RE: ESM 50cc Corsair
Ron, I used hyperion DS20-UMD's but have 4 (2 per side) so lots and lots of torques! I had your problem with my T28 so the trim would change with flap as the speed reduced. Horrible! The JR's you have should do the trick. Just make sure your linkages are not getting to the point where they go over center and cant hold the force of the flap.
It always takes a few flights to teach a bird to fly, so stay with it. You will get there!