IV. (Intermediate) steering and braking

IV. (Intermediate) steering and braking

Objectives

• More thought needs to be put into reliability/efficiency of bogie
• Main goal: To modify/improve steering mechanism while maintaining structure/function of last year’s bogie
• Stepper motors replacing linear actuators
• New braking system next to guiding wheels to be implemented (has direct braking force)

Design Requirements and Specifications

• Steering

i. Bogie is half-scale

ii. One stepper motor used to control both bottom/top steerings links simultaneously

iii. Switching time goal is 3 seconds

iv. Upper control arms need to rotate 70 degrees, lower control arms 35 degrees from one dead position to another

v. Two pairs of wheels on upper steering link, low vibration on switching

vi. Steering force to counter “flying out” of bogie during centripetal acceleration

• Braking

i. Average brake power to be 1.971 Kw for half scale for straight track

ii. Wii nunchuck control used to control braking system

State-Of-Art/Literature

• Steering: Stepper motor will be used due to high static torque and precise rotation
• Braking: Brake discs will be used due to being good in heat transfer, easy to maintain, have strong braking power and no fading  in wet condition
• Design concepts

i. Most major components are retained from last year

ii. Changes:

1. Upper/lower steering connected
2. 2 linear actuators replaced with stepper motor
3. Extra green guiding wheels installed
4. Lower steering arm now has triangular support for linkage

• Upper/lower steering arms have different angular radiuses (Upper was has higher angular velocity as a result)
• Gear reduction ration is 3.34 and 0.45 respectively
• Hall effect sensor used to determine which side steering mechanism would be engaged

i. Starting point: beginning of track before intersection

ii. Left section is straight

iii. Right makes S-curve and 17 degree incline downhill/uphill before it enters intersection again

iv. Control arm will not switch at beginning/ bogie enters right section of guideway

v. When bogie comes to stop, the control arms will rotate clockwise to have the left wheels  engage  against  the  guideway

vi. Bogie then travel straight back on the left section of guideway all the way to beginning

vii. Hall effect sensor will sense magnet near end of guideway which tells bogey to stop and reverse direction.

viii. When bogie comes to stop, control arms will rotate clockwise to have the left wheels  engage  against  the  guideway

ix. bogie  would  then  travel  straight  back  on  the  left section  of  the  guideway  all  the  way  to  the  beginning

x. Hall effect sensor be triggered again near beginning of track, Bogie would slow down, come to stop, and set direction forward

xi. The  control  arms  would then  rotate  counterclockwise  to have the right wheels engage against the guideway

• Brake placed on outer sides of guiding wheels (power can be directly distributed on there)
• Brake mounting position relocated to hub motor
• Brake motor mounted on right side of hub-motor
• Y-bar handle bolted down on the sides of the hub motor
• Space between caliper and hub-motor roughly 1/16 inch
• Brake  motor mount  had  an  L-shape  and  are  made  out  of  A36  steel
• Motor had 9275.6 on-in and 327.8 RPM meanwhile calculated torque for brake was 1227.0768 oz-in as the entire system went  down  the  17  degree  slope
• L-shape mount made out of A36 steel
• Supporting block/shaft pulley made out of aluminum 6061 (very strong backbone for motor)
• Brake housing for brake cable is    necessary  to  prevent  friction  between  contacting  surfaces  and  damage  the  surface  of  the bogies.

Analysis and Concept Selections

• Parts can handle stress caused by stepper motor
• L-shaped  bracket has the  highest Von Mises Stress of 9.935*10^6 N/m2 at the inner radius of the joint and the bracket may bend for 1.65mm under such load
• Von Mises Stress at edge of cylindrical parts is 5.594*10^6 N/m2
• L-bracket S.F. = 2.5164
• -Triangular link S.F. = 44.6872
• -Brake bracket S.F. = 38.1128
• Maximum deflection 0.39 mm

Testing and Validation

• Steering mechanism utilizes two stepper motors to actuate the control arms, one for each bogie
• Steering motor first tested without putting it on guideway
• Stepper motor does not have encoder
• Tiaihua switch used
• Problems encountered during initialization
• Servo used for brake system

Fabrication method

• Most parts of bogie fabricated out of A36 steel
• Upper/lower control arms were first built in order to fit test body
• Pieces then welded together using a MIG-welder

Outcomes

• CAD  model  of  the  steering  mechanism  successfully  synchronized  the  motion  of  both  the upper  and  lower  steering  links
• Stress  analysis  on  the  steering mechanism shows that the L-bracket and tie-rods are able to handle the stresses generated during switching.

Discussion

• Last years design was built upon not thrown away
• Upper switching arms were extended to fit the fail safety hooks

Conclusions/suggestions for future work

• Design of steering mechanism met specifications
• Torque needed to actuate arm was 5 Nm
• Stepper motor (12Nm) far exceeded expectations
• Room for improvements:

i. Excessive play in pivot point of control arms

ii. Coupling is not able to grip the shaft of the L-shaped bracking firmly

• Design of brake system met specifications
• Main motor broke down

What should be done by the next group of Super way engineers to improve upon your work and take it to the next level?

• Stepper motor be mounted in better position
• Use lower spec motor
• Stepper motor that can go forward and reverse while holding good torque

Overall project conclusions, broader impacts, and recommendation

• Cap for subteams
• Divide subteams up evenly