Launcher study for Gyropup's head turret: ammo, launcher, feed, motors, jams, safety

Checked 2026-10-25. This extends turret-and-safety.md (read that first: launcher basics, recoil, toy-standard energy limits, pan/tilt, the S1–S23 safety list). It does not repeat that file's tables; where a number here differs from it, §0.2 says so. New parts are appended to catalog/turret.json. The interface it has to fit is docs/head-payload.md.

Conventions. "n/p" means not published. calc marks my arithmetic on sourced inputs. est marks an engineering estimate that is not sourced and needs measuring. Out of Darts (OOD) and other Shopify data were read from each product's /products/<handle>.js record, whose weight field is a shipping weight unless the description gives a part mass. 1 fps = 0.3048 m/s.

The settings the user asked for. Foam balls (Nerf Rival size) are the candidate for indoor play and gel blasters for outdoor play. So §7 compares one ammo for both settings with an interchangeable launcher "cartridge" per ammo.

0. Summary

0.1 Recommendation

0.2 What changes from the earlier study

• Rival balls are no longer "a poor fit". At the same fps they carry about 1.8× the energy of a 1.0 g short dart, but over 3× the contact area. Capped at 70 fps, a ball stays under EN 71's 0.5 J and far under ASTM's 2500 J/m² (§6.1). Balls also feed without orientation and can be poured in at the dock, which darts cannot.
• RoboMaster numbers have moved. The 2025 RMUC rules specify a 16.8 mm, 3.2 g TPU ball and a 25 m/s cap for 17 mm launchers. The 30 m/s and 2.9 g figures were from 2018.
• Official RoboMaster prices are lower. DJI lists the Snail 2305 at $29, the C615 at $39 and the M2006 P36 at $41, against $40–$95 from resellers.
• Hasbro's own Rival round averages 1.83 g in a reviewer's weighing (BlasterHub), heavier than Worker's 1.75 g.
• A dart belt does exist: the Nerf Vulcan's 25-dart belt, now only sold used. No modern belt-fed short-dart design was found.
• The power plan is out of date. The default design now runs on a 15S FLEXVOLT (45–58 V, D25). Its 12 V rail is a 30 W Mean Well DDR-30L-12 that already feeds the lidar and headlights, so the launcher cannot hang off it (§8.5).
• "Hy-Shot" is not a project. The nearest match is torukmakto4's Hy-Con flywheel system. Captain Xavier has YouTube videos but no design of his own was found.

1. Custom foam-dart blasters and robot launchers on the internet

These are the designs not covered in turret-and-safety.md §1.3. That table already lists the Blitz, Gryphon, Protean, Stryfe kit, Nightingale, Atrox, Diana, Vesper, Momentum, FDL-3, Tops76 turret, Juno, TerraScout and RoboMaster S1.

1.1 Foam darts

Not found: Captain Xavier's own designs, "Hy-Shot", "Cyclone" as a blaster (only the ZWQ Cyclone CNC barrel insert, $44.99), any triple-stage brushless build, and T-Motor F-series motors in blasters.

1.2 Foam balls and robot launchers

What the robot launchers teach. Every robot that fires many rounds (RoboMaster, the S1, FRC) uses round ammo, a hopper and a motorised indexer, not magazines. Every one of them also has a jam detector or a way to clear the feed.

2. Ammo for a compact robot turret

2.1 The ammo

2.2 Energy at kid speeds (calc)

KE = ½mv². KED = KE / (π d²/4), taking the whole face of the projectile as the contact area as in the earlier study. EN 71-1 allows 0.5 J for resilient projectiles and 0.08 J for rigid ones; ASTM F963 allows 2500 J/m² above 0.08 J.

What the commercial gel products deliver, for comparison (calc with 0.22 g unless noted):

So a gel bead is low in energy but high in energy per area: a commercial gel blaster at 150–250 fps is 2–6 times ASTM's 2500 J/m² (calc). To stay inside the toy limits, gel has to run at ≤ ≈ 100 fps, which is the Mythic and S1 class, not the Surge class.

