Skip to main content

Ping-Pong Ball Makes Great PID Example

It is a common situation in electronics to have a control loop, that is some sort of feedback that drives the input to a system such as a motor or a heater based upon a sensor to measure something like position or temperature. You’ll have a set point — whatever you want the sensor to read — and your job is to adjust the driving thing to make the sensor read the set point value. This seems easy, right? It does seem that way, but in realitythere’s a lot of nuance to doing it well and that usually involves at least some part of a PID (proportional, integral, derivative) controller. You can bog down in math trying to understand the PID but [Electronoobs] recent video shows a very simple test setup that clearly demonstrates what’s going on with an Arduino, a motor, a distance sensor, and a ping-pong ball. You can see the video below.

Imagine for a moment heating a tank of water as an example. The simple approach would be to turn on the heater and when the water reaches the setpoint, turn the heater off. The problem there is though that you will probably overshoot the target. The proportional part of a PID controller will only turn the heater fully on when the water is way under the target temperature. As the water gets closer to the right temperature, the controller will turn down the input — in this case using PWM. The closer the sensor reads to the setpoint, the lower the system will turn the heater.

For some applications, this is enough. But what if there are very small errors? Perhaps the set point is 90 degrees and you are 89.8. That won’t correct quickly in a proportional-only control loop because the heater won’t be on very much due to the small error. The integral part of the loop will react to small errors over time, adding a small bit each time the system isn’t in the right state. The derivative part is the opposite. It affects the output in reaction to sudden changes such as an ice cube landing in the tank.

The example rig is a seesaw-like balance beam and uses a lot of 3D printed parts and some plywood. The input driver to the system is an RC servo that can tip the seesaw to a different angle. An IR sensor determines how far the ping-pong ball is from the edge of the beam. With everything wired to the Arduino, you have a pretty good testbed for a controller.

If is common to “tune” a PID by setting Kp, Ki, and Kd constants that determine the “strength” of each action. With the beam, you can watch how tuning affects the system. By setting a constant to zero you can turn off that part of the algorithm, and it is very instructive to see what each part of the equation does to the ping-pong ball.

Even if you have used PID before, you will enjoy seeing this illustrative demo. It would be great in the classroom.  If you want to see a temperature example, we’ve seen that done with an Arduino, too. PID is integral — sorry — to flight control systems and self-balancing robots, too.



from Hackaday https://ift.tt/2SUu1m1
Labels:

Comments

Post a Comment

Popular posts from this blog

How To Play Doom – And More – On An NES

Doom was a breakthrough game for its time, and became so popular that now it’s essentially the “Banana For Scale” of hardware hacking. Doom has been ported to countless devices, most of which have enough processing ability to run the game natively. Recently, this lineup of Doom-compatible devices expanded to include the NES even though the system definitely doesn’t have enough capability to run it without special help. And if you want your own Doom NES cartridge, this video will show you how to build it . We featured the original build from [TheRasteri] a while back which goes into details about how it’s possible to run such a resource-intensive game on a comparatively weak system. You just have to enter the cheat code “RASPI”. After all the heavy lifting is done, it’s time to put it into a realistic-looking cartridge. To get everything to fit in the donor cartridge, first the ICs in the cartridge were removed (except the lockout IC) and replaced with custom ROM chips. Some modifica...
Post a Comment
Read more

The Flexible Permanence of Copper Tape Circuits

Somewhere between shoving components into a breadboard temporarily and committing them to a piece of protoboard or a PCB lies the copper tape method. This flexible Manhattan-style method of circuitry formed the basis for [Bunnie Huang]’s Chibitronics startup, and has since inspired many to stop etching boards and start fetching hoards of copper tape. [Hales] hit the ground running when he learned about this method , and has made many a copper tape circuit in the last year or so. He offers several nice tips on his site that speak from experience with this method, and he’ll even show you how to easily work an SMD breakout board into the mix. Generally speaking, [Hales] prefers plywood as the substrate to paper or cardboard for durability. He starts by drawing out the circuit and planning where all the tape traces will go and how wide they need to be. Then he lays out copper traces and pads, rubs the tape against the substrate to make it adhere strongly, and reinforces joints and laps w...
Post a Comment
Read more

The Newbie’s Guide To JTAG

Do you even snarf? If not, it might be because you haven’t mastered the basics of JTAG and learned how to dump, or snarf, the firmware of an embedded device. This JTAG primer will get you up to snuff on snarfing, and help you build your reverse engineering skills. Whatever your motivation for diving into reverse engineering devices with microcontrollers, JTAG skills are a must, and [Sergio Prado]’s guide will get you going. He starts with a description and brief history of the Joint Test Action Group interface, from its humble beginnings as a PCB testing standard to the de facto standard for testing, debugging, and flashing firmware onto devices. He covers how to locate the JTAG pads – even when they’ve been purposely obfuscated – including the use of brute-force tools like the JTAGulator . Once you’ve got a connection, his tutorial helps you find the firmware in flash memory and snarf it up to a file for inspection, modification, or whatever else you have planned. We always apprec...
Post a Comment
Read more