Progress update December 16, 2006:

As you can see from these two images I have made great strides in building the mobile base.

Today I:

• Mounted the two lower decks where the casters mount
• Mounted the casters
• Machined some standoffs from acrylic rod (see the second image)
• Attached the motor mount assemblies with angle brackets (very stiff and perpendicular)
• Made a mount for the sonar (using 3mm PVC)
• Redid the sonar cabling (using 22ga stranded versus the solid, and following my wiring standard layout)
• Mounted the sonar

From the front:

Note: the front lower deck will also be the mount point for the line following sensors. You can see two of the angle brackets I'm using to shore up the motor mounts. At this time the bot weighs just over 2 pounds ... largely due tot he motors and encoders.

From the rear:

Note: I used the acrylic rod because I have 20 feet of it that a friend gave to me. I am considering lighting it with LEDs … but that's for a later time. This deck with also hold the Lipo pack.

To do:
It might help if I actually kept up with my todo lists but I use them as a brainstorm tool and right now my mind is racing with ideas.

1. Resolder the motor controller circuit
2. Rewire the encoders with longer leads using my wiring standard (which is to say the same as a servo lead) | GND | 5V | SIG1 | SIG2 …
3. Get this bot mobile with some simple code to count encoder pulses and drive a square
4. Add in PID to start using waypoints and let the "algorithm" decide how to get from A to B

Onwards,
Jay

December 11, 2006 progress,

I was on a roll this weekend and have some photos of my progress to share.

This first photos shows how I printed templates for my motor mounts. I first cut the mounts to their final width and height, glued them together with wood glue (tried spay adhesive first but it was too messy), glued the template on, marked the holes with a center punch, and drilled the mounting and clearance holes on my drill press. The photo below is my first design. Taking a page from my RC airplane days of constructing planes from foam, I added tabs and slots.

Note: I originally drilled the holes the same for both side, but due to the motor shaft being offset it was not symmetric like the encoders. Also, the mounting hole closest to the output shaft is too shallow for the screws I had. What is, was symmetric are the two mounting holes at 180 degrees which is what I am using.



The second image shows the motor and encoder mounted along with the gears and wheel. The motors are heavy and the assembly feels like it weighs half a pound or more (will measure it and update this post).



To add the mounts again I when with a tab-slot design. I printed a template for the base to locate the slots and used a razor knife to cut them out. I also had to make slots for the small portion of wheel that protrudes through the base.



Next steps are to:

• Strengthen and square the mounts using l-brackets and a cross bar of some sort. I have some acrylic rod I am going to try. Failing that, I’ll add a skin of 3mm PVC along the bottom to tie them together.
• I have decided to redo my motor controller board using the ribbon cable wires versus wire wrap. The insulation is better, and I had an issue with intermittent shorts when I tested it before.
• Create the cables for the encoders to the interface board
• Make some mounts for the caster wheels (it’s really back heavy right now so 1 may be enough)
• Write some code to drive in a square

Onward,
Jay

December 4, 2006 update:

Well, I received the gears and wheels that I ordered. The wheels from www.budgetrobotics.com are great.

I used to be fairly proficient with my Taig microlathe, but not Sunday. The gears are bored for .25” (1/4”) but the shaft diameter on the motors is .234”. I decide to make an adapter that would fit better on the shaft and integrate with the wheels and gears. I tried to use some Fortal aluminum, but it wasn’t cutting as well as I had remembered. It took my quite an effort to hacksaw a chunk to chuck in the lathe, and then it kept bogging down on anything but light cuts. It would have taken a day for one adapter to whittle 1.5” down to .375”. So I switched to nylon. All told it took 5 hours to crank out one adapter.

The good news is it works great; the bad news is I have 1 more to make. I’ll post a photo tonight.


Onwards,
Jay