Deirdre MettleBocks

The following is a pictorial diary of the construction of Deirdre. The main goals behind her construction were:


1. Robustness. I was tired of the dogs stepping on my robots and crunching them.

2. Larger size – I wanted to be able to add lots of things to Deirdre without fighting for real estate.

3. Significant payload. She is designed to carry more than 80 pounds.

4. Extended cruise time – she is designed to carry a laptop around for more than two hours without recharge.

5. Reasonable size so she could negotiate the house – she is 12” square – a compromise



Basic Construction 


Deirdre’s Motors Are Strong For a 12 inch ‘Bot

She uses recliner chair worm drive motors from Diverse Electronics. They suck about ˝ amp with no load and about 8 amps at stall. They have 354 inch pounds of torque and are driven by a 24 volt 7.5 amp hour gel cell pack (two 12 volt cells in series). With a 70-pound load, she could just about lift herself straight up with one wheel. A hub, machined from brass, fits the motors to 6" lawn mower wheels.

Deirdre’s Frame is Steel and Aluminum Angle Iron

 You can see the hub inside the wheels and the pin that fixes the hub/wheels to the motor (on the left picture). The main batteries fit on the shelf behind the wheels and under the main frame (right picture).

Deirdre’s First Layer (Motor Control)

Her motors are driven by two 30 Amp motor controllers from Diverse Electronics

Motor Controller Layer From Behind

The battery in the above picture is a 1500 mAH 12 volt for the electronics. The controllers are interfaced to a 16F873 and the PIC controls forward, reverse, turn, stop, shutdown, and drives the motor controllers with a PWM signal. The PIC is controlled serially by a Master controller – which can be nearly any RS232 serial connection.

Sensor layer (to be filled in!).

The terminal posts on the back are the charging posts for the batteries.

Deirdre’s motor base ready for initial testing.

Temporarily, she has a homebrew stamp in her sensor box. It just sends serial commands to the motor controller to make Deirdre do a square and spin around. This is the second set of tests – the first set had some warts so I completely disassembled her and tuned up things (trimmed metal, restrung wires, replaced the tail wheel, painted, squared the main wheels up a tad, reworked the lower battery box, etc.)

First Test Drive

300K-15 second mpeg of Deirdre’s base doing two turns.  Her sound is a nice low hum. She is traveling at about 2/3 rds throttle. No wireless commands yet.




Above is the Top Level Diagram (TLD) for Deirdre. Since the onboard world is happening real time and the network world (especially if it is the web) can have significant delays, Deirdre must follow the First Rule of Household Robots: "Do no harm." - or was that the First Rule of Medicine???  Anyway, Deirdre's loyalty is to her onboard Master Controller whose job is to keep her from screwing up. 

Communication with Deirdre is through wireless Ethernet cards (Addtron) using TCP/IP. The software right now is VB6 although an early version was tested with Java. The reason for going to VB was to get the ease of programming sockets AND serial communications at the same time. The onboard Ethernet system is controlled by a laptop that takes commands from the mother machine using TCP port addressing. The onboard machine then converts those commands to serial commands and relays them to the Master Controller.

Second Test Drive

Windows Media File of Deirdre's First Drive on Ethernet (1.6 meg requires Windows Media Player 7)