Electric Paramotor: Technical

The devil is in the details. It seems so easy, just ramp up the R/C airplane technology, which has indeed come a long way, and put it on a frame. Well, it turns out not to be so simple, and for very good reason. Some techniques are quite dangerous and most just don't work out.

Batteries

Lithium Polymer batteries have revolutionized the electric model industry and have created our opportunity for success. Their high energy density offers huge current flow, rapid recharges and high cycle-life. But they can explode if mistreated, primarily if they are overcharged. They are also quite expensive although that price will likely come down as manufacturing capability comes on line. Other types of batteries work but have drawbacks, namely weight.

Motor

The brushless motors used by even the largest R/C airplanes are just not quite powerful enough. Special motors must be used that can tolerate these high power uses but weigh as little as possible. They're coming, though, electric dirt bikes have gained in capability as motors and battery technology have improved.

Throttle

It's not as easy as you'd think. A throttle must somehow vary the voltage presented to the motor. The type of controllers that do so for Radio Controlled modeling are not that efficient and they cannot handle the current flow required of our application. Another approach may be to sequentially increase the number of batteries in series (rather than parallel) but that would be jerky.

Reduction Drive

The propeller dictates maximum RPM and gas engines have to spin quickly to get maximum power, especially for lightweight engines. Thus they have reduction drives or redrives. An electric motor can be built to produce the necessary torque even at propeller-happy rpm. A reduction drive introduces complexity, weight, and drag (on the drive train) so doing away with it can be quite beneficial. Current electric models do have redrives but hopefully future ones will be able to do away with them.

Equivalent Cost

The power available in one $3 gallon of gas costs about 60 cents when charged using electricity from the average household outlet.

Environmental Matters

One attractive aspect of electric anything is that the energy can be produced locally. In the U.S. that means coal. While coal plants certainly pollute, they are much, much cleaner than burning fuel in a car, which is much, much cleaner than burning it in a four-stroke paramotor which is much cleaner than burning fuel in a 2-stroke paramotor!

Electric Power Tidbits

Energy density is the amount of power a battery has for a given weight. For example, a five pound battery with a 8 amp-hour capacity has half the density of a battery weighing 16 pounds with the same capacity.

Internal Electrical Resistance: The amount of resistance to current flowing inside a battery. If you short out a battery by putting a wire from one terminal to the other, a large current will flow. In a battery with low internal resistance this current will be more than a battery with high internal resistance. In practice, high internal resistance reduces the maximum current flow available from the batter. 

Car Industry

Given the price of gas, eventually help will come from market forces in the auto industry. They are also seeking this technology and that will hopefully spur more development that will trickle down to us.