These three motors solve different motion problems. Tradinor writes the load and the drive first, then the motor. A larger frame that the drive cannot control is not a safer purchase.
Match the motor to the motion
An induction motor wants a voltage, a frequency, a power or torque, and a speed. On a variable-frequency drive, also state the speed range and whether cooling is a shaft fan that dies at low speed. A servo wants continuous and peak torque, speed, inertia match, and the feedback the drive accepts. A stepper wants holding torque and torque at speed, the supply voltage of the drive, and whether you can accept an open loop.
The mechanical interface is part of the order: flange, shaft diameter, key, and encoder connector. An electrical match with the wrong flange is a machining job. Environment is the other half. A washdown motor is a sealing and a material specification, not a hope that the standard frame will survive.
- Motion: continuous speed, positioning, or a few locked speeds.
- Supply and the drive model or the drive requirements.
- Torque or power at the speed that matters, not only at zero.
- Feedback, if any, and the protocol the drive can read.
- Flange, shaft, and the enclosure.
| Motor | Specify | Poor substitute |
|---|---|---|
| Induction | V, Hz, kW or Nm, poles, duty | A servo where a fan only needs speed |
| Servo | Nm continuous and peak, encoder | A stepper that will stall unseen |
| Stepper | Nm at speed, frame, drive voltage | A larger current with no torque curve |
Sample check
Read the nameplate voltage and speed. Confirm the encoder part if the drawing names one. Turn the shaft and confirm the key and flange against the coupling you already bought. Do not treat a successful no-load spin as a torque test. File the torque or power figure from the datasheet at your speed next to the drive setting you intend to use.
What to lock on the order
Start the RFQ with the motion profile in one sentence: speed, how often it starts, and whether position must be known after power loss. Then name the drive, because the motor and the drive are one purchase even if two vendors supply them. For an induction motor on a drive, state the speed range and ask whether the motor needs a separate blower below base speed. For a servo, state continuous torque, peak torque, and the encoder protocol the drive accepts. For a stepper, state torque at the high speed, not only holding torque. Add flange and shaft dimensions on the same document as the electrical data so a mechanical substitute cannot arrive with the right nameplate and the wrong fit. On the sample, check the nameplate and the shaft fit. Save the no-load spin for after that. File the datasheet curve you designed to next to the drive parameter list.
Questions buyers actually ask
Is a servo always more precise?
A servo is a motor plus a feedback device plus a drive. Precision is the encoder and the mechanics, not the word servo on the carton.
When is an induction motor enough?
When the load is a fan, a pump, or a conveyor that a drive can ramp. You do not need a servo for a speed that may vary slowly.
What fails first on a stepper?
Missed steps when torque falls at speed, and heat when the drive is left at a high current. Specify torque at the speed you need.