Gateway CoalitionGateway Coalition

Wright State University

Shoulder to Elbow Design

February 4th, 2000

• Jenny Broering

• Mike Hill

• Rahul Shah

• Michael Wasco

Agenda

• Introduction

• Base/Shoulder Design

• Upper Arm Design

• Elbow Joint Design

• Conclusions

• Questions

Introduction

Conclusions

Designs

Current Base Design

Base Design

• Swivel– Cross Roller Bearing

could replace both Thrust Bearings

– 90 degrees of rotation (object constraint)

– base plate extends 9” from wheelchair

Shoulder Design• Shoulder Motor

Placed Vertical– Right Angle

Gearhead vs.Bevel Gears

– Right Angle Gearhead much easier to integrate and only costs $200 more

• Comprises of two links

• Provide support for the shaft and the forearm

• Elbow brackets introduced

• Lighter compared to tube

Upper Arm

Encompasses the parts

Elbow Joint• Elbow brackets

– attaches to I-beam bracket

• Bevel gears– 2:1 ratio in addition

to 50:1 gear-head

• Compact home position

Elbow Motor

• Elbow motor placement depends on motor dimensions

Gearheads/Gearing• Shoulder :

– K & D Magmotor servo motor – 100:1 right angle planetary gearhead – 477 in-lbs provided

• Elbow:– Brush Type DC servo motor– 55:1 planetary gearhead– 160 in-lbs provided– Possible 2:1 gear ratio provided at elbow joint

Torque Calculations

upper arm [b] 1.274 a 8 a 4.25upper arm shaft [b] 0.4093 b 2.1833 b 7.75gears [b] 0.5 c 3.170 c 21.5elbow motor and gh [a] 8 d 1.3 d 24.5I-beam [c] 2.67 e 1.380 e 28.5elbow bracket [c] 0.5 f 3.6 f 31.5differential [e] 0.48 x 15.5bevel gear [e] 0.36 y 20pinion gear [e] 0.04differential bracket [e] 0.5 Application Factor = 1.5gripper [f] 2.5wrist motors [d] 1.3object [f] 1.1

Shoulder Motor 455.5 lb-in 227.7 lb-inElbow Motor 159.4 lb-in 79.7 lb-in

2:1 gear ratio

Lengths (in)Weights (lbs) Weights (lbs)

x

fe

dc

y

ba

Torque Comparisons• Shoulder motor on base

– torque required:

• 462 lb-in

• Shoulder motor placed within arm– torque required:

• 665 lb-in

44% increase in torque required if both motors were to be placed inside the arm

(Both calculations used an application factor of 1.5)

Q: What are the best benefits of our design?

• Meets all the torque requirements

• Motor outside of arm reduces torque on motor, thus reducing the size and cost.

• Length of arm need not be increased to accommodate motor (19 inches of motor; 21 inches of arm)

• Thinner upper arm allowing compact design

• Horizontal placement of swivel motor allows lower mounting of arm thus increasing reach

A: All of the above

Dimensions

Conclusions

• Swivel base

• Vertical shoulder motor

• Elbow motor inside upper arm

• Elbow brackets allow compact folding

Questions ¿