Vertical Spinners

A vertical spinner (often just called a "vert") is a robot whose weapon spins on a horizontal axis, so the teeth come up from underneath the opponent and strike upward. A good hit both damages the opponent and throws it into the air. Verts are one of the most popular weapon types in the insect classes. This page covers what's specific to verts; for the shared engineering (stored energy, tip speed, bite, spin-up, materials, shafts and bearings) see Spinner Design. For other weapon types see Weapons.

Safety: even a 150 g vert can cause injury. Only spin it up in an arena or a test box, and always fit a weapon lock outside the arena. See Safety, Failsafes and the Safety section below.

Variants

The line between a vert and a drum is blurry. As a rough guide, a vert's weapon is tall and narrow (a bar or disc that's taller than it is wide), while a drum is short and wide.

Bar: a flat bar with a tooth at one or both ends. Simple to make and strong for its weight, and a single-tooth (asymmetric) bar with a counterweight gives the most bite. A bar stores the least energy of the common shapes for a given mass and diameter.[1]
Disc: a round or near-round plate with one or two teeth. Stores more energy than a bar of the same mass and size because more of its mass is near the rim, and it's harder to stop.[2]
Eggbeater: an open loop (often a square or rounded frame) spinning between two supports. It puts most of its mass far from the axis, so it stores more energy than a disc of the same mass and diameter.[3] Eggbeaters are wide, so they sit somewhere between a vert and a drum. They also create a lot of air drag, which grows quickly with speed and can overload the weapon motor or ESC.[4]
Dual or twin verts: two discs or bars side by side. Some spin the same way; others spin in opposite directions so their gyroscopic forces cancel when the robot turns. Two weapons need two drive systems (or a shared belt/gear), which costs weight and complexity.
Overhead and arm-mounted verts (spinners or saws on a moving arm) are a separate, more complex family – see Weapons.

Strengths and weaknesses

Strengths

Big, damaging hits. The upward strike throws opponents, causes fall damage and can break parts off.
Recoil goes into the floor. When a vert hits, the reaction pushes the vert down into the arena floor rather than sideways, so it usually stays where it is and keeps attacking. This is a big advantage over horizontal spinners.
Compact and forward-facing. The weapon only needs to point one way, so the robot can be short and narrow.
Can self-right with the weapon. The gyroscopic effect lets many verts right themselves (see below).

Weaknesses

Gyroscopic turning effect makes fast turns hard (see below).
Usually not invertible. Upside down, the weapon hits downward, which is much less effective (see Self-Righting).
Only dangerous from the front. A fast, nimble opponent that gets to the side or back can push or flip a vert freely.
Weapon-to-weapon hits with another vert or drum can wreck both weapons, belts and bearings.
Big hits are hard on the vert itself. Weapon shafts, motor mounts and the frame take the same force the opponent does.

Matchups

Weapon matchups are often compared to rock-paper-scissors: no design beats everything, and driving and build quality usually matter more than the weapon type.[5][6] Typical tendencies:

Opponent	How it usually goes for a vert
Horizontal spinner	Often favorable. The vert can hit the horizontal's blade from underneath and throw the whole robot, and its own recoil goes into the floor while the horizontal gets knocked away. A well-built horizontal can still break a vert's forks, wheels or weapon. Some builders use special vert weapons shaped to give a horizontal less to catch.[7]
Drum or another vert	Close and violent. Weapon-to-weapon hits are common, and the faster tip speed tends to win those.[8] Weapon durability and a stable chassis matter a lot.
Wedge or control bot	Depends on who gets underneath. A low, strong wedge can deflect the teeth and push the vert around; a vert with good forks and a fast charge can get under the wedge's edge and launch it.
Flipper or lifter	A dangerous matchup. The vert can do heavy damage to the flipper's front, but if the flipper gets under it, a vert that can't self-right can lose quickly.
Hammer or axe	Usually favorable for the vert, since hammers tend to be slower and have exposed arms, but a hammer that lands on top of the vert's weapon or electronics can do real damage.

