Servo - February 2009

FIGURE 14

FIGURE 15

FIGURE 16

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 Figure 14.

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.

The Cradle

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.

The Laptop

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.