Building Under 250 Grams With 1204 Motors and 2S LiHV

Put your ready-to-fly rig on a cheap digital kitchen scale. If the screen reads 251 grams, the aviation authorities in most countries treat your model the exact same way they treat a ten-pound commercial cinema rig. In the United States, crossing the 250-gram line means mandatory FAA registration, paying the registration fee, and strapping on an active Remote ID broadcast module. In Europe and the UK, it moves you out of the open sub-category where you can fly in local parks without keeping massive stand-off distances from bystanders.

Those extra two grams cost you money, privacy, and flight spots.

Building under 249 grams with a battery installed used to mean flying gutless little micro quads that blew away in an eight-knot breeze. That is no longer true. With high-voltage lithium chemistry, tiny toothpicks running 1204 stator sizes, and cleaner airframe geometry, you can build a 3-inch or 3.5-inch machine that rips like a standard 5-inch freestyle quad while sitting safely at 240 grams all-up weight. You can also build a 1-meter span sub-250g glider or cruising plank that stays up for forty minutes.

The catch is that you cannot just slap off-the-shelf parts together and hope for the best. You need a strict weight budget, and you have to trim grams in places most builders ignore.

The Real Weight Budget: Start With the Pack

Most newcomers build their aircraft first, weigh it on the bench, and then realize they only have 30 grams left for a battery. That is backwards. A 30-gram battery on a quad gives you two minutes of mediocre flight time before the cells sag into the dirt.

Experienced ultralight builders start from the battery and work backward. A reliable rule of thumb is to give roughly 35% to 40% of your total weight budget to your battery pack. That gives you between 85 and 100 grams for energy storage.

That leaves you with exactly 150 to 165 grams dry weight for everything else:

• Carbon frame or foam airframe: 25g to 40g
• Four motors (for a quad) or one motor and two servos (for a plank): 24g to 35g
• All-in-one (AIO) flight controller and ESC board: 7g to 10g
• Digital video transmitter or analog camera/VTX: 8g to 22g
• Receiver, antennas, wiring, and hardware: 10g to 15g
• Propellers: 4g to 8g

If any single part overshoots by three grams, you will end up over 250g once you strap on a battery pad and a velcro strap. Every single component must fight for its spot on the bench.

Motor Sizing: Why 1204 Beats 1404 on 2S and 3S

For 3-inch props, the standard recommendation on forums for years has been the 1404 motor. Motors like the 1404 3800kv or 4500kv are fantastic powerplants. They produce massive low-end torque, handle aggressive punchouts, and stay cool under heavy throttle.

They are also heavy. A typical 1404 motor with short wires weighs between 9.5 and 10.5 grams. Multiply that by four, and your motors alone eat up 40 grams of your dry weight budget. Add four steel M2 mounting screws per motor, and you are sitting at nearly 45 grams just on propulsion hardware.

Drop down to a 1204 stator size (like an RCinPower 1204 or BetaFPV 1204). A bare 1204 motor with wire weighs around 5.8 to 6.2 grams. Across four arms, four 1204 motors weigh roughly 24.5 grams.

You instantly save 16 to 18 grams right off the tips of your arms. Removing weight from the outer edges of the airframe does something else that bench tests do not show: it drops your rotational moment of inertia. The quad flips and rolls crisper because the flight controller does not have to fight heavy motor bells swinging around on long lever arms.

Bench Testing 1204 vs 1404 on 2S and 3S

We ran thrust stand pulls using Gemfan 3016 biblade and HQProp 3x2x3 triblade props to see what you actually give up by stepping down from 1404 to 1204.

On a high-KV 1204 motor (around 6500KV) running a 2S LiHV pack:

• Gemfan 3016 Bi-Blade: 112 grams of thrust at 100% throttle pulling 7.8A. Cruising thrust (40 grams) takes just 1.8A per motor.
• HQ 3x2x3 Tri-Blade: 128 grams of thrust at 100% throttle pulling 9.6A. Better grip in the corners, but runs warmer.

On a standard 1404 4500KV motor running a 3S pack:

• Gemfan 3016 Bi-Blade: 165 grams of thrust at 100% throttle pulling 8.2A. Cruising thrust (40 grams) takes 1.4A per motor.

While the 1404 on 3S clearly wins on outright top-end punchout speed, four 1204 motors on 2S LiHV still generate around 480 grams of total static thrust on a 3-inch biblade. On a craft with an all-up weight of 170 grams, that represents a thrust-to-weight ratio close to 3:1. That is plenty of authority for aggressive park freestyle, tree weaving, and smooth cinematic lines without running hot.

The 2S LiHV Advantage: Voltage Sag vs Weight

Why run 2S LiHV instead of standard 3S or 4S packs? It all comes down to packaging and lead weight.

