Control Techniques75UMD300CAAAAUnimotor UM Brushless AC Servo Motor, 75 mm Frame, 3000 rpm, 4.0 Nm Stall / 3.6 Nm Rated, Resolver Feedback, Keyed Shaft, No Brake

Product Description

A Control Techniques Unimotor UM brushless AC servo motor on the 75 mm square frame, D stator length, 3000 rpm rated speed, with resolver feedback and a keyed shaft. The carton confirms the model as 75UMD300CAAAA, made in the UK.

Model code decoded field by field

Control Techniques’ Unimotor code is positional, and reading it correctly tells you almost everything:

75 — frame size, 75 mm square.UM — Unimotor, the Unidrive winding variant. (SL was for MultiAx / M’Ax, DM for DigitAx — different windings, not interchangeable.)D — stator length D, the longest of the A/B/C/D options on this frame, so the highest torque available in a 75 mm body.30 — 3000 rpm rated speed.0 — brake NOT fitted.C — connector termination (as opposed to H hybrid or T terminal box).A — output shaft with key.A — feedback device: resolver.A — standard inertia.A — IEC flange.

Performance — and a correction to the previous listing

From Control Techniques’ resolver-fitted data table (125 °C rise):

Stall torque 4.0 NmRated torque 3.6 Nm at 3000 rpmPeak torque 12.0 NmStall current 2.50 ArmsRated output 1.13 kWTorque constant Kt 1.6 Nm/Arms; voltage constant Ke 98.0 Vrms/krpmWinding resistance 8.67 ohm, inductance 22.80 mH phase-to-phaseRotor inertia 1.9 kgcm²; mass 5.1 kgEarlier copy on this listing quoted a “holding torque of 4.4 Nm / 2.8 A”. That figure is wrong and has been removed. No 75-frame Unimotor publishes 4.4 Nm in any Control Techniques table — the 75 frame tops out around 3.6–4.0 Nm. 4.4 Nm at 2.75 Arms at 3000 rpm is the published figure for the 95-frame 95UMB300, so the original data appears to be a frame transposition from an adjacent row. “Holding torque” is also not a Control Techniques term, and it implies a brake this motor does not have (the fifth code digit is 0).

One further honest caveat: Control Techniques published several data tables for the Unimotor UM at different temperature rises and feedback types, and they disagree. The encoder-fitted 100 °C-rise table gives 3.6 Nm stall / 3.3 Nm rated / 2.25 A, and the 2002 UM brochure gives 3.9 / 3.5 / 2.5. We quote the resolver 125 °C table above because code position 8 on this motor is A, resolver. If your sizing is marginal, work from the table that matches your actual duty and rise.

Mechanical interface

75 mm square frame with an IEC flange: register spigot Ø60 j6 and four Ø5.8 mm holes on a 75 mm PCD. Overall length 301 mm maximum. Output shaft Ø14 mm x 30 mm long, keyed, key 5 x 22 mm. The key matters commercially: a keyed shaft suits pulleys and couplings with a positive drive, but a keyway is a stress raiser and introduces backlash in a high-reversal application, which is why the smooth-shaft option exists.

Electrical and feedback

Resolver type 55RSS116(P), 3:1 ratio. Windings are 400 V class, intended for 380–480 Vrms PWM drives. Class H insulation, UL file E214439. IP65 with the mating connector fitted, dropping to IP54 above 3000 rpm. Thermal protection is a PTC thermistor. Terminations are a 17-way signal connector and a 6-way power connector — order the matching cordsets, as they are not included.

Drive pairing

Control Techniques specified this motor against Unidrive UNI1403 and UNI1404 at a 12 kHz switching frequency with a 2.5 A current preset. Any 400 V-class servo drive can run it provided you can configure the resolver interface, the pole count and the correct Kt — but note that a resolver needs a drive with a resolver feedback option, not an encoder input, and that is the most common reason a Unimotor UM will not commission on a modern drive.

Lifecycle and what actually replaces it

Nidec lists the Unimotor UM and EZ ranges as superseded, with the stated upgrade path being Unimotor hd. There is a catch worth knowing before you plan a retrofit: Unimotor hd has no 075 frame — the range runs 060 to 190, so the nearest options are 067 or 089, neither of which shares this flange and shaft. The true dimensional drop-in was the Unimotor fm 075U2-D300. In practice, replacing a 75-frame UM with current product usually means new mounting and new coupling work, which is exactly why an exact-match new motor is worth having for an existing machine.

Condition and configuration

Supplied in the original factory-sealed Control Techniques carton — the photographs show the box still taped and unopened, carrying the model label 75UMD300CAAAA, “Made in UK EC”, the Control Techniques logo, a CE mark, the Control Techniques-Americas address in Eden Prairie, Minnesota, and a factory PASS test label with serial number 926160. Because the carton is sealed, the motor itself has not been removed for inspection; the model identification comes from the factory label. Note that the serial on the carton reads 926160, while this record also carries the reference 928604 — both are retained above for searching.

Interchange and searching

Also written 75UMD300CAAAA, 75-UM-D-300-CAAAA and 75 UMD 300 CAAAA. Related codes: 75UMC300CAAAA and 75UMB300CAAAA (shorter stators, less torque on the same frame), 95UMB300 (95 mm frame, 4.4 Nm). Commonly searched as “Unimotor 75 frame servo motor”, “Control Techniques brushless servo 3000rpm”, “Emerson Unimotor” and “Nidec Control Techniques UM servo motor”.