Displacement

The type of displacement dictates a lot of things from the number of motor to buy to the type of actions the robot will be able to do. It is very important to understand the implications of each solution.

• Differential: Those robots have two wheels/motors, often centered (recommended), allowing them to move in straight line, turn on themselves, and (in rare cases) follow some curves. This is the most common displacement type due to its apparent simplicity and historical reasons.
• Omnidirectionnal: Those robots have between 3 and 4 wheels/motors and exists in different configurations (holonomic, meccanum, etc.). They allow a full range of motion, meaning that they can turn of themselves while moving in any direction. This is a rapidly growing type of displacement among robots of the event.

Other type of displacement exist, and have been seen at the competition, but are whether too complex or too unpractical to be listed here as a potential recommendation.

Differential (RCVA)	Differential (MiAM Robotique)	Meccanum (Mars Attack)	Holonomic (Karibous)	Holonomic (Hololutek)	Holonomic (TDS Team 72)

Criteria	Differential	Omnidirectional
Displacement speed	Acceleration and peak speed are high, but some time is lost maneuvering	Acceleration and peak speed are often a bit lower, but this is more than compensated by their lack of maneuvering needs
Agility	Some movements, especially close to the borders, are complex to do reliably. In reality, curves are often too complex for teams to implement	They are the most agile, being able to do any movement anywhere on the table, in any orientation
Mechanical complexity	With only two motor/wheel, they are, in a way, simpler to build. But to reach reasonable performances, they'll require two additional encoder wheels that must be precisely aligned with the driving wheels (while freely moving vertically to keep floor contact).	Starting at 3 motors, the complexity is low as less precision and no additional wheels are required.
Software complexity	Controlling the robot position / orientation is complicated as both cannot be corrected independently.	Might be counter-intuitive, but this is the simplest type of displacement to implement. Position and orientation can be corrected independently, at the same time, with basic rules. As an example, for holonomic robots, here is the formulas complexity.

Motors

They are 3 main types of motors available and they each have their own pros and cons. As a general recommendation, don't fall in the trap of trying to use too cheap motors, they quality and capabilities have a very high impact on the performances of your robot and on the time spent in software development. Motors are an investment and will be reused for many years. They are expected to be a bit expensive the first time.

The choice of the motors it also linked to the choice of the battery. The battery voltage should match the rated motor voltage, so you can directly use the battery power without having to rely on a voltage regulator for the motors.

• DC: This is this most knonw motor technology, their rotation speed only depends on the voltage you apply to them, however their torque is very low and you'll need to use a reducer (gear assembly) to reduce speed and increase the torque. Many solutions exists on-the-shelf with very different prices. When using a reducer, take attention to the backlash, the bigger it it the more issues you'll having getting your robot where you want reliably.
• Stepper: They are by far the most simple motors to use and the go-to recommendation for a first robot. They can achieve good and smooth displacemnts with minimum mechanical/electronic and software complexity. First a full-size robot, NEMA17 steppers are widely used, but keep the maximum speed a bit low. NEMA 23 allow faster movements, but at the cost a being bigger.
• Brushless: This motor technology can achieve the best performances but are whether complex to use or very expensive to buy. This is far from something that could be recommended for a first robot or a reasonable budget. Depending on the budget solution used, electronic and software complexity can be out of reach of many teams. Many traps are on the way of having great control of brushless motors.

Criteria	DC	Stepper	Brushless
Price	medium	low	high
mechanical complexity	high unless $$$ (cause reducers en encoders)	simple	high unless $$$$$ (cause reducers and encoders)
electronic complexity	simple	simple	high unless $$$$$ (brushless motor drivers are complex to design or expensive to buy)
software complexity	high, having a reliable and precise control of DC motors is not trivial	simple, stepper motor drivers are very simple to use	high unless $$$$$ (implementing brushless motor control is complex, drivers that solve this for your are expensive)
robot speed	high	medium	high
encoder needs	on motor axis or on external wheels	No need (much simpler)	At least required on motor axis

Notice that a reliable but slower robot have WAY MORE chancesd to score during the competion than faster but less reliable ones. The history is full of exemples.