Model Boat Mayhem
Mess Deck: General Section => Chit-Chat => Topic started by: Dave Cook on June 17, 2014, 08:45:02 am
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Hi Gents , I am building a 1:24 scale Perkasa and its is coming along fine due to a lot of advise from yourselfs , My power train will be 1 off MFA 850 in the center and 2 off JP Power Speed 660s 1 on each side. The 850 will run all the time and the 660,s will be used for a bit of action now and then . I will have 2 off 12V 5000 MAH Nimh sticks wired in parallel . What run time should i expect from this setup.
Thanks Dave :-)) :-)) :-)) :-)) :-)) :-))
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looking at the specs of the motors...
850 Typical current draw: 5.3 amps
660 Current @ max. efficiency: 12A
your probably not going to get much over 30 mins driving, dipending on the speed you drive at... and whether this is continuous.. !!
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Hi Colin , Thanks , Thats not long at all <:( <:( <:( <:(
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from your set up, you only have 10 Amps an Hour to play with... (wired in parallel = 12v 10 Amps)
your 850 draws 5.3 Amps... so that motor should run for over an hour... closer on two hours.
the 660's draw a lot more.... 12 Amps.. each... thus taking the time down rather quickly...
current drawn also depends on the type of Prop... and if you have any sealant in your propshafts such as grease...
either you need to look for High RPM with low drain (ampage) motors... or up the ampage you have in your batteries... for longer running time.. :-))
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Sorry to make things worse Dave, but MFA rate the 850 at nearly 11A at maximum efficiency - and I reckon you can probably justify double that because I've regularly heard of them blowing 20A fuses and speed controllers. The props on your 600 motors will act as drag anchors when they're not being turned by the motors, adding to the load on the 850. It's more usual to run the two outer motors all the time and use the centre one for "boost speed". I'd advise running all three together at a medium cruising speed and using the throttle stick for any speed increase you need.
If ever there was a model crying out for brushless motors it's the big Perkie.
DM
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WoW Top Tip Use the 850 as a door stop O0 cos thats all it is use for With that set up you are likly to get 5 mins flat out running time.I have seencurrent draws in excess of 25amps .So with 2x600 that draw 12amps each and lets say15amps for the 850 thats a total of 39amps supplied by a 5000milliamp batt........not looking good is it!
Soloution
Buy single 900 motor off Steve model boat bits a ACTion high power speed controller a 55mm 2 bladed prop Wire your stick pacs up togive 24 v and you will get a run time in excess of 50mins.....been there had the tee shirt .It will be as docile as you want and also a hooligan boat.
Ditch the 600 and the 850 you will not regret it
Dave
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I guess the boat will weight something around 7kg.
If you want it at around 20 km/h you will need around 250-300W outgoing power of the motors so ~ 25A without taking the motor efficiency into account.
With these motors (check the efficiency of the 850 slightly above 50% {:-{ ) you will probably have 35-45 amps getting out of the batteries, so max. 15 min flat out run time.
Getting better motors will maybe enlarge this period to 20 min.
Realistic (in my experience) you dont run the boat full speed at all time. So you can calculate with around double run-time.
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Thanks , For the feed back lads , This is depressing can i just ask Stavros what makes the 900 motor better than the 850 when it does not have as many revs .
Cheers Dave :-)) :-)) :-)) :-)) :-)) :-))
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Simple ans it revs to around 15000 on 24v and draws around 5 amps so it is not CURRENT hungry at full revs.
Sorry i did forget to mention it needs watercooling at 24v
Dave
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Thanks Stavros , :-)) :-)) :-)) :-)) :-))