2.3 Scores for Gyropup

5 is best. Scores are my judgement from the sourced facts in §§1–6; the reasons are in the cells.

2.4 Foam or gel, head to head, for a highly compact head turret

Gel looks simpler, and in the ammo it is: no orientation, hundreds of rounds per hopper, no pickup, cheap. The rest of the system is not simpler.

• Mechanism. Every proven gel blaster is a motor + gearbox + spring piston, "mostly identical to airsoft AEG" (Wikipedia). No flywheel gel launcher was found; beads were long thought too fragile even for spring followers. A piston's velocity is set by the spring, not electronically, so the turret loses its RPM velocity guard and keeps only the chronograph lockout.
• Logistics. Gellets soak ≥ 2 h (4 h for Starfire), keep 2 weeks sealed or 3 months under water (FAQ); DJI says use within 24 h. An under-soaked bead makes the blaster "function poorly". The dock would need a soak tank, a drain screen and a metered wet feed, all with water next to the robot's charge contacts.
• Outdoor mess. Broken beads dry to "slush powder" (Wikipedia), but whole misses lie hydrated in the grass. The water-bead rule exists because children swallow them.
• Kids. Gel Blaster and Nerf Pro Gelfire are all labelled 14+; Hasbro requires eyewear "for players and people within range". An Ophthalmology series (Lin et al., 2023) covers 19 injured eyes and recommends paintball-grade eye protection (AAO EyeNet); Queensland Children's Hospital saw 8 children aged 4–14 in six months (Wikipedia).
• Regulation. The US water-bead toy rule (16 CFR 1250, effective 12 March 2026) puts "water bead toy guns designed to shoot water bead projectiles" in scope when they are designed or marketed for children under 14, and requires expanded beads to pass a 5.0 mm funnel gauge. Guns marketed 14+ for paintball- or airsoft-style play are out of scope (Federal Register 2025-22643, CPSC guidance). Standard 7.5 mm beads are made to be bigger than 5 mm; whether one squeezes through the gauge in the test was not checked. A Tritium game for children under 14 should assume it is in scope. In Australia, gel blasters are firearms or regulated imitations in NSW, SA and WA (Wikipedia, Mondaq).
• Power. An AEG motor on 7.4–11.1 V while cycling draws far more than a dial motor (no published current found; est 100+ W), and needs its own high-current stage.

Verdict: foam, not gel, for Gyropup's kids. Gel makes sense "because of simplicity" only for the ammo, and only for 14+ players in sealed goggles. Keep a gel cartridge as a possible later module for teen or adult outdoor events (§7), capped at ≤ 100 fps with a chronograph lockout, and never fielded with younger children.

2.5 Indoors and outdoors

• Indoors: Rival balls at ≤ 70 fps. They are big, visible and roll out from under furniture.
• Outdoors on dry grass: the same balls. They are easier to find in grass than 36 mm darts (est).
• Outdoors on wet grass: no foam ammo is reliable (S22 already bans play in rain or on wet grass). Wet-ball feeding has not been tested anywhere I found, so test closed-cell EVA balls on damp grass before relaxing S22.
• One ammo for both is the recommendation. The cartridge boundary (§7) keeps short darts and gel possible without redesigning the head.

3. Feeding

3.1 Capacity against size

3.2 How robots feed

• RoboMaster: a hopper above a dial (the "trigger" motor, an M2006 P36), stepping a fixed angle per shot (π/10 rad in DJI's example code). The friction wheels must be at speed before the dial may turn. Jams are detected by dial stall and cleared by reversing (§1.2).
• S1: a sealed 430-bead container with a sliding plate that opens when it is fitted, and drain holes to let water out after loading.
• Nerf hopper blasters: a conveyor belt from the hopper to the wheels. Hasbro's own patent (US11346624B2) says soft, tacky spheres "tend to aggregate or bind in the hopper", especially at the feed-tunnel entrance, and adds gear-like agitating rollers and a compression roller (Google Patents).
• Infinite Pack: a gear-motor agitator plus a brushless blower that pressurises the hose.

