NXT Puppy

Fun Projects for your LEGO^® MINDSTORMS^® NXT!

Puppy

Building:
Program:

Building Instructions

Note: The two size 4 axles in this step would really be better as size 5 axles, but all the rest of the size 5 axles from the standard NXT kit are used elsewhere in this project. If you have any extras, you could use size 5 axles instead.

Important: Make sure that the wire from port 4 ends up coming out under the body as shown below:

The motor will attach to the body with 3 pegs on this side,...

...and 2 pegs on this side,...

...then you will need to work a bit to get the last peg in the 7-hole beam brace as shown below:

Make sure that the axles are centered on the wheels as shown below.

Attach the other side of the two sensor wires as follows:

Sound Sensor	Port 2
Ultrasonic Sensor	Port 4

Important: Make sure that the sensor wires go on the left side of the puppy's neck as shown below.

Attach the three motor wires and route them under the puppy as shown below:

1.	Neck Motor	Shortest wire (20 cm)	Port A
2.	Left Leg Motor	Medium length (35 cm) wire	Port B
3.	Right Leg Motor	Medium length (35 cm) wire	Port C

Important: Make sure that all five wires go on the left side of the puppy's neck as shown below.

Puppy Programming

Two programs are provided for your puppy. With the Puppy Leash program, you can walk your puppy with its leash and control when it stops and which way it turns by pressing the touch sensor on the leash. See the instructions below. With the Puppy program, the puppy will explore around your room by itself, trying to avoid walls and listening for your voice to call it. See the instructions below.

Important Instructions


Use on smooth hard floors.	Do not use on carpet.	Make sure the head starts out pointing straight ahead

How to Walk your Puppy with the Leash

When using the Puppy Leash program, the ultrasonic and sound sensors in the puppy's head are not used, but you can control the puppy with the touch sensor on the leash.

Connect the leash wire to port 3
Make sure the head starts out pointing straight ahead.
Run the Puppy Leash program.
Press the touch sensor to make the puppy stop.
After stopping, the puppy will turn its head to look left and then right.
To make the puppy turn, press the touch sensor when the puppy is looking in the direction that you want it to turn.

How to Control your Puppy without the Leash

Can you really control a puppy that is not on a leash? Well, with this puppy you will have some limited control... When you use the Puppy program, the puppy will start to explore around your room, trying to avoid walls and other obstacles using its ultrasonic sensor. But you can also get it to turn the way you want by calling out to it, and it will (hopefully) hear you with its sound sensor.

Make sure the head starts out pointing straight ahead.
Run the Puppy program.
If the puppy sees a wall or something with its ultrasonic sensor, it will stop, then turn its head to look left then right, then turn in the direction that appears to have more room (like the Explorer project).
Even if it doesn't see a wall, the puppy will stop every two seconds and turn its head left and right to listen for you.
To get the puppy to turn the way you want, call out to it when it is looking in the direction that you want it to turn.

Why the Puppy Doesn't Turn Well on Carpet: Weight Balance

The front castor wheels on this puppy work OK on smooth hard floors, but if you try the puppy on carpet, you will find that it doesn't turn well. This is an example of a very common problem with LEGO robots -- poor weight balance. To turn easily, you want most of the weight of the robot on the wheels that are driven by the motors, and less weight on any other wheels or parts that are just along for the ride. But this puppy has less than half of the total robot weight over the drive wheels.

As determined by the experiment below with a small scale, the Puppy has 474 grams of weight over the front castor wheels, and only 432 grams over the rear drive wheels. This works out to only about 48%
(432 / (432 + 474)) of the weight over the drive wheels. At least 65% would be better, as with the Castor_Bot or the Crazy Lawnmower.


Weight over the front is 474 grams (52%)	Weight over the back is 432 grams (48%)

Challenges

See if you can use the Puppy program to get the puppy to follow you around the house (smooth floors only) by saying "Here Boy!" at the right times.
There are other strategies you could think of to control the puppy, perhaps even using different sensors. Try writing a new program to control it in a different way.
As explained above, the puppy doesn't work well on carpet because it has too much weight over its front wheels. Can you figure out a way to modify the design to get more of the weight over the back wheels, but still keep it looking something like a puppy?

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