Battery for Slo-mo-shun

[JeremyParticipant @jeremy15845]

I plan to use a Graupner 600 7.2V speed motor in a Billings Slo-mo-shun kit.  I intended use a Tamiya type Nimh battery linked to a Mtronics Viper25 speed controller to power this.  Looking at the Billings instructions, they show two 4.8V accumulators mounted either side of the motor.  Is this type of battery still available and, if so, is it the best solution?  Any advice would be much appreciated.

[JeremyParticipant @jeremy15845]

[JeremyParticipant @jeremy15845]

Regretably not a reply but just a further question which is maybe the one I should have started with.  If Dave Abbott sees this post, please tell me how you set up the motor and battery in your build of Slo-mo-shun.  Your review of this kit plus all the pics is going to be very helpful – thanks!

[Mark Beard 1Participant @markbeard1]

Beware a language complication.  In English an ‘accumulator’ is a lead-acid type wet cell rechargeable battery.  In German, the word ‘accu’, (as written in the instructions) means battery.  The drawing shows a pair of cylindrical batteries with 4-cells each.  This is consistent with NiCd or NiMH batteries, and not lead-acid accumulators.  So I think the plan calls for 2x 4.8V cylindrical battery packs.

 

If you can’t find such packs off the shelf, you can buy individual NiMH cells with solder tags and construct your own.  I’d suggest getting the biggest cells you can fit in the space – C or D size probably.

Since you’ll be running way above the nominal speed of this motor, and possibly above its peak power point, you may want to ensure you leave enough room to add a water cooling jacket to the motor.  Since there is a wide range of voltage- and speed-combinations in the Speed 600/700 range, you should be able to arrive at a reasonable match by changing the motor, if you go with the 7.2V option at first.

[ashley needhamParticipant @ashleyneedham69188]

Several companies will make whatever battery packs you want, and so 2x 4 cell packs will be no problem to get made up. 

 

As Billy says, there are motors in all voltages in the 600/700 range. Get one to match your 9.6V (overall) voltage and you cant go wrong.  Graupner do about 5  600`s in various guises alone.

 

Ashley

[JeremyParticipant @jeremy15845]

Ashley

 

Thanks for your reply – thanks also to Billy

 

The motor I have ordered is the Graupner Speed 600 Race 7.2V, weight 235g, operating voltage 6.0 to 8.4, cost £14.30.  Their alternative 600 Race is an 8.4V, weight 195g, operating voltage 4.8 to 9.6, cost £26.95.  The Race versions have integral fan cooling which I am advised eliminates the need for water cooling.  Why would the 8.4V version be significantly lighter but cost almost twice as much?  What, if anything are their relative advantages?

 

Should the battery voltage match the nominal voltage of the motor or the top of its operating range?  If it is the nominal voltage, I need to have two 3.6V sticks.  Can this configuration be made up?  Would it be possible to split a Tamiya type 7.2V battery pack into two sticks and then place one either side of the motor?

Sorry to ask such basic questions but my knowledge of electrics is to say the least basic.  You mention companies who will make up battery packs – would you have any links to recommend?  I would not be placing bulk orders!

 

Jeremy

[Mark Beard 1Participant @markbeard1]

Sadly I don’t know the details of the Mtronics Viper 25 ESC, but any half decent ESC should allow you to run a motor efficiently at a lower voltage than the battery, so a 7.2V motor should be fine on a 9.6V battery, just beware if you crank it up to 100%!  (Ashley recommends extra power for emergency manoeuvres, so not a bad idea to have a bit in reserve).

 

My guess about the reason for the different price is that the 8.4V motor is made in much lower quantities, and therefore is priced at a premium.  No idea why it should weigh less: perhaps there’s either a mistake in the published weights, or there are other unspecified differences between the motors apart from their windings.

 

You could try re-working the Tamya 7.2V pack, but this could be harder in practice than it seems.  So be prepared to right off the pack!  These packs are usually made by connecting cells with strips spot-welded to the pack, not soldered, so terminating each half-pack may be your biggest problem.  Anyone out there tried this?

 

Please let us know how you get on.

 

 

 

[Mark Beard 1Participant @markbeard1]

Tagged Cs sized cells, part number 199-731 available from http://rswww.com at £5.40 each, would seem suitable.  Eight of these would make 2x 4.8V 3Ah NiMH packs.

[ashley needhamParticipant @ashleyneedham69188]

Who knows why these things are? (motor cost) the manufacturers have it all worked out. I am not sure that a few fans on the armature end replaces water cooling, however it will help if the motor is not being worked too hard. i would like to think that a motor drawing its rated “efficient” current at a voltage within its grasp would not get so hot as to need water cooling, but other things come into play, such as volume of hull and air flowing through it (or not).

 

I have never read anything regarding this “nominal” voltage spec, the racing boys over drive their motors by quite a bit so i dare say it is the manufacturer being cautious.

I cant imaging that an 8.4V motor would be blown up by 9.6 volts, unless you thrash it for hours on end at full throttle, or allow it to get red hot.

 

I made an “instant” flying boat for the lad just a while ago and have three toddy cheap motors in it of the sort normally rated at 3v, running at 4.8v. Doesnt sound like much, but its 50% above their nominal voltage and they are quite happy chappies. They are of course running in a cooling breeze!

A Billy says, splitting a pack may not work too well. I have not priced up buying

individual cells, my hunch is it will be cheaper to buy a pack, complete with connector and nicely heat shrunk wrapped.

 

Ashley

 

 

 

[Mark Beard 1Participant @markbeard1]

The advantage of a built-in fan is that it cools the windings directly by drawing air through the motor.  Water cooling a brushed motor is a bit hopeless, since you’re cooling the magnets.  Heat from the windings has to pass through the armature and bearings to get out (a clear advantage for in-runner brushless motors).  However, I’m not sure I’d bet on the efficiency of these fan designs.  So perhaps it’s six of one…

 

A pre-made pack would certainly be cheaper, if you can get them.  But I’d put my money on the life and capacity of the RS industrial ones, over the model variety, any time.  You may find some kindly electronics whiz willing to solder them up and shrink them for you!

 

Mark

[JeremyParticipant @jeremy15845]

I have found a source of 4000mah Nimh C cells at £3.45 each and plastic holders which will take 3 in line.  Two banks of 3 will give me 7.2V, the same as a Tamiya type battery which also matches the 7.2V rating of the motor.  If I go this way, I would charge the cells individually in a standard charger.  If I get packs made up as suggested above, I would save on space and weight.  Next question is how would I charge these?  Linked together, can I use the charger which I already use for the Tamiya batteries?

 

Thanks again for all the input.

 

Jeremy

[Mark Beard 1Participant @markbeard1]

Excellent.  Just make sure the holder will take the temperature!

 

Making a trickle charger is not difficult.  I’ve posted info at http://www.modelboats.co.uk/forums/postings.asp?th=43083.

 

Mark

[george KaprouliasParticipant @georgekaproulias19775]

Dear friends

 

I have constructed the boat “VEDETTE” from the free plan of the issue Noe/1997.

i put a motor 540 and a batery 6 volt PB, althouth i have no the result i hopped.The

total weigth is 2.900 gr.The speed control is ROBBE RODKIE 35.If i give more velocity

the system stops to work. Perhaps the aal combination is not right. Could you help me

indicating what change or the right combination of the accecories ?

Thank you very much.

 

[ashley needhamParticipant @ashleyneedham69188]

George, You need to put in a new thread or topic on this forum to get the most people looking at it, and so advise you .

 

Ashley

 

 

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