The Fundamental Geometry: Why Right-Angle Input Changes the Space Equation
In an inline (coaxial) precision planetary gearbox, the servo motor mounts directly behind the gearbox along the same axis as the output shaft. The total axial installation depth is therefore the sum of the gearbox body length (L1) plus the motor length (L_motor) — both occupy the same axis behind the output face. In most industrial machine designs, this combined depth is the constraint that limits how close the output shaft can be to a structural wall, a bearing block, or another mechanism.
A right-angle input precision planetary gearbox (EP-ZDWE or EP-ZDWF series) incorporates a bevel gear stage at the input that turns the motor shaft 90° relative to the output shaft. The motor now exits perpendicular to the output shaft axis. The total axial installation depth behind the output face is only the gearbox body length L1 — the motor is housed in the perpendicular direction and does not add to the axial depth behind the output face at all.
Critical trade-off to keep in mind: The right-angle input approach saves axial depth but introduces a perpendicular height constraint (L12 — the total assembly height including the motor mounted at 90°). On an 80-frame ZDWE, L12 = 119.5mm. The machine must accommodate 119.5mm in the perpendicular direction to mount the motor. On a compact machine this may be acceptable; on a very flat machine it may introduce a new constraint. Both axial and perpendicular dimensions must be verified before specifying the right-angle configuration.
The Axial Depth Calculation — All Four Frame Sizes, Both Stage Options
The following tables use verified EP series dimensional data (L1 values from the official EP-ZDE and EP-ZDWE product specifications) combined with a reference 750W servo motor length of 100mm — a representative value for this power class from Mitsubishi, Panasonic, and Yaskawa. Adjust the motor length to your actual motor for an exact result.
Single-Stage (Ratio 3:1 to 10:1)
| Rám | ZDE L1 | + Motor (750W) | ZDE Total Axial | ZDWE L1 | Axial Saved | Saving % | ZDWE Height L12 |
|---|---|---|---|---|---|---|---|
| 60 mm | 113.5 mm | 100 mm | 213.5 mm | 150.0 mm | 63.5 mm ↓ | 29.7% | 93.0 mm |
| 80 mm | 144.0 mm | 100 mm | 244.0 mm | 184.5 mm | 59.5 mm ↓ | 24.4% | 119.5 mm |
| 120 mm | 195.2 mm | 100 mm | 295.2 mm | 249.2 mm | 46.0 mm ↓ | 15.6% | 167.5 mm |
| 160 mm | 291.0 mm | 100 mm | 391.0 mm | 368.0 mm | 23.0 mm ↓ | 5.9% | 229.0 mm |
L1 values from official EP-ZDE and EP-ZDWE dimensional specifications. Motor length 100mm = reference 750W servo (Mitsubishi HG-SR or equivalent). L12 = total assembly height of ZDWE unit (perpendicular to output shaft axis). Actual savings scale proportionally with your motor length — longer motors produce larger absolute savings.
Two-Stage (Ratio 9:1 to 64:1)
| Rám | ZDE 2-stage + Motor | ZDWE 2-stage L1 | Axial Saved | Saving % | Best for |
|---|---|---|---|---|---|
| 60 mm | 226.5 mm | 163.0 mm | 63.5 mm ↓ | 28.0% | Cobot wrist, small AGV, compact arms |
| 80 mm | 262.0 mm | 202.5 mm | 59.5 mm ↓ | 22.7% | Machine head spindle, industrial robot J4 |
| 120 mm | 323.0 mm | 277.0 mm | 46.0 mm ↓ | 14.2% | Heavier indexing heads, transfer arms |
Five Machine Design Scenarios Where Right-Angle Input Is the Correct Engineering Choice
Right-angle input is not always better — it introduces a bevel gear stage that adds approximately 2% efficiency loss and widens backlash to <25–30 arcmin. The axial depth saving justifies these trade-offs only when the saved depth actually enables a design that would otherwise be infeasible or requires structural compromises. The five scenarios below represent the most common situations in Korean servo automation engineering where right-angle input delivers decisive value.
CNC tool spindle heads, laser cutting heads, and waterjet nozzle assemblies often have a hard depth limit imposed by proximity to the machine column or a structural wall. In these configurations, the available depth between the output shaft face and the machine structure may be 180–210mm — insufficient for a ZDE-80 plus motor (244mm) but exactly right for a ZDWE-80 (184.5mm). The right-angle input allows the motor to route along the back face of the machine column rather than projecting behind the gearbox.
Low-profile AGVs targeting chassis heights of 100–160mm require the drive gearbox plus drive wheel to fit within this envelope. An inline motor-gearbox stack projects upward into the chassis body. With a right-angle input EP-ZDWF unit (square flange, for direct plate mounting), the motor is positioned horizontally inside the chassis body and only the gearbox L1 protrudes downward toward the drive wheel. This layout is standard in flat AMR designs from Korean manufacturers in Hwaseong and Ansan.
Korean cobot OEMs target wrist outer diameters of 60–100mm. At J4 and J5, the wrist diameter is directly determined by what fits inside the arm cross-section. An EP-ZDWE-60 with the motor exiting perpendicular has L12 = 93mm — fitting within a 100mm wrist. An inline EP-ZDE-60 plus motor stack at 213.5mm makes the wrist 2× longer, adding distal mass and reducing reach. See the robot joint selection guide for the full J1–J6 analysis. The closed-loop position feedback of the servo controller fully compensates for the ZDWE’s wider (<30 arcmin) backlash at these joints.
Some machine designs require the motor power cable and encoder cable to be routed away from the gearbox output face — either to avoid cable fouling during rotation or to route through a cable chain that only has space on the side of the assembly. Right-angle input places the motor on the side, allowing cables to route laterally through cable chains designed for perpendicular cable exit. This is common in gantry systems with long horizontal travels where cable management is a significant design consideration.
