NXT Zoo Part Substitutions

If you don’t have the exact parts used in these NXT robots, you may still be able to build many if not all of these robots using other parts you may have available.
Before we get into specific robots, let’s look at part substitution in general.

CAMEL FOOT Contest results can be found here.

Connections

Because the beams in LEGO MINDSTORMS NXT are studless, it is sometimes a challenge to change direction and connect pieces at right angles. The connectors shown in figures 1 and 2 were introduced with the NXT and often provide the easiest and most secure connections between parts.
Technic Beam 3 x 3 Bent with Pins, otherwise known as a Hassenpin. This pin is so versatile that it’s easy to fall into the trap of depending on it to fix most building problems---and that can lead to a poor design.

Technic Axle Joiner Perpendicular 3L with 4 Pins

If you're short on connectors, or simply want to reduce the number that you are using, you may be able to replace the four-pin connector (Figure 2 above) with a 3-hole beam and two long Technic pins, as shown in here.

The next example shows another common substitution. The first example is the connection used in some of my robots. The second example shows the connection if we were to use the same size of beam (9-hole) with a different connector. The third example shows how you can maintain the original height when you substitute this connector by using a beam with two more holes---in this case, an 11-hole beam.

Be Cautious With Pin Substitutions

There are very few yellow axle pins or gray TECHNIC pins in the base kits but there are no substitutes for them if you want your robots to move correctly. These axle pins come in blue or yellow. The blue pins are used when you want to hold a connection fast. They are described as “with friction”. The yellow axles pins are used when the joint must move, as when it is connected to a gear.

The short TECHNIC pins come in black or gray. The black pins are used when you want to hold a connection fast (with friction). The gray pins are used when you want to connection to rotate freely.

These long connector pins, like the short pins, come in black

Bushings

In many instances, regular bushings and half bushings can be substituted for each other.

Axles

I’ve found the #7 axle to be the best choice for many of my designs, but only the retail base kit contains any size 7 axles. Luckily, you can often substitute smaller or larger axles.

When you use #6 axles to replace the #7 axles, as show in the ‘Gator here, the motors will still move the gears correctly.

Axles are a convenient way to connect many pieces together. Below on the left, we've used axles to connect the beams on the alligator head. At the right you can see how we've used a #3 axle plus an arrangement of pins in the ‘Gator head also works well. In the image below, I’ve made the pins apparent so you can see how I have arranged them. (Note: The eyes are blue axle pins with bushings.)

Beams

Beams are among the easiest parts to substitute. Sometimes a longer beam will work on a model, even if it protrudes. Just make sure it doesn’t interfere with the robot’s action. The two bent beams shown below are commonly substituted for each other. The 3 x 5 L-shaped Beams (shown on the left) can sometimes be replaced with 2 x 4 L-shaped Beams (shown on the right).

When you build legs, you are making multiple copies of the same assembly, which means that the parts you use for legs are often the parts you’ll lack in sufficient quantities. This alone is a good argument for buying extra parts, such as the 3 x 5 L-shaped Beams, which I’ve found very helpful in creating feet and other design solutions for my robots.

Center of Gravity

If you decide to design your own legs and/or feet for a robot, keep the general size and shape in mind. Also, pay attention to your robot's center of gravity. Ignore the center of gravity and your legs are likely to splay outward and pull apart when your robot starts moving. You will notice that the feet on my robots extend further under the robot than away from the robot. It’s giving a nod to the center of gravity.

Here are some possible substitutions you might use on specific models:

Camel

Note: Half bushings can substitute for regular bushings, but use the larger bushings to attach the tire feet to the camel legs (those parts directly on top of and under the wheels), since you need the stability larger bushings offer.

Alligator

The back legs of the ‘Gator are particularly easy to replace, as they don’t actually walk. (They just look like they do.)
The tail is another place where you can be creative without affecting the function of the robot. Note: The tail offers some of the support for the alligator, so make sure any alternate design is sturdy enough to do that.

Stegosaurus

While I think the legs are just right on this robot, it’s possible you might have an equally good idea for constructing similar feet with the parts you have. Just don’t make the feet too big.

The beams that make up the backbone of the dinosaur (and which hold the armor plates) could be assembled out of different sizes of beams. It just takes a bit of experimentation.

Peacock

Different pieces can be used for the box that makes up the base of the peacock (shown below). Just make sure to leave the same spaces and pin holes needed for part connections.

The wings are another place you can substitute. For example, use smaller beams with long craft feathers, or connect multiple smaller beams , as shown below:

Elephant

There are many ways you can create feet. But, remember, the legs all need to be the same and be positioned primarily under the body. It is possible for you to change the size of the leg beams, but be aware that the longer the legs get, the less stable your elephant will be.

Skunk

Spider

I cannot come up with an acceptable substitute for these 3 x 5 L-shaped with Quarter Ellipse beams used in the spider. My best alternative designs caused the spider to walk in circles. You may have a part from other LEGO kits that would successfully substitute.