Planetary Geared Motor for a Motorized Gate Actuator Arm

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Planetary geared brushed DC motor

Problem

The remote control motorized gate (commonly known as auto gate) did not move.

Troubleshooting

When pressing the control switch, a sound from the actuator arm (swing arm) indicated that there was no issue with power input.

Solution taken

The planetary geared motor was replaced.

The impact of not solving the problem

Opening the gate by hands after detaching actuator arms.

Unit-specific parameters (for DNOR 212 or MIRIES arms)

  1. Voltage: 12V
  2. Current type: DC
  3. Weight: 430 g
  4. Motor type: 555, brushed
  5. Motor base speed: 6000 rpm
  6. No-load speed after reduction: 120 rpm
  7. Reduction ratio: 6000/12 = 50
  8. Mounting hole size: M3
  9. Shaft profile: D-shape
  10. Shaft diameter: 8 mm
  11. Motor length: 57 mm
  12. Planetary gearbox diameter: 36 mm
  13. Planetary gearbox length: 38.5 mm
  14. Actuator arm fastener type: socket head
  15. Actuator arm support fastener size: M10 x 30
  16. Actuator arm housing fastener size: M5 x 20

Notes

  1. Torque = power ÷ rotational speed, thus with the same input power, higher torque requires lower rotational speed, and increasing speed reduces torque. A balance should be sought between faster but weaker gate motion and slower but stronger gate motion. It is like riding a bicycle. Climb a hill at the low gear, slow but strong. Go on flat roads at the high gear, fast but weak.
  2. Planetary gearbox length increases with the number of reduction stages needed to achieve higher output torque. For typical swing arms, 38.5 mm is common. Check the size of the old planetary geared motor for the correct fit.
  3. Higher output torque generally leads to greater stress on gears.
  4. For the same motor base speed, lower reduction ratio gives lower output torque but higher gearbox longevity. To achieve higher torque with the same motor base speed, the sun gear (center gear) has to be smaller. Smaller gears are weaker.
  5. For the same reduction ratio, higher motor base speed gives lower output torque but higher gearbox longevity. To achieve higher torque with the same reduction ratio, a motor with lower motor base speed is used to deliver more torque, giving stress to the gear teeth.
  6. It is normal that brushed motors experience gradual performance degradation due to carbon brush wear, resulting in lower torque and possible speed variations over time. Just replace the planetary geared motor without replacing the entire actuator arm.
  7. If the input power cables are only two (positive red and negative black), then a brushless motor cannot be used because such motor has more cables and needs to connect to an electronic controller.
  8. When a motor begins to weaken, if the input voltage at the controller box is adjustable, adjust it to its maximum, if not already, to provide a temporary boost until the planetary geared motor is replaced. Also check if the gate is sagging.
  9. Before reassembling the actuator arm housing, ensure all moving parts move smoothly and lubricate as necessary.
  10. Another possible scenario is when pressing the control switch, there is no sound from the actuator arm, indicating there is no power input. In this case, check that a solder joint has come loose or the cable has been chewed by rats.

Tools used

  1. Calipers
  2. 6 mm L key
  3. 4 mm L key, ball end for faster screwdriving at an angle because the short arm of the L key interferes with the workpiece when the long arm is inserted in straight position {axially) into the socket head
  4. 2.5 mm L key
  5. Long pin punch, to push the motor out of the actuator arm housing
  6. Soldering iron and solder
  7. Lubricant

This is problem-first learning. The knowledge was learnt because there was a problem to solve.

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