Servo - June 2010

junk, is another man’s ... robot.” You’re also going to need a servo for the hand. The servo doesn’t have to be a powerhouse; it just needs at least 45 oz/in of torque, which is what I’m using. Currently, it is the TS- 53 standard servo from Tower Hobbies.

Besides being a robot fanatic, I’m also hot glue junkie. I use it for everything ... well, almost everything. I live in the northern part of the US where the temperatures are not that hot all the time, so using hot glue for keeping things together is not an issue. For those of you who live in warmer regions, you might want to use either a high temperature hot glue stick or go with epoxy. When it gets too hot — say around 90 degrees — the glue will get soft and eventually cause your creation to fall apart. I’ll show you a little technique I do to keep things together a little longer, in a moment. A nut and bolt alternative is more durable, but using this method can add extra weight to your humanoid.

Finger Food

FIGURE 3.

I call this section finger food because this is where your cutting skills will be used. Extreme care must be taken here. Let’s begin work on one hand. In Figure 2, I’m cutting the tubing into 30 mm lengths. I usually work in millimeters for simplicity and accuracy’s sake. Three fingers and a thumb should be enough for grabbing things, so you need to cut four pieces. If you decide to make the fingers longer or go with an extra finger, it will be harder for the servo to pull the extra resistance — so get a stronger servo to do this. I’ve found that too long of a finger looks creepy and adding an extra finger is really unnecessary.

Next, we need to cut “v” notches in the tubing. Like human fingers, there are three joints per finger which means we need to pain-stakingly cut three notches into each tube finger. Please be careful! Take your time with this part. Make sure that you cut the v notch pretty wide, in fact, the wider the better. A wider notch makes it easier for the finger to bend. Also, make sure that your cut goes all the way to the bottom of the tube.

You’re probably wondering why we even need the notches. The notches give the finger a “direction” to move. If you do not cut these, your finger will just bend willy-nilly in any direction. There is also much more resistance to make the finger bend. Another thing to keep in mind is to make sure your notches are in line with one another. Otherwise, your finger is going to bend in different directions (Figure 3). It’s easy to misalign the cuts when you’re working with something so small, so take your time.