Wright State University

• Jenny Broering

• Mike Hill

• Rahul Shah

• Michael Wasco

Problem Statement

The purpose of this project is to design and manufacture robotic manipulator to assist younger patients with daily activities, such as retrieving things from the ground or immediate environment.

• Basic Requirements– 0.75 m reach from front of wheelchair

– Each linkage must move no more than 0.25 m/s

– Lift 0.5 kg mass (1.1 lbs.) with 7.5 cm in diameter

– Maximum cost of $4,500 (excluding controllers)

Agenda

• Design Constraints

• Robotic Arm Design (detailed)

• Conclusions

• Questions

Design Constraints

• Arm, including motors, must weight less than 30 lbs.– Keeps wheelchair balanced

• Dimensions of arm/base must not exceed 6 inches– Wheelchair must be able to fit through standard

doorways

Design Constraints

• Keep shoulder and elbow motors at the base– reduces weight on arm itself– transmit power to elbow via shaft

• Aluminum 2024– High Strength-to-Weight ratio– Lightweight compared to steels

(2770 vs. 8030 kg/m3)

WSU Arm Design

Orientation of Base Motors• Mounting position

– Length along chair allows space for base plate

– Straight layout allows for easy mounting possibilities

• Two large motors displaced from arm– Reduces torque

– Makes links slimmer and lighter

Base Configuration

Shoulder Motor

• Required Torque: 465 in-lbs (7433 oz-in)

• Speed Requirement: 2.65 RPM

• Suggested motor and gearhead: – K & D Magmotor servo motor

(model # C33-I-200E08)– Carson 34EP100 NEMA 34 gearhead (100:1)– 477 in-lbs provided

Shoulder Motor

• Servo amplifier suggested to slow speed down to required speeds– connecting directly to 24 VDC will give an

output of 10 RPM– connecting 24 VDC to a servo amplifier, we

can set a speed from 0-10 RPM

Shoulder Motor Dimensions and Costs

• Motor – 5.15” length – 3.38” diameter– apr. 5 lbs.– $134.00

• Gearhead– 5.43” length– 3.25” diameter– 9.68 lbs– $700.00

• Amplifier– $439.00

Elbow Motor• Required Torque: 237 in-lbs (3797 oz-in)

• Speed Requirement: 4.4 RPM

• Suggested motor and gearhead is the same as shoulder motor: – K & D Magmotor (model # C33-I-200E08)– Carson 34EP100 NEMA 34 gearhead (100:1)– 477 in-lbs provided

Elbow Motor Dimensions and Costs

• Same as Shoulder motor choices

• Motor – 5.15” length – 3.38” diameter– apr. 5 lbs.– $134.00

• Gearhead– 5.43” length– 3.25” diameter– 9.68 lbs– $700.00

• Amplifier– $439.00

Upper Arm

• Comprises of two links

• Dimensions: 410 x 50 x 5 mm.

• Weight: 0.8772 lbs.

• Advantages:– slots cut to reduce the weight– Provide support for the shaft and the lower arm– encompasses the parts

Upper Arm

Bearing Plate• Provides structural support

• Slot provided for compact closing of the arm

• Dimensions: 100 x 50 x 10 mm.

• Weight: 0.23 lbs.

• Elbow motion using the shaft, bevel gears and rod.

• Weight:– Rod : 0.045 lbs.– Shaft : 0.614 lbs.– Bevel Gears : 0.0278 lbs. each

Elbow Joint

• Advantages:– eliminates the motor-on-joint assembly.

– reduces torque on the shoulder motor.

Elbow Joint

Lower Arm

• Single shaft design

• Two slots– decrease weight

• Symmetric placement between the two upper arm links reduced unwanted torsion.

Lower Arm

• Dimensions: 320 x 50 x 5 mm.

• Weight: 0.3498 lbs.

Differential Assembly(wrist)

• Motor-on-Gear Design

• Off the Shelf vs. Machined

• Dimensions

Design

• Two Axes Movement– Gears spin in same direction, gripper pitches

up/down– Gears spin in opposite directions, gripper rolls

cw/ccw

• Motor-on-Gear Design – Gear is attached to motor shaft– Motor shaft/gear have same axis of rotation

Off-the-Shelf vs. Machined

• Currently searching for off-the-shelf models that can be incorporated into the design space

• Machined differential will drive the cost up significantly

Dimensions

• Approx. Size (w/o motors) : 162x120x50 mm

• Weight (w/o motors) : 1.7 lbs

Differential Assembly(wrist)

Differential Motors

• Orientation of motors provide a direct application of the gear movement

• Differential design allows motors to work together thus reducing the size and cost of motors

Differential Motors

• Torque requirement: 107.2 oz-in

• Speed Requirement: 15.7 RPM

• Suggested motor: – Barber-Colman permanent magnet DC Motor

with gearhead (model # EYQF-33300-661)– 12 VDC– 160 oz*in– 9 RPM

Differential Motor Dimensions and Costs

• Motor – 2.5” length – 1.5” diameter– weighs 9 oz.– $74.00 ea.

End Effecter(Gripper)

• Motor-screw powered movement

• Three Fingers

• Dimensions

Gripper

Motor-Screw

• Powers the closing action

• Will weigh less then 1.5 pounds

• open/close control• variable closing pressure

Three Fingers

• Better stability

• Pick-up a wide variety of sizes 7.5cm-.5cm

• Middle finger has lip for round objects

• Fork lift design

• Non-slip cork/rubber padding

Dimensions

• Each finger is 95 x 25 x 2 mm

• Weighs only .333 kg w/o motor-screw

• Hollow casing 50 x 95 mm– 2 mm wall thickness

Torque Calculations

• Note that the weight of the materials were taken to act at the farthest distance possible

Upper Arm [a] 0.8772 a 1.4912 a 14.17Upper Arm Shaft [a] 0.614 b 0.3498 b 10.63Lower Arm [b] 0.3498 c 2.825 c 4.72Differential [c] 1.7 d 3.351 d 6Diff. Motors [c] 1.125Motor-Screw [d] 1.5 Application Factor = 2gripper [d] 0.751object [d] 1.1

Shoulder Motor 464.6 lb*in 7432.9 oz*inElbow Motor 237.3 lb*in 3796.9 oz*inHand Motors 6.702 lb*in 107.232 oz*in

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

a b c d

Motor Speed Calculations

0.902 m0.542 m

0.1524 m

RotationalLength Velocity Speed

Motor (m) (m/s) (RPM)Shoulder 0.902 0.25 2.65Elbow 0.542 0.25 4.41Differential 0.152 0.25 15.71

= L/V

Summary • Main motors placed at base

• Design uses 5 motors

• Design gives 5 axes of motion.

• Upper arm is slightly longer than lower arm

• Differential Design

• Three finger Gripper

Summary • Motor cost: $2768.00

• Material cost: $ 150.00 (est.)

• Machining cost:

• Total weight. 36 lbs

Disadvantages

• Improper folding of arm– not certain if folding is within 6 in.– motor placement on differential makes wrist

bulky

• Overall assembly is overweight by 6 lbs.

Advantages

• Meets nearly all of the constraints / requirements.

• Shaft– allows transfer of more power to the lower arm– allows reduction of torque on the shoulder

motor.

• Use of plates instead of tube reduces overall weight considerably

Advantages

• Can lift objects from the floor or from table-tops.

• Torque requirements met by motors.

• Versatile gripper.

• Use of Aluminum 2024 in most parts– consistency in material– high strength to weight ratio (used in airframes)

?? Questions ??