Princeton University Prospect Eleven Nov. 17, 2005 Control Systems Speed control module: –Receives...

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.