Model Boat Mayhem
Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: Nige52 on December 05, 2010, 07:17:24 pm
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I have a 700BB Turbo 9.6v which I am considering putting in a new boat. Reading the spec, this motor will handle over 14 volts, but I don't actually have any batteries up to that size.
Seeing that this motor comes in different voltages, ie. 7.2v, 8.4v, 9.6v etc, could someone tell me if a 9.6v motor running on a 9.6v racing pack, is any different to a 7.2v motor running off a 7.2v pack?
Why all the motor voltage differences?
Much obliged
Nige
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Graupner motors are rated for the MAX efficiency so the 7.2 volt motor will still take 12 volts but at a far higher output.
Although not at maximum efficiency they do go well when overvolted with no damage (with a bit if common sense as it obviously wont take 100 volts).
Bob
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Why all the motor voltage differences?
Different people have different requirements for batteries. Boats needing to float have a natural limit for weight, so one person might prefer to run a lower voltage having fewer cells, but still want the power, so will pick a lower voltage motor and get the performance by pulling more current without sinking the boat. There are lots of threads discussing the merits of various combinations of motor/battery/prop in any particular hull. If there was only one voltage catered for, the question would immediately be "Why?", and the first company to offer a choice would have all the customers.
The 14 volt figure normally indicates that you are unlikely to break the motor using a fully charged 12 volt SLA, which should be towards the 14 volt sort of area.
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Hmmmm, ok so I see that by using a low voltage 7.2v motor combined with a 10 cell sub C pack will give loads of power, so to get the same power with my 9.6v motor, I would need a 12 or 14 cell pack? I think I'm having a senior moment at present %%
So my original question still stands....
will a 9.6v motor on a 9.6v pack give the SAME power as a 7.2v motor on a 7.2v pack?
Ta so
Nige
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Hi Nige, what boat are you thinking of putting the motor in, I did a lot of testing a bit ago with the graupner 7.2, 9.6 and 12v, and the 12v neodyme all 700bb turbo, so perhaps I can offer some of my findings to help you. I run a 9.6v with 2:1 gearbox in a 3 foot Aerokits 1/16 scale Fireboat. Run it on 19.2v (two 9.6v nimh packs, 4600mah). When changing to a 7.2v motor with same set up and packs, the gps speed was no real difference, but now the motor is running over voltage, and hot. The 12v motor was useless with same set up, with the gearbox. Different story with all motors on direct drive, the 12v on 19.2v was much quicker, ran cooler and longer.
Back to the two motors you want to know about, the 9.6v runs a bit cooler, but very little in it, if you run the 7.2 on 7.2v, and the 9.6v on 9.6v, both battery packs with same c rating and mah, I doubt there will be much difference, but the 7.2v on the 9.6v pack will be quicker , you have to get them working a bit if you want speed, but then run time suffers, now the neodyme is a different kettle of fish, this was by far the fastest on same set ups, but it costs more money.
All the results are documented on "whats my set up" in the Fireboat website :-)), hope that helps
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Ah....I'll have a read of that, thanks!
The boat I am planning to put the 700BB Turbo in is an Equipage Gold Coast. It's 38" long and as usual, made from wood with glass fibre reinforcement. I haven't received it from the seller yet but it should be here tomorrow. I already have the new motor in my spares box, I bought it to put in a Fairey Spearfish, but at the time I had a brushless 3600kva motor and a 60A esc going spare, so used that instead, leaving me with the 700BB spare.
I only have Nimh's up to 8.4v and as the 700 is a 9.6v, it looks like I will have to buy something beefier. But I do have Lipo's of 11.1v and 14.8v which I could use I suppose? To be honest, although I find the Lipo's to be fantastic regarding power and performance, but I'm fed up of them puffing up on me. The last one was in an Astec 32"Pursuit fast electric, I had only done a few runs with it and I always allow them to idle between the runs, when I noticed a sudden drop in performance, bringing it in and un-taping the lid, it was puffed up, sizzling and about to blow. Luckily I managed to remove it before it did. That's yet another £48 up the Swannee and about the 4th one to blow. Hence me asking about sub C cells........... %)
Cheers for the help so far lads!
Nige
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Its very important with any high current use, to get a Lipo with the highest C rating available...Alway use a proper Lipo charger/balancer and make sure the "settings" are right for the battery you wish to charge.
Having said that..there is an awful lot of very poor Lipo's out there ;and some them are not always the cheapest ones.
My suggestion is find out what brands the fast electric boat racers use....
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Good Lipo's these :-))
http://www.astecmodels.co.uk/catalog/index.php?cPath=27&osCsid=0f2294016fe20ef7885a8936eab6270b
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I sometimes use in the fireboat two 7.4 5000mah 30c lipos as 15v, as said prev, the c rating needs to be high, and the mah will give a better run time, so as an example, the 7.4 5000mah 30 c will run longer, and better, than a 7.4 1500mah, 15c, I suppose its down to the performance you want to achieve :-))
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If its any help I run a 700 BB in my 34inch fire boat, on 9.6v it,s fun on 12v it really sits up and planes, you do nee a goo ESC though (I use a Action P98) as it does pull the current on 12v :-))