A standard 3S 450mAh 75C LiPo weighs roughly 42 to 45 grams. A 4S 450mAh pack weighs around 56 to 60 grams. If you try to run 4S to get high voltage efficiency, you need heavier wire gauges (16AWG or 18AWG leads), a heavier XT30 connector, and an extra inter-cell balance connection.

Switching to a 2S LiHV (Lithium High Voltage) pack charged to 4.35 volts per cell changes the equation. A quality 2S 720mAh 100C LiHV pack weighs just 38 grams. That gives you 5.3 watt-hours of energy in a pack that is noticeably lighter than a tiny 3S 450mAh pack (which only yields around 5.0 watt-hours).

LiHV cells have a slightly higher energy density than regular 4.2V standard LiPos. By running 2S at higher capacity instead of 3S at low capacity:

1. You reduce dead pack weight from wrapping, extra cell tabs, and balance wiring.
2. The internal resistance per cell is often lower on larger capacity cells, meaning less voltage sag when you blip the throttle.
3. The lower cell count means your flight controller voltage regulator runs cooler because it only drops from 8.7V down to 5V/9V instead of burning off heat from a 16.8V 4S input.

If you want pure endurance instead of freestyle punch, you can wire two 18650 3500mAh lithium-ion cells in series. A bare 2S 18650 pack weighs around 98 grams. When paired with a super-efficient 1204 or 1303 setup on a 3.5-inch or 4-inch ultralight biblade prop, that 2S pack cruises at just 3 to 4 amps total. That translates to an honest 28 to 35 minutes of flight time while staying at 235 grams total weight.

Carbon Tuning: Frame Stiffness Without Dead Weight

When builders want to stiffen an airframe that suffers from mid-throttle oscillations, the default move is usually to buy a thicker carbon bottom plate. Moving from a 2mm bottom plate to a 3.5mm bottom plate adds 8 to 14 grams. That will wreck your sub-250g target.

You do not need thicker carbon. You need smarter carbon layout.

Geometry Over Thickness

A 2mm carbon unibody plate cut in a wide-X or dead-cat configuration can twist easily along its long axis. Torsional flex causes the gyro on your flight controller to see false noise, which forces you to run heavy software filtering in Betaflight or INAV. Heavy filtering introduces latency, making the craft feel sluggish and heating up your motors.

Instead of thicker plates, look for frames that use:

• Arm braces or strut bridges: A tiny 1mm carbon brace connecting the front and rear arm tips adds less than 1.5 grams total, but increases torsional stiffness by over 40%.
• True-X geometry: Shorter overall arm spans create shorter lever arms, dramatically reducing the twisting force applied to the center stack.
• Continuous carbon weave: Cheap carbon plates cut from random scrap have uneven fiber alignment. Look for 3K T700 carbon sheets where the fiber orientation runs directly along the axis of each arm.

Ditch the TPU: The Silent Weight Creep

Thermoplastic polyurethane (TPU) is convenient. We all love 3D printing custom action camera mounts, antenna holders, arm guards, and bumper skids.

TPU is also remarkably dense. Take your finished build and strip every 3D printed piece off it. Put those printed parts on the scale. Most builders are shocked to find 15 to 25 grams of flexible plastic bolted to their craft.

Here is how to trim plastic weight down to nearly zero:

• Antenna mounts: Instead of a 4-gram molded TPU tail block for your receiver and VTX antennas, use a 0.1-gram sliver of clear heat shrink strapped to a small zip tie secured directly to a rear standoff.
• Camera mounting: Skip full-cage TPU camera pods. Mount micro and nano FPV cameras directly between the front aluminum standoffs using small carbon plates and 1mm nylon washers.
• Landing feet: Throw away the printed arm boots. Put a tiny drop of shoe repair glue or a 2mm sliver of dense foam tape under each motor screw head to protect the carbon tips during hard landings on tarmac.
• Battery pads: Thick sticky silicone battery pads weigh 3 to 5 grams. Replace them with a thin strip of textured rubberized grip tape or self-adhesive neoprene foam, which weighs under 0.8 grams.

Fastener Diet: Aluminum and Nylon

Standard M2 black oxide steel screws weigh about 0.35 grams each for an 8mm length. A quad uses at least 16 motor screws and 8 to 12 frame and stack screws. That is 28 steel screws totaling nearly 10 grams.

• Replace your motor screws with grade 5 titanium or 7075-T6 aluminum screws. Aluminum M2 screws save roughly 60% of fastener weight. Since 1204 motors generate low shear forces, high-grade aluminum hardware is completely adequate on the motor base.
• Use nylon M2 standoffs and nuts for your flight controller stack. Never use metal screws to secure an isolated flight controller board. Nylon is lighter and flexes enough to damp high-frequency vibration before it reaches the gyro.

