Understanding N20 Motor Selection
The N20 is one of those tiny gearmotors you see everywhere in hobby robotics, small automated projects, and student engineering builds. It's a 12V DC motor with an integrated planetary gearbox, usually in a 28mm body diameter package. The problem is that not all N20s are the same, and picking the wrong one will waste your time faster than anything else in this project type. Here's how I approach it in practice. First, figure out your torque requirement. Take your load, multiply by the lever arm distance from the motor shaft to where the force is applied, and that's your minimum output torque. Then divide by the gearbox ratio to get the required motor shaft torque. Most N20 motors produce somewhere between 0.5 Nm and 2.5 Nm of output torque depending on the gearbox ratio you pick. The speed comes next. N20 motors typically spin anywhere from 50 RPM to over 2000 RPM at the output, depending on the reduction ratio. If you need precise speed control, you're better off using a PWM driver with an encoder rather than trying to dial it in through gear selection alone.
I ran into a real issue last year when I was building a small robotic arm. The datasheet listed the N20 at 100 RPM and 0.8 Nm, but after assembling everything, the motor would stall under a light load. Turned out the actual stall current was much higher than spec because the supplier had quoted parameters from a different variant. I ended up swapping to a motor from a different batch and adding a current limit on the driver, which solved it. Always verify your supplier's specs against actual measurements rather than trusting the sheet blindly. When it comes to the gearbox, there are two main options: plastic or metal gears. Plastic is quieter and lighter but the teeth strip relatively easily if you bind the motor. Metal gears handle higher loads but add friction and wear. For most light-duty applications under 2 kg of payload, the plastic version is adequate. Anything heavier and you should be looking at the metal gearbox variant or sizing up to a larger motor entirely. One thing people consistently miss is the voltage relationship. The N20 is rated for 12V nominal, but running it at 6V or 9V is actually useful if you need lower speed without a more complex control setup. The torque drops proportionally though, so don't expect the motor to pull the same load at reduced voltage. A 12V N20 running at 6V will roughly halve both its speed and torque output.
For wiring, these motors typically draw between 0.1A no-load and 1.5A at stall. Your driver needs to handle at least 2A continuous to be safe, and preferably 3A for short bursts during startup or load spikes. If you're using an H-bridge driver board, make sure it has adequate heatsinking for your application. Small MOSFET-based boards can overheat quickly under sustained load. If you need something more powerful than an N20 can provide, the GG20 or N130 are natural stepping-up choices. The GG20 shares similar mounting patterns but delivers significantly more torque at the cost of size and weight. There's no perfect substitute if you're constrained by the N20 form factor, so plan your sizing from the start rather than trying to push a marginal motor further than it should go.
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