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[red181]

I think I am in the right place with this, if not perhaps a moderator will kindly move! I have a Graupner 700 bb turbo, direct drive, 40mm 2 blade "s" plastic prop, on 16.8v nimh, in my 48" Huntsman 28. It planes lovely and fast, but after approx 8 mins or so, starts to decline rapidly. I think the Graupner motor is amp hungry, I could be wrong. I have the opportunity to change the motor cheaply to a DPI JOHNSON 785 "DARKE HORSE" 700 SERIES Motor, which will take up to 22v ( I have a 24v esc so all ok).

Before I do this, has anybody got any experience of these 2 motors and could offer some advice. If I change, will the performance be as good, can I expect longer run times (15 mins would be great!), what prop should I use, what batteries should I change to (currently using 2 x 8.4 packs, 3300amps, wired to get the 16.8v ).

I would like to remain at at reasonably fast speed, to me, 15 minss of "fast" is better than hours of plodding around as this boat looks fantastic at speed, hence I dont use lead acid etc.

Relative novice here, so please explain your replies!!

Many thanks,

Paul

[Stavros]

Dont do it the Johnson Dark Horses are more power hungry than the 700bb,what is the capacity of teh packs that you are using

Stavros

[DickyD]

He's already told you Stavros "currently using 2 x 8.4 packs, 3300amps, wired to get the 16.8v"

Happy new year.

[Stavros]

Dicky me half asleep old boy !!!!!!!!!!!!!

Stavros

[Martin (Admin)]

Do you have a weblink to the "Johnson Dark Horse 700"?

Graupner Motor specs:  http://shop.graupner.de/webuerp/servlet/AA?wgr=821

Product information
High-quality SPEED electric motor with neodymium magnets and a 5-segment dynamically balanced armature. Standard features include ballraces, 1.1 mm thick stator ring and an internal cooling fan. Hotline models with 7 to 8 NC cells and the folding propeller, Order No. 1312.23.12, offer a very good climb performance with this power plant. This new motor also gives outstanding results in electric racing boats with 12 NC cells for the HYDRO II class using a 39 to 42 mm Ø carbon propeller.


Specification
Nominal voltage 8,4 V
Operating voltage range 4,8 ... 12 V
No-load rpm 14700 min–1
No-load current drain 2,5 A
Current drain at max. efficiency 15 A
Current drain when stalled 75 A
Max. efficiency without gearbox 72 %
Length of case, excl. shaft 67 mm
Diameter 44 mm
Free shaft length 14 mm
Shaft diameter 5 mm
Weight 350 g

Specification
Nominal voltage 9,6 V
Operating voltage range 4,8 ... 14,4 V
No-load rpm 15000 min–1
No-load current drain 2 A
Current drain at max. efficiency 12,5 A
Current drain when stalled 65 A
Max. efficiency without gearbox 75 %
Length of case, excl. shaft 67 mm
Diameter 42,2 mm
Free shaft length 14 mm
Shaft diameter 5 mm
Weight 320 g

Specification
Nominal voltage 12 V
Operating voltage range 7,2 ... 19,2 V
No-load rpm 11600 min–1
No-load current drain 2 A
Current drain at max. efficiency 12,5 A
Current drain when stalled 43 A
Max. efficiency without gearbox 75 %
Length of case, excl. shaft 67 mm
Diameter 44 mm
Free shaft length 14 mm
Shaft diameter 5 mm
Weight 350 g

Specification
Nominal voltage 9,6 V
Product information
High-revving SPEED 700 class electric motor with internal cooling fan.
Operating voltage range 7,2 ... 9,6 V
No-load rpm 19000 min–1
No-load current drain 3,3 A
Current drain at max. efficiency 17,5 A
Current drain when stalled 90 A
Max. efficiency without gearbox 69 %
Length of case, excl. shaft 66 mm
Diameter 44,5 mm
Free shaft length 10,5 mm
Shaft diameter 5 mm
Weight 362 g

[malcolmfrary]

Its a big boat that you are making go quickly.  That does take a lot of power.  It is possible that your set-up is using what is available to best advantage, so the only way to get a longer run at the same speed is to have a bigger fuel supply, i.e. a battery with more capacity.  Usually this means a heavier battery which has an adverse effect on performance, but Lithium might be the answer (cant believe I said that).
Looking at Martin's figures, the run times look reasonable considering the high rate of discharge.
Silly questions - at the end of a run, are both batteries the same-ish voltage? are they evenly warm?

