| Project MiniBot | 1999 |
| [ Homepage ][ Send me mail ] | © Kam Leang |
The Minibots are a family of small autonomous mobile robots designed and built for a microcontroller design class project. Walter Barnum and I worked together on the project, which lasted for two quarters. Some of the main features of the Minibots are: multiple sensors, RF communication system, and small size. The objective of the project was to design and build a group of small autonomous robots that could be used for multiagent control applications, study of social behavior in mobile robots, and the analysis of decentralized systems. We managed to build about nine of these guys; I built six and Wally built three. It was impressive to see these little guys running around, but unfortunately, we didn't get much of a chance to use them for multi-agent research purposes. I've had a lot of request for more information about the Minibots, but unfortunately for now, this is all the available documentation. I'll see about scanning in the original report that Wally and I wrote for this project and post it up, but it might take some time, so please be patient. Enjoy what information I have about them.
MCU
For each Minibot, we used the Marvin
Green Botboard as the controller. The Botboard was perfect because
of its small size and simplicity. The Botboard was configured in
"Special Bootstrap Mode" with the addition of extra electronic support
circuitry such as 2 voltage regulator chips (LM7805 and LM787L05) and a
few LEDs as indicators. Each Minibot ran off of two power supplies,
one for the HC11 and the other for the motors. In addition, the motor
power supply also powered the commuication system, sonar senors, IR light
sensors, etc. We used the "E2" version of the HC11 because
of the 2Kbytes of EEPROM.
Sensors
Wally and I tried to stuff as many sensors as we could
on each Minibot. Ultimately, we managed to put a total of 6 sensors
on each Minibot: 3 IR light detectors, 2 touch sensors and homemade sonar
sensors. Putting sensors on the Minibots was a challenge, considering
their size (4"x2"). We built individual senor boards that could be
"plugged" into the robots using a standard bus and connector system.
Therefore, sensor modules between each Minibot were interchangeable.
Each Minibot was able to comunicate to either a host computer or to another Minibot via an onboard RF communication system. The RF transmitter/receiver boards were simple and inexpensive 300Mhz RF units available from Ming Microdevices. Digikey sells both the transmitter and receiver for about $11 each. Each Minibot was able to communicate up to a range of 75 feet at 1200 bps! The Minibots used their ability to communicate to talk to each other while performing a task or to receive commands from a host computer. The RF units were quite small and were easily mounted on the robots.
Locomotion
Locomotion was made possible by two standard servo motors
purchased from Tower
Hobbies. We bought the cheapest servos they had to keep the costs
down for each robot. The servos were modified to rotate continuously.
The motors were arranged in a differential drive configuration and a small
rubber O-ring connected two sets of wheels together on each side.
Basically, they moved around with a "tank-like" motion, but without treads.
Body
The body of each Minibot was machined out of high density
polyethyelene (HDPE). HDPE was used because (a) it was easy to machine.
Have you ever tried to take a 0.5" depth of cut using an endmill through
aluminum? An endmill can handle a 0.5" depth of cut through HDPE
with ease! (b) It was the only thing that was free--it was a byproduct
from a previous design project!! The figure below shows a picture
of the body of each Minibot. Two pockets were machined out to fit
the two servo motors. This way, the motors simply snapped into the
plastic bodies without the use of any fixtures such as screws, glue, etc.
To hold the motors in place, we simply used a thin rectangular piece of
aluminum that was bolted to the top opening of the frame. All electronic
circuitry was attached to the top of the aluminum plate. At the front
of each robot was a plastic mount that held the sonar transducers, one
for the transmitter and the other for the receiver. Each Minibot
looked like it had "eyes". A 9-Volt battery clip was attached
to the rear of each robot to hold its power supply.
Some of the behaviors we got the Minibots to display included: maneuvering through a forest of COKE cans using sonar, taking commands from a host computer telling them where to go, telling each other when and where to go, finding IR light source, avoding obstacles with sonar and touch sensors, etc. Overall, the Minibots were fun to watch.