Design considerations

Gyroscopic turning effect

A vert's weapon resists changes in direction. When the robot turns, the gyroscopic force tries to tip it sideways, lifting one wheel; a quick turn with the weapon at speed can lift a wheel off the floor completely (the "gyro dance"). This reduces traction and pulls the weapon out of line.[9] Ways to tame it:[10]

Widen the wheelbase. Wheel lift depends on the square of the track width, so a wider robot is much more stable.
Limit turn rate with dual rates or travel adjust on your transmitter (see Radios/Mixing).
Drive smoothly and make big turns with the weapon at speed, or slow the weapon before tight turns.
On magnetic arena floors, chassis magnets near the wheels can resist the lift (check your event's rules on Magnets).
Counter-rotating twin weapons largely cancel the effect.

The T.i. Combat Robotics gyroscopic effect calculator (mirrored by Team Run Amok) estimates whether your design will lift a wheel.

Self-righting with the weapon

The same gyroscopic effect lets many verts right themselves: spin the weapon up while upside down, then turn sharply so the robot rolls over. It takes practice, and it only works while the weapon still spins. See Self-Righting for this and other srimech options. If your vert can't gyro-right, plan another method, since a vert that gets flipped and can't recover has lost.

Invertibility

Most verts are not truly invertible: they may drive upside down, but the weapon then hits downward. Some builders design the weapon to be usable both ways, or accept a weaker inverted hit and focus on getting back over quickly. Decide early, because it affects wheel size, chassis height and where the weapon sits.

Front wedges and forks

Verts need to get their teeth under the opponent's front edge. Most use forks or wedgelets (narrow prongs) or a wedge in front of the weapon to lift the opponent slightly and feed it into the teeth. Forks slid under the opponent also help stop the two robots simply bouncing apart when the hit lands.[11] Builders often carry several sets to swap between matches. See Weapons for wedgelets and Wedges and Control Robots for the other side of the fight.

Weapon shape and teeth

One or two teeth give the most bite; a single counterweighted tooth lets the weapon spin faster without losing bite.[12] See Bite.
Supporting the weapon shaft on both sides is far stronger than a one-sided mount.

Powering a vert in the insect classes

As of 2026; parts change quickly.

Brushless outrunner motors are the standard weapon motor at every insect weight, run from a brushless ESC (see Motors, Insect Class Motors and ESCs). As a rough guide for beetleweights, Ask Aaron suggests about 150 W per pound of robot and about 6% of the robot's weight, which usually means a 28 mm or 36 mm outrunner.[13] Antweights and fairyweights use correspondingly smaller motors.
Belt drive is the most common layout: the motor sits beside or behind the weapon and drives it with a belt, which protects the motor from impacts.[14]
Direct drive (the weapon bolted to the motor, or the motor inside the weapon hub) is compact and common in small verts, but the motor takes every hit.

See Spinner Design for the trade-offs.

Safety

SPARC rules require a clearly visible weapon lock whenever the robot is out of the arena, and it must be in place when you power on. Spinners must stop within 60 seconds of power being removed, using their own braking, and must not spin outside the arena or a testing area.[15] Check your event's own rules too.
Test the weapon only in a test box or arena, never on the bench. Check your failsafe every time you change radio settings.
Verts throw broken teeth and parts upward and forward. Wear eye protection and keep people out of the weapon's plane.
Battery packs take a beating in spinners; see LiPo Battery Safety.

Famous examples

From BattleBots robot profiles, as of 2026.

Bite Force – listed as a vertical bar spinner; Champion of BattleBots Season 1 (2015).[16][17]
End Game – vertical disc spinner from New Zealand.[18]
HyperShock – vertical disc spinner.[19]
RIPperoni – vertical disc spinner.[20]
HUGE – vertical bar spinner.[21]
Black Dragon – eggbeater spinner from Brazil.[22]

Open-source designs

A few printable vertical spinners from the list on 3D Printing (more there):

Polachrome (1 lb plastic ant) – 2WD vert with forks and a full build guide.
Tribute to Bite Force (1 lb plastic ant) – with STEP and Fusion files.
Printed First Measured After (1 lb plastic ant) – a nationally ranked design.
Vertical Spinner Battlebot (150 g).
MicroNova (3 lb) – 4WD eggbeater with a STEP assembly.