Electrics - 2010/02 | Model Aviation Library

Author: Greg Gimlick

Edition: Model Aviation - 2010/02
Page Numbers: 99,100,102

ParkZone Sukhoi tips

TAKING OFF:

Here we are in the dead of winter, and most aeromodelers across the country should be building and doing maintenance that they have waited to do all flying season.

I'm going to cover some brief topics this month for you to think about as you build or repair those models. I'll also look at a simple cure for those winter flying blues.

ParkZone's Sukhoi:

I saw this little gem at last year's Joe Nall Fly-In. That's a strange venue at which to learn about such a tiny aerobat. Weighing a scant 1.2 ounces, it didn't fit into the Giant Scale offerings that filled the place, but it stood out.

One of the Horizon Hobby employees was flying the Sukhoi out back by the group's trailer, and it drew a heck of a crowd. I knew then that I had to have one as soon as it became available.

You might have seen a review of this model by now, so I won't go into all the details. But I will point out a few things I've learned. You will probably break a propeller at some point. The good news is that there is a spare in the box. And even if you have to buy one, they're cheap.

My first incident occurred over pavement and the original propeller broke, so I grabbed the spare and looked at changing it. Guess what? There are no instructions for how to do it, nor is it readily evident whether it screws onto the shaft or is a press fit.

After trying to hold the shaft with a pair of needle-nose pliers and spinning the propeller with no apparent effect, I decided that it was a press fit. Guess what else? It isn't!

I unscrewed the propeller quite a bit without noticing it had moved. When I employed the pliers to both shaft and propeller, I managed to pull it off of the remaining threads. Score one for ham-fisted mechanic and, fortunately, I did no damage to the shaft. The moral is: unscrew the propeller until it comes off completely; it takes awhile. When replacing it, I found it easiest to open the fuselage and hold onto the gearbox gear while screwing on the shaft.

While you're in there, you can decide whether or not you want to increase the aileron throws on the bellcrank. The instructions address this, so I won't describe it in detail, but before you act be sure you're unhappy with the throws you have. Mine is plenty touchy for my skills, so I haven't changed it. The Horizon Hobby team changed the one I saw, and it was incredible on the roll rate.

The fuselage is opened by simply cutting tape on the edges and letting it hinge back on the other side. This reveals the little AR6400 DSM2 6‑channel ultra-micro receiver/ESC that comes installed in the Sukhoi. I've included a corrected diagram here, showing all of the pinouts and parts. These bulletins are posted on the Horizon Hobby website.

The beauty of this little model lies beyond the fact that it flies great. Once you've trashed it, its components can be removed and installed in a model of your own design. All parts are available too, if you want to rebuild.

My last tip concerning the Sukhoi is to set it up conservatively, using dual rates and exponential. Mine fits me with low rates at 50% of full, and I use 40% exponential on high rates. This makes it plenty lively for me. I do not recommend test-flying on full rates without exponential.

I love my little Sukhoi, and the neighbors seem to enjoy watching it fly in my front yard.

ESC Wiring 101:

I'll start with my usual disclaimer: I am not an electrical engineer! This information is meant for the everyday flier who is trying to keep from ruining his or her equipment, and it is gleaned from engineers who design speed controls for various manufacturers. I've tried to keep it accurate and put it in laymen's terms.

Many thanks to Doug Ingraham for helping me work through this debate. He has been designing some of the top ESCs and chargers on the market since I got involved in electric-powered flight 19 years ago. He tolerates my silly questions and puts things in plain language for me.

The main question I want to address is one I get repeatedly: is it better to lengthen the wires from the battery to the ESC or lengthen the wires from the ESC to the motor?

The online forums are full of ideas, opinions, conjecture, and debate about this question. From the mail I've gotten lately, that has seemed to do more to confuse the issue than to answer the question.

I'll give you the simple answer first. It is better to lengthen the wires from the ESC to the motor and keep the battery wires as short as possible.

The debate arises about resistance and inductance. Some argue that using a larger-gauge wire reduces the resistance, making the longer battery wires acceptable. That doesn't address the increased inductance it causes.

Proponents of lengthening the battery wires say that the problem can be overcome by adding capacitors to the front of the ESC. That is not really a fix, but a patch.

The ESC comes with capacitors installed as the designer determined for its intended application. Without specific knowledge about current and how good the flyback diodes are, the FETs' switching speed, the FETs' voltage rating, and the types of FETs, you're grasping at straws. If you do know those things, you'll still need to do a lot of math to figure out which capacitors to add.

Following are Bob Boucher's thoughts about which wire to lengthen:

"I will repeat the message previously given. I hope you heed some sound advice based on theory and practice.

Wire resistance may rob you of a bit of power but will not destroy your speed control or motor.

Wire inductance will not damage your motor nor will you be able to detect any effect even with 100 feet of wire.

Wire inductance will kill the MOSFETs in your control and may even blow the caps. [Bob is comparing inductance in the motor-to-ESC wire to inductance in the ESC-to-battery wire.]

I've been a design engineer and manufacturer of motors and controls for over 30 years. You must keep battery wires as short as practical. Short means 1 foot or less, brushed or brushless makes no difference."

Bob is better known as "AstroBob." He owns AstroFlight and holds a patent on electric flight. When AstroBob talks, I tend to listen.

I could include much more text on this subject, but you probably get the idea. If it's possible, lengthen the wires from the motor to the ESC. The best possible solution is to keep all wires as short as possible, but sometimes that's not easy when you're working on that special scale project.

Thanks to AstroFlight, Castle Creations, Schulze Elektronik, and Doug Ingraham for the help. If you want links to more information, drop me an e-mail.

More Spektrum Options for the Royal Evo:

Horizon Hobby is now offering a 12-channel Spektrum module for the Multiplex Royal Evo radio. For those of us who have hacked Spektrum Futaba modules to use in our Evos, this gives us back the rest of our channels.

Spektrum item SPMMS3132 will provide you with the module and a 12-channel receiver. The price looks to be roughly $339, and the package should be available by the time you read this.

Got the winter boredom, no-fly blues? Don't be glum, chum; go flying! Do it in your shop or living room.

Check out the photo of my Bind-N-Fly collection of helicopters that keep me flying all winter. I even got my wife to try the E-flite Blade mCX. The Blade CX3 is a bit big for my shop, but it's been known to fly there.

This will require you to use the CX3's 2.4 GHz transmitters or one of your own Spektrum/JR DSM2 radios. But even if you don't have one, you can get the RTF version of the model that comes with a suitable transmitter for a few bucks more. Then you can use the system for all of the other helicopters if you buy the Bind-N-Fly versions.

If you think you're beyond the coaxial phase of your helicopter training, I urge you to look at the Blade mSR. It is a single-rotor, active-tail-rotor model that is incredibly stable but uses a "normal" helicopter's controls. These models have helped me get better at orientation and control.

If you have a gym or other indoor facility to use, check these aircraft out and see what people are doing to feed that urge to fly during the long winter. Even here in North Carolina, we're seeing more and more indoor groups pop up, and it's a ton of fun.

You have plenty of time to build something for an indoor meet, such as the one held at the Toledo Show every year. There are ARFs, RTFs, and kits for builders that are suitable for indoor flying. Check out Stevens AeroModel for some great kits that build quickly and use inexpensive equipment.

Final Approach:

I hope I cleared up the wiring question. Let me know what other topics you want to see covered. If you don't supply the ideas, you're left to my imagination!