The economics
What an hour of digging really costs.
Most of what a contractor pays for an hour of digging is the person in the seat. The R8 is designed so one remote supervisor can oversee several machines; the model assumes six. Below, the same 8-ton class, the same bucket and the same dirt: a diesel excavator with an operator next to the R8. Every number is a stated assumption; open them at the bottom.
A motor at every joint.
The R8 has no hydraulics. Electric motors drive roller screws at the boom, stick and bucket, and turn the swing and tracks directly, all from the battery. That is what makes it a machine software can drive well.5
Design target while the joints are moving, from component ratings. The only published prototype we found, Volvo CE and Cascade Drives' electric boom actuator, used 20–35% less energy than a hydraulic boom on the same battery machine, so we expect real-world numbers below this until we measure our own.5
Assumptions
Labor is the average US operator wage with payroll tax, benefits, workers' compensation and insurance added ($46/h; the BLS median gives $41). On union or prevailing-wage work the operator costs about $94/h, and the R8's cost advantage grows to about 3×. Ownership is straight-line depreciation to 20% residual over the machine's life plus interest and insurance, spread over the hours the machine works each year; the R8 works a little more because it never waits on an operator. Production is bucket size × fill factor × cycles per hour × working minutes per hour, converted to bank (in-place) cubic meters. The R8's energy use is the diesel machine's work per cubic meter divided by the R8's own energy chain, plus 0.5 kW for sensors and compute. Diesel holds 40.7 kWh per gallon. Sound power is the EU label figure for Hitachi's diesel and battery-electric 8-ton ZX85; 10 dB(A) less is heard as about half as loud. These are planning estimates for comparison, not quotes.
Sources
- First hydraulic excavators: Poclain TU, 1951; Badger Hopto, 1951 (Construction Equipment Guide).
- Operators: O*NET / BLS, operating engineers and other construction equipment operators (47-2073), 489,500 employed in 2025 and 39,200 openings a year through 2035; BLS wages, median $28.78/h or $59,850/yr, so about $29B a year in wages and $42B with benefits; BLS employer costs, construction, benefits add 44%; IUOE Local 4 wage sheet, $93.59/h with fringes; machine cost from Caltrans 2026–27 equipment rates, CAT 308 about $57/h.
- Productivity: Goolsbee & Syverson, The Strange and Awful Path of Productivity in the U.S. Construction Sector, NBER Working Paper 30845 (2023); construction value added per worker about 40% lower in 2020 than 1970.
- Diesel energy chain: Rundo et al., energy audit of a mid-size excavator (J. Phys. Conf. Ser., 2025): engine about 32%, cylinders receive 16.4% of shaft energy in a dig-and-dump cycle; pump efficiency from Li et al. 2023; fuel use from the Cat Performance Handbook (308 CR, 0.95 gal/h at medium load); sound power from Hitachi's ZX85-6EB and ZX85USB-6 data sheets.
- Electric drivetrain: Danfoss Editron motor and inverter systems, up to 95% from battery to shaft; planetary roller screws usually above 80% mechanical efficiency (Ewellix figures, via Humanoid Guide); measured prototype: Volvo CE and Cascade Drives electric boom actuator (Vinnova, 2021–2023). Battery discharge at 95% and 0.5 kW for autonomy are our assumptions.
