What is PWM, and how does it work to control a motor or any other output?
PWM stands for Pulse Width Modulation and allows you to easily control an output in a digital system. Some things that you can control with it might be the speed of a DC motor, or the brightness of a light source. You can even use it to control the speed & direction of a constant rotation servo to drive a robot very simply.
Here’s a great video that explains how it works:
Watch the video above and see if you can answer the following questions:
Pulse Width Modulation (PWM) is a digital signal. What is a digital signal?
(0:57) What is the resistor for in the circuit he builds at about 0:57 of the video?
(1:30) Why is the wave’s shape square?
(1:40) What does a PWM signal have to do with the binary number system?
Define duty cycle.
(2:30) Explain how duty cycle has an affect on the average output of a PWM System
(2:45) Explain why you cannot see the light or the motor pulse in a PWM system.
(3:13) The circuit shown at 3:13 is used to generate a PWM signal. What kind of IC chip is used to build it?
(3:32) Why can’t we just use a Potentiometer to vary the voltage? What might happen?
(4:00) When using PWM to control a servo, what are the limits of the widths of the ON pulses?
(4:40) He uses a potentiometer in the circuit. What is it used to control?
(5:00) List the steps of the design process he used to build his circuit.
(5:15) What is the transistor used for in this circuit?
(8:40) What type of microcontroller was used to do the same thing?
Can you answer this question and label the signal?
We did it! We made a dobot magician talk to another one and make it start. We even added a VEX switch as an input to start the first one. It is easy to do, but one word of caution:
Never connect or disconnect any wires to the dobot while it is powered on; always power it down first. Damage may result!
Ok, now on to the good stuff. If you bought your dobot through InPosition HERE, not only did you get a $100 discount, you get access to the documentation to make this happen for free! just email us! This includes worksheets and wiring diagrams.
Tony Koppers, my senior EDD student has done all of the legwork to make this happen, so special thanks to him!
So you have new Lynxmotion robots for your classroom, so now you have to build and wire them. I’ve put together 4 videos to help you assemble and wire them. This is not meant to replace the manual, but rather to supplement it. You can find the manual here: PLTW-AL5D-Guide-11. Lots of new stuff in the manual too, especially about how servos work.
How do you center the servos when you build your lynxmotion AL5D?
Best way is to NOT turn the servos; like that’ll happen! There is a whole section in the new manual that can help you teach how servos work, so check the manual too! You can find it here: PLTW-AL5D-Guide-11. One way is to do it with a special tool called a servo driver. You can buy these on line, or at your local hobby shop. RobotShop used to carry it, but I do not see it there any more. See the video below on how to use one.
My new Lynxmotion AL5D robot arm from RobotShop came with a new servo called a Feetech. How come my arm works backwards now?
Well…. because the servo may be installed backwards. I know, you looked at the picture on the directions, but the first one may be wrong. When they switched servos, from the HiTecHS-805BB to the FeeTech FS6535M, there was one little hitch…. the Feetech runs OPPOSITE the Hitec. Because of this, the shoulder servo needs to be installed backwards. Once you get the directions, ignore the first picture and follow the directions. They can be found HERE. Want to buy a robot? Buy one HERE.
How do you fix a wrist rotate servo with stripped gears? It’s a pain in the butt as well as costly to replace.
See the steps below for an inexpensive and simple solution! Note that te metal gears cost almost as much as the servo; it takes 5-10 minutes to change the gears, and a lot longer to change the whole servo! You choose.
If you purchased your Lynxmotion robotic arm before 2011, chances are you got a batch of glitchy shoulder servos. HiTech€™s, the servo company, solution to fixing them was to discontinue them. This left Lynxmotion with only one choice: change the servos. To do this, the brackets had to change as well. Also, this upgrade makes the arm much stronger and smoother, and I believe they will last a lot longer as well.
So, if you want a stronger, smoother robotic arm, and you have some money in your budget, follow the steps bellow to an upgrade! The products below come in packs of two, so for about $110.00 each, they€™ll be good for many more years.
How do I make sure my servos are centered before I build my robot? How can I test my servos once it is built? Answer:
The I.L.A.R. (It Looks About Right) method works ok, but if you want to be precise, you need a servo driver. This video shows you how to use one to test your servos. One of the best ways to spend $25! You can buy one HERE.