ZL02 Wheel Drive Planetary Gearbox

The EP-ZL01 proved that a high-speed, multi-stage wheel drive planetary gearbox could serve the AGV and electric vehicle market. The EP-ZL02 takes that architecture outdoors. At 1,500 Nm continuous — double the ZL01 — the ZL02 drives the heavier, rougher-terrain machines that indoor AGV gearboxes cannot handle: autonomous yard tractors hauling 8-tonne trailers across intermodal terminals, last-mile delivery robots crossing kerbs and climbing car park ramps, electric construction site vehicles loaded with pipe and cabling on muddy access roads.

The 5,200 rpm maximum input speed is the highest in the entire Korea Ever-Power wheel drive catalogue — 4% above the ZL01 and 73% above the 6xx series. This ceiling accommodates the fastest commercially available BLDC and PMSM motors without any electronic speed limiting, allowing the motor controller to extract the full power and efficiency range of the motor across the entire speed envelope.

Rain and Standing Water

IP67 certifies immersion to 1 metre for 30 minutes — far exceeding puddle depth and rainstorm exposure. The multi-lip FKM seals prevent water ingress even during thermal breathing cycles (when the housing cools after operation, it draws air and moisture inward through any gap). For vehicles that operate continuously in tropical monsoon conditions, specify the desiccant breather option to capture moisture during thermal breathing before it reaches the oil.

Mud, Sand, and Abrasive Dust

Abrasive particles are the primary threat to outdoor wheel drive seals. The FKM multi-lip seal design uses an outer dust lip that deflects particles away from the primary oil seal. For vehicles operating in sustained dusty environments (construction sites, quarry haul roads, agricultural fields), reduce the seal inspection interval from 10,000 hours (indoor) to 3,000 hours (outdoor dusty). Replace seals at the first sign of lip wear — waiting until oil leakage appears means particles have already reached the bearings.

Freeze-Thaw and Ice

The ZL02 operates down to -20 deg C with standard oil. Below -20 deg C, switch to full synthetic SAE 75W-90, which extends the cold-start limit to approximately -30 deg C. Avoid parking the vehicle with the wheel drive gearbox submerged in standing water that could freeze overnight and lock the output shaft to the ground surface. If ice formation on the housing exterior is expected, verify that the motor controller limits the starting torque during the first 60 seconds of cold-start operation to allow the oil viscosity to decrease as the gears generate friction heat.

UV and Chemical Exposure

The QT600-3 ductile iron housing is inherently UV-resistant — it does not degrade under sunlight. The factory paint coating provides corrosion protection; touch up any chips or scratches with cold-galvanising spray to prevent rust formation. FKM (Viton) seals resist degradation from road salt, de-icing chemicals, agricultural herbicides, and petroleum-based cleaners. NBR seals (used by some competitors) degrade rapidly under ozone and UV — verify the seal material before specifying any wheel drive for outdoor autonomous vehicles.

Autonomous Yard Tractors and Trailer Movers

Battery-electric yard tractors that haul 5-8 tonne trailers across intermodal terminals, distribution centres, and port back-lots at 10-15 km/h. The ZL02 2-stage at ratio 20-30 paired with a 3-5 kW BLDC motor provides the tractive effort to move loaded trailers on gravel and cracked asphalt surfaces, including the 5-8% ramp grades common at warehouse loading docks. The 3,000 Nm peak handles the breakaway torque when pulling a loaded trailer from a standing start on a sloped surface.

Last-Mile Delivery Robots

Autonomous sidewalk and pavement delivery robots in the 100-300 kg payload class that must cross kerbs (50-100 mm step), climb wheelchair ramps (8-12% grade), and navigate gravel paths in residential areas. The ZL02 3-stage at ratio 60-120 paired with 500 W-1 kW PMSM motors provides the wheel torque for kerb mounting and the positioning accuracy for docking at delivery points. The tarkkuus planeettavaihteisto handles the steering actuator on these robots.

Electric Construction Site Vehicles

Battery-electric material carriers, crew transporters, and tool carts for construction sites where diesel emissions are restricted (indoor construction, hospital campus builds, urban residential projects). The ZL02 1-stage at ratio 4-6 paired with a 2-4 kW high-torque BLDC motor provides the 15-20 km/h site transit speed and the torque to climb temporary construction ramps (15-25% grade) under full load. The IP67+ sealing handles the concrete dust, rain, and washdown water common on active construction sites.

Why choose the ZL02 over the ZL01 for an outdoor delivery robot weighing only 200 kg?

A 200 kg robot on flat warehouse floors needs less than 700 Nm per wheel — the ZL01 is sufficient. The same 200 kg robot outdoors on grass, gravel, or snow needs 2-3 times the tractive force due to higher rolling resistance. At a rolling resistance coefficient of 0.10 (soft grass) versus 0.02 (warehouse floor), the same robot needs 5 times the wheel force to maintain the same speed. The ZL02 at 1,500 Nm provides the margin for these outdoor conditions without oversizing the motor — the motor runs at higher torque on grass but the gearbox has the capacity to transmit it without overloading.

