That is what the Hall effect switches do. To make sure each motor spins at exactly the right speed, the controller must measure the speed of rotation of each axle. The STM MCU implements a velocity feedback loop, driving the motors faster or slower based on the difference between the commanded velocity and the sensed velocity. Hall sensors on the PCB detect the passing of gear teeth in the drive, feeding back this information to the STM motor controller. There can be changes in the tire friction as the car moves, as well as other variables that can slightly change the motor speed.Ī close-up of the wheel-drive motors and gearing shows how the Overdrive cars steer and get power. The reason is that just putting in a specific amount of motor current won’t guarantee that the motor will spin at a precise velocity. To begin, the speed of the motors can’t be controlled precisely enough to steer the car without some kind of closed-loop control. (One widely followed teardown site analyzed the Overdrive cars and botched the explanation of components related to the motor control, probably because those involved didn’t really understand motor control techniques.) It is worth examining how the motors are probably controlled. So the car steers by slightly increasing or decreasing the speed of each rear wheel as need be. Instead, the car uses two tiny electric motors, one to power each of the rear wheels. Once it’s out, the mechanism by which the car steers becomes clear. The PCB sits in the chassis sandwiched between the two halves of the car shell so it comes out easily. Removing the top of a car exposes the circuit board, the chassis, and a large ballast weight. Noteworthy in this view is the chunk of metal used for weight ballast, the multicolor LED giving battery charge status, and the LEDs that help simulate weapon strikes. Under the covers Removal of the car shell reveals that the Overdrive cars are basically circuit boards on wheels. The cars are powered by rechargeable lithium batteries, and the set comes with a recharging station where cars sit until their batteries are ready. To flawlessly traverse every layout thrown at it, each car takes a training lap before a race and basically memorizes the track using a built-in optical sensor to sense track position. An interesting feature of the track is that its sections use magnets to click together, and the track can be configured in a variety of racing layouts. The Overdrive starter kit we analyzed contains sections of track that can go together in various ways and can even include jumps.
#Anki controller software#
Robotic race cars make clever use of software and infrared optics to follow lines slyly hidden on the track.
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