One of the nice surprises during CES 2016 ought to be the claimed first ever concept drone that can autonomously fly a human being – the EHang 184.
It is essentially a quadcopter with a big enough cabin. According to the specs on the company’s website, there are two 1.5m propellers loaded on each shaft, 8 in total. The cabin is roughly 2 meters high and 1 meter wide, quite roomy for a person.
Inside the cabin, it’s got a good-looking seat and a 12-inch touchscreen stretching to the front. There are features like air conditioning, 4G network, a trunk for up to 16-inch luggage, a reading light and a downward camera. This thing can hover for 23 minutes and fly at an average speed of 100 km/h (or 62 miles/h). It translates into roughly 38 km or 24 miles in distance.
Now let us talk about different scenarios for the battery. Our starting point is the 14.4 kWh needed for a trip and the 106 kW maximum output, from the specs online.
One scenario would be to use a battery of just 14.4 kWh. Based on the specific energy data of current lithium-ion battery packs in electric cars (available at our homepage), a 14.4 kWh battery pack most likely weigh more than 100 kg. For example, the newly released Chevrolet Bolt electric car from GM has a 60 kWh battery which is as heavy as 435 kg.
The net weight of EHang 184 is 200 kg. Can half of the weight come from the battery for drones?
Even if the answer is yes, there certainly is room for batteries to improve. United State Advanced Battery Consortium (USABC, formed by Fiat Chrysler, Ford and GM) set a goal of 235 Wh/kg for battery packs by the year of 2020. Then the 14.4 kWh would weigh around 60 kg.
Now say EHang can carry the 14.4 kWh battery around. Pulling 106 kW out of it can be another issue. The Chevy Bolt 60 kWh battery’s power is 150 kW – a power-to-energy ratio of 2.5. In this scenario for EHang 184, the power-to-energy ratio is over 7.
Actually there is high-power batteries on the market, like the Microvast LpCo batteries. They can have a power-to-energy ratio of 4, but at the sacrifice of the specific energy, meaning the batteries are much heavier at the same energy.
As another scenario, say the drone needs 20% additional energy reservoir (it probably should), then the battery size is 17.3 kWh. It leaves 80 kg for other components of the drone. And still, the power-to-energy ratio is too high.
What if we keep the power-to-energy ratio and the power requirement at 4 and 106 kW respectively? Then we need a 26.5 kWh battery. The mass of this battery will be very close to 200kg already.
As we can see, EHang 184 put quite some pressure on the battery technology, namely higher specific energy so batteries can weigh less, and higher power-to-energy ratio so batteries can output more power. These (and many other parameters like cost, safety and temperature tolerance) are in line with the current demand on battery performance from the car industry.
EHang 184 looks like a nice technical concept with good market outlook. Maybe we should build such a battery to make it fly.