EMAX ECO II 3115

What you get for $41.56

• About 5 kg of pull on 6S

  On EMAX’s 25 V bench the 900KV pulled 4,960 g at full throttle on an AVAN 1050 three-blade, drawing 80.6 A.

  Source: EMAX 900KV thrust tables

• Five KVs, 4S to 12S

  EMAX sells the 3115 in five KVs, from 900KV for 4S–6S to 400KV for 10S–12S, and tested each on three 10-inch props.

  Source: EMAX spec sheet, EMAX 400KV thrust tables, EMAX 900KV thrust tables

• 5,270 g on 10S

  The 500KV pulled 5,270 g at full throttle at 40 V on an HQ 10 × 5 × 3, drawing 48.8 A.

  Source: EMAX 500KV thrust tables

• 7.13 g/W at 510 g

  Making 510 g of thrust at 48 V, the 400KV ran at 7.13 g/W on an HQ 10 × 5 × 3.

  Source: EMAX 400KV thrust tables

What to pair it with

Our reading of EMAX’s numbers, so your build matches what the motor was tested with.

ESC

EMAX rates the peak current at 85 A (900KV) and 68 A (800KV) on 6S, 63 A (640KV) on 8S, 49 A (500KV) on 10S and 41 A (400KV) on 12S; on its bench the 900KV drew up to 84.4 A. Size the ESC for both: 85 A or more for the 900KV on 6S, and ESCs rated for 8S, 10S or 12S for the three lower KVs. (EMAX spec sheet, EMAX 900KV thrust tables)

Props

EMAX lists 10-inch props (9 to 10-inch for the 800KV and 900KV) and tested three 10-inch three-blades on every KV: Gemfan 1050, AVAN 1050 and HQ 10 × 5 × 3. (EMAX spec sheet, EMAX 400KV thrust tables, EMAX 500KV thrust tables, EMAX 640KV thrust tables, EMAX 800KV thrust tables, EMAX 900KV thrust tables)

Battery

6S for the 800KV and 900KV (rated for 4S–6S, tested at 25 V), 8S for the 640KV (6S–8S, 32 V), 10S for the 500KV (8S–10S, 40 V) and 12S for the 400KV (10S–12S, 48 V). (EMAX spec sheet, EMAX 400KV thrust tables, EMAX 500KV thrust tables, EMAX 640KV thrust tables, EMAX 800KV thrust tables, EMAX 900KV thrust tables)

Frame

Four M3 holes on a 19 mm circle (19 × 19 mm). (EMAX spec sheet)

Where to buy

• EMAX USAthe maker’s US store; same price for every KV (the 800KV was listed as sold out)
  $26.99seen Oct 19, 2026
  Visit
• EMAXthe maker’s global store
  $41.56seen Oct 19, 2026
  Visit

Plain links, not affiliate links. Prices change; the store’s page has the current one.

Full specs

Bench data

Redrawn from EMAX’s test reports. Thrust is static pull on a bench, more than you get in flight. Power is volts × amps; efficiency is thrust divided by power.

Inside the motor

A brushless outrunner: the coils stand still in the middle and the magnets spin around them. From the top down:

• Shaft. M5 thread, protrudes 17.5 mm; 5 mm through the bearings. (EMAX spec sheet)
• Stator. The coils are wound on a stack of thin steel laminations: 31 × 15 mm (3115). (EMAX USA product page, EMAX spec sheet)
• Base. 4 × M3 holes on a 19 mm circle (19 × 19 mm). (EMAX spec sheet)

How fast it spins

KV is the motor’s no-load speed per volt. With nothing on the shaft, the 900KV version reaches about these speeds; a prop loads the motor and brings it down, typically to around 70–75% of these figures at full throttle.

A 14-pole rotor has 7 pole pairs, so every turn of the shaft is 7 electrical cycles, and a six-step ESC switches the phases 42 times per turn.

About the 3D model

A generic outrunner drawn from EMAX’s published sizes: the 31 × 15 mm stator, 37.3 mm bell, 31.15 mm height, 5 mm shaft, 19 mm mounting circle and 12 teeth and 14 magnets. Anything EMAX doesn’t publish is typical for a motor this size, and the bell’s spoked top, the base and the inside are a generic design, not this motor’s. The colours are read off the maker’s product photos. There are no logos or markings: it is our drawing, not the maker’s.

Sources

1. EMAX USA: ECO II 3115 Brushless Motor (product page, with EMAX’s spec sheet). Retrieved Oct 19, 2026.
2. EMAX: ECOII3115 400KV / 500KV / 640KV / 800KV / 900KV (product page on EMAX’s global store). Retrieved Oct 19, 2026.
3. EMAX: ECOII-3115 spec sheet (dimension drawing and spec table for each KV; image on EMAX’s product pages). Retrieved Oct 19, 2026.
4. EMAX: ECOII-3115 400KV thrust tables at 48 V, three 10-inch three-blade props (image on EMAX’s product page). Steps of thrust, then “Max” at full throttle; EMAX’s rpm column is left out because it has no figure at full throttle.. Retrieved Oct 19, 2026.
5. EMAX: ECOII-3115 500KV thrust tables at 40 V, three 10-inch three-blade props (image on EMAX’s product page). Steps of thrust, then “Max” at full throttle; EMAX’s rpm column is left out because it has no figure at full throttle.. Retrieved Oct 19, 2026.
6. EMAX: ECOII-3115 640KV thrust tables at 32 V, three 10-inch three-blade props (image on EMAX’s product page). Steps of thrust, then “Max” at full throttle; EMAX’s rpm column is left out because it has no figure at full throttle.. Retrieved Oct 19, 2026.
7. EMAX: ECOII-3115 800KV thrust tables at 25 V, three 10-inch three-blade props (image on EMAX’s product page). Steps of thrust, then “Max” at full throttle; EMAX’s rpm column is left out because it has no figure at full throttle.. Retrieved Oct 19, 2026.
8. EMAX: ECOII-3115 900KV thrust tables at 25 V, three 10-inch three-blade props (image on EMAX’s product page). Steps of thrust, then “Max” at full throttle; EMAX’s rpm column is left out because it has no figure at full throttle.. Retrieved Oct 19, 2026.