FRC Robot Electrical Overview

• Prerequisite: Electrical Overview
• Summary: Overview of the major electrical components that are used in FRC robots

Battery

FRC robots use a ​SLA1116 12 volt 18Ah sealed lead acid rechargeable battery. These are large, powerful batteries capable of supplying up to 250A in bursts and 80A continuous power. That's a lot of power. 12v * 250A = 3000W. This is enough power to launch a 120lb robot into the air or to melt steel; these batteries must be treated with respect. Car batteries are a little larger, but watch how a battery can easily ​vaporize a steel nail to get an idea of how much power we're talking about. These batteries are full of lead and are very heavy, so be careful not to drop them on anything either.

To carry all of that power to the robot, FRC batteries have heavy metal terminals that connect to 1-foot long, very thick (6-Gauge) wires using a nut and bolt (preferably a split washer and lock nut). The wires end in a heavy-duty ​SB-50A connector capable of carrying 50 Amps of continuous current. The connectors allow the battery to be plugged into the battery or charger easily.

DO NOT CARRY THE BATTERY BY THE WIRES OR CONNECTOR

It's important that all of the connections to battery remain tight (this is true for your car battery too for the same reasons): a loose connection provides resistance to the flow of electricity and as you know, resistors convert electrical current into heat energy. A loose connection to your battery can result in enough heat to start a fire. The reason we don't carry the battery by its wires or connector is that the weight of the battery will loosen those connections.

The FRC batteries are rechargeable. A lead-acid battery charger must be used; this pushes electrical current back through the battery, causing the spent chemicals to reverse their reactions, restoring the battery to its original state (almost). Reversing the chemical reactions must be done slowly and so charge current is limited to 5A.

The state of charge of a battery can be checked with a special tester. Team 2537 uses a tester called a ​battery beak that plugs onto the battery connector and has a digital readout that describes the battery's condition including an overall assessment of how fully charged it is.

Motors

FIRST has a long ​list of motors that are legal to use in FRC Robots. The list includes loads of detail and many different kinds of motors. Some of the most commonly used motors are the RS775, CIM, and mini-CIM motors. All of the FRC-legal motors operate on 12VDC. Different motors offer different sizes, weights, speeds, and torque (turning strength). The more force a motor generates, the more electrical current it will consume. When designing a robot it's important to choose the right motor for the task and it's important to make sure all of the motors that may be operating at the same time won't overload the battery or electrical wiring.

The most powerful legal motor is the CIM motor (CIM is an acronym for CCL Industrial Motors - the manufacturer of the motor). CIM motors are capable of ​generating 300W of force and were designed for motorized wheelchairs. FRC rules usually allow a maximum of 6 CIM motors per robot and 4 usually power the drive system (wheels/treads) where the robot needs both speed and power. FRC rules usually do not limit the number of smaller motors (mini-CIM, RS775, etc.) that can be used.

​RS775 motors are commonly used in power tools (e.g. cordless drills) and radio-control vehicles; they can provide up to 150W of force and very high speeds.

Motors are usually mounted to the robot with special ​motor mounts and their shafts are connected to wheels and axles using ​gears which trade reduced speed for increased torque.

Safety

Wiring and Insulation

Fuses and Breakers

Power Distribution

Voltage Regulation

Motor Controllers