You can see Ken Gracey's absolutely beautiful CNC'ed wooden robotic platform at http://forums.parallax.com/showthread.php?p=869245·
I'm here to show the other end of the homebrew spectrum,·
the "poor cousin" robot I cobbled together with just a Harbor Freight bandsaw and drill press! The only thing·
have in common is wood, but I'm excited at the possibilities of my inexpensive platform.
simply an overgrown Boe-Bot right now, but·
having a larger, heavier·
platform with large wheels means it can really move repeatably through a house and is significantly less affected by carpeting, bumps,·
and other real-world·
factors. I am working·
towards getting this robot to navigate from room to room with encoders and some IR beacons. The photos tell the tale and show the simplicity of my design. My lightweight wooden platform is·
x 18" L. It is 1/4" plywood cross-braced with 1x3's for rigidity, and my·
gearmotors are firmly held in place by an aluminum 'L' extrusion from Home Depot.
No surprises in the battery department: two big dumb SLA gel cells! One large 12V powers everything, and a smaller 6V gets switched in for speed control. A funky combination, but it yields great results. Most of the robot's total weight is in those batteries. I could use lighter batteries, but these are cheap and provide·
the traction I need.
I posted previously about these $10 gear motors at http://forums.parallax.com/showthread.php?p=853015·
. They are rated at 24V, but I am only running them at 18V for full speed or 12V low speed.·
My goal was·
make a fast robot, but ultimately an accurate one. I·
this robot to carry some cargo safely and reliably from room to room.
My "motor controller" is·
a 5-state H-bridge made of six TF2-5V DIP DPDT relays. The relay coils each draw only 17 mA so I drive them directly from·
six BS2E pins, no transistor switch required. I parallel the·
relay contacts to get 2A switching capacity; motor stall current is less than one amp on these high-voltage motors. Three relays per motor give forward/reverse, high/low, and coast/brake. Nothing too sophisticated, but it works surprisingly well. Besides offering crude "ramping" to avoid·
wheelslip on acceleration, high/low and coast/brake will be used effectively in the future for wheel odometry, dead reckoning, wall following, and IR·
Wheel encoder electronics are coming next, you can see the encoder disks on the wheels already. Additionally, I have a variety of IR sensors to calibrate and mount for remote control, distance measuring, collision avoidance, and wall-following.
simple rectangular shape of my chassis may get a bit more streamlined, but it will·
not end up completely circular. Circular is great for getting out of an accidental jam, but my plan is to know where I am at all times and use the corners of the robot to verify position. I'll·
radius the front of the robot, and maybe taper the sides a bit, but the back will stay·
nice and square for 2-corner wall contact.
The platform drives very straight and displays good·
repeatably even without any encoders or sensors. I have programmed in a variety of oval, square·
and figure-8 driving patterns to test the unit and it is encouraging to see how well it works. More as it develops. I'll make predictably slower progress after returning to work next week, but the show·
will go on!
3/5/10 Title Edit (AKA Retrobot) for ROBOT magazine article reference·
·"If you build it, they will come."
Post Edited (erco) : 3/5/2010 7:29:13 PM GMT