Robot 1: “Little Jimmy” based on PICAXE-18M2




Robot 1: “Little Jimmy” based on PICAXE-18M2

I wanted to build this little robot to give me a fun and flexible platform for learning more about programming, RC (radio-control), drive trains (the mechanics that make it go) and the newest PICAXE processor, the 18M2. Under a modest budget, I sought to salvage materials and build as much as I could rather than purchase a kit. Since I live in an apartment, my available tools were also limited to some basic hand tools: drill, hacksaw, files, etc. This will be a remote-controlled tele-presence once I purchase a wireless video camera from E-Bay and mount it on the pan and tilt servo: otherwise, the robot is complete. ‘Little Jimmy’ has entertained my wife and neighbors with his nimble agility. Most of all, this project taught me a lot and earned a sense of genuine pride and accomplishment. Though the robot is RC controlled, it can just as easily become fully autonomous by reprogramming its PIC ‘brain’.

Some basic specs:

1 Size 10x10x9.5 inches
2 Weight 9.5 lbs (half the weight is in the battery, you could use a smaller one)
3 Weight Class Hobby Weight <=12lbs
4 Speed 0.45 MPH
5 Speed 0.67 FPS
6 Wheel Rotation 53 RPM
7 Battery Dimensions 4×3.5×2.75 inches
8 Battery Weight 4.5 lbs
9 Battery Gel Cell 12 V, 5Ah
10 RC System 2.4 Ghz
11 Current Draw F or R 0.5 A
12 Current Draw rotate 1.2 A
13 Estimated run time 6 h

Robot

Attach Motors to Wheels

I lucked out in obtaining 4 surplus gear-head motors that rotate at about 53RPM at 12V, 120mA each at no cost; you would expect to pay $15-$25 a piece for equivalent units. These have a 1/4″ D-shaft.

Attaching wheels to motors is not as trivial as you might think. The key piece of hardware is called a wheel hub adapter, and I found a good selection at ServoCity [Link] . They also manufactured ABS wheels and motor mounts I used. (Parts list is at the end of this article).
The wheel hub adapter attaches to the motor shaft via a set screw, and the wheel is secured to the hub with 4 socket-head cap screws.

Motor Mount to Aluminum Frame

From the ‘Big-Box’ Builder Supply I purchased aluminum angle 1″X1″x48″. It is inexpensive, light-weight and easy to drill. The aluminum frame will add strength to the press-board panels  used for the robot as well as provide a means of securing the shaft-end of the motors in place. First, I drilled a hold slightly larger than the motor shaft (@5/16″), then I made a paper template of the 3 motor mounting holes using rice paper from some Chinese Take-out I was eating. A nail set and a hammer banged little dings to make the locations for the 3 holes for each motor, which were then drilled out for the tiny metric screws (2mm) needed. Getting those holes right was the hardest part of the job (it would have been easier with a drill press). For the holes that I did not get quite right, I simply had to drill them out a little more.

Robot Undercarriage

With the 4 motors duly mounted on 2 aluminum rails, both assemblies were bolted to an 8″x10″ piece of press board (1/8″ thick).

Robot Undercarriage

Battery Box

Using 1/2″ thick craft wood I built a frame around a salvaged gel cell battery I had. The frame was extended to also support the top panel and to provide mounting surface for circuit boards to be added later.

Battery Box on Base

Using wood glue and wood screws, the battery box is mounted to the robot’s base.

 

For more detail: Robot 1: “Little Jimmy” based on PICAXE-18M2




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