Two Gearbox Types, Fundamentally Different Strengths
Worm gearboxes achieve efficiencies of 40-90% and offer self-locking from a ratio of i=30; planetary gearboxes reach 90-98% and are the better choice for dynamic servo applications. Both transmit torque and reduce speeds, but rely on fundamentally different principles — with direct implications for efficiency, size, noise and cost.
This comparison highlights the most important differences and provides clear guidance on which gearbox is the better choice in which situation.
Key takeaway
Worm gearboxes score on self-locking and high gear ratios. Planetary gearboxes convince through efficiency, compactness and dynamics. The right choice depends on your specific load case.
Operating Principle at a Glance
Worm Gearbox
In a worm gearbox, a helical worm shaft drives a worm wheel. The input and output axes are at right angles to each other. Due to the high sliding component in the tooth contact, this principle generates comparatively high friction — which on one hand reduces efficiency, but on the other hand enables the desired self-locking.
- 90-degree axis offset between input and output
- High single-stage ratios (up to 100:1) possible
- Sliding friction as dominant contact mechanism
- Self-locking from approx. 30:1 ratio (depending on design)
Planetary Gearbox
The planetary gearbox consists of a sun gear, several planet gears on a carrier and a ring gear. The coaxial arrangement (input and output on one axis) enables a very compact design. The load is distributed across multiple tooth meshes, resulting in high torque densities and excellent efficiency.
- Coaxial design (input and output on one axis)
- Load distribution across 3-5 planet gears
- Ratios per stage typically 3:1 to 10:1, multi-stage up to 100:1
- No self-locking — holding brake required
Direct Comparison: Worm Gearbox vs. Planetary Gearbox
The following table summarises the decisive differences between both gearbox types:
| Criterion | Worm Gearbox | Planetary Gearbox |
|---|---|---|
| Efficiency | 40-90 % | 90-98 % (per stage) |
| Ratio (single-stage) | 5:1 to 100:1 | 3:1 to 10:1 |
| Self-Locking | Yes (from approx. i=30) | No |
| Torque Density | Medium | Very high |
| Noise Level | Quiet | Medium to quiet |
| Backlash | Medium to high | Low (backlash-reduced) |
| Axis Arrangement | Right-angle (90°) | Coaxial |
| Size | Medium | Very compact |
| Heat Generation | High (sliding friction) | Low |
| Price Level | Low | Medium to high |
At a Glance
Worm gearboxes are more affordable and offer self-locking, but lose considerable efficiency through sliding friction. Planetary gearboxes are more compact and efficient, but require an additional holding brake for vertical loads.
Which Gearbox When? Decision Guide
The choice depends strongly on the specific application. The following guidance helps with the pre-selection:
Choose a worm gearbox when:
- Self-locking is required — e.g. for hoists, flaps or actuators that must hold their position without a brake
- High single-stage ratios are needed (up to 100:1 in one stage)
- Low noise is a priority — worm gearboxes run inherently quieter
- A right-angle axis offset is structurally desired or necessary
- The budget is limited and the application does not require high efficiency
Choose a planetary gearbox when:
- High efficiency is decisive — e.g. for servo applications and continuous operation
- Compact size and high torque density are required
- Low backlash is needed for precise positioning (backlash-reduced versions under 3 arcmin)
- Dynamic applications with frequent direction changes and high accelerations are present
- A coaxial design (motor and output on one axis) is structurally advantageous
In some cases, a combination also makes sense: for example, a planetary gearbox as a first stage with a downstream worm gearbox to combine high ratios with acceptable efficiency and self-locking.
Those comparing acquisition costs, energy consumption and maintenance over the full service life will find a structured method for both gearbox types in the total cost of ownership guide for drive trains. Calculate the efficiency of a specific gearbox arrangement step by step in the gearbox efficiency calculation guide.
TEA Recommendation: Finding the Right Gearbox
Technische Antriebselemente offers both gearbox types in numerous sizes and configurations. Our range includes worm gearboxes in aluminium and cast iron housings as well as single-stage and multi-stage planetary gearboxes for servo and industrial applications. Worm wheels to drawing — also available as custom gears in customer-specific dimensions.
We are happy to advise you on the selection and dimension the gearbox to match your motor, your application and your budget. On request, we deliver motor-gearbox combinations as complete units — including flange adaptation and shaft configuration.
Conclusion
For cost-conscious applications with self-locking: worm gearbox. For maximum efficiency, dynamics and compactness: planetary gearbox. Unsure? Talk to us — we will find the right solution.
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