[red181]

Thanks for replies, yes after the run both batteries are same "warm" temp. If I then disconnect, and run seperatley, there is very little difference in remaining run time, but one of these batteries will not get it on the "plane", yes a big heavy lump!! so there prob isnt much between them, I just thought the Johnson might have been a bit more efficient, I dont have any performance figures for the johnson. The graupner is a 12v one, and runs very hot, its cool with a water jacket, but without it I cant run it its too hot, thinking again not very efficient. I have tried other props, this seems to be the best, THe prop is lined up perfectly, and runs nice and smooth, even the esc is water cooled.
Interesting about the batteries, I prefer nimh to nicad because of "no memory effect". By lithium, do you mean li-po? I use these with helicopters, being a bit unstable, I would be a bit nervous with one in an old, not so water tight wooden boat incase of fire!
Any other suggestions and feed back would be welcome, is the general feeling dont bother changing the graupner to the Johnson?
Thanks

[pakirk]

Hi
Are theas the motors you mean?
http://www.pandanmodelboats.co.uk/acatalog/New_Range_of_Darke_Horse_Planetary_Motor_Gearboxes.html
You will be pleasantly suppressed.
We have been testing these with good results.
We ran them on 36V 45mm 3Blade props and 3300mAh NMhi
Ran for 20 – 25  mins

[Stavros]

I also have a Huntsman and run a MFA850 water cooled running a 55mm prop and a single 12vgell cell and yes it planes but not spectacularly,what you and I have to consider is it is a heavy boat designed fro a petrol engine that is it's problem

Stavros

[bradboat]

Much the same as Stavros, but my MFA850 runs with 12v 3700NIMH - cuts down the weight a bit.  With a SLA, poor thing is more like a snow plough.

Run time about 15-20 mins flat out.  Battery ends up pretty warm.

[red181]

OK...
Pakirk, I think that they are the motors, but no gearbox. I thought direct drive was the answer. Going slightly off topic, will a gearbox not slow things down? or am I totally off the mark. I was thinking,  with say 3:1, everytime the motor shaft revolves one turn, the propshaft will only turn 1/3rd, whereas direct drive, one motor shaft revolution equals one propshaft revolution?Are you running 3 x 12v nimh's? to get the 36v?

Stav, yep its a heavy lump, but a 55mm prop? Am I running the totally wrong prop at 40mm 2 blade "s" type prop. It had a 3 blade cheap plastic 50mm on it when I got it, and it was very slow, Hence I went to a small 2 blade (dont really understand the prop thing) but I remember turning up at 2006 Fireboat funday at Branston water park with my Dad's Fireboat, which had a 3 blade brass 45mm prop, and it immediatly attracted a whole host of people saying I needed a much smaller 2 blade "x" or "s" prop to make it move at any sort of speed!

Bradboat, 15 to 20 mins would be utopia for me! I tried a 12v 3300nimh, but it was slower, and no increase in run time, I think because I can go up to 19.2v with the graupner motor at 12v I was underpowering it

Malc and Martin, I dont really understyand the figures provided on the Graupner motors. I tried to get some info from the graupner boys at the Ellesmere Show, but just got more confused! I just thought, the 12v will take more power, although the revs are lower. I tried a very high revving Graupner 600 bb turbo ballraced 9.6v motor, but it was working too hard and kept overheating, draining the battery quickly.

So lets assume you guys with the knowledge, have my boat, 48" Huntsman, all ply, and quite heavy. Ignore the esc. You are entering a competition, and have to obtain the longest "flat out" runtime, so you are against the clock, and have to cover the greatest distance. You have to choose from a Graupner 12v 700bb turbo, the Johnson dark horse, any battery combo, any prop. What will you use, there is no practise or set up allowed, its just experience and gut feeling!

Off you go!! (maybe this should have been on the main forum?)

(many thanks!)

[HS93 (RIP)]

I thought yours was a Veron huntsman.?? there 42"  go with a gear box get hold of a Hughey gear box they are able to take all the power of a 700bb and there are lots of gears available.

Peter

[red181]

Peter, does the gearbox not slow the prop down, or am I the wrong way around!
Check your emails, I have sent something foryou to have a look at
Paul

[HS93 (RIP)]

Yes and no it does slow the motor down but it works more efficiently and when you put the boat in the water on load it will prob be similar prop speed . bit like a car going up hill in first gear or forth gear, in first it is less strain so less fuel.
Peter

[red181]

Still struggling sorry!!

So in the water, lits like starting off in 4th gear, bit of a struggle, but when up to speed the motor is using less revs, therefore less amps, so I will have more revs left to achieve a bigger speed or longer run time. With direct drive, its like starting off in first gear, quick off the mark (possible cause of cavitation?) quick up to max speed, but revviing its nuts off using more amps, getting hot, overevvving, if a car you would change gear to a better ratio, however a boat gearbox cannot change gear so you pick the ratio according to the required useage? IS THAT IT!!!!, The gearbox myth!!

So back to original question, will the johnson motor, capable of much more revs and much higher volts,( This motor is designed to run on 12 - 22 Volts 10 to 18 Cells)be a better proposition than my current graupner, or instead of changing the motor, and having to upgrade the batteries, get a gearboxc for the graupner!!

PS.... Why are Graupner motors more expensive that most others? Is it quality, or just because of brand name?

Thanks

[cos918]

hi i was looking at getting the graunper 720 bb torque it was about £25 in the end i went for the protech 720 bb torque it was about £12.50 half the graunper unit. My friend has the graunper unit and we did a bench test on both , both were identical .So theres no difference apart from price so graunper must put a big mark up on there units. john

[Stavros]

Woah the 720 only revs to 4000rpm a totally different animal to the 700 I have in fact got a 720 protech in my Tid Tug and it's the dog's wotsits !!!

Stavros