For the B-17 are the MPS-1(a) motors capable of handling the 3 cell pack?

In another Q&A thread it talks about using the MPS2(a) engines on the b-17 with the 3 cell pack. Should the motors be wired in parallel as shown in the plans or do you need to put 2 pairs in series to handle the 3 cell?
Or did I just screw up and order the wrong thing?

From : Don Stackhouse

Well, umm... knowledge evolves. Our early indications were that the 3 cell pack would do fine with four MPS-1's in parallel. Original indications were that the load from four MPS-1A's in parallel was enough to depress the voltage (and therefore the current per motor) sufficiently to be within the motors' individual capabilities. However, later data indicates that prolonged running at full throttle can burn out single motors. I'm not sure if this was because the original data was optimistic, or if the batteries got better, but the bottom line is that those 1200 mah cells can pump out an amazing amount of current and still hold their voltage.

OTOH, as long as you use a little common sense you can fly an MPS-1A on three cells just fine. Just don't use full throttle other than for short bursts. Of course, the power at full throttle on three cells is so great that you really don't need it other than for very brief emergencies. The other benefits of three cells, such as longer flight times and better ability to tolerate the effects of cold temperatures on the batteries and high altitudes on the props are still there. Just try to stay below half throttle most of the time and don't go over about 3/4 throttle for more than maybe 5 seconds or so.

I flew my Triplane with an MPS-1A on three cells for quite a while that way with no problems. Then I let someone else fly it and forgot to warn him about the need to avoid full throttle for more than a few seconds, and he just left it at full throttle from the start of the flight. At almost exactly sixty seconds the motor coughed once, then the prop suddenly locked up (that's a very bad sign with an MPS-1A, normally they should windmill in flight when power-off). I suspected the brushes had fried, but we found during the subsequent autopsy that the brushes were OK. The little nylon brackets on the ends of the armature laminations had melted, filling the inside of the motor with "nylon wool". That allowed the windings themselves to come off the armature and wrap themselves around the outside of the armature till they jammed between the armature and the magnets.

However, remember that this motor had survived quite a few flights prior to this, with most of those flights between half and 3/4 throttle, and only brief bursts to full. It took a full minute at full throttle to cause the meltdown.

Quite honestly the B-17 does not need the extra power of a third cell. It's so big and draggy that no amount of power will make it go fast, and although it might be interesting to see a B-17 that can hover, it certainly would not look very scale-like. The climb rate and reserve power on just two cells is plenty for any "normal" flying. If wildly non-scale maneuvering is what you really want to do with it, I suggest upgrading to four MPS-2B twin-motor units (the ones that use the 5-4.3 props). Do not use the MPS-2A units, the bigger prop diameter will make the inboard and outboard prop disks overlap by about an inch, which could be bad if some unusual situation causes them to touch. You'll also probably want to use an ESC good for about 8-10 amps, since the MPS-2B's can pull about 2 amps each.

If you fly in the winter and have trouble with power sagging due to the cold, the third cell can be a big help. If you want to fly in Denver or Albuquerque, a third cell can be useful. As long as you use some discipline on the throttle stick, you'll have the extra power available if you need it. However, it also means dragging around the extra weight of that third cell during all the times that you don't need it. If you don't have a good reason to need it, you're probably better off with the 2-cell 1200 mah pack.

Don Stackhouse
DJ Aerotech