Roko.ca » H-Bridge

A Blast From The Past (Sumo Style) Part I

Roko — Fri, 04 Jun 2010 02:40:53 +0000

It’s been a busy summer (and then winter), involving getting a new job and moving to a new city, so I haven’t had much time to work on my robots much recently, let alone update my blog! So, instead of posting any updates on my robots (those will come later on when I get more work done), I’ve dug up some information on one of my older Sumo Robots, aptly named:

Chomp!

Chomp! in Competition

Chomp! was my first sumo robot, and first robot beyond BEAM robotics. Built in my High School years, it competed for the first time in the 2000 Western Canadian Robot Games, and placed first in the 5kg Autonomous Sumo competition. Although slow and lumbering, this robot had a good (for the time) vision system and protective skirt system that deployed on startup.

The brains of the Sumo was the rustic Basic Stamp II, powering an L298 H-bridge that controlled 4 motors, one per wheel. An aluminum frame held the robot together, and a custom made decals gave the robot a nice fierce personality

Back before the days of commonly available Sharp IR Rangefinders, I used a solution involving Modulated IR sensors (40 kHz) and modulated IR LEDs. By toggling the LEDs on or off, from a single sensor I could determine if the robot was to the left, right or front of me. A far cry from ‘1.21 GW‘, my current mini sumo, but it worked, and helped get the robot first place!

Chomp! preparing for Battle, before deploying protective skirts

Chomp! went on to compete in the 200 WCRG for the next year or two, but other robots rapidly improved over the years, and Chomp! became too slow and the protective flaps too weak for stronger robots.

Chomp! actually had a sister (brother?) robot, named “Fatal Discharge”, which never ended up working right. Unfortunately, this was before I figured out enough about motor controllers to know that the L298 wasn’t quite up to the task.

After Chomp!, I went on to build “Event Horizon”, which was a moderately successful robot, and one of the first in Canada to have a vacuum system for increased traction. But more on that later…..

Quadrupeds Need a Whole Lot of Motor Controllers

Roko — Fri, 05 Jun 2009 04:35:02 +0000

Blank PCBs

It’s

Motor Controller in the Leg

been a while since my last update on the Quadruped’s build progress, but I finally got my PCBs back for the motor controllers. Since the robot has twelve motors, I need six motor controllers in total (Each of my controllers controls two motors). They’re an updated version of the h-bridge I prototyped last fall, and used in my mini sumo robot. Although definately more than is really required, the motor controllers boast ultra-low RDSon Direct FETs, and HC9S12C32 micro-controller to handle the control and monitoring of the h-bridges. The black soldermask really enhances the look of the PCBs mounted in the robot.

Each leg has it’s own motor controller to manage the two motors in each leg, and another two motor controllers will manage the four motors in the core. The leg motor controllers are shaped specifically to fit within the frame on one side. The other side of the upper leg frame will hold another PCB with some sensors (I’m planning on e-field and/or pressure sensors in the robot’s feet and on the leg itself.)

Motor Controller and Angle Sensing Boards

Each

Programming Adapter

joint requires angular feedback for the motor controller’s closed loop system. This is accomplished by using special potentiometers through which the joint shaft will pass. The potentiometer is wired as a simple voltage divider, and as the angle of the shaft changes, the potentiometer will give a different voltage output. This voltage will in turn be read by the motor controller and turned into useful data. The special potentiometers used here were a bit of an obscure find, but luckily they are a stock item at Digikey.

In order to ease the routing of all the connections on a 2 layer PCB, I decided to offload the large BDM header onto a separate board, which can be screwed onto the leg frame when I load the motor controller firmware. Several pogo pins then make the programming connections to the test points on the controller PCB. I decided to get creative with the shape, and it turned out pretty neat.

I’m toying with the idea of putting a customized boot loader in the 9s12 controller, and giving the main processor (the Gumstix) programming control over all motor drivers. This way, instead of individually updating firmware on the motor controllers as I continue development down the road, I can instead just load one hex file into the Gumstix’ file system, and it will automatically update the firmware on all six motor controllers.

