Servos and receivers

I am building a racing sparrow from scratch and I have come to the radio control bit. I have purchased a Hitec HS-815BB mega sail servo as recommended, and I have a Futaba S303 servo (left over from a previous project) for the rudder. I need to buy a receiver and would like suggestions as to what to buy, the problem is that the 2 servos have different connections. The information with the sail servo has a note regarding B.E.C receivers and it says the power supply  needs at least 1,200mA NiCd/NiMb with it connected direct to the servo. Then it states that if the receiver is a non B.E.C type the battery can be plugged into the BAT connection, so is that still the 1,200mA? I am totally confused, so any help would be much appreciated!

Welcome to the Forum

I don't know what the Sparrow is, but I assume that it is a yacht. In that case you will need a receiver battery. The comments about BEC only reply to electric powered models where you can use the drive battery, via a suitable receiver, to power the servos. In your case any receiver will be OK, provided its compatible with your transmitter.

I am a little surprised that you say the two servos have different connections. Unless the Futaba is very old both servos should have the same connectors, although the wiring colours may be different.

What make is the radio?

Barrie

Thanks for that, very useful. On further investigation the Futaba does fit, there was a lug that I have cut off. The radio is a Fly Sky model: FS-CT6B. I have a receiver from another model that I have tried, a Fly Sky FS-R6B, this works the Futaba servo, but not the sail servo. The power supply to the receiver
is 4 AA batteries, which is fine for another model. When I first switch on the power, the sail servo "twitches" but thats it, so I suspect that there is not enough power?? Bearing in mind that I am looking for a new receiver is there one that can take 1,200mA as suggested by the sail servo?

I am not a yachtie and have no experience of sail winches, however I think you need a new battery, not a new receiver. As far as I know there are no specific high current receivers.

If you unplug the standard servo, does the winch operate then?

Are you in the UK? If so check out the Component Shop website, and maybe give them a call. They sell both batteries and servos and should be able to advise you on a suitable re-chargeable battery pack which will deliver the current you need.

Barrie

Thanks I will check that out. The servo still does not work when the small servo is disconnected.

artdeco wrote:

Thanks for that, very useful. On further investigation the Futaba does fit, there was a lug that I have cut off. The radio is a Fly Sky model: FS-CT6B. I have a receiver from another model that I have tried, a Fly Sky FS-R6B, this works the Futaba servo, but not the sail servo. The power supply to the receiver
is 4 AA batteries, which is fine for another model. When I first switch on the power, the sail servo "twitches" but thats it, so I suspect that there is not enough power?? Bearing in mind that I am looking for a new receiver is there one that can take 1,200mA as suggested by the sail servo?

I'm more of an aeromodeller than a boat person but I do have a barge hull part completed and I have 1 metre yacht I used to race so I'm familiar with sail winches.

All servos have 3 connections and they all use the same connectors though some have that irritating lug which is there primarily to ensure their orientation. It isn't really necessary because all that happens if you plug them in backwards is that it doesn't work and correcting the error makes it all work. The centre connection is positive (nominally 4.8v - ie 4x1.2v - but can be more so check the specification). The other 2 are common (ie zero volts) and signal.  On aircraft and presumably boats with moderate demands on torque the power comes from the receiver.  However, sail winches can be very demanding, particularly in high winds with big sails, so it might be worthwhile to provide the positive (ie middle pin) from a battery capable of supplying sufficient current and not over stressing the printed circuit in the receiver itself.  As it implies, the common (negative or zero volts) connection must be connected to both the receiver and the bigger battery.  The signal, which tells the servo or winch that it needs to move, goes to the appropriate channel on the receiver.

Any receiver will work that matches the transmitter.  You can use either a 40 Mhz system which needs exclusive use of the channel to avoid controlling the wrong model or (as the vast majority of flyers do) 2.4gHz which tend to need to be from the same manufacturer and use the same protocol.  A receiver needs to be bound to the transmitter (see the manufacturer's instructions as the method varies).

I suspect in your case the receiver is limiting the current to the sail winch, though it should work off-load.  A different receiver won't help that.  In aircraft, it's quite common to use a separate battery to operate retractable undercarriages so that if there are problems and they get stuck, the subsequent battery drain doesn't compromise control of the flying surfaces. So supplying your winch directly from a bigger battery shouldn't be a problem.  On my barge I'm using a sealed 6v lead acid battery as weight isn't a problem - I use LiPos to power my aircraft  - up to 24v.

I use Frsky transmitters and receivers for flying.  Most people used 27Mhz 2 channel systems when I raced my 1 Metre Rhythm.