Moped Army

That gearing is way too low. Here is why:

A "26 inch" bicycle wheel is actually 559mm diameter wheel. This is about 22 inches; if you're using standard tires, the total diameter will be about 25 inches.

Each time that wheel spins once, you travel a distance equal to its circumference - that's 78.5 inches, 6.5 feet, or one 807th of a mile. Each time your wheel spins 807 times, you've gone a mile.

You want to go up hills at what, 15 miles per hour? To go fifteen miles in one hour your wheel would spin 12,100 times; during each minute of that hour your wheel would spin approximately 200 times.

So, that's your goal with this math - 200rpm. A good motor for electric bicycle applications spins between 2 and 3 thousand times per minute - a bad one spins even faster.

Let's assume you have the awesomest of all awesome ebike motors, and it operates at 2000 rpm (which is very optomistic). You would need 1:10 gearing to get your 15 mph, and you've currently got a little bit better than 1:2. With this ideal motor, you're geared to go 75 miles per hour.

So, gear WAY down. They do not make bicycle sprockets in the size that you will need - consider using a washing machine belt, or running the motor through two gear reductions using a jackshaft.

If you are still having problems, you will then need to look at your batteries (the real motor that is pushing your ebike), and your motor controller.

The way you are running your electric motor right now is very likely damaging it.