NQD jet boat up grade need help

[sundog]

Maybe because it sounds faster you just assume it's going faster. Is your transmitter trimmed to provide full throttle? You might check that. Then pay close attention to the speed (don't let the sound of the increasing motor speed influence you) and I believe you'll see boat speed stops increasing before motor speed. This has been noted several times on the RCU site with the 4800KV motor. It WILL burn up on 3S at WOT - it's just a matter of time. The motor is borderline on torque in this application. Jet drives require considerable more power than prop drives.

[TheShaughnessy]

i noticed what you are talking about (more noise but no more speed) with a 1800 kv motor on 4s with the 29 mm drive. Maxed out the efficiency of the drive, which i remember reading it being something like 21,000 rpm.

[sundog]

There should be a name for that. Maybe MES for maximum efficient speed, or SDR - speed of diminishing returns.

[C.B.R.]

Maybe because it sounds faster you just assume it's going faster. Is your transmitter trimmed to provide full throttle? You might check that. Then pay close attention to the speed (don't let the sound of the increasing motor speed influence you) and I believe you'll see boat speed stops increasing before motor speed. This has been noted several times on the RCU site with the 4800KV motor. It WILL burn up on 3S at WOT - it's just a matter of time. The motor is borderline on torque in this application. Jet drives require considerable more power than prop drives.

Oh yea, I'm getting full throttle. I'm running a $40 boat with a DX3R! I noticed what you are saying with a 3s, it does reach the limit of the pump. With 2s this little motor is perfect. With a 4800kv on 2s you are only supposedly getting around 35,000 "no load" rpm. Works for me.

[C.B.R.]

Sundog, I watched this video of you boat, http://www.youtube.com/watch?v=8LiVQ...eature=related . It sounds like it is turning a lot more RPMs than mine does, but mine appears just as fast. I can see by watching when it reaches the pumps limit. I also don't have as much problem with cavitation as your boat was having. Maybe I just got a really good pump out of all this chinese junk. I never ran mine stock, took it apart as soon as I got it. One of the motor screws wasn't even in the motor, the rubber seal on the impeller shaft wasnt in the housing, and so much of the shaft was in the coupler the shaft was barely hanging in the rear bushing. Once i spent several hours putting things as they should be and making a new coupler because the stock one was out of balance and shook the boat like an earthquake, this is the most fun I have had in my 30 something years of R/Cing.

[sundog]

Ha! yes, that was my first Tear Into conversion. It had a 3200kv outrunner in it and lots of problems. I had eliminated the intake ramp and installed a grate over the (large) opening. It caused some cavitation as you could see. My newst incarnation has a larger air-cooled 3000KV outrunner on 3S 2200mah 30C and blasts out of the hole - similar to 'Big Bird's' 29mm conversion. I used a 28mm adapter plate (made for trucks) and Jeff Woldt custom connector. I agree, these are great fun and excell in rapids. During this last conversion I found it had a wobbly connector, and I went through 3 others in my parts drawer before I found a suitable one. Iv'e had one boat where the hole cut for the jetdrive was crooked! Didn't affect the running as far as I could tell, but another cry for quality control.

[C.B.R.]

Ok I did that earlier as well, 5 acres

Sorry, forgot about the picture.
002-9.jpg

[pmdevlin]

there is a massive thread about upgrading these boats on rc universe, The ride plate (stator protector) is made from some mesh, cut from desk tidies (uk peeps go to staples or somewhere similar) the motors are very cheap, hobbyking or simiar. THe only problem is the drive impeller is very weak, and its very difficult to lubricate and make water tight, I used a syringe with light grease

I modified 3 of these boats to have fun with my two sons, but they just didnt get them! kept driving into each other and flipping them over. They are awsome fun on a shallow stream etc, but we have boating lakes near us, they are a bit boring on them, also, the motors get very hot and only really like short runs, well the ones I used anyway

[BILL OXIDEAN]

You guys need to quit teasing me with these jet boats, Imma' have to order me one if you keep it up : )

[triumphjon]

no teasing here , go on they are great fun !

[sundog]

I wanted to show these a while ago, but the computer they were on blew a power supply. Here is my latest incarnation. The 3000kv outrunner has a built in fan with no supplemental cooling but the esc is watercooled. Had to attach a ride plate to keep it from porpoising. These boats are a blast to build and run.

[C.B.R.]

Ran mine in some very shallow creeks this morning. It's hard to navigate rocks and make a video with a phone at the same time!

[faqcya]

C.B.R I tried that motor in my NQD on 3s and burnt it up in under 2 minutes. And I had good water cooling going through it.

[wparsons]

Oh yea, I'm getting full throttle. I'm running a $40 boat with a DX3R! I noticed what you are saying with a 3s, it does reach the limit of the pump. With 2s this little motor is perfect. With a 4800kv on 2s you are only supposedly getting around 35,000 "no load" rpm. Works for me.

The stock drive loses efficiency quickly above 25k rpm, anything more than that just makes more noise. A 4800kv motor on a fresh 2s pack is about 40k unloaded RPM, WELL above the efficiency of the pump.

I'm running a 3200kv motor on 3s in mine, and above 3/4 throttle just makes more noise and heat. I would go with about 3500kv on 2s if I were to build another one, that gives about 30k rpm unloaded. Less heat, and plenty of power/speed for rapids/creeks.

I can barely get above 1/2 throttle on mine in rapid sections without it getting too light and losing prime.

For anyone building one with an outrunner, hobbyking is now carrying water cooled outrunners and also a cooling plate with 19mm bolt spacing (it's like $5 for the plate, good deal).

[C.B.R.]

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