Motors

Motors convert electrical power into rotating mechanical energy. There are multiple types of motors, including brushed, brushless, and stepper motors. Most active mechanisms on FTC robots use motors to provide motion.

Motor Selection

Choosing the right motor for your application requires understanding the balance between speed, torque, power output, and gear reduction. There’s no one-size-fits-all motor—each use case demands careful matching of motor characteristics to the mechanical load.

Gearboxes: Amplifying Torque or Speed

Most FTC motors come with pre-installed gearboxes that affect output in two key ways:

• High gear ratio = Low speed, High torque

• Low gear ratio = High speed, Low torque

For example:

• A motor with a 19.2:1 gearbox will turn slowly but provide strong torque—great for lifting heavy arms or driving slides.

• A motor with a 5.2:1 gearbox spins faster with less torque—better for wheels or shooters.

How to Calculate Torque and Speed

Motor power output is a measure of how much work the motor can do per unit time, and is defined as:

Calculating Motor Power, Torque, and Gear Reduction

Given:
- Voltage: 12V  
- Current: 9A  
- Free Speed: 6000 RPM  
- Efficiency: ~75%

1. Input Power  
Electrical power = V × I = 12V × 9A = 108W  
Mechanical output = 108W × 0.75 = 81W

2. Free Speed Torque
Convert RPM to rad/s:  
6000 RPM × 2π / 60 = 628.3 rad/s

Use: P = τ × ω  
So: τ = P / ω = 81 / 628.3 ≈ 0.129 Nm

3. Gearbox Effect (Example: 20:1 reduction)  
- Speed: 6000 / 20 = 300 RPM = 31.42 rad/s  
- Torque: 0.129 × 20 = 2.58 Nm  
- Power stays the same: 2.58 × 31.42 ≈ 81W


Gearing doesn't create power—it **trades** speed for torque (or vice versa). 
Use gear ratios to match motor output to what your mechanism actually needs.

Torque vs Speed

Every motor has a performance curve. At one end is maximum torque at zero speed (stall torque), and at the other is maximum speed at zero torque (free speed). In between is the power peak—the point where the motor is doing the most work.

When designing a mechanism:

• Too much torque = Slow and inefficient

• Too much speed = Can’t move the load

The ideal balance happens when you operate near the motor's peak power, which is around 50% of its stall torque and 50% of its free speed.