Repairs Between Matches

At an event, the time between your matches goes fast. In those minutes you need to make the robot safe, find out what broke, fix what matters, charge, re-test and get back to the queue. A calm routine and a well-packed kit make the difference between fighting your next match and forfeiting it. This page covers how much time you get, a post-match routine, what to fix and what to leave, safe quick fixes, and when to withdraw. For what to bring see Pit Kit and Event Checklist; for diagnosing faults see Troubleshooting.

Safety: work with the battery unplugged and the weapon lock fitted. Never power a robot on in the pits except where the event allows it (a test box or the arena). See Safety, LiPo Battery Safety and Failsafes.

How much time you have

SPARC events: the SPARC Match Rules give robots from 150 g to 6 lb at least 20 minutes between matches, and robots over 6 lb at least 30 minutes.[1] If officials call your robot for a re-weigh, that time doesn't count against your guaranteed time.[2] Events can change these rules, but must say so publicly before the event.[3]
NHRL runs its own schedule. Be ready 10 minutes before your posted fight time; each robot can use a single 15-minute extension, once.[4] Its event-day page describes a 30-minute repair break before the final rounds, and 20 minutes after each fight in those rounds to repair and recharge.[5]
Other events set their own rules. Robot Smashing League, for example, has a 20-minute minimum, and its Swiss-style format can mean seven to ten fights in a day for a robot that does well.[6]
Minimum doesn't mean typical. In a big bracket you may wait an hour; late in a double elimination you may get only the minimum. Watch the bracket or the "next fights" screen, and keep your robot fight-ready whenever you can.
Charging is often the bottleneck. A battery can take more than 20 minutes to charge, so bring at least two and rotate them.[7]

Post-match routine

Do the same steps in the same order every time, so nothing gets missed when you're rushed. Write them on a card at your pit table.

Make it safe. Weapon lock on before anything else (it should already be on from load-out), robot blocked up so the wheels can't touch the table, then unplug the battery or pull the link.[8]
Check the battery for dents, puffing, cut wires and heat before you charge it (see below). Then start charging it, or the next pack, right away so the charger works while you do.
Look over the whole robot. Note everything that's damaged before you start fixing anything. A phone photo helps.
Wires and connectors: look for cut insulation, pulled solder joints, loose servo plugs and a loose antenna (see Wiring and Soldering and Connectors).
Weapon: spin it by hand. Feel for grinding, play or rubbing; check the belt, teeth, hub and retaining hardware; check the blade for cracks (see Weapon Shafts, Bearings and Mounting).
Screws: check every screw you can reach, especially motor mounts, weapon hardware and set screws. Replace any that are bent or stripped, and re-apply threadlocker to metal threads (see Fasteners and Hardware).
Drive: spin each wheel, check tires and hubs, and check that the motors are firmly mounted. Foam wheels may need replacing every match or two.[9]
Armor and frame: look for cracks, bent wedges and forks, and parts that now rub or stick out.
Fix, then re-weigh. Replacement parts often weigh more than the originals. Under SPARC rules, if you've modified a robot it's your job to keep it within the weight limit; a robot found more than 5% over forfeits its previous match.[10] See Weight Management.
Re-test what you touched, and the failsafe if you changed any electronics (see below).
Get back in the queue early, with the weapon lock on, the battery charged and the transmitter ready.

Triage: what to fix and what to leave

You rarely have time to fix everything. Ask Aaron's rule for spares also works for repairs: put first anything that stops the robot working and anything that can't be fixed quickly.[11]

Priority	Examples
Must fix (safety)	Damaged battery; exposed or chafed power wiring; a weapon lock that no longer fits; a power switch or link that doesn't work; a failsafe that doesn't stop everything; a weapon that won't spin down within the rule time
Must fix (to compete)	No drive on one or both sides; no radio link; a weapon that won't spin; parts loose enough to fall off
Fix if there's time	Damaged weapon teeth or belt; a torn tire; a bent wedge or fork; cracked but intact armor
Leave for later	Cosmetic damage, scuffs, paint, small dents that don't affect function

Fix the cause, not just the symptom: if a screw backed out, check its neighbours too.
If a repair will clearly take longer than you have, decide early whether to swap a module, run with reduced capability, or tell the event you may not be ready.
In the insect classes there isn't time for major rebuilds, so build the robot to be repaired by swapping parts, not by fabricating new ones.[12]

Batteries: assess before you charge

Any dent, puffing, cut wrapper, damaged lead or unusual heat means the pack is retired for the day. Don't charge it or put it back in the robot. A swollen LiPo can't be fixed.
At an event, put a damaged pack in a LiPo bag, move it somewhere ventilated, and tell the event staff. Follow LiPo Battery Safety for what to do and how to dispose of it.
Never leave a charging battery unattended.[13]
If a battery was damaged, find out why before fitting a new one: a battery that moved inside the robot, or armor that crushed it, will damage the next one too. Mount batteries securely and with shock protection; Ask Aaron's advice is not to rely on a press fit, zip ties or duct tape to hold them.[14]

