When I was a boy I learned to fly using IC engines. When I started flying electric I put aside my IC things… (Don’t you love postings that begin with paraphrased parables???)
A few years ago, Castle Creations launched a new set of programming parameters geared toward the Electric Control Line enthusiast. Castle made it so the excellent Helicopter “governing” features were available now with a Prop Brake, then they went one giant step farther – they created new “Set RPM” mode. With this ECL flyers could literally program the RPM setting they wanted and the ESC would deliver that same setting, flight after flight. The program actually lets you program up to 3 settings at a time so if you get to the field and decide you want to fly a little faster or slower you can call up those speeds and get an EXACT change in the RPM setting every time – sounds like “Stunt Heaven”, eh?
I keep reading about people’s set ups and in some cases their issues to overcome when using Castle’s High Gov (or Low Gov as the case may be) particlulary when using low pole count motors like the old style Brodaks & Plettenbergs, and cannot fathom why these folks have not adopted the “Set RPM" mode. More to the point, I cannot fathom why folks still insist on using analog “sundials” (tachometers) to SWAG at their RPM settings when digital electronic control is available.
I suppose that some of it is comfort; the High Gov modes let us “set the needle” just like we used to do with IC power – however, that is its weakness. Usually the perpetrator uses an optical tach, dials in the RPM the best they can and gives it a go. Just like IC it means that you will likely miss the setting as often as you hit it. No worries, if it is too fast or too slow the process is repeated next flight. Once the “happy RPM” is determined then the consistency of electric flight sets in and all flight speeds are the same – until the flyer hits conditions (temperature shift, altitude, wind or calm) and the user has to dial in the new somewhat faster or slower setting all over. Heaven forbid you accidentally TOUCH the needle (the adjustment pot) between flights!
The basic flaw of this system begins with the measuring device. The optical tachometer is the primary feedback tool for determining whether the RPM is correct, yet it is the least accurate least repeatable component in the system and completely at the mercy of outside influences (60 hz light sources, prop color, tidal stresses, planetary motion – you get the drift) Thus the analogy: using a tach to set the correct RPM on an e-powered stunter is literally like trying to use a sundial to set an electronic clock.
Consider the Set RPM alternative. Again, the flyer goes through a similar trial & error process to get to their favored RPM. However, instead of that RPM being the by-product of a throttle setting determined using a sundial (tachometer) the RPM is PROGRAMMED into the ESC and is used in the ESC feedback loop to actively control the motor.
To me the game-changing advantage occurs when I want to change the RPM setting for conditions. With the Castle system you can program 3 RPM’s. Using a Hubin FM-2SR or FM-9 timer, you select the RPM you have programmed. The overwhelming advantage is that you select EXACTLY what RPM increment you want to use. You can also revert back to EXACTLY the RPM you started with – no sundial required. I usually try setting up the MIDDLE RPM setting as the regular setting, then make the LOW setting 100 RPM lower and the HIGH setting 100 RPM higher. I have found that 100 RPM makes a pretty good step for most airplanes, but I could just as easily make it a 50 RPM step (as I do on the ultra clean Mythbuster) or 150 RPM step (have not needed that yet).
The one most commonly noted “downside” to Set RPM mode, is that you need a PC to access the ESC and change (reprogram) the three available RPM presets. If you have a laptop PC then doing so in the field is really not that big a deal, if you do not then you have to go to where your PC is to change the presets. I will counter with the thought that changing RPM well outside your normal settings is always a bit of a pain, the key difference with Set RPM is that you can change exactly where you want it to be, without guessing and doing the tachometer two-step.
The more I learn about High gov and Low gov, the more I appreciate Set RPM. I suggest that if you have not tried it that you give it a go and see if it will break you of that needle valve habit left over from your IC days..!
Topic: THE CASE FOR CASTLE’S “SET RPM” MODE (Read 1467 times)
