The first sketch for a custom direct drive motor often has a large blank space in the middle. On the left is an existing motor. On the right is a process shaft. Somebody has crossed out the gearbox between them and written “direct drive?” above the gap.
That question mark is the beginning of a useful RFQ. It is also a warning. The old gearbox did more than change speed. It influenced torque, inertia, alignment, external loads, maintenance access and the way a fault reached the process. Once it disappears, those jobs do not disappear with it. They move.
An illustrative project team spreads the old drawings across a table. Operations has a production log. Maintenance brings photographs and a worn coupling. Electrical engineering has drive alarms. Procurement has two quotations that cannot be compared. Their task is to turn this mixed pile into one controlled inquiry.
The process gets the first page
The team does not begin with the motor rating. It writes the machine name and operating story. The conveyor can start full. The extruder sometimes sits at low speed while pressure rises. The mill needs inching before a normal start. Those details lead to different torque, cooling and control questions even when two nameplates show similar power.
A simple timeline follows. Black blocks show normal operation. Short red blocks mark acceleration, reversal, loaded restart and a possible jam. The quiet spaces matter too: dwell at low speed can keep current and heat present while a shaft fan contributes little airflow.
Starts per hour, acceleration time, stopping method and emergency behavior go in the margin. If the process can back-drive the shaft, that earns its own note. The direct drive selection guide supplies the wider input list; the timeline gives those inputs a sequence.
Torque receives a clock
One engineer writes “peak torque” on the board. Another asks, “For how long?” That short exchange saves the project from a common error.
Breakaway torque, acceleration torque and running torque are placed at their actual speeds. Each peak gets a duration and a recovery period. Continuous torque is tied to the longest operating stretch, not to the most impressive number in a brochure. A jam is handled as a protection event unless the process truly expects the motor to work through it.
Where measurements are missing, the blank is labelled. A torque inferred from motor current is not presented as a shaft measurement. A power figure from production records keeps the speed used in its calculation. The low-speed high-torque sizing guide helps the group keep continuous duty, transient duty and uncertainty apart.
The resulting sheet is untidy but honest. It contains minimum stable speed, base speed, maximum speed, direction and the time spent near each corner. That is much more useful than “0–100 rpm, full torque.”
The old drivetrain stays in the room
Removing equipment is not a reason to stop documenting it. The current motor, gearbox, ratio, couplings, brake, backstop, bearings and lubrication system are drawn as they exist. Maintenance adds failure history: a hot bearing, oil leaks, a coupling that rarely holds alignment.
If energy reduction is part of the business case, the group records electrical input beside useful process output. Production condition and sampling time travel with the numbers. The U.S. Department of Energy’s motor and drive systems sourcebook treats controller, motor, transmission and driven equipment as a system. That boundary keeps a guessed gearbox loss from turning into a guaranteed plant saving.
Some old parts may remain. Perhaps the foundation stays; perhaps the brake and guards do. Each retained component is circled. The supplier can now see which interfaces are negotiable and which are not.
The tape measure settles arguments
Photographs show access, but the dimensioned survey decides whether the proposal fits. Shaft height and extension come first, followed by diameter, key or spline, flange pilot, bolt circle, feet and allowable envelope. Cooler connections, terminal-box direction, lifting route and tool space join the drawing.
External loads are not buried in an email. Radial and axial forces receive direction, application point and transient condition. The bearing boundary is drawn: does the new motor carry only its rotor, or is it expected to support part of the driven machine? A correct torque calculation cannot rescue a bearing arrangement that was never agreed.
The foundation gets a separate discussion. Existing vibration, anchor positions, grout, stiffness assumptions and alignment ownership appear on the RFQ. A good factory reading on a rigid support does not predict behavior on an unknown site structure.
Cooling grows into a small system
At low speed, the group follows heat rather than rpm. Ambient temperature, altitude, dust, moisture, washdown and nearby hot equipment are added to the layout. A shaft fan may be adequate for a brief low-speed visit; it may be the wrong answer for a long high-torque dwell.
An external blower solves one problem and creates several manageable ones: power, filter, duct, interlock, noise and cleaning access. A liquid circuit adds pump, exchanger, valves, fluid condition, drainage and leak response. The direct drive motor cooling guide gives these auxiliaries the same scrutiny as the motor.
The RFQ names who supplies each item. It also says what happens when cooling disappears. An alarm, torque reduction and trip are verbs; “temperature sensor included” is not yet a protection strategy.
The drive file belongs beside the motor drawing
Incoming supply, proposed converter, cable route, braking method and feedback are pinned to the same board. If a converter has already been selected, its exact hardware and firmware are recorded. If it has not, the supplier is asked to state the drive assumptions behind the torque-speed envelope.
Near-zero-speed control, loaded starts and rapid torque changes may alter the feedback decision. “Sensorless” is therefore tied to a stated operating region. Encoder type, interface card, cable and mounting are named when feedback is needed.
The protection list is read as a chain. A winding sensor rises; which controller sees it? A cooling switch opens; what does the drive do, and after what delay? Feedback disappears while the process is moving; what is the safe state? Every device gains an owner, a limit and a test.
Factory and site have different jobs
The factory can verify identity, electrical condition, direction, sensors, dimensions and agreed running points. It may demonstrate load or thermal behavior where the facility and purchased scope allow. The test plan fixes method, condition, instrument and limit before anyone books a witness visit.
For general rating and performance language, the team checks IEC 60034-1 where its scope fits the proposed machine. If efficiency is being compared, IEC 60034-2-1:2024 provides machine-test methods within its scope. Neither source knows the plant foundation or chooses whether the quoted efficiency includes the converter. The purchase file still has to say.
Site acceptance takes the remaining work: final alignment, actual cooling utilities, long cables, coupled load, plant interlocks and process output. Early site runs move from inspection to controlled rotation and then to agreed load. Those first readings become a maintenance baseline rather than a ceremonial sign-off.
Two quotations finally become comparable
Procurement redraws each offer in the same columns. Motor, converter, feedback, cooler, sensors, interface work, tests, documents, packing, spares and commissioning no longer hide inside a total. Exclusions sit beside inclusions. Currency, freight basis, payment milestones and the event that starts the delivery clock are visible.
One offer looked cheaper because it omitted the encoder, blower and site support. Another included them. After normalization, the ranking changes. That is not an accounting trick; it is the result of comparing the same machine boundary.
Each bidder returns a marked RFQ or deviation list. “Complies” without qualifications is not enough when the duty contains unknowns. The direct drive products overview can frame a configuration discussion, but only the approved project data sheet can freeze it.
What leaves the meeting
The final RFQ package contains the process story, torque-speed-time sheet, existing drivetrain, interface drawing, environmental notes, drive and feedback assumptions, protection schedule, test objectives and commercial response table. Every blank has an owner.
No one claims that this package selects the motor by itself. It does something more useful: it gives a direct drive motor manufacturer enough evidence to propose one controlled configuration, reveal exceptions and price the complete scope.
Archived ENNENG material supports historical direct-drive family and customization context only. It does not prove a current torque range, factory capacity, delivery time, certification or savings result. Those points require the current offer and evidence package. Buyers can send the duty sheet and interface drawing when that package is ready.
