Help determining comparable motor

I have an old balsa plane of my father’s from the early days of RC electrics. It has a motor on it called a promax 400 7.2 volt - can someone help me determine an appropriate updated motor?


Elite member
That's and old brushed motor. Not very powerful (about 60-80watts). 1 inch diameter and 1.5 inches long puts its approx C-pack size but a lot lighter. It might be easier to simply spec a new motor for the plane regardless of the original brushed unit. What are the specs for the plane (wingspan, estimated all up weight with motor and battery)?


Well-known member
Also, what diameter prop did the old plane use? Might not be as important as the specs @DamoRC asked about but might help in spec'ing a brushless motor replacement.

The key thing is to find a motor/prop combination that will give you adequate thrust for the airframe.


Site Moderator
Staff member
The size of the old motor & size of the prop are great ideas. I would also look at the all up flying weight of the plane and the flying style you prefer.

• 50 to 70 watts per pound is the minimum level of power, good for park flyers and lightly loaded slow flyers.
•70 to 90 watts per pound is perfect for trainers and slow-flying aircraft.
•90 to 110 watts per pound is good for fast-flying scale models and some sport aerobatic aircraft.
•110 to 130 watts per pound is what you want for advanced aerobatics and high-speed aircraft.
•130 to 150 watts per pound is needed for lightly loaded 3D models and ducted fans.
•150 to 210+ watts per pound gives unlimited performance for any 3D model.