how to calculate the power of the energy harvester

this is a tough question for me.looking for your guys's help.This energy harvester use DC motor to collect the energy.And an external electrical load R is connected to the generator,i got an oscilloscope to to record the curve of voltage.Then the power of output is

is it right？ and i tried the resistance of 200ohm,the curve likes this

but i tried the 1Mohm the curve is almost keep the same. If you can help me with this i wll be really really grateful for you kindness.

• What is the winding resistance of the DC motor? Useful search term : "maximum power transfer theorem". Try loads equal to, and either side of, the predicted load for maximum power. – Brian Drummond Jul 21 '17 at 10:36
• the wingding resistance is about 2ohms.but is the load is too small the motor will be really hard to work(or turn) have a forve against the motor to work. – 章哲人 Jul 21 '17 at 11:23
• Exactly - if you want more power out of it, you have to put more power in - of course. – Brian Drummond Jul 21 '17 at 11:29
• thans.so it's normal phenomenon. – 章哲人 Jul 21 '17 at 11:31
• A normal phenomenon called the Conservation of Energy. Decide how hard you want to work turning the motor, adjust the load to match that force (torque), and see ow much electrical power you get. – Brian Drummond Jul 21 '17 at 11:32