Does the ZL02 have a parking brake for slope holding?

No internal brake. For outdoor vehicles that park on slopes, use one of three solutions: (1) an electromagnetic brake integrated into the motor, which is multiplied through the gear ratio to the wheel; (2) electronic motor braking via the controller (motor short-circuit braking or active current braking); or (3) mechanical wheel chocks for long-duration parking. Most outdoor autonomous vehicle controllers implement option 2 as a standard function. Option 1 is required if the vehicle must hold position on a slope with the controller powered off.

What oil change interval applies for an outdoor autonomous vehicle operating 24/7?

For outdoor 24/7 operation: first change at 250 hours, subsequent changes every 3,000 hours (reduced from 5,000 hours indoor due to dust and moisture ingress through thermal breathing). If the vehicle operates in sustained dusty conditions (construction, agriculture), reduce to 2,000 hours. Oil sampling every 1,000 hours is cost-effective for outdoor fleets where seal contamination is a gradual process — early detection of water or particle ingress prevents bearing damage months before it would otherwise become apparent.

Can the ZL02 handle the shock load from an autonomous robot hitting a kerb at speed?

The 3,000 Nm peak rating covers the impact loads from kerb climbing at speeds up to approximately 5 km/h for a 500 kg robot with 150 mm diameter wheels. At higher approach speeds, the torsional impulse can exceed 3,000 Nm for a fraction of a second. The carburised alloy steel gears tolerate occasional overloads up to approximately 2x peak (6,000 Nm) for sub-10 ms impulses without permanent damage. However, designing the robot navigation system to slow down before kerb crossings is better engineering than relying on gearbox overload tolerance.

How does a planetary wheel drive gearbox compare to a belt reduction for outdoor EV applications?

Belt reductions (timing belt or poly-V) are lighter and less expensive than planetary gearboxes but fail rapidly in outdoor conditions. Water, mud, and abrasive dust accelerate belt wear by 3-5x compared to indoor operation. A belt that lasts 10,000 hours indoors may last 2,000-3,000 hours outdoors. The ZL02 sealed planetary gearbox eliminates this exposure entirely. The cost difference between the ZL02 and a belt system is typically recovered after 2-3 belt replacements, making the planetary gearbox the lower total cost of ownership option for any outdoor vehicle operating beyond the first year.

What is the noise output of the ZL02 relative to the ZL01?

The ZL02 uses the same helical-cut planet gear design as the ZL01 but with larger gear modules to carry the higher torque. Larger gears at the same speed produce approximately 2-4 dB more noise due to the increased tooth engagement length. At 3,000 rpm input, the ZL02 2-stage typically measures 62-68 dB(A) at 1 metre versus 58-65 dB(A) for the ZL01. For outdoor applications, this difference is masked by ambient noise (wind, tyres on gravel, motor cooling fans). For indoor use at the heavier end of the ZL02 vehicle range, the 2-stage configuration remains the quietest option. Contact Korea Ever-Power for noise data at your specific ratio and speed.

Fleet of 16 autonomous yard tractors at an intermodal container terminal. ZL02**2 ratio 24, paired with 4 kW BLDC motors. The tractors haul 6-tonne trailers across 800 metres of mixed asphalt and gravel at 12 km/h average, 20 hours per day. After 10 months (approximately 6,100 hours per unit), zero drive failures. The IP67 sealing has survived two winter seasons of North Sea rain and one period of standing saltwater on the terminal surface during a storm surge. We initially evaluated the ZL01 but the tractive force calculation on gravel showed we needed the ZL02 torque margin — the decision was correct.

Sidewalk delivery robot, 180 kg payload capacity, ZL02**3 ratio 85, 750 W PMSM motor with electromagnetic brake. The robot delivers groceries in a suburban neighbourhood with grass verges, gravel driveways, and 75 mm kerbs. The ZL02 handles all of it — including a 12% wheelchair ramp at a commercial building that was our most challenging test case. The electromagnetic motor brake holds the loaded robot on the ramp with power off. Battery range is 22 km per charge, which covers our current delivery radius with 30% margin. We have 14 robots deployed across two cities.

Electric crew transporter for a hospital campus expansion project, ZL02**1 ratio 5.77, 3 kW BLDC motor. The vehicle carries 6 workers plus tools across a 2 km site with temporary gravel roads and 20% ramps to upper floors of the parking structure. Performance is excellent and the concrete dust exposure has not affected the seals after 7 months. The 4-star is a ZL01-vs-ZL02 observation: we initially ordered ZL01 units based on the flat-terrain calculation, but the gravel ramp test showed the ZL01 was at 95% of its continuous torque limit. We switched to ZL02 for the full fleet, which runs at 45% of its limit on the same route. The product data sheet could benefit from an outdoor rolling resistance reference table so engineers like me catch this during the specification phase instead of during prototype testing.