Switches
To avoid injury, competition rules for combat robots in most cases require them to be turned off when entering or leaving the combat box or arena. Many also require a power indicating light so people can see if the bot is "live." Check the rules that govern your events before participating.
Design Considerations
- The switch must be direct-acting; it can't be a small switch that turns off a larger, inaccessible relay or contactor.
- Switches that maintain contact through moderate spring pressure may fail or momentarily open if your bot experiences high impacts. This is why maintaining positive contact with screws is so common.
- Normally switches need to be reachable from outside the bot. Assume the bot could be in a dangerous state when approached, and consider how to safely turn off the robot's power while it is active. Any bot capable of injury should be able to be switched off without touching the bot, normally with a tool. Place your switch(es) making sure that both the tool and your hands are far away from moving parts. In larger robots, think about being able to access the switch without having to flip over the robot.
Removable Link
In place of a switch, a removable link (loop of wire, jumper plug, or shorting bar) can be used. This link is pushed into a connector, which is placed where the link can be safely plucked from the robot without tools at the end of the match, or in case of emergency. These are required by the FRA rules and so are commonly seen in UK/EU matches. Larger bots may require more than one link on opposite sides of the bot.
No Switch
If the rules allow it, some people with smaller robots will omit the switch and simply plug and unplug the battery instead. It may be awkward to secure the wires and close the cover on the bot before the match, and could make it difficult to turn the robot off if it has sustained damage during the match. Only do this on bots with non-destructive weapons with no possibility of injury to the person handling the bot.
Power Switches
Most people choose some readily available power switches to turn their robots on and off. A small slide switch, placed where it will not protrude and be bumped, might be fine for a small insect-weight bot. The best switch is one that won't turn off during a match no matter how hard your bot is hit, or how far it falls.
Nano Power Combat Robotics Switch
This very simple switch uses a screw to contact conductive pads to complete the circuit. At <1g, it is suitable for tiny 150g robots and for 1lb robots that don't draw a lot of current.
Fingertech
This tiny 2.15g switch is extremely popular. It is well built, affordable, and can handle current up to 40 amps, making it suitable for many smaller to medium sized robots. It is activated by a 3/32" hex wrench.
Whyachi MS-05
The smaller switch from Team Whyachi weighs 1oz, making it much too big for insect sized robots, but it will handle 140 amps for a 3 minute match making it great for medium sized weapon systems and sometimes, full-sized robot drive systems. It is activated by a 7/64" hex wrench.
Whyachi MS-2
This big switch comes in at 5oz but can handle tremendous amounts of current (500 amps for 3 minutes) and is suitable for most large weapon systems.
Battery isolator switches
The classic Hella-style rotary-operated switch allows 100 amps continuously, but you should eliminate the breakable plastic key for safety and rig it to allow tool insertion.
Multiple Switches
The larger the bot, the more likely you will be required to meet strict safety rules regarding switch placement and accessibility. Your bot may need a separate weapons switch, mobility power switch, safety kill switch, and/or control circuits switch, so that only required circuits will be activated at any given time.
High voltage precharge switch
If you're achieving high power using a higher voltage battery, your switch contacts will become pitted from arcing when power is applied or removed. Many builders at this level will add a precharge switch with a current-limiting resistor; turn this switch on first to charge the circuits before the large switch.
Power Lights
You and the crew running your event must be able to know if your bot is powered on for safety reasons as well as troubleshooting. It is a best practice and a rule in most events that a power-on indicator light is easily visible. The power light should be placed close to the power switch and be easily visible from the outside of the bot when turning it on or off. For small bots, the indicator LEDs on the radio receiver or control circuits can be made visible through the plastic body or through access holes. If multiple switches are required as noted above, each independent circuit needs its own power indicator light.