Crawler Test Platform

I build a lot of test equipment.  This time I got a request to build a test platform which is mechanized, and moves very slowly.  I've built a few mechanized test platforms, but this is the first one that has synchronous all wheel drive.  Take a look...

The really slow motion is provided by a Worm Gear Motor, which you could think of as a clock motor.  It provides the spinning force which can be less than one revolution per minute.  The Worm Gear Motor that is on the Crawler now is 64 RPM.  I bought a couple more Worm Gear Motors also, 14 RPM, and 24 RPM.  I'm still working on the drive mechanism, and the goal is 0.1 Miles per Hour.  The overall speed has a lot of factors like the weight of the platform, and test equipment, friction through the drive train, the Voltage applied to the Worm Gear Motor, and even the friction of the tires on the surface.  With all of these factors I want the end speed to be 0.1 MPH, or 8.8 feet per minute.

1.5 inch Aluminum angle bracket, and a 5" x 10" piece of 0.625" Aluminum make the frame on the Crawler.  My starting point on this project was a robot platform with tank treads.  The treads were the first idea to get thrown out because they were hard plastic, and would do nothing but slide on a hard surface.  Then the frame of the robot platform was pretty irregular, hard to route the belts, so it got replaced with the Aluminum pieces.  This way all the mechanization is under the Crawler, and we have a large surface area for the test equipment on top.

I used Synchronous Gear Pulleys for the power transfer from the Worm Gear Motor to the wheels.  The Synchronous Gear Pulleys have teeth in them like a gear.  The Gear Belts have matching teeth which make this drive train Synchronous, meaning all four corners move at the same rate.  There is one belt that couples the Worm Gear Motor to the first drive shaft, and a second belt which couples the first drive shaft to the second drive shaft.  The length of the belt is determined by the distance between the shafts, and the outside diameter of the gear pulleys.  Two times the distance between shafts plus the outer circumference of one of the gear pulleys.  In this case the distance between shafts is 5.9 inches, and the pulley outside diameter is 1 inch, so a 15" Gear Belt was the one.

Now that I have built a Synchronous Four Wheel Drive I'll need to apply this to some other things.  For this Crawler Test Platform 0.1 MPH is the goal, but I can see the next one being a little more powerful.  The next step in this process involves Speed Control.  The one factor I have control of we can use to vary the speed of the Crawler is the Voltage applied to the Worm Gear Motor.  This motor can go from 6 to 15 Volts, and move the platform.  Previously I had blogged about using a PIC to do Speed Control using Pulse Width Modulation of a DC Motor.  That same control system will get used here to do speed control on the Crawler.  I'm also looking at using the PIC to get wireless communications to, and telemetry back from the Crawler.  The device we are testing sends data back to a piece of test software running on a computer.  So the crawling part of the Crawler is done, now I need to get to work on the brains...  Brainz!