Quick field fixes

What works

Swap, don't repair. A spare wheel, wedge, armor panel, weapon or drive module bolts on in minutes; a repair to the broken one can wait until you're out.
Hot glue at connectors helps keep plugs from pulling out (see Wiring and Soldering).[15] It also tacks wires down away from moving parts.
Zip ties tidy and restrain wiring, and hold cracked non-structural parts in place for one more match.
CA (super glue) and quick epoxy re-bond cracked printed or plastic parts; FingerTech, for example, recommends a drop of CA to secure its press-fit hubs in Lite Flite wheels.[16] Ask Aaron's own minimal spares box includes zip ties, duct tape and 5-minute epoxy.[17] Give glue enough time to cure, and use CA in a ventilated spot.
Tape covers sharp edges for carrying, insulates repairs, and holds an antenna in place inside the robot.
Solder and heat-shrink for broken wires. A cold, rushed joint will fail again, so take the extra minute (see Wiring and Soldering).

What isn't allowed or safe

Nothing loose on the outside that can tangle. SPARC bans entangling weapons and defenses, including tapes, strings and nets, and an attachment that shows a real risk of entanglement can be disallowed for the rest of the event.[18] Trim zip-tie tails, and don't leave tape flapping where it could wrap around a weapon or wheel.
Batteries held only by tape or zip ties (see above).
Bypassing safety parts to save time: jumpering the power switch, fighting without a working power light, or leaving out the weapon lock. These are inspection items for a reason.[19]
Threadlocker on plastic parts – standard threadlockers can crack plastics (see Fasteners and Hardware).
Plastic classes: under the SPARC Plastic class rules, frames, weapons and custom parts must be printed from the allowed plastics, and off-the-shelf parts can't be used as armor or weapon impactors. Adhesives and fasteners are fine, but a metal patch or plate over damage isn't.[20]
A different robot. Under SPARC rules a spare robot must be mechanically and functionally identical and have passed inspection.[21] Some events don't allow a second copy at all; Bristol Bot Builders, for example, asks for one robot plus spare parts.[22]

Swapping electronics and re-testing

Change one thing at a time and label spare parts with what they're set up for.
Re-bind and re-test the failsafe after replacing a receiver or ESC, or after changing trims, mixing or wiring. Turn the transmitter off and confirm that drive and weapon both stop (see Failsafes).
Only power the robot where the event allows. SPARC robots may only be activated in the arena, a testing area, or with the event's permission.[23] At Bristol Bot Builders events, if you replace parts that could affect the failsafe, a crew member supervises your test-box check; the test box is never used unsupervised.[24]
Pre-configure spares at home: a spare receiver already bound to your transmitter with the failsafe set, and spare ESCs already calibrated and set up with the right firmware settings (see ESC Firmware and ExpressLRS and EdgeTX Setup). A swap at the event is then just plugging in and testing.

When to forfeit or withdraw

Sometimes the right call is not to fight:

The battery is damaged and you have no good spare.
The failsafe, power switch or weapon lock doesn't work and can't be fixed in time.
The weapon or frame is cracked badly enough that parts could come off at speed, or the weapon won't stop within the rule time.
Anything is smoking, smells hot, or behaves erratically when powered.

If you might not be ready, tell the event staff as early as possible. Some events can move your fight back a little if they know in time.[25] Withdrawing a damaged robot is always better than an unsafe match. A driver can also tap out during a match to stop further damage; the opponent wins.[26]

Asking other teams for help

Builders are usually happy to lend or sell a part, a tool or a hand; there's always someone with a spare ESC.[27][28]
Many regions have an event Discord or chat where builders post requests for parts during the day.[29] See Local Groups and RobotCommunity.
Some venues have shared facilities: NHRL has a pit store, a parts exchange bin, a workshop with staff, a grinding station and test boxes.[30]
Be specific: name the part (or show it), its size or connector, and how soon you fight. Return what you borrow, and offer the same help later.

Preparing between-match kits

The fastest repair is one you prepared at home.

Pre-built modules: a complete spare weapon assembly, a spare drive motor with its wheel or hub already fitted, a spare wedge or fork set, and an armor panel set. Ask Aaron suggests carrying complete spare motor and pulley assemblies where a part is hard to replace in the pits.[31]
Electronics pack: a bound receiver, a set-up ESC, a power switch or link, spare connectors and a short length of each wire size.
Hardware tray: every screw size on the robot, nuts, washers, spare set screws, belts and bearings, kept in labelled compartments.
Batteries: at least two, ideally three or four, so one is always charging.[32]
Consumables: threadlocker, CA, quick epoxy, hot glue sticks, zip ties, electrical and gaffer tape, heat-shrink.
Practice the swap at home and time it. If a common repair takes longer than your turnaround, redesign that part to be easier to change.
If you run several robots, choose parts they can share so one set of spares covers them all.[33]

How many spares to bring depends on the format: a double elimination may mean only two or three fights, while Swiss-style formats can mean many more.[34] See Pit Kit and Event Checklist.