A customer came to us with a familiar problem: their 42 mm stepper motor did not have enough torque. They had already tried increasing the current, and it only made the motor hotter. Increasing the frame size was not an option because the mounting bracket, the pulley and the machine envelope were all built around a 42 mm motor. What they needed was more torque inside the same footprint.
We built them the 42H-3007LS-17/11 — a 42 mm two-phase stepper with a 48 mm stack length instead of the standard 31 mm body. The torque met their requirement, and the customer's feedback was that the result was exactly what the application needed. Here is the engineering behind that choice.
Where Stepper Torque Actually Comes From
In a hybrid stepper motor, torque is produced by the interaction between the rotor magnet and the stator teeth. Holding torque scales roughly with the magnetic working volume — and in a fixed frame size, the only way to add volume is to make the stack longer. A 48 mm stack carries more than half again the lamination and winding volume of a 31 mm body, which is why the jump in torque is substantial rather than marginal.
That is the simple version. The honest version is that stack length is a trade-off triangle, and you are always paying somewhere.
The Trade-Offs, Laid Out
| Parameter | 31 mm stack | 48 mm stack | What it means in practice |
|---|---|---|---|
| Holding torque | Baseline | Clearly higher | More margin for the load, or the same load at a larger safety factor |
| Rotor inertia | Lower | Higher | Slower acceleration response; matters for very fast indexing |
| Axial length | Compact | Longer body | Must fit the machine envelope behind the mounting plate |
| Inductance | Lower | Higher | Torque falls off sooner at high step rates unless supply voltage is raised |
| Heat at equal current | Lower | Higher | Needs attention in sealed enclosures; may allow lower current for the same torque |
| Weight and bearing load | Lighter | Heavier | Relevant for moving-head designs and cantilever mounting |
When a Longer Stack Is the Right Answer
A longer stack usually wins when:
- The frame size is fixed by the machine design. Bracket, pulley bore and clearance are already defined — going to a 57 mm frame would mean redesigning the assembly.
- The application is low to medium speed with high load. Stack length pays off where the motor spends its time at modest step rates, not in the high-speed region where inductance dominates.
- You want margin without raising current. More magnetic volume can deliver the required torque at a comparable or lower current, often a better thermal answer than pushing amps.
- Axial space behind the plate is available. The body grows in length, not in width — if there is room behind the mounting face, the change is invisible to the rest of the machine.
When It Is the Wrong Answer
It does not help in other cases: If your problem is torque at high speed, the fix is usually supply voltage and driver choice, not more stack — a longer winding has more inductance and will roll off earlier. If your problem is acceleration of a light load, added inertia works against you. And if the real constraint is resolution or load holding rather than running torque, a gearbox or a different transmission ratio will be more efficient than brute-force magnetics.
The Part We Built
| Item | Specification |
|---|---|
| Model | 42H-3007LS-17/11 (42 series, two-phase hybrid stepper) |
| Frame size | 42 mm square, 42.3 mm max |
| Stack length | 48 mm |
| Output shaft | Ø5 mm, tolerance 0 / -0.012, length 19 ±0.5, with flat |
| Centring boss | Ø22 mm, tolerance 0 / -0.052 |
| Mounting holes | 4 × M3×0.5P, minimum thread depth 3.8 mm |
| Wiring | Four leads A+ / A- / B+ / B- (bipolar), S6B-PH-K connector |
The key detail for anyone replacing a standard 42 mm motor: only the body length changed. The 42.3 mm frame, the Ø22 boss with its 0 / -0.052 tolerance, the 4 × M3 mounting pattern, the Ø5 shaft at 0 / -0.012 and the S6B-PH-K connector are all unchanged. The customer's existing bracket, pulley and harness still fit — they gained torque without redesigning the machine.
How to Decide Quickly
Answer three questions and the choice usually makes itself. How much axial space is there behind the mounting face? What speed does the motor actually run at for most of its duty cycle? And is the shortfall in running torque, holding torque or acceleration? Send us those three answers with your load data and we will tell you honestly whether a 48 mm stack, a higher-voltage drive, or a different transmission is the better engineering answer.
Contact our engineering team with your application details — we will propose the configuration that solves the problem at the lowest total cost, not the one with the biggest number on the datasheet.
