Wire the Switch (Optional)
While removing the plug from the battery works pretty
well, you may want to add a switch. Just wire the switch in
series with the positive lead on your plug as shown in
The shaft on the switch I used was not long enough to
protrude through the 1/2" stock I used for the base. To solve
this problem, I used a larger drill bit and created a countersink on the top of the base as shown in Figure 15. There
are other ways you can mount the switch. If you decide to
do something different, I recommend mounting the switch
first. Once mounted, you can run your wires for the best fit.
Build a Stand
The actuators used on the Megabot are extremely
powerful. If the Megabot decides to make a move
unexpectedly while you are working on the program,
something is going to get damaged. A stand is a must.
I made the stand shown in Figure 16 out of some scrap
wood. It is simply two pieces of 3" x 12" wood connected
together with wood screws. It is designed so that the four
outside actuators sit on top of these two pieces. I made
some small notches so that the actuators sit firmly in place
as shown in Figure 17. You can make your stand out of any
material you have on hand. You can even use foam board
or heavy cardboard. The goal of the stand is to keep the
wheels off the ground. If you decide to proceed without
the use of a stand, don't say I didn't warn you.
I have seen many robots — both commercial and
do-it-yourself — that lack one main component:
When using a PC of any kind that has a hard drive,
you have to create some sort of cradle like the one shown
in Figure 18.
The cradle keeps every single bump and bounce from
transferring to the laptop’s internal hard drive. If you don't
build a cradle, be prepared to replace the hard drive the
first time you run the bot into a wall or go over a bump.
The cradle is just four pieces of wood connected
together with wood screws. The cradle is large enough to
give you about 1" clearance to the laptop on all sides. To
actually cradle the laptop, we connect some elastic straps
with some wood screws and washers.
The elastic can be purchased at most department
stores that have a craft or sewing center. For the laptop I
used, only four straps were needed as shown in Figure 19.
The key is to support the laptop without making it too firm.
If you find you need more straps, you can use thinner
elastic. If the laptop wants to bottom out when it’s
bounced, you should add a couple more straps.
Notice that I have cut out a portion of the cradle
with a jig saw. This is done to reduce weight and provide
ventilation for the computer.
Let's talk a little bit about the brain for Megabot.
For most of my medium and large robots, I tend to use
CE (consumer electronics) devices. The reason is that CE
devices are small and are fairly rugged. They are also
reasonably priced. In many cases, they can be purchased
for less than $400 new and less than $200 used. Well, the
times are changing my friends.
There is a new influx of laptops hitting the scene.