Good Judgment comes from experience. Experience comes from bad judgments!
OK, I am not ready to claim "expert" status, however on my journey to "goo roo" I have made, uh, some "experience enhancing discoveries" on how NOT to e-fly! As an engineer I am not satisfied in knowing "how" I want to learn as much as I can about the "why" our various e-setups work the way they do. Unfortunately some hardware got sacrificed along the way. Hope that I could share these, as well as encourage others to fess-up, so we might all learn a smidgen more.
MOTOR SIZES
Jack Sheeks Classic "Swinger" swept wing design is prone to build nose heavy, as I discovered when I build mine. Indeed, I cannot comprehend how Jack managed to get his to balance with the muffled Enya 35 he used. Because my bird also finished a little heavier than I wanted, I tried nose-lighteners rather than adding tailweight. I downsized the battery, pushed it as far aft as I could and still could not hit the balance point I needed. Next step was to downsize the motor - from the Rimfire 35-36 (3.6oz) to a 35-30 (about 2.5oz) It worked too - sorta. I was flying along, happy as a clam cuz the bird was really showing its potential - up to the 4-leaf clover. I did the first loop then I heard a screetchy sound followed by a free wheeling propellor that was not producing any thrust. Did not actually SEE a puff of smoke, but the CSI revealed what could best be described as a smoked out motor!
This year I tried again, this time with a Turnigy 28-36 motor. We have been having good luck with the "oversquare" motors - those that are longer than their diameter. Again the specs looked good, so we gave it a try. Again the Swinger was flying well, but it was obvious that the motor was really laboring to get the job done. No smoke this time, but the afterrun temperature was in the 150 degree range vs 105 max observed for the other motors that day. Concluded that this was not a good idea. Later on I also determined that the smaller motor used around 300 mah MORE battery than the larger motor. High current draws are a sure sign of overworked motor! I finally put the 35-36 back in it and added a slug of lead to the tail. The Swinger is now flying better than ever, and the motor is up to the task. However it still uses about 15% more power than the new Mythbuster. The new bird is lighter with more efficient aerodynamics, ironicallly the small motors would have stood a better chance with the new bird. Except....
I started flying the Mythbuster with a Rimfire 35-36 motor and a 10x5 prop, quickly moved on to the 11x5.5. Motor temperatures were good, power was great. While trimming I decided to add a subfin, and wanted to counteract that with a slightly heavier motor. Thus I replaced the Rimfire 35-36 with the 1 oz heavier Turnigy SK 35-42. Was happy everything worked per plan, but discovered that the slightly larger motor at the same RPM using the same prop was using roughly 100+ mah less battery power. My "conclusion" (with the small motor experience in hand) is that the larger motor is working less hard - and using less power as a result.
As a result of these two experiences, I am going to be a little more willing to use slightly larger rather than slightly smaller motors in the future.
CHEEP ESC's
Hard to remember that far back but roughly 1 year ago the Phoenix ESC still did not have a CL governor and would NOT let you use the prop brake with the Heli governor. While researching alternatives my Nephew found the Turnigy Sentry ESC WOULD allow you to use both features - plus it cost 1/3 the price of a Phoenix 45 - SUCH A DEAL! In my misguided exhurberance I bought FIVE Turnigy 40A ESC's to prepare for the coming ECL wars. Sure enough you COULD set the governor and prop brake, setting the speed was as simple as turning the pot on the Will Hubin timer - this ECL stuff is easy... EXCEPT the Turnigy did not hold RPM over the course of the flight - it kept falling off. I attributed this to the ESC overheating, and tried adding a heat sink to compensate, seem to be a little better but not nearly enough. I put all the Turnigy's in a box and set them aside.
Will Hubin did some bench tests and discovered the REAL problem, when he reported his results you may have heard a dull thud as I slapped myself in the noggin. The Turnigy was incapable of adjusting for the loss in battery voltage as the battery wore down (duuuuh!) His bench tests showed that a throttle-up compensating timer held promise by gently adding throttle to compensate for the loss in battery voltage over the course of the flight.
Armed with this, I installed a Turnigy in my new Brodak Stinger OTS and fitted it up with one of Will's FM-0c throttle-up timers. Successfully flew this at Brodak's, where the combination kept the lap times within a .1 second range - plenty good enough for the OTS pattern - or the CLPA pattern.
I am NOT going to suggest that the low-buck Turnigy ESC is an alternative to the Phoenix, however for OTS, sport models and probably even simple CLPA, I think the combination is workable. I know I have no plans on changing the Stinger, and have equipped Dad's new Zilch with the same system!