Robot MarketPlace - Magnum 775 Planetary Gearmotor

The Robot Power Magnum775 is a robust low-cost gearmotor which includes the planetary gearbox and a powerful RS775 motor. The gearbox output shaft is 0.5" diameter and 3" long with a precut keyway for easy mounting of wheels and sprockets.

The Magnum775 includes a planetary gearbox with a 20:1 reduction ratio. This ratio gives approximately 700 RPM output speed at low load at 14.4V. A heavy steel ring gear supports the steel planet gears riding on hardened steel pins. Note the final stage gears are twice as thick as the first stage gears. This helps the Magnum775 to handle the high torque produced by the 775 motor at heavy loads. The 3" long 0.5" diameter output shaft is supported by dual high-quality sealed ball bearings. As with all gearbox shafts a heavy load or high shock loads on an unsupported shaft can exceed the strength of the structure. For the most robust design support the outer end of the shaft with a ball bearing.

While the Magnum775 may seem lengthy but in fact it is just under 5" from the front of the gearbox to the back of the motor. This is actually shorter than many power drill gearmotor combinations with the added strength and convienence of the mounting flanges.

The shaft diameter of the motor pinion is 5mm. This allows other motors with a 5mm shaft to be used assuming the mounting holes match. Other makers of 775 sized motors offer compatible motors allowing for upgrades or different voltage ratings. Please verify the motor dimensions and mounting configuration.

The Magnum775 may be mounted to the target application via the 10-32 mounting bolts to the edges or face of the gearbox. A clamp style mount may also be used around the the motor can. If the gearbox is mounted securely it is not normally necessary to support the motor can but for high-vibration or shock applications supporting the motor along with the gearbox is recommended.

Gearmotor Specifications:
Size: 1.75" square flange x 4.92" long (excluding shaft)
Motor: Leshi LS-775PX (Mabuchi RS-775 copy)
Motor voltage: 14.4V nominal, may be run at 18V
Gear Ratio: 20:1 2-stage planetary
Output Shaft: 0.50" dia. x 3.0" long with standard 1/8" keyway
Gears: Machined Steel
Output Bearings: Dual Ball Bearings
Weight: 28oz motor and gearbox

Performance with stock motor
Peak Ouput Power: 400W at 12V (880W at 18V) motor spec
Gearbox output Speed: 720 RPM at 14.4V (KV = 50 RPM/V)
Gearbox torque (estimated): Kt = .12Nm/A - 17.0oz-in/A at peak power out 14.4V
Gearbox stall torque(theoretical): 17.6Nm - 2500 oz-in
Motor current: 3.8A no load at 14.4V
Stall current: 140A at 14.4V (motor mfr spec)
Motor Stall torque: 0.980Nm - 139 oz-in at 14.4V
Peak Efficiency: ~75% peak for motor (mfr spec) not including gearbox