily available, and the tools necessary to fabricate the lift are common to a well- equipped farm shop or the average machine or fabrication shop.

A cost analysis of accessibility modifications completed, the tractor lift cost about $4,500 to build. While over 90% of the materials and components used in the fabrication of this lift were donated, costs were considered for items that would have required purchasing if a similar lift and similar modifications were to be completed on another tractor.

X. Recommended Design Modifications

While this lift was tested for durability and function before it was delivered to Lashley, a medical condition has prevented him personally from testing the lift and tractor on his farm. During extensive shop testing, a few items to consider modifying were recognized. These modifications involve the cam follower bearings in the carriage, an additional fail-safe mechanism, and the wiring of the gear-motor. The smaller ¾ in. cam follower bearings listed a dynamic load rating of 1660 lb., but they did not appear to have sufficient strength when installed on the I-beam. The cam followers did not mate with the tapered flanges on the inside of the beam very well, and in redesigning a new carriage, this should be addressed.

In designing the wiring and controls of the gear-motor, limit switches were not used since the wiring associated with them could be easily damaged and incapacitate the lift. The rubber bumpers and the undersized circuit breaker are not preferred for this application. After Lashley has had a chance to personally test the lift, replacing the undersized circuit breaker with the implementation of limit switches should be considered.

References

Bowles, Jerry W., and William E. Field. 1992. Breaking New Ground -Plowshares #8: New
Concepts in Manlift Attachments for Tractors and Combines. Purdue University

Fields, William E., Robin Gaynor, and Terry WilIkomm. 1990. Breaking New Ground-
Plowshares #2: Hand Controls for Agricultural Equipment. Purdue University

Lifeessentials. 2000. Lifeessentials -Wheel Chair Lifts. http://www.life-essentials.net

Morris, D. Keith. 1996. Breaking New Ground-Increased Independence for Farmers with a
Physical Disability. Purdue University.