Design rules for Gyropup's hopper:

1. Put the dial at the bottom of the hopper, with pockets one ball wide, and stir the hopper with the dial (spokes or bumps on top), as the Hasbro patent does.
2. The tilt range is only about −25°…0°, so a hopper on the tilting cradle still feeds by gravity.
3. The hopper cannot be shaken, so a stall-reverse cycle is the only way to break a bridge.
4. Unpowered, the dial must block the path, so no ball can roll into the wheels after an e-stop.

4. Jamming

Rules for Gyropup's cartridge:

1. One round per feed step, with the pocket or stroke counted.
2. Fire only when both wheels are in range, from tach.
3. Stall-reverse on the feeder.
4. A chronograph on every shot, which also catches "no round left" and "slow round" as faults.
5. Approved ammo only, with the cartridge geometry rejecting other ammo.
6. At the dock, clear any stray round at low speed before arming.
7. Log every fault with its counts.

5. Motors and actuators

Gyropup's rails: the bus is 45–58 V. A 24 V rail (Mean Well DDR-120C-24, 120 W) is spoken for by the J501. A 12 V rail (DDR-30L-12, 30 W) feeds the lidar and headlights. Hobby blaster parts are built for 3S–4S (11–17 V). FPV ESCs reach 6S (25.2 V), and RoboMaster parts run on 24 V. So the payload should get its own 24 V (§8.5).

5.1 Flywheel motors

How fast the wheels need to go. On a Hy-Con cage, 35,000 eRPM (≈ 5,000 rpm on a 14-pole motor) gives ≈ 36 fps (torukmakto4). Scaling linearly, 70–80 fps needs ≈ 10–11k rpm (est), a quarter to a half of any motor here.

For balls, the wheel surface speed must be at least the exit speed. 21 m/s from 40 mm wheels needs ≥ 10,000 rpm (calc), about half the Snail's no-load speed at 24 V.

Brushed vs brushless for a robot. Brushless is the choice: RPM telemetry, closed-loop speed, no brush dust, and no 26–45 A stall currents on a shared rail.

5.2 ESCs

5.3 Pushers and feeders

5.4 Gel gearboxes

No mass or current was published for any gel gearbox or motor.

6. Safety

This adds to turret-and-safety.md §4 and §7, whose limits (S1–S23) still apply.

6.1 Speed and energy caps

Gyropup caps (one per cartridge, held in the cartridge and in the head MCU):

Minimum distance. S7's 2 m stays. No published minimum distance exists for low-fps foam play; the gel tables above start at 5–10 m only above 300 fps.

6.2 Eye protection

• Foam: Hasbro recommends eyewear for Rival players "and people within range" (earlier study). GameSchoolCon requires eye protection for every round.
• Gel: Hasbro requires eyewear for Gelfire players and anyone within range (Hasbro). Fields ask for ANSI Z87 full-seal goggles (Fox). The ophthalmologists ask for paintball-grade protection for bystanders too (AAO).
• Tritium's kids already wear safety glasses. For foam that matches the rules above. For gel, safety glasses alone fall short of every gel-specific rule found.

6.3 Making the turret physically unable to aim high

The body leans, so a body-frame limit alone is not enough (S5). Layers, from mechanical to software:

1. A hard tilt stop on the yoke at 0° body frame, and a cradle that cannot reach above it even with the servo off.
2. A body-lean rule. The balance controller already keeps forward lean small. If the body pitches nose-up beyond the margin, the arming line opens (next item). The S1 does this at 10° (DJI).
3. A hardware inclination interlock in the cartridge. A tilt switch or a small accelerometer with a comparator, wired into the arming loop, cuts feed power whenever the barrel is above horizontal in the world. It does not depend on the Jetson or the head MCU (concept; switch hysteresis must be measured, est a few degrees).
4. World-frame gating from the head IMU, with the ballistic head-zone prediction of S5.

