Smart car competition every year there will be a lot of white novice to join, most of the students are to start with electromagnetic practice, and then gradually start to the camera and so on, so for the electromagnetic algorithm has a certain research, for other algorithms will also have a – certain hands-on ability, but the electromagnetic algorithm although good understanding, but want to make the car run fast and stable, has been a bottleneck of the electromagnetic algorithm.
The electromagnetic guided intelligent car has a great advantage over the photoelectric or camera guided intelligent car because it is not affected by light, temperature and humidity, and has good environmental adaptability.
Electromagnetic car is to obtain track information by obtaining the signal generated by the track signal generator, there will be a magnetic induction line in the middle of the track, used to generate alternating electromagnetic signals. Car through the prospective inductor on the track information, why can inductors can get track information, in fact, it is very understandable, electromagnetic induction are like it, the conductor cutting the magnetic induction line will generate induction electromotive force, I inductor internal wire cutting the signal line generated by the magnetic field, there will be induction electromotive force in the inductor pins. The closer the inductor is to the magnetic field, the greater the induction electromotive force generated, and the farther the distance, the smaller the induction electromotive force generated.
Handling schemes for the elements of the electromagnetic smart car: traffic circle, ramp, trigonometry, and speed control schemes for straight and curved roads.
Roundabout: We use a stable electromagnetic judgment scheme for the identification of traffic circles. The two lateral inductors on the inside will reach their extremes at the traffic circle tangent point to determine the traffic circle.
Ramps: We use TFMiniPlus LIDAR distance measurement to determine ramps. The ramp is determined when the distance drops below a certain threshold.
Straight acceleration: The omnidirectional group will most likely not have a high speed when following the track at a constant speed, so straight acceleration is necessary. We use five kinds of straight acceleration judgment conditions.
Midline judgement acceleration: The upper half of the image is judged to be accelerated by the absence of an intersection between the midline and the two boundaries of the track.
Inductor layout scheme for electromagnetic smart cars
The inductor placement scheme is one of the key factors that restrict the performance of the EM smart car competition.
We know that the basic arrangement of inductors is divided into horizontal, vertical and figure-of-eight schemes, and the different placement of inductors may affect the car’s trajectory attitude. We found through real-world testing: horizontal inductors help straight track tracking, figure-of-eight inductors, then there are racing to help cornering, vertical inductors on the general track value is almost small, only in some special elements (such as traffic circles) will be a sudden increase. We use the horizontal and figure-of-eight inductors together to follow the track, that is, the figure-of-eight and horizontal inductors are placed at the left and right ends, and a horizontal inductor is placed in the middle of the electromagnetic rod and near the center of the racing car for special element judgment. In addition, the height of the electromagnetic foresight needs to be slightly lowered in order to collect the track electromagnetic values more accurately to the point of no distortion.
The analog servo is a DC servo motor controller chip can generally only receive PWM external control signals with a frequency of 50Hz (20ms period) ~ 300Hz, too high a frequency will not work properly. If the PWM external control signal is 50Hz, the DC servo motor controller chip to obtain the position information is the resolution time of 20ms, compare the PWM control signal is proportional to the voltage and feedback potentiometer voltage to derive the difference, the difference by pulse width expansion (duty cycle change, change the size is proportional to the difference) after driving the motor action, that is, due to the PWM external control signal frequency limit, the fastest This means that due to the limitation of PWM external control signal frequency, it takes 20ms to make a new adjustment to the servo rocker position.
Electromagnetic trolley operation principle
- The car model detects the path by sensing the alternating magnetic field generated by the wire in the center of the track.
- To make the car run along the track by itself, the car should be able to automatically identify the current position and the approximate distance from the center of the track through the signal of the sensor. We make the sensor to collect the analog signal, and then pass it to the microcontroller, and then program it to realize the car position discrimination and control the car to take the corresponding action.
