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[justboatonic]

Howdo!

Im fitting a G900 in the MSW Envoy civvie tug. Build coming along nicely (more pics soon) although the missus has just questioned the launch date as being in 2012 due to my 'normal' slow build progress. Hmmmm 

Any hoo, according to the motor spec, the current draw at maximum efficiency should be around 8 amps. Now, the specs doesnt say whether 8 amps is at 12v supply or 40v supply or some other supply voltage! 

Not being electrickery minded, maybe it doesnt matter on the voltage too much(?) but, can anyone confirm or give an indication what the current draw should \ may be for the G900 on 24v supply (since the foggy I got off Mark also uses 24v  )? The G900 is turning a 3 blade 70mm prop on direct drive.

[FullLeatherJacket]

David
Don't even think about running that motor on 24v in that model. The data given in the Graupner specs is based on the nominal voltage for the motor, which is 12v. That gives 6500RPM with no load, which is probably a shade too fast for the prop you mention anyway. On 24v you'd be looking at something around twice that speed - the world's first planing tug hull - and a current draw in the region of 15-20A with that big prop.
Stick to 12v as a maximum for the motor supply, and use a separate 12v battery in series with it for the MMB Foggy unit.
FLJ

[justboatonic]

David
Don't even think about running that motor on 24v in that model. The data given in the Graupner specs is based on the nominal voltage for the motor, which is 12v. That gives 6500RPM with no load, which is probably a shade too fast for the prop you mention anyway. On 24v you'd be looking at something around twice that speed - the world's first planing tug hull - and a current draw in the region of 15-20A with that big prop.
Stick to 12v as a maximum for the motor supply, and use a separate 12v battery in series with it for the MMB Foggy unit.
FLJ

Ah, didnt think of that! Wouldnt look too scale like woukd it.

Thanks Dave!

[debssnal]

Hi David,
           the graupner speed 900BB Torque @6500rpm is to fast for your tug.The graupner speed 720BB torque @4100rpm and at max eff it pulls
3 amp.
You need 1927rpm to get this tug to its max hull speed.so as you can see the 720 is the better motor for your tug,or you could fit the 900 speed to a mfa belt drive gear box @ 3:1.the 900 motor fits on it has the same fitting size as the mfa 800 and 850.We have this setup in the clubs 12.5 foot type23 and we took it 18 miles down the medway last year.each motor at full power pulls 4amp (and thats moving at 5mph).this come in at 80kg
hope this is of some help
Alan

[FullLeatherJacket]

I have to agree that a Speed 900 is a bit much for Envoy and that I would have used either a 755 or 720 Torque. However if it's of any help, Mark Windless has an MMB900 in his Canning tug which he runs from 12v but using the P93 Multicontroller on its 50% ESC Output setting. A 6v supply would have pretty much the same effect.
I think you've already gone too far to effect a motor transplant or install a gear/belt drive, so I guess you can experiment with speed controllers ( ) and supply voltage if you have the choice of batteries.
FLJ

[chrise]

You need 1927rpm to get this tug to its max hull speed.............
Alan

This is very interesting but to make it more useful how did you work this out? Did you allow for "slippage"

Do all 70mm 3 blade props have the same pitch? If it had been 4 blade would it have been different?

As long as the motor can power the prop surely a bigger motor is better for towing etc & you can set the throttle limits accordingly?

[justboatonic]

Hmmm. Just to clarify, I went for the G900 as MSW suggested a 900 as a direct drive alternative. The MFA geared motor is noisey (have 2 of them in Drumbeat) but Im beginning to think I'll have to go down this route for a couple of reasons.

First is the motor mount for the G900 means the motor and prop shaft centers are out by about half an inch. The second is, MFA's belt system for their 800 series motors (about the same size as the G900) is £45 on its own and £60 if bought with the 800 motor.

A 1:1 belt drive is available for about £7 but just causes other installation issues.

Motor supply is 12v since with the foggy, I need 24v which will use two 12's in series for this with one also supplying the motor.

[Model_Slipway]

Hello

To clarify, our 900-type motors are not the Graupner ones.

The specs for our motors are at:    http://www.modelslipway.com/motor_packs/MS%20900BB.htm

Jackie
ModSlip