Life as an idiot with RC fever.

Winter flying isn't working out so well for me so I thought I would write down some of my experiences from last season which happens to be my first and only season in the hobby, so far. I’d like to add my 2 cents to the mix of all that is already posted about RC plane scratch-building. I’m not even going to talk about the actual flying part of the hobby. Maybe, actually I’m pretty sure, this has all been covered before but I hope this could help someone avoid mistakes I’ve made. And I want to take the time to thank everyone else that has posted things that have helped me. You know who you are. Oh wait, you probably don’t.

Just so you know, my experience is limited. I started into the RC plane hobby back in July of 2014. I’m a newbie and I admit it. If anything I write in this post is incorrect or you disagree with it, I would appreciate if you would correct me.

So that you also know, I am a cheapie-bootied person. AKA cheapA$$. I like Dollar Tree (even before building with DTFB), Big Lots, and Marc’s deep-discount-overstock-buyout-of-the-weirdest-stuff stores. So, for me, getting into the RC plane hobby was never going to be about $1,000 balsa models with all the bells and whistles. I order most things from eBay and HobbyKing. MotionRC and Horizon have some nice things but I’ve only gotten in on a few of their sales.

A friend of mine admonishes me for always going cheap. He's of the mind that higher cost usually means higher quality and a better chance for reliability. There's some truth in that but I'm just too cheap to buy the expensive stuff. And to be fair, his philosophy is that better quality stuff WILL cost more and it's worth it. Anyhoo, I like Flite Test's attitude of doing things on the cheap.

Disco Servos.

Here’s a little of what I’ve learned. Cheap servos have been the biggest problem for me. I’ve had many that don’t return to zero consistently or that have strange twitches during flights. My first scratch build was a delta wing style model with elevon mixing. I lucked out that the two servos worked great in it and they still work good. It was with my second build that the cheapie servos started to bite me in das bootie.

With my second ever scratchbuild, I would get some erratic twitches during banking turns. The other issue was that sometimes the “elevator” function seemed to fail or not throw far enough. I would be pulling up while the model was heading towards the ground and the pitch on the control surfaces wasn’t enough to keep it from hitting the ground. Then, I would put the model back in the air, with the same settings, and it would act properly for the next several flights. I think the servos weren’t going to full throw at different times during flight. Or maybe I just suck at flying! Or both?

Continuing on, I built several more models and kept having similar servo problems. The planes would just do crazy things like they were trying to boogie at the disco. (yes, I’m old and show it with a disco reference) That’s when I bought a servo tester. What a great investment! Now I can check the “zeroing” and set all of the servos to zero before installing them.

One other thing to note on servos: I think I fried two after getting my tester. The servo tester I was using didn’t come with a battery pack. So, I wired it up to a 2s LiPo that I had sitting around. Yep, that’s when I found out that servos don’t really like going over 6 volts. I fried the first one and thought it was defective but when the second servo froze up, I suspected I had done something wrong. I used a third servo and it acted erratically but the voltage must have dropped enough to not fry it. I now have a battery pack with four NiMh AA cells that puts out 4.8V. This was me learning about scratch-building and being an idiot. Doh!

ESCs: my flux capacitor is da broken.

The next area I had issues with is cheapie ESCs. I’ve had them where they work intermittently and will not spin up properly every time I rev the throttle. Recently, I had two 30A ESCs that did this. I reset the factory defaults in the programming and they still had problems - I returned them and got a refund. When I rev the throttle, most of the time the motor just screeches and does not spin up. On a side note, I’ve found that some motors will screech to a halt if the prop is too big for them to handle. That’s different because the motor will always start spinning and then baulk when it hits a certain RPM because the prop produces too much load at that point.

One of the biggest problems I had, with a bad ESC, is when I plugged a 4s battery into one of my scratch-builds. The ESC was rated to handle 60A and up to a 6s battery. I had been running it on a 3s 2200mah battery. I made sure that the prop was a good size to not overload it since 4s voltage would push it harder. Well, I plugged in the 4s and the ESC initialized properly. The motor spooled up nicely and it seemed to have plenty of thrust. I decided to test the controls. When I moved the stick, the servos just barely started to move and then nothing – they just froze. The servos went silent. The motor would still spin up but the servos weren’t working. Wow! I disconnected the battery and then reconnected it – still nothing from the servos. I finally figured out that the BEC (battery eliminator circuit) didn’t do its job and let too much voltage through to the servos. All four servos were toasted and three of them were actually scorched to where I could see the burns on the inside of the clear plastic housing.