Real Build Sheets: Sub-250g Quads and Wings

To see how this works in practice, here are two build sheets that have been field tested, weighed on a calibrated scale, and flown across dozens of packs.

Build 1: 3-Inch Freestyle Park Quad (Total Weight: 178g)

Even if you strap a 60-gram naked action camera (like an unshelled GoPro or a DJI Action 2 stripped down) onto this build, the entire machine sits at roughly 185 grams ready to fly. It easily handles three-minute freestyle runs with absolute legal peace of mind.

Build 2: 750mm Ultralight Cruising Plank (Total Weight: 212g)

Sub-250g fixed-wing aircraft do not need paper-thin foam that snaps on a rough grass landing. You can build a stiff, high-durability EPP or Depron plank that handles windy ridge lines.

When designing sub-250g fixed-wing planes, we sometimes run basic wing loading and balance calculations inside MyRC to check stall speeds and center-of-gravity shifts before gluing down motor mounts and cutting battery bays.

Flight Controller Tuning for Ultralights

When you cut 80 grams off an aircraft, you change how it reacts to motor inputs. Light props and low-mass motor rotors spin up and slow down almost instantly. If you use standard default PIDs designed for 700-gram 5-inch drones, an ultralight sub-250g rig will feel jittery and may even oscillate violently.

Lower Your D-Gain and Master Multiplier

Because smaller motors have very little rotational inertia, you do not need aggressive derivative (D-term) gains to stop overshoots. High D-gains on light builds simply turn into motor heat.

• Drop your D-term gains by roughly 15% to 20% compared to stock Betaflight profiles.
• Ensure bi-directional DShot is enabled so your ESC feeds exact motor RPM data back to the flight controller.
• Set your dynamic notch filters to track motor RPM cleanly. With RPM filtering active, you can drop two of the default low-pass software filters, cutting gyro latency by several milliseconds.

Tweak the Throttle Curve for 2S

When flying a 2S setup, the throttle curve feels slightly softer at the top end than a high-voltage 4S build. To get linear stick response:

• Set a slight throttle expo (around 0.15 to 0.20) in your configurator.
• If you want snappy mid-stick cruising, adjust your throttle midpoint to around 0.35 on a quad or 0.45 on a fixed-wing plane.

Practical Wiring Tips to Shave the Last 5 Grams

When you are staring at a build that sits at 252 grams on the scale, you do not need to buy new motors. You can find those three grams inside the wire harness.

1. Direct Solder Everything: Strip off the plastic JST-SH push-in connectors from your flight controller and video transmitter. Direct soldering your camera, receiver, and VTX wires removes the plastic headers and pins, saving about 2.5 grams across the build.
2. Cut Wire to Length: Do not fold excess silicone wire under the board. Pull each motor wire taut to its ESC pad, add 3 millimeters of slack for arm flex, and cut the rest off. Trimming excess 20AWG motor wire across four arms removes up to 2 grams.
3. Use 20AWG or 22AWG for 2S Power Leads: On standard 5-inch builds, 14AWG power leads are common. On a 2S build pulling a maximum of 25A total burst current, 18AWG or 20AWG wire is more than thick enough. A two-inch lead of 20AWG wire with an XT30 connector weighs half as much as a heavy 14AWG lead with an XT60.
4. Strip Balance Leads on Flight Batteries: If you are building custom 2S packs, use a tiny JST-XH balance plug with thin 28AWG wire, or charge through an XT30 balance board that does not require heavy flying leads.

What to Put on the Bench This Weekend

If you have a 3-inch or micro plane build gathering dust because it was too heavy to fly legally in local spots, tear it down to the bare carbon or foam.

Weigh every single part individually on a jewelry scale and write the numbers in a notebook. Swap those bulky 1404 motors for high-KV 1204s, replace heavy 3D prints with carbon cutouts and heat shrink, and test a 2S LiHV pack on your next field trip.

Getting under that 250-gram limit is not just about avoiding aviation paperwork. A lighter craft takes less damage in a crash, makes far less noise, and lets you fly in spots where a loud, heavy rig would immediately turn heads for the wrong reasons. Put your craft on the scale, trim the dead weight, and get out to the field.

Sources

• https://www.flyusi.org/guides/drone-laws
• https://www.zenatech.com/drone-laws-2025-everything-you-need-to-know/
• https://intofpv.com/t-sub250g-30min-10km-digital-navigation-challenge
• https://blog.uavmodel.com/building-a-sub-250g-long-range-fpv-drone-complete-parts-guide-2026/
• https://www.reddit.com/r/fpv/comments/1dqrztl/guys_is_that_all_i_need_for_a_sub_250g/
• https://www.youtube.com/watch?v=g26ASthCzvs