Vintage Gentleman’s Cruiser

[Bob Abell 2Participant @bobabell2]

Had a short test at last….

7.2V Battery…… Running one motor, via the Watt Meter, driving the lay shaft, driving the prop shaft with 50mm x 3 blade prop and it all ran very smoothly and happily

The readings on the meter were flashing about and constantly changing

Spotted 36w and 5 amp appearing quite often

Any comments on this?

Bob

[Paul TParticipant @pault84577]

Bob

The set up has to be exactly as it would be under full power on the water, i.e. all motors connected to the shafts and running at full speed, powered by fully charged batteries and on the water in a fully ballasted boat.

This is the only way to establish the full amp load.

Paul

[Bob Abell 2Participant @bobabell2]

I'm only showing the World that I've connected the Watt Meter and battery to a motor

Since Dave was taking bets!

The current figures may be of interest to him

Bob

[Gareth JonesParticipant @garethjones79649]

Bob,

Was that 5 amps measured with the prop in the water or just run on the bench?

If its just one motor driving a propeller in free air its a pretty high current for an unloaded running case – seems like a lot of friction somewhere.

If it was measured with the prop in the water it seems your overall power consumption is going to be relatively modest (for a complicated 4 motor installation)

Gareth

[Dave MilbournParticipant @davemilbourn48782]

As Paul says, only one figure is relevant. You should be able to scroll through the options available on the meter and display the average current and power output. RTFM.

Ref Odds – I had no takers.

DM

[Bob Abell 2Participant @bobabell2]

It's a fresh air test, Gareth

The plain bearings may need running in?

Got plenty of power to spare, anyway?

Bob

[Bob Abell 2Participant @bobabell2]

"Only one figure is relevant" is not quite correct

When the water figure is known, it can be compared to the fresh air reading…..For future use?

i wanted to know it

Bob

[Paul TParticipant @pault84577]

Bob

The dry run results could have a value.

You could use the figures to check how much extra power is required to turn the propshaft and see if one or both are drawing high amps, this would be a useful indicator for misaligned bearings or a bent shaft.

Run each motor individually (not connected to the belts) to see what they draw. Connect one motor at a time to the belt and propshaft to see how much the draw increases.

The set of four results should be consistent but if they are not it would be a good indicator of where a problem is.

Paul

[Bob Abell 2Participant @bobabell2]

That's a good idea, young Paul!

Should make interesting reading?

Gareth, it would be nice to know what your Shemarah is pulling in fresh air too?

Bob

[Paul TParticipant @pault84577]

Not just interesting……. the figures will be immensely useful in helping locate any tight bearings or misaligned shafts, I know that, as you have built it, there wont be any such mechanical problems but Kevin might find it useful.

[Bob Abell 2Participant @bobabell2]

Thank you, Paul……That`s the nicest thing you`ve said all day!

We could invite further results from anyone with MFA850 motors, please?

Bob

[Gareth JonesParticipant @garethjones79649]

Bob,

If I get up early enough before I have to go to work tomorrow morning I will run Shemarah and get a comparable set of results – single Speed 900 motor driving through an MFA belt drive with 2:1 speed reduction. I can't do it tonight as Elizabeth has a yacht in the end of the workshop with the paint drying.

Gareth

[Bob Abell 2Participant @bobabell2]

Roger on that Gareth……Need the prop size also

Plain bearings?

Bob

[Gareth JonesParticipant @garethjones79649]

Bob,

Just managed to do a quick check with Shemarah still in its box. On 12 volts, it took 1.9 amps / 21 watts. It has an 80 mm 4 bladed propeller. The belt drive is the standard MFA unit with ball bearings on the layshaft. The propshaft is a sealed Raboesch unit.

Maybe you need to run your system in and put a bit of oil on all the bearings. If you are losing 36 watts on all 4 motors your passengers will be nice and toastie warm inside, but your batteries might not last as long as you would like.

Gareth

[Bob Abell 2Participant @bobabell2]

Many thanks Gareth

Regards to Lady Liz

It's early days at this end and being inefficient is true to scale!, I get extra points for that!

Capt Bob

[Bob Abell 2Participant @bobabell2]

Gareth

What ESC have you got in your Shemaraha, please?

Bob

[Dave MilbournParticipant @davemilbourn48782]

"Only one figure is relevant"

……to the continuous current rating of the speed controller(s) which are finally installed. I think this subject and I are done.

DM

[Bob Abell 2Participant @bobabell2]

Just for reference….

One MFA850 motor running light uses 1.7 amps

Bob

[shipwrightParticipant @shipwright]

The data for an 850 is here :

**LINK**

You can see that MFA 850 spec says that on no load the MFA draws 1.9 Amps at 9778 rpm with v = 12 volts …… so assuming that Bob is running his 850 off a 12 volt battery his result is close to the nominal specification. At maximum efficiency the motor draws about 11 amps (with 12v supply) though note that maximum efficiency is only 62% (so nearly half the of the electrical power input is wasted).

Ian

[Paul TParticipant @pault84577]

Bob

Are all of the motors giving the same No Load reading of 1.7A?

Now if you connect the drive belts (but not the main propshafts) and repeat the experiment you will see how many more amps are drawn operating your drive system.

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

I'll look into that and report back with the findings

I've got the shafts out at the moment, filing the flats on them for the pulley grub screws to bite onto

The motors are very well behaved, surprisingly…..There's no fierce running at all and is very pleasant to switch on and off

Ideal for this type of boat

I think twin motors in line would be ok too, as opposed to my side by side arrangement

Bob

[Paul TParticipant @pault84577]

Bob

This build-up of electrical information on the 850s will be useful for when Kevin decides to use the same motors on his build.

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

Starboard line

One motor powered….One motor back driven………..One 50mm prop

8.1 amp……6.1v……..48 w

Same test

One motor powered….One motor not connected……One 50mm prop

4.9 amp ……6.1v………36 w

So it takes 3.2 amp and 12 w to back drive idle motor

So if the RH stick controls motors 1 and 2……..There will be no back driving, as both motors will be driving RH prop

Bob

Edited By Bob Abell on 01/04/2015 20:35:08

[Bob Abell 2Participant @bobabell2]

Hello Paul

Ran test No1 again

Same readings

Then powered up No 2 motor……….Twice the power and sounded powerful too

4.0 amp………………………………………24 w………..On the one motor

Success!

Bob

PS The thread has had 350 views since last night!

Edited By Bob Abell on 01/04/2015 20:56:30

[Bob Abell 2Participant @bobabell2]

Oh dear!…..Paul has thrown a spanner in the works, by suggesting the current batteries my be a poor choice (7.2v)

He is proposing 12v jellies, they will certainly bump the ESC's up a bit

Luckily, We've got two in stock…….Bang goes my Gentle VGC……..More like a roaring monster now?

12v certainly provided the GE with a good turn of speed

Bob

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