LiPo Batteries

I also recently ordered the batteries I will be using to power the robot, 4x 2000 mAh LiPo batteries. I will be running then in a 2-series 2-parallel configuration to get 4000 mAh at 7.2 volts to run the entire robot. I still need to design and build a board that will fit underneath the batteries in the core of the robot, which will be responsible for battery protection/charging as well as power and control signal distribution to the four legs.

Still a lot of work to go, but it’s getting closer to walking…

Mini Sumo PCBs…

Roko — Tue, 28 Apr 2009 17:57:49 +0000

Bare PCBs

After

Fitting the PCB in the body...

a rushed PCB design marathon, I got my PCBs in last week, built by the good folks at APCircuits. The stencil came in shortly after. Since I made the PCBs into a panel, I had to cut them appart and file down the edges so that it would fit in the chassis. Overall the PCBs turned out nicely. I built them up and can sucessfully load code into the LPC2138. (No pictures of the completed circuit board yet). Things are comming togethor nicely.

You’ll also notice on the silk screen that I have given this robot a more creative name than Mini Sumo Version 6. I now call it “1.21Gw,” pronounced, of course, much as Doc Brown pronounced it in the timeless classic (no pun intended) “Back to the Future”

Now to finish it up and write some basic code for the robot games this weekend.

H-Bridge Fundamentals

Roko — Fri, 12 Dec 2008 04:07:20 +0000

An introduction into basic H-Bridge theory and operation, this article covers the fundamentals you need to know to make a working H-Brigde with N and P Channel MOSFETs

Obligatory Introduction

Since I began building sumo robots in late 1999, I’ve been wrestling (no pun intended) with motor drivers. At first I used single chip solutions like the L298 in “Chomp” which worked well most of the time, with only the occasional burnout. What most of you who know me and my robots probably don’t know is that Chomp had a twin named “Fatal Discharge”. It was built with almost the same design, with the main difference being the motors. On this robot, the L298 worked occasionally, burning out most of the time. It just wasn’t adequate for the motors, and at the time I didn’t have enough electronics knowledge to make it work. As such, Fatal Discharge never made it to competition.

Since then, I’ve built more robots, and have gained much more experience making motor controllers. This document is meant to provide some vital information on making a “bullet proof” motor driver, based upon my experiences and research into the field.

:::DISCLAIMER:::

I in no way guarantee that I haven’t made any mistakes, and I am not liable for any damage that may be caused by using circuits discussed in this page. If you spot any errors, please let me know.

Be careful when dealing with large batteries and H-Bridges. They require care in design and construction, and carelessness can lead to components overheating, and catching on fire.

If you have any questions of concerns, feel free to ask.

So Why Make My Own Motor Driver?

It’s a commonly known fact to roboticists why motor drivers are needed. 99.99% of the time, the micro controller or control circuitry of a robot just can’t provide the current needed to power motors. For motors with small current draw, single chip solutions such as the L293 or L298 can be used, however these are only useful for a range of less than one or two amps.

In the world of 3kg (and the now obsolete 5kg) autonomous sumo, having motors that can output high power is necessary, especially when vacuum systems are used. These motors are driven in extreme conditions, requiring abrupt speed and direction changes, as well as being subject to high loads. When driving motors under these conditions, an L298 will work only for very efficient motors in the lower power ranges, but these super efficient motors are not always easy to find when you are on a budget. Some motors produce plenty of output power, but can also be very inefficient, thereby causing many problems with associated control circuitry, and a simple single chip solution will no longer cut it.

For my 3kg robot “Event Horizon”, I made the switch from pre-made motor drivers to rolling my own mosfet h-bridges. There are plenty of designs out there, and I went for simplicity using P-channel mosfets for the high side of the bridge, and N-channel mosfets for the low side of the bridge.

H-Bridge designs using only N-channel devices are out of the scope of this article, although many of the concepts discussed in this article still hold valid. Eventually, I may make another page regarding the design of h-bridges using N-channel devices only.