HOWTO Wiki Choosing a Tail Drive Setup

From Heli-Wiki

There are several schools of thought on which tail to use. Basically the short story is the stock motor is inadequate if you want to step up to brushless or a HH (heading hold) gyro, and it's personal preference between the DD and the dual tail. It all depends on what you are looking for. For fun flying and piece of mind with redundancy I would say the dual tail. For hard 3d I would probably say the DD because that's what the "pro's" seem to be going with. If that's a simple enough and to the point enough explanation for you to decide... just stop there =P Otherwise you can read the lengthy part for more info. Just whatever you choose IMPO it's a good idea to heat-sink it and fuse it =) If you want to know why... just keep on reading.

There are also brushless setups that you can go with, but basically what it amounts to is that you would have to buy a separate ESC for the tail and know how to set that up, but basically what it amounts to is they are quite heavy for the 300 sized heli’s, most that have used them for a length of time say that spool up time lags, and at about $70 for a setup there are other more cost efficient options. See RCU brushless tail rotor setup thread for more details.

I have read several forums about this because I am trying to decide also. Several of the really pro fliers like nick Maxwell use the DD, so there has got to be good weight to power ratio, and good aerobatic flight qualities. If you haven't seen it yet, watch this video Nick Maxwell

SSG Scott over on RC Groups is a military chopper mechanic with 27 years experience, and he has done a lot of testing. In short what he has come up with is that the DD setup on average lasts about 2x the regular motor, and the twin tail lasts much longer than either of them because it keeps the motors much cooler (even compared to the stock motor with heat-sinks), which is the main factor for failure. From his estimates the order from the least tail authority to the most is stock motor, DD, and twin tail. The other benefit to the twin tail is redundancy. When you wire the motors up, you do it in parallel (cautions to be explained later), so that when one motor burns out, the other one keeps running, which allows you to land and replace the worn motors. Both the DD and the stock motors will have you doing crazy piro's if you don't catch a failing motor before you go out to fly. There are also brushless tails, but I am unsure of the exact weight on them, and those if properly taken care of rarely if ever go out.

And this is the explanation why

Basically the explanation for this is that the power mosfets on the esc for the tail are rated at something like 6A surge. The main esc has two mosfets and is rated at 12A surge. The normal tail motor draws 0.91A continuous at full power (dual motor is 1.26A), and averages probably around 500mA at lesser throttles and right turn rates. The problem is when you crash if the tail gets bound up, the motor goes into a full short current. The stock motor is about 1.7 ohm at 11.1v for a 3s lipo which works out to be 6.5A when the motor is stalled; this part of the reason why many people have fried their 4 in 1's. I'm not sure what the cn12's (GWS's DD) resistance is, but it is most likely less than 1.7 ohms which would increase the amperage, so it would be a good idea to fuse that motor too. When it comes to the dual tail, I would say it is a big risk of frying your 4 in 1 if you don't fuse it, because each motor can draw 6.5A in a stall which is 7A over what the tail esc mosfet is rated for, however this logic does not apply for running amperage. Running amps measured on the dual tail motor system run the same as the single motor, or slightly less because the dual tail system puts the motors in a more efficient power curve, and are sharing the load.

The stock tail with 2 heat sinks (each weighs 0.5g) weighs 18g. As configured with the super-skids and 2 heat-sinks it weighs 21g. The dual tail setup from micro heli with the CF fin weighs 31g, and the DD tail with plastic fin, 4530 prop and adaptor, and no heat-sink, is about 22g from someone else's measurement (with the heat-sink, it is likely 27 or 28g). If you decided to put the CF tail on the DD setup, which weighs 4g, it would weigh exactly the same as the dual tail setup (or if you decided to go with a plastic fin on the dual tail they would also weigh the same) note to editor, insert weight link here, also put in links for construction and links for the diff tail setups

One last thing to think about with the DD verses the dual tail is how they are connected. The DD tail is bolted on, so maybe not the best idea for people who bury their tail rotor once and while. The bolt on option doesn't allow the blade to pop off and avoid damage. The Dual tail has pretty close to the stock setup with the fuel tubing holding it on. If you are a beginner then this is ideal, but if you are more advanced you might want something that you don't have to check so much, like either using a very small wheel collar, or going with the bolt on DD setup.

A note on the micro heli cnc dual tail (here): because it is made up of aluminum, the heat transfers from the motors to the motor mount and acts as a big heat-sink. You will not need any additional heat-sinks on that particular setup. I ran mine for 30 min at 1.26A (so full power), and I could barely notice the difference above ambient.

All-in-all they basically weigh the same, and either one will get you better tail performance. I would definitely go with a fuse, because it's cheap and easy to replace a fuse, and more expensive to replace a 3 in 1. I would also make sure to at least single heat-sink each motor, if not double. If you like redundancy I would go with the dual tail, and if you want to follow nick Maxwell and others for hard 3d flying, then I would stick with their decision and go with the DD.

mrasmm

PS feel free to PM me either on RCU or RCgroups if you have any questions or comments

Also see RCU preferred tail setup poll