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Nov. 17, 2005
Princeton UniversityProspect Eleven
Control Systems
• Speed control module:– Receives desired speed from Speed Decision– Decides how to modulate throttle and brake
• Requirements– Gracefully reach and maintain desired speed– Smooth acceleration and braking
• To minimize skidding on loose sand wet grass
– Strict adherence to speed limit• Minimize overshoot
– Deal with integrator windup
Nov. 17, 2005
Princeton UniversityProspect Eleven
Speed Control -- Implementation
• Proportional Integral Control– Output = KPev + ∫KIevdt + KD (dev∕dt)
– Where evelocity = Vdesired – Vcurrent
• KP term deals with the bulk of error
• KI integrates up error to eliminate steady state error
• KD reduces overshoot and ringing by slowing response
Speed ControlDesired Speed
Current Speed
Latest Speeds
Percent Throttle
Percent Brake Tension
Nov. 17, 2005
Princeton UniversityProspect Eleven
Speed Control -- Tuning
• The selection of constants dependent on dynamics of car– Response of motor to percent throttle
– Dynamics of braking
– Car is naturally dampened• Air resistance
• Drivetrain friction
• Step response of car at various regimes studied
• Actual tuning was done through Nichols-Zieger closed-loop tuning at different regimes.
• Graphical debug GUI made tuning very easy.