6.4 Safe-off states

6.5 The aiming laser

• The FDA advises that laser pointers "are not toys and should not be used by minors except under the direct supervision of an adult" (via Wikipedia). Gyropup's laser is part of a supervised game, and it never points above horizontal.
• Recommendation: buy a module with a stated class from a maker that certifies it. One example is the Picotronic 520 nm, 1 mW, Class 2, 12–24 V, Ø12 × 40 mm module (16 g, €319.90; Picotronic). Cheap modules sold as "< 1 mW" have unverified output, so measure any of them with a power meter.
• Class 1 (≤ ≈ 0.2 mW, est at 520 nm) is safer but dimmer. Its visibility in daylight was not tested.
• The doc's current text ("Class 1 or low-power Class 2, ≤ 1 mW") is right.

6.6 Legal

• US federal: imitation firearms need a blaze-orange tip (15 U.S.C. §5001, via Wikipedia). The orange muzzle in S11 covers this. The water-bead rule is covered in §2.4.
• US states: New York and California restrict imitation firearms (same source). Check before any event there.
• Australia: gel blasters need a licence in NSW and SA, are banned in WA, and in QLD must be locked away and concealed in public (QLD Police). Foam blasters are not affected in anything found.

7. One ammo, or a launcher cartridge per ammo

7.1 What is shared and what differs

7.2 The cartridge boundary

• Mechanical: two dowels and one captive thumbscrew, or a cam latch, on the tilt cradle. The cartridge's centre of mass sits on the tilt axis.
• Electrical: one blind-mate connector carrying:
  • 24 V and GND, 10 A;
  • CAN-H and CAN-L;
  • the arming loop, so it opens if the cartridge is pulled out;
  • the chronograph gate lines;
  • two hard-wired ammo-ID pins.
• Why the ammo ID is in hardware. The ID picks the velocity cap. It is a resistor or pin code read by the head MCU, not a software setting, so a cartridge cannot be fired under another ammo's limit. Each cartridge's wheel geometry also caps its own velocity mechanically (§8.3).
• Cost: ≈ 25 g on the head side and ≈ 15 g on the cartridge (est), plus one connector.

Verdict: practical, and worth doing. The shared part is about two-thirds of the head's mass. Ball and dart cartridges fit the budget with room to spare (§8.6). A gel cartridge also fits on paper (≈ 0.5–0.6 kg, est), but it needs its own power stage, a water-tight hopper and its own velocity limiter, and it would only be fielded for 14+ players (§2.4). Build the boundary now. Ship the ball cartridge first, keep the dart cartridge as the second, and treat gel as a later experiment.

8. Recommended concept for Gyropup's head turret

8.1 The concept

8.2 Numbers

8.3 Velocity ceiling for balls

• Why darts and balls differ. Darts are limited by cage crush. A ball launcher can be limited by the regulated rail instead.
• The ceiling. The Snail's no-load speed at 24 V is ≈ 21,000 rpm (calc). The wheels' surface speed at that rpm is the most the ball can ever get.
  • With 40 mm wheels that is 44 m/s, so the motor-speed ceiling alone does not hold the cap.
  • Either fit ≈ 20–25 mm wheels, which give 22–27 m/s at full speed, or take the ceiling from a lower-KV motor.
• Bench check. Measure exit speed against wheel speed. Then show that at 100 % throttle the exit speed stays ≤ 70 fps, as S2(b) requires for darts.
• What it costs. The ratio of exit speed to wheel speed is not published, so the wheel size must be settled on the bench. Until then the cap rests on the RPM loop and the chronograph.

8.4 Dock reload

• The dock. It gains a short mast with a ball silo (≈ 100–200 balls), a servo gate and a break-beam counter at the spout.
• Docking. Gyropup sits down (D18), pans to a stored "reload" angle and tilts to its load pose. A spring flap on the hopper is pushed open by the spout.
• Filling. The dock dispenses the number of balls the robot reports as fired, which it knows from the chronograph log. A hopper-full beam in the cartridge stops the fill.
• Before the next round. The flywheels spin slowly and the dial cycles once to clear any stray ball, before re-arming is allowed.
• Game idea. Kids collect balls and drop them into the silo: "feed the robot". That doubles as the count-out and count-in in S20.
• Dart cartridge instead. A person swaps the magazine at the dock, which is the current doc's plan. A robotic magazine changer is a project of its own.

