Choosing Your Radio GearThe next decision is what sort of radio to use, and this will obviously be coloured by the sort of starter deals that many model shops will do. The choice falls between "traditional" 35 MHz radio and the newer 2.4 GHz sets (usually either Spektrum/JR or Futaba – needless to say, the two systems are not compatible). It's still possible to get interference or frequency clashes on 35 MHz, but interference on 2.4 GHz is (so far) almost unheard-of. 2.4 GHz equipment also provides a noticeably more immediate link between the transmitter stick and the servo because latency is lower, usually much lower for 9 channel sets and above.
2.4 GHz radio has (so far) proved to be safer than 35 MHz as frequency allocation is automatic and doesn't rely on manual control of a frequency peg (the only two crashes that I've seen with 35 MHz equipment that can be attributed to radio problems have happened when someone has switched on with the same frequency as a model already flying).
For an I/C aircraft, a good 35 MHz FM set is usually adequate but a synthesized PCM system is better. Some of the low-end sets can be a little problematic, there are a couple of 6 channel budget Futaba FM sets in the club that have glitching problems. If in doubt, buy better radio gear. As a general rule, the default these days should be 2.4 Ghz because there's effectively no interference issues and it's almost impossible to take off with the wrong model memory set, or with the antenna retracted (We know a song about that, don't we, Rich?...
), or on the wrong frequency - it's
much safer all round.
For electric, 2.4 GHz is a much better bet than 35 MHz because of its resistance to interference from brushless motors and speed controllers.
On the other hand, a 2.4 GHz signal is directional and can be blocked by servos, undercarriage, engines, silencers, motors and full fuel tanks so it is vital that the antennas are positioned as far apart as possible. For this reason, I tend to lean slightly towards the Spektrum/JR 2.4 GHz system rather than Futaba.
On balance, then, 2.4 GHz radio equipment is a better choice – there’s a very, very minimal chance of suffering interference so it’s safer than 35 MHz, follow the instructions to the letter and use a decent-sized battery and you shouldn’t have any problems.
Initially, a 6-channel set is probably adequate but extra features are often available with sets that have more channels - that's how the manufacturers make their money
.
Given the number of instructors in the club with JR or Spektrum gear, it might be worth considering one of these but it's always better to take it out of the box and see how the sticks feel before committing money (I have JR equipment because it has a very quality feel, but in this country it's often priced at the expensive end of the market).
If asked for an opinion at the time of writing (December 2009) I'd be inclined to look very closely at the Spektrum DX-7 (NOT the DX-7se because it hasn't got a buddy-box port), the DX7 can be buddied from JR and some Multiplex units. There's nothing fundamentally wrong with Futaba 2.4 GHz, there are people around who use them and we do have a Futaba buddy box, but if you're considering it I should have a very close look at receiver prices - Spektrum receivers (which are compatible with JR) are often rather cheaper.
And don't even consider a radio supplied without rechargeable batteries!
ServosServos can be categorized (very broadly) into two categories;
a) Analogue (e.g. JR 591)
b) Digital (e.g. JR 811)
Analogue servos are generally cheaper, less precise and use less power. Digital servos are generally more expensive, more precise, usually faster but can use enormous amounts of power - this is important for 2.4 GHz receivers which are sometimes sensitive to the supply voltage being dragged down under load. If you use digital servos, use a big battery pack; as a general rule of thumb I'd suggest
at least 800 MAh for 4 standard-size analogue servos or 3 standard digital servos, or 1000 MAh for 5 standard analogue servos or 4 standard digitals.
For a fixed-wing trainer, you're probably going to be OK with analogue servos, but buy the best you can find - cheap servos are cheap for a reason (they probably haven't been tested or burnt-in to any great extent) and if, for example, you lose the elevator servo, there will be Regret and Recriminations.
