Would the only difference be the servos? Many have said I won't need to run HV on the 6s setup, but making sure my plans are on the right path. Going to run Vbar, so which servos for a non HV set up? I thought I was going with the CC 120hv, but maybe I can go with the 100 and a bec pro. What else should I be aware of with the differences between a low voltage and high voltage setup? This will be my first build larger then a 450 so I'm still learning new things as far as set-ups. The motor is a scorpion HK4020-1100 and that's all I have so far. Haven't picked servos yet, still debating on that topic.
Thanks!
Greg
Greg, I think you are confusing a couple of topics here. I'll attempt to help you sort them. Low or high voltage servos have nothing to do with "standard" or high voltage ESCs.
Servos:
Most "low voltage" or normal servos operate in a voltage range from 4.8 to 6 volts (in truth a 5 cell NiCd fully charged is near 7V, which is what a 6V servo was originally designed to operate from). Servos being termed as high voltage servos typically operate between 6V to 7.4V. The idea being that they can operate off of a 2 cell LiPo battery which fully charged is actually 8.4V. Typically servo transit speeds and torque increase as voltage increases. An example of this is the JR 8717s that I run in both my E7 and E5 on the collective. At 4.8V the transit speed is 0.09 sec/60° and torque is 160 oz / inch. At 6.0V the transit speed is 0.07 sec/60° and torque is 196 oz / inch. As you can see the speed and torque increases with the increase of voltage. The other component that is mostly over looked when talking about RC electronics is current. Ohms Law states that as voltage increases current decreases. Why is this important to you? Because higher current equals more heat and heat is the number one cause of electronic failure period (Yes, i know there is a caveat
frequency)! So by increasing the voltage on the servos you can increase speed and torque and reduce heat. I run a Futaba BLS256HV on the tail of both of my Synergy's. But .... that is a high voltage servo why would I do such a thing? Because the Futaba BLS256HV has a voltage range of 6V to 7.4V (actually 8.4V) and allows me to operate my collective servos at there maximum speed. Having fast collective servos translates into a responsive crisp feeling. In truth I operate all of my electronics at 6.9 volts. (I'm not advocating that you do this as it is outside the voltage range specified by JR for the 8717s but, the JR8717 is a tried and tested servo and it operates fine at 6.9V). This is what you need to know. First the performance of a flybarless helicopter is going to be no better than the servos on the collective. If you use slow servos your helicopter is going to feel sluggish. No flybarless system can compensate for slow servos or for servos that don't center correctly (sloppy). Another thing to consider is that all three collective servos must move at the same speed. Lets say that you have three of the exact same servos on the collective but one is a little slower than the other two (for what ever reason lets say quality control (China)). In this scenario if you raised the collective stick rapidly the helicopter is going to pitch in the direction of the slower servo (the FBL unit will reduce some of this but can not eliminate it). This is the same reason that typically when you replace and aging servo on the collective you replace all three. Generally an old servo is not going to be as fast or precise as a new servo. I had a discussion with Matt recently about tail servos. Matt said that most of the tail related problems he sees are related directly to tail servo. Aside from speed and torque when selecting a tail servo there are a couple of other things to consider. Resolution and deadband. Deadband reflects the time it takes for a servo to respond when stick movement is given. Standard servos have a deadband of around 8 micro seconds and high performance servos have a deadband of 1~3 micro seconds (Zero dead band is ideal for a tail servo because the tail gyro is making constant corrections to hold tail orientation and compensate for torque). Resolution, without getting into a long technical definition is how small a movement your servo can make. Resolution is effected by frequency and pulse width. Here is an example. I was flying a JR 8900G on the tail of my E7. The JR 8900g was 5 thousands of a second faster than the Futaba BLS256HV that I'm currently using but lacked the resolution therefor the tail of my E7 didn't feel as solid or as responsive as it does now. And last but, not least keep your tail servo voltage in mind. Things are greatly simplified when all of your electronics can operate at the same voltage eliminating extra components like voltage regulators (or step downs as they are commonly referred to). The bottom line is if I were looking for a place to save money it would not be on servos. Buy the best servos you can afford. Your helicopter will reward you with hundreds of trouble free connected feeling flights. This link is a good resource for looking up servo specs.
http://www.servodatabase.comBec:
Digital servos are power hungry, some more that others. This is why most helicopter pilots do not run ESCs with built in BECs. Simply stated most ESCs with built in BECs cannot supply enough current to supply four digital servos under load. For instance you mentioned a "Castle 100" in the above text (and a CC BEC Pro to your credit). The Castle Phoenix 100 has a built in BEC with a maximum current of 5 amps. A single JR 8717 under load can draw up to 2.2 amps. A total of 6.6 amps for the collective alone and we still haven't powered the tail servo, Vbar or receivers. I think you can see where I'm going with this. The Castle Creations BEC Pro can deliver 20 amps peak and would be a good choice. I'm sure others will chime in with other options.
ESC:
The primary difference between a standard ESC and a high voltage ESC is the number of cells that can be connected to them. Standard voltage ESCs generally support up to 6S where most HV ESCs support up to 12S. I stayed with the CC Ice2 120HV because it gives me more options. If I decide to stretch my E5 later I don't have to buy another ESC to run 12S. On the flip side of that coin I have run my HV ESC on 3S. Maximum flexibility! Also remember that a ESC that is rated for a higher current can dissipate more heat than one rated for a lower current and will therefor run cooler and should last longer.
I hope this helps. There are a lot of people out there confused about this stuff so don't feel like the Lone Ranger. In the beginning it's like trying to get a drink of water from a fire hose without getting wet.
Rich