We don’t need no stinking BECs!

Oh yes we do. The fried servos, in the previous part, leads me into the BEC and how much load they can take. I’ve learned the hard way that digital servos draw much more current than analog servos. I had read about that but it didn’t lock/sink (locksink?) into my brain. I bought some pretty nice 12.5gram metal gear, digital servos thinking that they should be more accurate and durable than the plastic gear analog servos. I put them in a model and was getting ready for a maiden. When I was triple-checking the control surfaces, I noticed that the receiver would “drop out” and the servos would freeze until the receiver powered back up. The receiver would shut off for only a couple of seconds when I worked the controls hard. But even an idiot like me knows that it’s never good to lose control of the model.

I thought it was a problem with the radio system. It turns out that the servos were drawing so much current, the BEC couldn’t keep up. The voltage would drop low enough that the receiver couldn’t stay powered and it would shut off. The BEC would then recover and start putting out enough voltage to start the receiver back up. A friend of mine helped me get this figured out. If I am using the digital servos, I make sure the ESC has a SBEC or UBEC that is rated for at least 3A. Now I don’t have the problem of the receiver shutting off anymore even when I work the controls a lot. Lesson learned.

Trusts in my Thrusts.

For my first scratch build, I started out with a motor I bought on eBay. It’s a generic 2212 1000kv brushless motor along with a 30A ESC that came as a combo package. I paired it up with a 7x5R APC prop for this delta wing pusher model. I had no idea what I was doing but I just wanted to see if I could build something that would fly. My maiden flight lasted about 20 seconds but I was able to control it enough so as to not crash too hard. I knew that the motor and prop didn’t give enough thrust but I didn’t know why. For that first flight, I had to keep a high angle of attack because it couldn’t go fast enough to get to a nice cruising speed. I was at WOT (Wide Open Throttle) the whole time and it was probably doing barely 10mph.

I was still learning about all of the variables. Motor KV, motor size, prop diameter, prop pitch, how many cells the battery has which dictates voltage, and so on. I was reading posts on forums and getting acquainted with all of the different ideas about model RC design and flight. My next order was for a Turnigy 2826 2200KV Aerodrive motor. I wanted “more power” and figured this would give it to me. I matched it up with a 6x4 pusher prop on a 3s battery and it made all of the difference in the world. Now I could get plenty of speed and thrust for the delta wing models I was building.

WATTMETER? Ohhhh, that meter.

I was getting more speed and performance but I still didn’t really understand what type of load I was putting on the motor, ESC, and battery. The only thing I was doing was checking to see how hot things were getting after flying. I decided to get a wattmeter but only after a certain incident that I will mention later. The wattmeter was my second best investment after the servo tester. Now I could actually measure the current draw in the power system. Knowledge is power and I needed knowledge about power. Ha!

As I started getting different motors and propellers, the wattmeter allowed me to see if I was putting something together that would overload the components. I’ve found several power system calculators online and use them to get an idea of what the power system will draw. I’ve used the wattmeter to find out exactly when I’m pushing the components too hard. Luckily, I had kept most of the power systems relatively modest and I wasn’t damaging anything. However, it was just luck that almost all of my configurations weren’t too taxing. Almost all except for one design – more on that later.

Batteries are bad to me.

This is where the guidance from an experienced friend helped me immensely. I would have probably burned my house down had it not been for his warnings about LiPo technology. He gave me a run down of treating them with respect when charging, discharging, and storing them.

Well, it wasn’t long before I needed to throw out my first 3s 1800mah battery. I had crashed the model and because of the way I installed the battery, it slammed into the back of the firewall with the end that the leads come out of. This broke one of the thin metal plates that the wires are soldered to. It would work if I squeezed the battery at the top but it wouldn’t work otherwise because of the damage. I read about proper discharge and made a saltwater bath. I watched as the magic bubbled out of it. Sigh….

My friend told me how he read that some of the experts recommend disposing of a battery that was in a hard crash even when it still seems to work well. I have violated that with two of my batteries but I inspected them thoroughly and feel comfortable using them.  But I have had to dispose of several batteries due to damage from crashing.

Battery Low-Voltage Warning Beeper, yea right.