8.5 Power: where the payload's 24 V comes from

Proposal: a fused tap on the bus (5 A, est) through the turret arming contactor, feeding a dedicated 24 V converter for the payload, mounted in the body.

• Converter: a second DDR-120C-24 ($69.20, 33.6–67.2 V in, in power_electronics.json), or a DDR-60L-24 (60 W, 18–75 V in, ≈ $33; onlinecomponents) if bench tests show the peaks fit.
• Why regulated 24 V: it gives the flywheels a fixed voltage, which makes the hard ceiling in §8.3 possible.
• 12 V parts: the STS3215 (and a dart cartridge's solenoid) get a small 24 → 12 V buck in the head (est 10 g).
• Flywheel spin-up is small at these speeds. Est 3 × 10⁻⁶ kg·m² per wheel and rotor, at 10,000 rpm, stores ≈ 1.6 J per wheel (calc on est inertia), so spin-up in 0.2 s needs only ≈ 30–60 W with losses (est).

8.6 Mass budget

Shared head (est unless noted):

Ball cartridge:

Total ≈ 1.16 kg, leaving ≈ 0.34 kg of the 1.5 kg budget.

Other cartridges:

• Dart cartridge ≈ 422 g (est), with 23 rounds (one Koda 23-round magazine):

  Part	Mass
  2 × Snail	56 g
  ESCs	10 g
  Wheels	10 g
  Lailaps solenoid	63 g
  Koda magazine	115 g
  23 darts	23 g
  Cage and structure	120 g (est)
  Chronograph and connector	25 g (est)

• Gel cartridge ≈ 0.5–0.6 kg (est; no gearbox mass is published).

Centre of mass. The pan motor is at the bottom, about 25 mm up; the cradle about 80 mm up; the hopper about 140 mm up. That puts the whole payload at ≈ 75–85 mm above the head plate (est), inside the 120 mm limit.

8.7 Jam mitigation in this concept

1. One ball per dial pocket, and the dial stirs the hopper.
2. The dial turns only when both wheels read in range on tach.
3. Stall-reverse on the dial, as in DJI's code: < 1 rad/s for 700 ms, then reverse 500 ms. Three tries, then SAFE with a "jam" message.
4. The chronograph flags no-ball and slow-ball shots.
5. Stray-round clear at low speed on every arming.
6. Approved balls only (the 23–24 mm bore and pocket reject darts and gel). Wet balls are kept out by the no-wet-grass rule.

8.8 Fit to the head payload interface

9. What should change in docs/head-payload.md

designs/*.json (head_payload):

• Set magazine to "24-ball hopper, refilled at the dock".
• Add ammo_mass_g: 1.83, muzzle_speed_m_s: 21.3 and kid_rate_hz: 3.
• Keep mass_g 1500 and com_above_top_mm 120. The concept fits under both.

10. Open questions

• Ball exit speed against wheel speed and diameter, for the hard ceiling in §8.3. Settle it on the bench with a chronograph.
• Foam balls on damp grass. Does closed-cell EVA (Worker Cheetah) or PU (Dart Zone) pick up water and jam? Test it.
• AM32 RPM telemetry on the Repeat ESC. Confirm bidirectional DShot works; otherwise use C615 + a hall tach.
• Whether a Tritium robot game falls under 16 CFR 1250 if gel is ever used, and whether a soft 7.5 mm bead passes the 5.0 mm funnel gauge.
• The RoboMaster S1's launch mechanism (spring piston or friction). This decides whether a compact flywheel gel launcher is proven.
• Mass of the M2006 dial assembly and hopper as printed, and the real CoM. Measure once CAD exists.
• Laser visibility. Class 1 at ≈ 0.2 mW against Class 2 at 1 mW in daylight. Test both before choosing.