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Hi, I have just finished my 1/8th scale crackerbox. I am running a mamba 6900kv with a mamba max I removed from my rc car with a apogee 2cell lipo. I was told that the 6900 is way way too hot for what I am doing. It is really fast but it does overheat, though I now have fans and water cooling on it I have not ran it since. What do you think? I don't see why it would be too hot for a boat because the prop is small and the boat is a flat bottom, so drag is minimal. I am a noobie so be nice. By the way the prop is a x431.
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Twin power =
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how big is the 1/8 scale crackerbox? I have only seen small ones(18") so it sounds HUGE. -
its 24" from nose to transom, and 27" from nose to end of hardware, here are some picsLast edited by ace028; 04-06-2008, 05:34 PM.Twin power =Comment
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NICE boat!
I would have to agree with the motor being way to hot of set up, approx. 50000 unloaded rpm. The mamba 4200kv would be a better choice. even then, IMO I think that motor is a little small side(can size) for that size of boat.
how heavy is it?
those cooling coils are inefficient, get yourself a water jacket.
dont mean to sound rude but I type s-l-o-w. and can be looooooooooong winded! I try to make it short and to the point.Last edited by Jeepers; 08-20-2007, 02:03 AM.Comment
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Thanks, I was in a hurry to build it and so some of it isn;t perfect but after I painted it it looks 100% better lol. I'm not sure how much it weighs, its not much I know that. Its made of 1/64 ply on balsa bulkheads. I just thought that if that motor could power my losi xxx4 buggy, which weighs more then the boat does, then it would be plenty powerfull for my boat. When I first put it in the water, it has soo much power that it did a barrel roll with a jab of full throttle from a stop, I also had to make a few flex cables because they broke from all the power, I have .098 to 1/8th inch subshaft, I think that I should have gone with a larger one, but once I finially solderd the shaft right it has held up pretty well. I just don't want to remove the stuffing box and but a new strut. Also, I didn't want to run alot of cells, I like to run 6 cells or a 2 c lipo. I would like to try a 3c lipo but the motor can't handle more then a 2 c lipo.Twin power =Comment
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Dont forget though your XXX4 has a gearbox in it helps reduce the amp draw, your running direct drive in your boat.
Sound like its very light, I would try the 4200 kv motor on that 430 prop, or use 4-5 cells on the motor you have. You maybe able to move up in prop size but thats a good start until you figure out were your temps are at.
one of the guys i run with uses the Novak GTB 7.5 motor (5800)kv and 6 IB4200s, in a 22" hydro built out of balsa, the pack weighs more than the boat does, he runs until it thermals which is a long time!Last edited by Jeepers; 08-21-2007, 11:53 PM.Comment
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Yeah, I think you are right, I will probably sell the 6900, and go with the 4200 or the 5400, then I could run a 3c lipo and really make some heat lol. I don't really care about running it in a "class" it seemed to handle ok when it is running, I just want it fast. Is the hyrdo fast? I bet it is faster then some boats that run twice as many cells. I like the unexpected out of things, like mini rc cars, or the renegade rigger, you look at it and are like thats cool, then you see it move and are like WOW, but thats just me though.Last edited by ace028; 08-22-2007, 12:07 AM.Twin power =Comment
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Dude that little hydro screams! he can push it faster but it so hard to see!Comment
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Last time I drove the crackerbox I used a 6 cell gp3300 pack and I had just installed the fans and the water cooling, it was really slow. I had also just solder new battery wires to the esc, deans wet noodle 12 gauge, and I think I may have messed up the esc, the wires didn't want to come off the board. After I tried it with the gp3300 it was really slow and the batteries got very hot, like didn't want to hold them hot. I think I am going to try the lipo battery again to see if it regains the power it had, just I won't drive it till it overheats this time lol. That might tell me if my gp's are junk or my esc. Last time I drove it it melted the deans connector solder off the lipo (opps) but that was before any type of cooling, so hopefully things will work out, I will also try to get a smaller prop along with a lil milder motor. Once I get it running better I will make a video, it was really fast.Last edited by ace028; 08-22-2007, 02:05 AM.Twin power =Comment
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This one should fit. you maybe able to use the one listed underneath it also
http://www.offshoreelectrics.com/pro...?prod=gnd-4196
check your drive line for friction.
how hot is your motor getting and what are your run times? with that hot of set up your run times should be VERY short.Comment
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K thanks, I'll have to get that coming soon. I don't have a temp gun so I'm not sure of the temp. Should I get one, I seen some touring car racers tune with a temp gun?
I haven't got a full run yet, I'll hopefully be going to the pond saturday, so I will see what my runtimes are like. I will hopefully pick up a smaller prop too. Last time it ran, it went for a good 5-7min before the battery deans connector solder unmelted, I know it would have gone longer too.
Should I have used a 's' bend in my stuffing tube? I have just a curve, I could prpbably redo the stuffing box. Is there a way to tell if it has too much friction? It seems smooth. Sorry for the long posts, i'm kind of new to the boat stuff so I have lots of questions. Thanks for putting up with me lolTwin power =Comment
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does that stuff tube come from under boat or through rear. looks kinda deep.= more resistance?Comment
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Most cracker boxes that I have seen run had straight shafts.Comment
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The stuffing tube goes through the bottom. I was told that I should use a straight shaft instead, but im a noob and don't really know why it would matter. I figured that if I used a flex setup then I could adjust the way it drove. I don't really care about it being "scale" like the real ones, I wanted to build a fast one.Twin power =Comment
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