Press transfer feeders and servo-driven part transfer arms often operate inside a press gap with defined clearance behind the output shaft. A transfer arm running between press strokes may have 190mm of clearance behind the drive shaft — enough for an EP-ZDWE-80 (184.5mm) but not for an EP-ZDE-80 plus motor (244mm). The 59.5mm difference is the difference between a design that clears the press frame and one that interferes. Right-angle input in these applications is not a convenience — it is what makes the machine physically possible.
The Trade-Offs Quantified — Efficiency, Backlash, and Temperature
Every right-angle input planetary gearbox carries three inherent characteristics relative to its inline equivalent at the same frame size. These are not quality deficiencies — they are the physical consequences of adding a bevel gear stage to turn the input 90°. Understanding their actual magnitude prevents both over-specification (specifying inline unnecessarily) and under-specification (using right-angle input without accounting for the differences).
The bevel gear input stage has its own mesh efficiency of approximately 97–98%. Combined with the planetary stage efficiency of 96% (1-stage), the total ZDWE 1-stage efficiency is approximately 94%. Two-stage ZDWE efficiency is approximately 92% vs 94% for ZDE 2-stage.
Conclusion: For intermittent-duty machines (robot joint cycles, press feeders), the actual efficiency cost is a fraction of this. For 24/7 continuous-duty machinery, verify the housing temperature budget — the additional heat generation may require forced cooling.
The bevel gear input stage adds its own angular clearance (approximately 15–20 arcmin) to the planetary stage backlash (<8 arcmin for ZDE). The total ZDWE backlash is therefore <25 arcmin (frame 80–160, 1-stage) and <30 arcmin (frame 60, 1-stage). This is not a measurement of lower quality — it is an inherent geometric property of bevel gears that applies to all manufacturers.
| Config | Negatívna reakcia | Linear error at R=200mm |
|---|---|---|
| ZDE-80 (1-stage) | <8 arcmin | 0.47 mm |
| ZDWE-80 (1-stage) | <25 arcmin | 1.45 mm |
| ZDWE-60 (1-stage) | <30 arcmin | 1.75 mm |
For servo closed-loop axes: The servo position feedback loop compensates for the backlash dead band completely during normal position-controlled operation. ZDWE backlash only matters for open-loop stepper motor drives — which should not be used in precision planetary gearbox applications anyway.
Unlike inline configurations where the motor simply bolts to the rear of the gearbox in one defined orientation, right-angle input gearboxes can be ordered with the motor exiting in four directions: Left (L), Right (R), Up (U), or Down (D) — as viewed from the output shaft. This direction is fixed by the bevel gear housing design and cannot be changed in the field after manufacturing.
- Specify motor exit direction in the order — default is typically Left unless specified
- Plan cable routing path from the motor exit point through cable chain or conduit before finalising direction
- Consider the motor exit point relative to axis travel — ensure cable length accommodates full range of motion with appropriate slack
- For vertical axis installation with motor exiting downward: confirm water drainage from motor connector does not conflict with gearbox housing
EP-ZDWE vs EP-ZDWF — Round Flange vs Square Flange at Right-Angle Input
Once you have determined that right-angle input is the correct configuration for your application, the next decision is output flange type: round flange (EP-ZDWE) or square flange (EP-ZDWF). These two series share identical internal components, gear ratios, torque ratings, and bevel gear input stages — the only difference is the output mounting interface.
Right-Angle Input Installation — Three Points That Do Not Apply to Inline Units
The bevel gear housing sets the motor exit direction permanently. Specify L/R/U/D on the order form. If the wrong direction is ordered and received, field modification is not possible — the unit must be returned and re-manufactured. Allow 2–4 weeks additional lead time for non-standard direction requests.
During the first 50–100 operating hours, the bevel gear mesh undergoes surface conditioning (run-in). A slight metallic scraping or clicking sound during this period is normal and will diminish to background level within 100 hours. If the noise persists or worsens beyond 100 hours, investigate motor-shaft concentricity at the bevel input interface.
The axial depth saving is only half the geometry check. You must also verify that the L12 dimension (total assembly height including motor mounted at 90°) fits within the perpendicular clearance in your machine. L12 values: ZDWE-60 = 93mm, ZDWE-80 = 119.5mm, ZDWE-120 = 167.5mm, ZDWE-160 = 229mm. A machine that avoids an axial problem should not introduce a height problem.
Complete Decision Summary — When to Choose Each Configuration
| Decision Criterion | EP-ZDE Inline Round |
EP-ZDF Inline Square |
EP-ZDWE RA Round |
EP-ZDWF RA Square |
|---|---|---|---|---|
| Axial depth available | ✅ L1+Motor | ✅ L1+Motor | ⚡ L1 only | ⚡ L1 only |
| Backlash (1-stage) | <8 arcmin | <8 arcmin | <25–30 | <25–30 |
| Efficiency (1-stage) | 96% | 96% | 94% | 94% |
| Output mounting face | Round bore | Square 4-bolt ★ | Round bore | Square 4-bolt ★ |
| Bore machining needed | Yes | No ★ | Yes | No ★ |
| Best application match | Precision axes, robots, CNC | Plate-mount, fabricated frames | Compact heads, cobot wrist | AGV chassis, welded frames |
Provide your servo motor model, frame size target, and available installation depth. Korea Ever-Power’s application engineering team will calculate the exact axial depth saving for your configuration and confirm whether ZDWE or ZDWF is the correct choice — including the L12 perpendicular height check and motor exit direction recommendation. Korean and English support for OEM manufacturers.
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