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Hi there, in common with a previous thread I am being driven nuts by the 'works in air - but not in water' issue. I recently completed a scratch-built conversion of a Trumpeter, 1/144 scale, HMS Astute. Like the real thing, when launched, she is full of promise but seems to be suffering 'first of type' issues.
Basically, as soon as the prop shaft touches water the engine starts to pulse - which is annoying because it effectively only offers about half the power it should or could. This occurs when the shaft is connected by the dogbone to the screw - or not. Everything else seems to work fine. The batteries - two parallel pairs, in series, of lithium ions are external, delivering I believe about 8 amps, and situated just aft of the 'pressure hull' (a 2.5 inch perspex tube with delrin end caps and double 'o'rings) and sit under the prop shaft.
The battery solder connections are all liberally covered in silicone sealant and the power enters the pressure hull at the forward end via screw contacts. All power cables are twisted and the servo lines, where extended, are all of the braided type. The receiver is a little 6ch 40mhz corona reciever.
The problem is worse, the farther aft you bring the antenna - although the wire is fully insulated as far as I can tell. The motor is an 12v mtroniks 400 which is perfectly suited to the three-to-one gearbox.
The astounding thing is that, when the hull is wet, I can detect small postive (+/- 1v) charge in one of the servo rods, all of which are wholly electrically isolated from any other componant, and I got a full 6v out of the shaft - even though this is not apparent when dry. There is or has been no free water in the pressure hull except one time when a supposedly waterproof switch revealed itself not to be. That was rectified and she remains a dry boat.
My guess is that, somehow, a current carried between the motor and the batteries / contacts somehow blanks out the antenna or that a short is happening between the shaft and one or other of the battery terminals - or perhaps both at once. I have tried swapping the engine with a 6v version but this produced a submarine that almost barrel rolled with the torque but still had intermmitant signal.
Very grateful indeed for any experiences or observations.
Meanwhile, of possible interest are some of the other features of the boat. For the sake of amusing my children she has a tiny camera in the bow so when you open the bow door (possibly the anchor door on the real thing?) you get a real-time view of what's going on forward of, and below, the bow. The signal works down to 'periscope depth' as is based on a 1.2 ghz transmitter. She also has a hydrophone that works down to the 3 to 4 metre depth of the local pond. This works on FM.
However, the problems I describe all occur with none of this equipment rigged or present, and in any case they have their own electrical supply.
She also has two torpedo tubes with a small water pump (which can only be rigged with the camera removed) to blow the tubes. Am working on very small electric torpedos to go with these but so far she has only fired dummies. I'll keep in touch on how these work out.
Basically, as soon as the prop shaft touches water the engine starts to pulse - which is annoying because it effectively only offers about half the power it should or could. This occurs when the shaft is connected by the dogbone to the screw - or not. Everything else seems to work fine. The batteries - two parallel pairs, in series, of lithium ions are external, delivering I believe about 8 amps, and situated just aft of the 'pressure hull' (a 2.5 inch perspex tube with delrin end caps and double 'o'rings) and sit under the prop shaft.
The battery solder connections are all liberally covered in silicone sealant and the power enters the pressure hull at the forward end via screw contacts. All power cables are twisted and the servo lines, where extended, are all of the braided type. The receiver is a little 6ch 40mhz corona reciever.
The problem is worse, the farther aft you bring the antenna - although the wire is fully insulated as far as I can tell. The motor is an 12v mtroniks 400 which is perfectly suited to the three-to-one gearbox.
The astounding thing is that, when the hull is wet, I can detect small postive (+/- 1v) charge in one of the servo rods, all of which are wholly electrically isolated from any other componant, and I got a full 6v out of the shaft - even though this is not apparent when dry. There is or has been no free water in the pressure hull except one time when a supposedly waterproof switch revealed itself not to be. That was rectified and she remains a dry boat.
My guess is that, somehow, a current carried between the motor and the batteries / contacts somehow blanks out the antenna or that a short is happening between the shaft and one or other of the battery terminals - or perhaps both at once. I have tried swapping the engine with a 6v version but this produced a submarine that almost barrel rolled with the torque but still had intermmitant signal.
Very grateful indeed for any experiences or observations.
Meanwhile, of possible interest are some of the other features of the boat. For the sake of amusing my children she has a tiny camera in the bow so when you open the bow door (possibly the anchor door on the real thing?) you get a real-time view of what's going on forward of, and below, the bow. The signal works down to 'periscope depth' as is based on a 1.2 ghz transmitter. She also has a hydrophone that works down to the 3 to 4 metre depth of the local pond. This works on FM.
However, the problems I describe all occur with none of this equipment rigged or present, and in any case they have their own electrical supply.
She also has two torpedo tubes with a small water pump (which can only be rigged with the camera removed) to blow the tubes. Am working on very small electric torpedos to go with these but so far she has only fired dummies. I'll keep in touch on how these work out.
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