So, late last summer, after having built, bought, and flown several planes, I was over at my friend’s house getting ready to fly my Parkzone P-51BL Mustang. My friend has one of those and that’s why I wanted one – it’s an awesome flying model. I had only flown it a couple of times. I bought the bare airframe and added the motor, ESC, and servos that I picked out myself. Being an idiot, that's me, I might have been using parts that were a bit too power hungry. I didn’t know this at the time but what happened next is what made me decide to get a wattmeter.

Up until that evening, I had been flying without a low-voltage warning beeper in my models. I decided that I liked this model so much, I wanted to make sure to take care of it. I put in one of the cheapie 2s to 8s LED low-voltage warning beepers and got ready to fly. I had been using that meter for checking battery voltages before and after flying, so I was pretty confident in it.

Remember, this was going to be the first time I flew WITH the low-voltage warning beeper in the model. I had set it to go off at 3.8V per cell – that should be very safe. This was also when I was still figuring out the custom motor I put into this Parkzone airframe. Anyway, I hand launched it and it took off beautifully. That plane flies so well, I highly recommend it.

I was flying for about 3 minutes when I decided I should bring it down and check the components. The low-voltage alarm hadn’t made any noise at all. I had started with a fully charged, 3s, 1300mah, Admiral brand battery in it. When I banked the plane to bring it around for a belly landing, the plane started to drop and I lost all control. It was in a banking turn and about 60 feet up in the air. It was like slow motion. It smoothly turned the nose down and continued into the soy bean field. Thump! It was almost at a 90 degree angle when it nosed in.

It hit about 200 feet from where I was standing. I walked out to get it and, luckily, it wasn’t too bad off. Phew! It only cracked one side of the fuselage in front of the battery hatch with a few wrinkles here and there. Just a bit of glue and it still flies great.

But what happened? Well, the other telling thing is that I could barely pull the battery out of the compartment. It was so hot and puffy that it had melted into the foam! The cheapie low-voltage alarm had failed to beep. It was still registering when I opened the hatch and it showed 2.4V on one cell and 2.8V on the others. It should have been beeping like crazy! I won’t use that beeper in a plane ever again. Needless to say, I discharged that battery in saltwater and got rid of it.

Power and Prejudice.

Or was it pride? Let’s go back to the Parkzone P-51BL Mustang airframe I just mentioned. I had a power system in it that I thought would work. Horizon did an awesome job designing that plane and their PNP and BNF versions are classics. But since they don’t sell those anymore, I had to get the bare airframe. I started looking at what motors would fit and what I should use for an ESC. I knew I wanted to stay with 3s batteries but I also wanted something that would fly fast. Faster, faster, make it go faster! Yea, I’m an idiot.

So, I settled on getting a Turnigy 3536 1450kv motor. I hooked it up with a 60A ESC and a 3s 1300mah battery. Remember, this was before I had a wattmeter and I really didn’t know what I should expect for current draw. I put the P-51BL together and used the stock 9x6 prop. The original design used a 960kv motor from EFlite which meant that I was way over that with the 1450kv motor. Ignorance is not bliss.

I flew it that way a couple of times and kept my flight time very short because I noticed it was getting pretty hot - both the battery and ESC. After the failure of the low-voltage alarm, I bought a wattmeter and tested the setup in the Mustang.  It was pulling 53A! I was OK with using the 60A ESC but the 1300mah 3s battery was only rated at 25c. That means that the battery has a theoretical max of about 32 amps. I was pulling 20A more than that! No wonder why I killed that battery. I changed the 1450kv motor out for an 1100kv. It still moves pretty decent but it draws a little over 30 amps now.

I’ve been learning about how the propeller size combined with the motor kv rating drives how much power the system will draw. Since kv is based on RPM per volt, the battery voltage is also a critical factor. So, I looked back at my other builds and decided to test all of them. My go to setup is the 2200kv motor, 30A ESC, 6x4R prop, and a 3s 1300mah battery. That measures at about 26A of draw at full throttle. I can get about 5 to 6 minutes of flight time if I’m not too aggressive. The only thing I can say about that setup is that the motor does get a little warm if I run it hard.

Wrapping this burrito up!

I had been meaning to post about some of the separate issues I had. Stuff like the servo problems both the faulty ones and how the digital servos draw too much for some BECs. I’m betting that most fliers will already have experienced these issues or are maybe smart enough to have avoided them.

This was my first scratch-build:

And here are some others: