Advise on electrics

[Rustypig]

Hi

 

I recently purchased a plane fitted with 3 x grauper speed 400 motors. All three motors appear to be wired together and the plane is controlled using rudder and elevator. Please advise what I need to get it flying again. No batteries or transmitter included. Thanks 

[MattyB]

What voltage are the motors optimised for? On the old Graupner versions it is normally marked on the can. probably you will want a 2S lipo for that, but the motor specs should help us know for sure.

[Allan Bennett]

I suppose the first question is, do you want to keep the model 'original', or do you want to equip it with a modern reliable radio system?  The Digifleet equipment in there, while good in its day, is about 40 years out of date now!

 

Second question is how sound is the airframe?  Is the covering material perished, are the glue joints sound, and are there any 'spongy' areas caused by previous use with a glow engine?

 

You can test if the motors are in running order by briefly connecting a 6v or 7.2v battery to them WITH THE PROPS OFF.  If they run, and if you want to go for current equipment, you'll need a brushed speed contoller rated at about 30A, a transmitter and associated receiver, and replacement modern servos.

 

If you decide to proceed, more detail such as aircraft dimensions and weight will allow other more-kmowledgeable people to advise more specifically on component specs and battery size.

[Tom Gaskin 1]

That speed controller was designed for NiCd / NiMh batteries, so the built-in safety features will not necessarily be compatible with modern LiPo cells. Also you probably won't be able to source a compatible transmitter.

 

Mind-you, that is not to say that once air-worthy it won't be an excellent model!

 

Tom

[Shaun Walsh]

If it was me and I wanted to keep it with 3 motors then I would fit:

3 brushless outrunner motors

3 brushless speed controllers

2.4 GHz receiver

2 new servos.

Lipo battery to suit motors and required duration, will depend upon size and weight of models. Probably a 3s or 4s battery for ease of availability and cost. 

[Don Fry]

Shaun has it about right, some folk love that old tech radio, but it deteriorates, and unless I know your spuds, can cause tears. Brushed motors like fitted have limited life spans, are heavy. Designed for Nicad batteries, which you can’t get nowadays, and Nickel hydride batteries can struggle to give the power out, and won’t keep it up for long. 
And the whole thing is heavy, so won’t be a nice flier. 

[Allan Bennett]

11 hours ago, Don Fry said:

Shaun has it about right, some folk love that old tech radio, but it deteriorates, and unless I know your spuds, can cause tears. Brushed motors like fitted have limited life spans, are heavy. Designed for Nicad batteries, which you can’t get nowadays, and Nickel hydride batteries can struggle to give the power out, and won’t keep it up for long. 
And the whole thing is heavy, so won’t be a nice flier. 

Just one point;  brushed motors don't care what the battery type is, so long as the voltage is within their design limits.
 

 I agree though that brushless equivalents will be lighter, more efficient and longer lasting, but thr OP would have to factor in the weight and cost of three brushless speed controllers instead of a single brushed one required for multiple brushed motors.

[Frank Skilbeck]

OK re the radio gear, the Digifleet Rx will operate off any 35 mhz set you'll need same channel on the tx. Note if you do.decide to.change out the receiver you'll need to replug all the servos as Digifleet used a different wiring order.

 

For the motors a 2S lipo would be fine, we upgraded an old Multiplex Twin Star with two 400 motors and it flies great, the existing ESC will work but doesn't have a setting for lipo low voltage cut off so if you fly too long you could damage the lipo, you can buy cheap alarms that plug into the balance lead if you wish.