Choosing the wrong frame size is the single most common reason a gear motor returns from a trial fit. The motor may run, but the bolt circle, shaft height, or torque output does not match the driven machine, and you end up re-machining brackets or sourcing a new unit. A reliable gear motor size chart ties frame number to physical footprint and to the power, speed, and torque envelope so you can pick the right unit before you order. This guide shows how to read the chart, what dimensions actually control fit, and which Tenchuan series to choose for the most common small-frame jobs.
A frame size is a coded number — usually the motor body diameter in millimetres for small AC gear motors, or a NEMA/IEC number for industrial units — that locks together the four dimensions you need to mount the unit:
Because those four dimensions are fixed by the frame, the same frame can usually accept a range of output powers, gear ratios, and shaft speeds. That is also why you can drop a 60 W motor into a machine that previously ran a 40 W unit on the same frame, without re-machining the bracket. See our small AC gear reducer motor line for current frame and power combinations.
Every size chart answers three questions in this order:
Two units with the same frame but different gear ratios will have different output torque at the same input power, so when comparing charts, compare like-for-like at the output shaft.
The most common small AC induction gear motor frames are 60 mm, 70 mm, 80 mm, 90 mm, and 104 mm body diameter. Each frame covers a power band and a typical torque envelope:
| Frame (mm) | Typical Output Power | Common Series Examples | Typical Output Torque Range | Output Speed Range |
|---|---|---|---|---|
| 60 | 6 W – 25 W | 4GN / 4IK small AC right-angle | 0.1 – 1.5 N·m | 5 – 600 r/min |
| 70 | 15 W – 40 W | 5GN small AC | 0.3 – 3.0 N·m | 5 – 600 r/min |
| 80 | 25 W – 60 W | 5RK / 5IK small AC | 0.4 – 5.0 N·m | 5 – 500 r/min |
| 90 | 40 W – 140 W | 5RK 60 W, 5GU / 6GU right-angle | 0.7 – 14 N·m | 5 – 500 r/min |
| 104 | 90 W – 200 W | 5GU high-power right-angle | 1.5 – 25 N·m | 5 – 400 r/min |
Treat these as planning bands, not absolute limits. Real torque depends on the gear ratio you select; a 90 mm frame at 10:1 will deliver very different torque from the same frame at 60:1.
To make the chart concrete, here is the rated output data for the Small AC Gear Reducer Motor 60 W on the 90 mm frame. All values are taken from the published nameplate data for that model.
| Motor Model | Duty | Output Power | Voltage | Current | Rated Torque | Rated Speed |
|---|---|---|---|---|---|---|
| 5RK30GN-C | Reversible 30 min | 60 W | 1-phase 220 V | 0.50 A | 670 mN·m (67 kg·cm) | 1350 r/min |
| 5RK30A-C | Reversible 30 min | 60 W | 1-phase 220 V | 0.52 A | 554 mN·m (55.4 kg·cm) | 1550 r/min |
| 5RK30GN-A | Reversible 30 min | 60 W | 1-phase 110 V | 1.00 A | 670 mN·m (67 kg·cm) | 1350 r/min |
| 5RK30GN-S | Reversible 30 min | 60 W | 3-phase 220 V | 0.52 A | 441 mN·m (44.1 kg·cm) | 1350 r/min |
Same frame, four supply variants. This is exactly why a frame-based size chart works: pick the frame, then choose the voltage and duty that match your site supply.
Beyond the chart values, four dimensions decide whether a gear motor drops into your machine:
For a deeper look at how the motor and gearbox halves share the same envelope, our gear motor parts identification guide shows which dimensions belong to which side of the assembly.
Three mounting styles cover most small AC gear motor installations:
The matched accessories — torque arms, couplings, flanges, and base kits — are summarised in our gear motor accessories guide.
Gear ratio multiplies motor torque at the output shaft, at the cost of output speed. The relationship is roughly:
Output torque ≈ Motor torque × Ratio × Gearbox efficiency
For a 60 W motor at 1350 r/min on a 90 mm frame, the published allowable load at common ratios is:
| Ratio | 5:1 | 10:1 | 20:1 | 30:1 | 50:1 | 100:1 | 180:1 | 300:1 |
|---|---|---|---|---|---|---|---|---|
| Allowable load (N·m) | 1.08 | 2.64 | 4.80 | 6.24 | 9.64 | 14.4 | 19.6 | 19.6 |
| Approx. output speed (r/min) | 270 | 135 | 67 | 45 | 27 | 13 | 7.5 | 4.5 |
Notice that beyond about 180:1 the allowable load flattens — gearbox torque capacity, not ratio, is the limit. For ratios above 200:1, install a second reduction stage between motor and gearbox, or pick the next larger frame.
Use this five-step process before you commit to a frame:
For small AC induction gear motors, the frame number is the motor body diameter in millimetres. A 90 mm frame has a 90 mm body diameter and a fixed shaft height, pilot diameter, and bolt-circle pattern across all models on that frame.
Usually yes. The 5RK 40 W and 5RK 60 W share the same 90 mm frame, so the mounting dimensions match. Confirm the rated torque, duty cycle, and supply voltage before swapping, and verify that the driven machine can accept the higher output torque.
Use the conversions 1 N·m ≈ 10.2 kg·cm, and 1 N·m = 1000 mN·m. Always read rated torque at the output shaft, not at the motor shaft, when comparing gear motors.
For output speeds below 10 r/min, choose a frame one size larger than the chart suggests and stay within the published allowable load for that frame. Ratios above 200:1 on a single stage reduce efficiency and raise backlash; consider a two-stage reduction instead.
Frame size and IP rating are independent. A 60 mm frame motor can carry IP65 sealing just as easily as a 104 mm frame. The IP rating is set by the seal design and the cable entry, not by the body diameter.
A good gear motor size chart saves a round of bracket re-machining. Match the frame first (body diameter, shaft height, pilot, bolt circle), then read the published rated torque for your chosen ratio, and finally confirm duty cycle and supply. When you are ready to specify a unit, send Tenchuan your required output speed, load torque, supply voltage, and mounting style — we will match the frame and ratio against the chart above and confirm the right model on the same day.
