Designing Robots How to make a stable robot! Much of the information in this power point is from Winning Design! By James J. Trobaugh

Brainstorm as a team Throw out ideas Either take turns drawing them, or elect an artistic team member to draw all of them (quickly and roughly!!!) These designs are just starting points – your design will change as you build OR – team member can come up with ideas alone or in pairs, and present their drawings to the team

Draw your design Once you decide on one design, draw a sketch of what you want the robot to look like. The sketch should not be detailed, but should include all the basic concepts Save all your design diagrams, even the ones you don’t use. If you are a competitive team, keeping you design ideas is a great way to start your team documentation

Chassis design Designing an efficient robot means you have to balance size, power and speed. Look at what your robot has to do, and decide what is important for it: – Should it be fast? – Will it have to be strong because it needs to push things? – Does it need to get through narrow spaces?

Size Imagine the size as a box, and keep your robot small enough to fit in that box. If you build a big heavy robot, it will require a lot of power to move it around

Power Power means how strong your robot is. If your robot has to push or pull heavy things, it needs to be strong. Usually a strong robot moves more slowly. Be careful – if you use gears to increase the power, you can overdo it, and break pieces like gears and axles

Speed If your robot goes very fast, you will have to make it small, and it will have less power. Very fast robots often make mistakes, as it is hard for a fast robot to be accurate

Batteries Batteries add weight to the robot If you are competing, make sure that your battery pack is easily accessible, so that you can charge it easily If you are competing, you should use fresh batteries for each run to ensure consistent performances from your robot

Finding the Center of Gravity Your robot needs to be properly balanced All wheels or threads need to keep in contact with the field at all times so that the robot runs will always work the same way Balance depends on the wheelbase of the robot and the center of gravity The wheelbase is the area created by drawing lines between each of the wheels on your robot A balanced robot has the center of gravity inside the wheelbase (next slide)

Go to this power point for more informationthis power point wheelbase

More information about center of gravity The red dot in each picture shows the location of the center of gravity Robot one (top left) is a stable robot with its center of gravity located low and equally between the wheels. Robot two (top right) is very unstable and is in the process of falling over because its center of gravity is outside of its support base. Robot three (lower left) is not stable because the center of gravity is high and if any of its wheels are lifted, it will not take much for the center of gravity to move outside the support base. Robot four is fairly stable because the center of gravity is low and between the tires, although it should be noted that if this robot were to pick up a game piece, it could easily move the center of gravity and make it unstable.

More about stability The support base is determined by drawing lines between the points of contact with the ground and NOT the robot frame. For instance a robot with larger wheels inside the same frame will have less stability than one with smaller wheels, because the points of contact (radius of wheel) can be further apart with the small wheels. By the same reasoning a tricycle drive base will not be as stable as a square drive base.

Gearing Up You can use gears to make your robot either faster or more powerful. But that is another lesson

Wheels The larger your wheel, the farther your robot will move in one rotation, because the circumference will be larger. Remember circumference = Π Diameter

Common Problems with Wheels Common Problem 1: Missing Bushing between Tire and Motor A full bushing should be placed between the tire hub and the motor. This bushing prevents the hub from sliding along the axle and having the tire rub against the motor housing. This component is easy to miss, but its effects can be rather large.

Common Problems with Wheels Common Problem 2: Wheels are Placed on Backwards The two sides of the standard NXT wheel hub are not made equal. One is intended to face the motor, and one is intended to face away from the motor. This problem often supersedes the lack of a bushing because the construction of the wheel hub makes it that even with a bushing in place between the hub and motor the tire can easily rub against the motor housing.

Which side of the wheel?

Properly Seated Tires An improperly seated tire is easy to spot because at the point where the rubber tire meets the plastic hub there will be a couple millimeter gap, and the rubber tire will easily move across the hub. A properly seated tire will have a tight union and a much sturdier feel.

More about Mounting Wheels When mounting wheels on your chassis, you must give your axles proper support. This single spaced bushing is only supporting the axle on one side. This creates friction on the axle.

Mounting wheels The wheel is further away from the chassis, so more force is put on the axle and chassis. Also, the wheel may tilt (camber) giving unpredictable results each time you run a program. The axle may even bend over time.

The best way… Is to have a chassis that fully supports the wheel axle on both ends, giving maximum support to the wheel and axle and removing a great deal of friction from it.