III. (Intermediate) Propulsion

III. (Intermediate) Propulsion

Background and context for the work of the sub-team

• Propulsion helps other teams design moving prototype

Description of the Sub-team and Objectives

• Propulsion must handle a 17 degree slope
• New power/torque requirements needed to accomplish above task
• Objectives for intermediate scale propulsion:

i. Determine requirements/specifications for theoretical model

ii. Select a motor and controller

iii. Design a mount for the motor within the bogie

iv. Develop a code that integrates the steering and/or braking code

Design Requirements and Specifications for the Sub-team’ s Work Products

• Motor must be able to move bogie up slope with following requirements

i. Extern 465 N of force at it’s radius

ii. Output power of at least 415 W or 0.55 HP

• Motor/mount must be able to fit within intermediate scale bogie
• Mount must exert 465N of force upwards

State-of-the-Art/Literature Review for the Sub-team’ s Sphere of Work

• Hub motors are being used
• Different types of hub motors:

i. Direct drive hub motors

1. Pros: More durable, faster, quiter
2. Cons: Drag when pedal, less range, larger, heavier

ii. Geared hub motor

1. Pros: Less drag, smaller, lighter, more torque
2. Cons: More noise, Lower top speed

• Crystalyte hub motor was chosen (specifically RoadRunner Crystalyte Motor Model 408)

i. Torque provided proportional to total current flowing around each pole

ii. Most cost-efficient

iii. the 8 in 408 represents number of turns of copper around each pole

iv. 400 series motor can provide same amount of torque

• Electrical Engineering team will be providing 20 amps, with 160 amps around pole
• Maximum torque of 51.2 can be provided (44.4 needed to traverse incline)
• Drawbacks of using 408:

i.  4 times the resistance/net electrical loss

ii. need twice the voltage to be powered to spin the same speed as the lower 408

iii. Battery needs to be larger than average

• Battery protected from dirt

Description of Your Design

• Chosen motor and tire would not exceed 9 inch in diameter
• Motor:

i. Operate at 800 W

ii. Exert a torque of 44.40N-m (enough force at the hub motor’s 3.5 inch radius to move bogie)

iii. Crystalyte 4825F controller used to interface with propulsion system/logic

• Mount was made using a 90 degree bent bar (used to provide stability against torsion, press hub motor against ceiling
• Angled bars cut to length with a 15 degree angle, then welded together
• At end of mount, 1”x 1” 11GA A36 steel square tubing was welded
• Coefficient of friction for rubber against wood varies from 1 to 4

I. If the coefficient = 1, then spring would need to exert load of 470N

Analysis/Validation/Testing

- Motor could be controlled with Arduino

- Mount would press motor into ceiling with at least 100lb-f to gain traction in bogie

- Hall effect sensors used for testing

Money Spent on Project

• Overall cost: $516.06

Results and Discussion

• Code used for testing was buggy

Conclusions and Suggestions for Future Work

- Because of time and design constraints + late start, the propulsion team was unsuccessful.

- Areas of improvement:

i.  Controls: More features could be used such as an encoder to detect the turns of the motor, electronic braking, and cruise control

ii. Method of pressing hub against ceiling: Linear actuator would be beneficial