Mini JET Drive

[inventing_man]

Does anyone use the Graupner GR2349 Mini JET Drive ..... $ 38.90 from Hobby lobby? I was needin' some measurements and feed back on the units performance . THANKS!
http://www.hobby-lobby.com/images/gr2349.jpg

[Umi_Ryuzuki]

You can look up the specs for most available jet drives here...

http://home.wanadoo.nl/stuipsmulders/jetboats/jetboats_jetdrives.htm

:cool:

The mini is
100mm long (motor mount to end of nozzel)
110mm long to the back of the steering nozzel
130mm long to the back of the reverser in the raised position.
36mm high bottom of intake to top of motor mount/output collar
Pump ID diamter is 21mm
2 blade impeller is 19mm

[inventing_man]

Mucho Thanks!

[Umi_Ryuzuki]

What are you planning on building? :)

And don't say, "an amphibious hot air rigid dirigible..." :p

[inventing_man]

LOL! Escape pod for the hot air dirigible for when it hits the drink. Brake away gondola..... No ! thats not it . I'm wotking on a concept pontoon boat ..of sorts ... It will use 2 of the drive units . Needed to know the area of the pump / motor compartment so i can lay it out correctly .

[tsenecal]

I have two mini jetboats with those mini jetdrives installed in them. What do you need to know?

Tim

[inventing_man]

How is the low end power

[tsenecal]

I have no problem moving water with it. It is really dependent on the ESC you use as to how well the low end is utilized. I use it with an Align 430L helicopter outrunner (the 3550 Kv version), and the CC mamba ESC, and it works fine in my little jet boats, across the full range from wakeless to full throttle. I do not use it with the reversing bucket, so I can't say how well that works.

[Tugboat Andy]

I understand that high RPM is the ticket for these drives. Would you recommend brushless over brushed motors?

I've down a little bit of pricing and it seems that you can get some inexpensive aircraft ESC (no reverse) and simply use a second channel to control the reverse bucket.

How big/heavy of a hull can these little jet drives push effectively?

Thanks! :)

Andy

[tsenecal]

The whole reason I went with the brushless was for weight. In combination with lipos, the brushless setup weighs considerably less than a brushed/Nimh would have weighed. even the brushless motor weighs less than half of an equal powered brushed motor.

I have no idea what type of hull you want to use these on. I don't think they would have trouble moving something like a destroyer or other displacement hull that is narrow. I don't think something like a tugboat or an SDM would work well.

I have seen two of these move a planing vhull about 3 feet long.

the other question about airplane ESCs only has to do with what kind of transmitter you have. If you plan on using a pistol grip style, it is better to get a car style ESC and disable its reverse. The Airplane ESCs expect you to use the full range of the throttle stick. pistol radios are designed to use half the range for forward, and half for reverse or brake. I tried an airplane ESC on one of my jetboats, and quickly swapped it out, because I got tired of "holding" the throttle at full brake to get the ESC to arm when I turned the (pistol style) radio on.

most of the documentation I have seen usual recommend a second channel for the reversing bucket, that way the mechanical setup is much simpler than it would be if you tried to gang it to the throttle servo.

Tim

[tsenecal]

Andy,

one more caveat. the jet drives definitely have a sweet spot on top speed.

In the original setup, I used CC mamba inrunners as well as the CC mamba ESCs.

one used the 4200kv inrunner, the other used the 5400kv inrunner. the only difference between the two was that the 5400 would start starving or cavitating at full throttle. It would literally just start pumping air through it instead of water, so you would have to stop to let the inlet prime the jetpump again. very annoying.

tim

[inventing_man]

Thanks Tim. At no wake, what would you say the aprox, RPM is ? I ask because, I'm going to need to do some traction wheel to drive line gear calculations with bevel gears ( possably gearing up) on the drive line to get the power turning in the right direction and rpm for the pump. . Basicly I'm running both pumps from a drive line that runs across the boat . A single motor turns a tire, that inguages a wheel mounted to the drive line , the drive line right angles with bevel gears to the pumps. The drive line wheel is smaller than the drive motor tire aprox 4:1 I dont know at this point to stay 1:1 with the bevels or do a final gearing ...? I just love ( Hey, Can you do this? ) jobs
Anyway your best guess at your no wake RPM would help a lot.

[Tugboat Andy]

Thanks a bunch, Tim.

That answers the question that's been nagging me. I have heard about full scale boats cavitating the impellers. I wasn't sure how much this applied to the scale Graupner units. For the price, I'm tempted to purchase one of the small units and try it out.

Thanks for the tip on the ESC's as well. ;)

[tsenecal]

inventing_man,

hard to ponder on the wakeless speed...

simple math for the setup I use puts top speed at roughly 26,000 rpm (3550 * 7.4v)

I would think that the wakeless speed was less than quarter throttle or maybe 6000 rpm...

remember that is my small 16" planing hull as well...

[mistel]

FWIW, I put one of these in an 18" Dumas Sk Daddle Jr. It worked well, was fun to drive. It would turn really sharp and spin out. Definitely needs a turn fin. The problem I had was that the jet is designed for a thin ABS hull and I was trying to put it through the thick Dumas transom. Lots of sanding and cutting was needed. The bottom/transom angle needs to be 90 degrees for it to fit well.

[Idriveaboxster]

Does the mini jet have a turning nozzle?

JPP

[Umi_Ryuzuki]

Does the mini jet have a turning nozzle?

JPP

Mini jet comes with steering nozzle and reverse bucket.

[Idriveaboxster]

Ahh thanks. found my graupner catalog here.

Any one know how much thrust this thing has?

JPP

[Umi_Ryuzuki]

Ahh thanks. found my graupner catalog here.

Any one know how much thrust this thing has?

JPP


http://home.wanadoo.nl/stuipsmulders/jetboats/jetboats_jetdrives.htm

:cool: