50 MPH Miss Geico 17?

[knotsofast]

I found a thread regarding a 50mph MG17 project in this forum using a Google search, but I cannot find it by searching this forum from within.
Long story short version: got my 8 year old son an MG17 for Christmas last year, was disappointed with its performance, made a few mods to it, and got here:

Motor: 380 Traxxas Velineon 4000kv
ESC: Hobbywing 60amp
Batteries: 2 Tenergy 3s 1350mah 20c- to be used first in parallel, then if needed, in series
Drive: OSE flex
Propeller: I have a 2inch pitch stainless Proboat, but I would like advice on choosing a better for this application

Any helpful hints before I try my latest upgrade version of this boat? Has this been accomplished before? Is it physically possible to push this boat to 50 mph?

Thanks in advance for any help you may offer.

[TheShaughnessy]

Not really an ideal motor selection. I would opt for something closer to 2800. If you decide to try it as is run a small prop.

[Make-a-Wake]

Thats really a 2s motor, you are gonna be in the high 40's in rpms with 3s. It should be fast on 2s and a good prop selection.

For 3s I think this would be best, the 3Y 2960kv model. http://www.offshoreelectrics.com/pro...o-2845&cat=148

If you have room you could really amp that sucker up with a 2860 Leopard in similar kv or a tad higher.

[knotsofast]

Thanks for the responses.
I picked this motor based on size- it is 1+7/8 inches long and just fits in. When I bought it I did not understand kv's as well as I do now. But I have 2 of the Traxxas Velineons now and no small trucks or cars to run them in, so I am sort of committed to these for now.

As for a small prop, do you mean small diameter or small pitch, or both? I figure a smaller than 2inch pitch due to the high rpm/low torque ratio of a 4000kv motor. I figure I only need about 10 seconds of run-time at full throttle to accelerate from about 30 to top speed. I am comfortable with frying a motor in a speed attempt, but not the ESC. I am long on motors and short on ESC and funds at the moment (divorce).

Question: would running this 2 to maybe 3s motor on 6s create more power, even if for just 10 to 20 seconds, or would the extra energy just be converted to waste heat in the motor and ESC?

[Make-a-Wake]

"Question: would running this 2 to maybe 3s motor on 6s create more power, even if for just 10 to 20 seconds, or would the extra energy just be converted to waste heat in the motor and ESC? "

You would br turning 80,000 rpms on 6s!!! I would NOT do that. You can easily sell those two motors on a forum, here, RCGroups or RCUniverse in the Traxxas section or General truck section. That would allow you to buy one Leopard 24x45 as suggested earlier.

The best suggestion I can make is to run it with the 4000kv on 3s if you are set on them and try an x435 or x632. To keep spending to a minimum you can buy a Graupner K 40mm Carbon prop cut down to 35mm for testing purposes, only $5.95 here. Use that as a baseline to buy a permanent beryilium prop.

[knotsofast]

Well, I've been pretty busy with work and just finished up the details of this set-up yesterday, 10-13-14. I was worried about all the electronics crammed together under the deck, which I had to do to make room for 2 batteries, but it seemed to work OK on the bench and in the bathtub. Bathtub test confirmed it sits pretty low in the water with the 2 batteries and 60 amp Seaking esc adding significant extra weight over stock. Glued everything together with Locktite Stick and Seal Outdoor. Going to try to do an open water test this weekend. Still don't have an appropriate prop, but I am going to probably order one or two of the props suggested above, or cut one of mine down a bit, and gonna give it a try. I'll shoot some vids.

[Make-a-Wake]

What motors and voltage did you decide on?

[knotsofast]

What motors and voltage did you decide on?

I am using the Traxxas 380/4000kv motor in the picture with the two 1350mah/3s/20C batteries wired in parallel. I looked up the specs on the suggested motors and they were way too long to fit in the existing motor mount. Going to make do for now with what I have. I ordered the x435 and x632 props from OSE this evening and hope to have them by the weekend. Still working on prop height and angle before I shape a strut out of aluminum or stainless steel. My teak strut now may drag in the water a bit but is easy to replace and/or move. Thinking of angling the shaft up slightly to simulate how I trim my outboard out on my Hydrostream (18 foot ride-in boat) to create bow lift, right now the shaft is about parallel with the bottom of the boat.

[Fluid]

First run = strut flat and 1/8" above the sponson bottoms. CG @ 33% ahead of sponson transoms. Run no longer than one minute (use a stopwatch!) and check temps....and for water in the hull. Good luck.


.

[knotsofast]

Well I plugged in my numbers into the OSE speed calculator and I get a theoretical 49mph with the x435 prop. Maybe 50mph is an attainable goal, but I have my doubts. It just looks like such a small motor to push out that kind of speed. Maybe it will just go up in smoke and flames- but it should be a good show! Will shoot vids of the test runs this weekend if the weather permits.

[ray schrauwen]

Your main hurdle will be keeping right side up at 50.

[knotsofast]

First run = strut flat and 1/8" above the sponson bottoms. CG @ 33% ahead of sponson transoms. Run no longer than one minute (use a stopwatch!) and check temps....and for water in the hull. Good luck.


.

Here is a picture of the shaft with a piece of piano wire under the sponsons. It looks like I am a little low. Worthwhile to try like it is or should I rework it before the trials this weekend?

[iop65]

Your main hurdle will be keeping right side up at 50.

that's what i was thinking

[knotsofast]

Sorry, no vids yet. New props did not arrive and the weather was not the greatest. Scrapped my teak strut and made an adjustable teak/aluminum assembly and raised the shaft axis a bit. All I have is a Proboat 2.05 pitch stainless and some unknown plastic props, probably in the 2.5inch pitch range by the looks of them next to the Proboat prop. Might try what I have Sunday 10-19-14 if weather permits. Will post vids if I run it, but will not have real speed info since I decided I could not afford the $150 with tax for the least expensive sportwatch GPS that my local Best Buy had in stock, especially since the GPS could go up in flames with the rest of the boat!

[knotsofast]

Project suspended. Water trials went poorly. Boat appears to be too bow heavy and appears to have too much torque for the length of the boat. The boat just spun in circles at low speed even with the rudder all the way to the opposite direction to compensate. Giving it more speed would let me get it going straight barely on a plane with strong opposing rudder, but when I would give it more power it would spin out and/or submarine. Lowering the prop shaft axis about 1/8 inch helped some, but not much. I don't think this project deserves more effort when suppliers such as OSE our sponsor offer such nice hulls. I have a 21inch monohull from OSE that just handles nice and goes like a bat out of 'ell. My son wants a big 29 inch Geico, but I am going to get a cat hull from OSE and paint it green and put a gecko on it instead.