December 28, 2009, 7:46 pm
My build for the Sparkfun Autonomous Vehicle Competition continues. Slowly. I intended to be busy with system integration by now, but I haven’t even built the physical platform.
Mechanical design is difficult because there are many inter-related factors to consider. For example, the motor selection partially determines weight which in turn partially determines motor selection. And, motor selection determines battery selection which in turn determines weight which influences motor selection. Both motor selection and battery selection affect physical size necessary to hold both components. Never mind the matter of finding components with the desired specifications at a reasonable price …
The easiest solution is to buy an existing robot, like the fancy new Stingray, or repurpose a radio-controlled (RC) vehicle. I’ve elected to build my own because I enjoy DIY, believe I’ll learn more, and need to control costs.
So, here are my requirements for the physical platform:
- Carry the GPS receiver, magnetic compass, MRM micro-controller, motors, motor drivers, LCD, and batteries
- Travel on paved terrain with sufficient clearance for speed bumps and pebbles at least 1/4″ tall
- Have a chance of matching last year’s winning ground time of 1:32
The Society of Robots has an excellent introduction to robot dynamics and discussion of topics like torque, force, velocity, and acceleration. After many hours with this page, pencil and paper, a scale, and a spreadsheet, I’ve decided on the following design.
- Two Polulu Micro-Metal Gear Motors: Last year’s winning ground entry was a retro-fitted RC race car that, by my calculation, must have moved pretty fast. I estimate it moved at an average speed of about 7 mph. Coming anywhere close to this speed is difficult with commonly available gear head DC motors and wheels. A custom gear train is beyond my time, skill, and ambition at the moment. I think the Pololu motors slightly over-volted will give adequate performance with a maximum speed only slightly lower (estimated at 6.8 mph) than last year’s average winning speed. The weight of the robot will have to be low since the torque from these motors is low. I’ll be happy if I can just finish the race, which is a significant challenge by itself.
- Two Model Aircraft Wheels (3.25″ diameter): I wandered around the local hobby store looking for fairly large diameter wheels (to increase speed) made of fairly firm rubber (because the robot is running on pavement). These wheels seemed like the best choice, and I think the Pololu hubs will attach easily.
- Three rectangular decks made from expanded PVC: This material is light, inexpensive, and sturdy. Plus, I already own enough. The robot will grow up via additional decks rather than out due to limited size of the material I own, ease of transporting a small robot to Colorado, and reduced turning radius. Plus, I like the look of multiple decks more than a single large deck. I estimate that I’ll need three decks, each roughly 17cm square with sawed off corners, to hold the parts.
I haven’t solved weather resistance. As is, my robot will have to stay home during inclement weather. Based on photos from last year’s competition, I suspect many builders just hoped for good weather, too. I might consider a plastic housing for the expensive electronics, just in case.
I think I’m ready to make a full size template of the decks and start cutting.
December 24, 2009, 2:49 pm
From KansasFest:
KANSAS CITY, MO — December 22, 2009 — Mark Simonsen, employee number three and later owner of Beagle Bros, will be the keynote speaker at KansasFest 2010. At Beagle Bros, whose popular software products for the Apple II hobbyist demonstrated the publisher’s quirky sense of humor, Mark developed software including Flex Type, Beagle BASIC, Beagle Graphics, Triple-Dump, and Double-Take. In the early 1980s, Mark decided that he “wanted to work with the Apple for the rest of [his] life,” a statement that captures the enthusiasm and spirit of Mark, Beagle Bros, and many Apple II users.
Beagle Bros started in 1980 under the direction of Bert Kersey to provide software to casual users of the Apple II. A year and a half after graduating with a degree in computer science from Brigham Young University, Mark “fell in love with the Apple.” Mark published Flex Type through Beagle Bros in 1982, joined the company as a programmer in 1983, and bought it in 1987 at the age of 29.
Besides software like Shape Mechanic, GPLE, and DOS Boss for budding programmers, Beagle Bros produced books, posters, and even advertisements full of clever and useful tidbits demonstrating the capabilities of the Apple II. Later, the company produced highly regarded productivity software like Platinum Paint, BeagleWrite GS, and the TimeOut line of AppleWorks add-ons. Beagle Bros earned many loyal followers thanks to the combination of quality products, enthusiasm, and humor.
Mark sold the company’s product line in 1991 and 1992 to Quality Computers. Today, Mark helps save memories as the CEO of iPreserve, a company specializing in photo, film, video, and document preservation.
KansasFest 2010, the 21st annual Apple II conference, is set for July 20th through July 25th at Rockhurst University in Kansas City, Missouri. KansasFest was originally hosted by Resource Central and has been brought to you by the KFest Committee since 1995. Any and all Apple II and Macintosh users, fans, and friends are invited to attend this year’s “summer camp for geeks.” Registration details will be announced on the KansasFest Web site in early 2010. Please heed the warning from Beagle Bros and refrain from feeding your disks to alligators. For photos, schedules, and presentations from past year’s events, please visit the event’s official Web site at http://www.kansasfest.org/
CONTACT:
KansasFest 2010
http://www.kansasfest.org/
http://twitter.com/kansasfest/
If you’d like to read more about Beagle Bros and Mark Simonsen, I suggest checking out the following:
And, here are a few slightly less relevant but still relevant references:
December 2, 2009, 9:44 am
I’ve run off and entered the SparkFun Autonomous Vehicle competition in April. The rules are pretty simple:
Create a vehicle that can autonomously navigate around the SparkFun building
Autonomous vehicles (robots!) fascinate me. But, there’s a problem: I don’t have a robot. I have assorted parts and plenty of ideas but no robot. My personal goals include:
- Get the motivation to finally build a robot
- Learn
- Meet like-minded people
- Maybe finish the course
Let’s decompose the rules into smaller, more frightening problems:
- Mechanical: Does the vehicle travel over land or through the air? How? For a ground vehicle, does the vehicle have wheels, tracks, legs, or something else? How does the vehicle steer? What’s the design and construction of the vehicle?
- Sensors: How does the vehicle detect and avoid obstacles, like cars, people, bushes, and lakes? Cameras, IR range finders, sonars, and contact bumpers are leading contenders for sensors. How does the vehicle find its way around the building? Does the vehicle use a GPS, odometry, cameras, or something else?
- Control: Which micro-controller(s) do I use? How do I design the control software? What algorithms and architectures are appropriate?
- Electrical: How do I connect and power all of this?
I’ve decided on a three-wheeled ground vehicle with differential steering. Several competitors last year retrofitted R/C cars or trucks, which is an easy way to get most of the mechanical design and construction done. In the spirit of Do It Yourself and Not Invented Here, I’m building my own platform. I’ve chosen differential steering because there are plenty of examples, websites, and books about this design. Additionally, differential steering permits a very small turning radius. Building Robot Drive Trains and Constructing Robot Bases are great references on mechanical design and construction of small robots.
I’m using the MiniRoboMind micro-controller because I already have one, and it’s a very capable controller (32-bit 68332 at 25 MHz with 512 KB RAM and 512 KB Flash) compared to more popular controllers for small robots.
Like most if not all of last year’s competitors, I’m using a GPS to navigate around the building. The alternatives that I see, like cameras or an IMU, seem more complicated. I may need to supplement the GPS with a magnetic compass and wheel odometry.
I’ll use an IR range finder as the primary method of detecting obstacles. Sonar seems like a better choice with longer range, but a competitor last year had trouble with ground reflections disrupting sonar readings. If time permits, I’ll explore sonars and contact bumpers.
Details on last year’s competitors are scarce. Despite the requirement to document the build, I’ve only found technical details on Deathpod 3000, the winning ground vehicle. RoboMagellan is a similar outdoor autonomous competition devised by the Seattle Robotics Society, and several RoboMagellan competitors have published very useful technical details.
I’m off to fret about motor and wheel selection.