OM21 build

[saleens7]

well while i was at Bimini for the last few days my OM21 hull came in....its alot better suited for the stuff going into it than the micro patriot..so far there hasent been much progress since i just got back from a 2 hour boat ride and im very tired....ill take some pics of the progress tomorrow but there isnt much....just cut out the wood backing for the transom and some of the motor mount...thats it....for those who dont know yet the power will come from a 540 motor pulled from a tiger drive running on 7 cells and a proboat esc....i also have two 550 motors ill test it out with also....im using a 4mm solid shaft (so i dont need a strut) and a rudder i had lying around...i only have a 31mm and 34.5mm props to use with it...ill try working on it more tomorrow...

[saleens7]

here are some pics

[saleens7]

some more progress...i glued in the motor mount and the glue is still drying that holds in the driveshaft....im planning out a battery tray and the positions for the esc and receiver...

here are some pics of what i have done so far

[saleens7]

well i gave it a test run in the pool (without the top on, just the bottom hull)...just going from one end to the other...well when it got to the other end the bow rode up on the edge, the transom dipped down, and it took it about 1/2 a second to hit bottom....i got it out as quick as i could and took the receiver and servo apart and they are drying right now...the esc should be waterproof...and even if it wasnt i couldnt take it apart anyway....im just wondering, would there be any problems with the nimh batt now that it got wet?....

it also turns out the shaft vibrates, even with the flex coupler....probably because there is too much angle to it....i just hope all the electronics turn up all right....

[saleens7]

im already rebuilding the setup in this hull...i pulled out the old motor mount (lucky epoxy doesent hold that strong to ABS)....this time instead of having the motor up high on a wood mount, ill glue the metal mount directly to the hull...this will put less bend in the flex coupler and decrease resistance and hopefully stop the vibrations...this time ill have the hull together and with flotation and completely sealed before i test run it....

[saleens7]

well i got everything installed and im now gluing the two peices of the hull together...i sanded the areas where the glue will be since im using epoxy, that way it will grip the ABS better...i have the batt all charged so once the glue dries ill be ready to go out and run it...i also found a small boot i can use the seal up the hole that the pushrod goes through...im trying to make this boat as waterproof as possible...

[SJFE]

Dude you are the king of just slapin boats together with what ever you have layin around....lol. Sweet:p .

[saleens7]

tested it out today...alot faster than i thought it would go....definately in the 15-20mph range..and thats with the small prop with the lower powered motor without being properly trimmed out...(it porposes, but ill move the batts forward to solve that)...

Dude you are the king of just slapin boats together with what ever you have layin around....lol. Sweet :p .

if i had another hull (or two) i could probably build another 2 boats just with the stuff i didnt use in this boat....:D

[saleens7]

ran it again...i put a heatsink on the motor to help keep it cool (still doesent get that hot though)...it seems to go faster with the 31mm prop..i moved the batt forward (as far as i can without it hitting the shaft) and it still bounces....i would get some vid, but it started to rain, so ill have to wait till that calms down...

[saleens7]

well i took it out for another run with the 34.5mm prop this time....seems i was wrong, it actually goes a little faster than with the 31mm....when i first take off with a fresh batt the boat is definatly doing 20 something mph....is pretty quick with this setup in it....too bad my run was cut short because a thunderstorm rolled in...now i have another problem....im out of hatch tape and i know my parents arent going to be "eager" to get me some more....if im lucky i might be able to convince them to get me some today, but just in case they dont, does anyone know any alternatives to hatch tape?

[Ctonez]

vinyl tape like electrical tape is stretchy and should provode plenty of adhesion without mucking up your boat.

[saleens7]

actually, i hve found electrical tape to leave a sticky, black residue...id does all the time when i use it to cover exposed wires and when i used it to seal up some of those batt packs piranha2 gave me...

[saleens7]

well i got some bad news, some good news, and some worse news news...

bad news:

i was running and the prop got caught in some weeds...i hit reverse for a second liek i normally do when it gets in the weeds to get em off the prop and the rudder...well...it worked...but the boat wasnt moving even though the motor was...i paddled over on my kayak and found the prop was gone...it sank in about 5 feet of water...however, the water there is so murky that you cant see your hand if you put your arm one foot into that water....so i lost the prop..

good news....i had another prop...it was smaller, only 31mm...i put it on, but it went slower...however i remembered that high rpm motor i had...so i took out the old one and put the faster motor in and it works....it went about the same speed as the old motor with the larger prop went, if not, even faster...

worse news....because of the more rpms, the shaft vibrates A LOT now....and its very high pitch and loud...the kind of sound that makes your ears ring and give you that ants under your skin feeling...and it sounded like it was vibrating so bad that it was just about to shake the epoxy loose from the hull...

i dont really know why it vibed, since with the other motor it didnt...but whatever, those props are cheap to replace (ill get the same prop i lost as well as a different one....ill also buy some more hatch tape (i found that electrical tape does leave a black, gouey residue when you take it off)...)..i also moved the batt pack even further up front and it still porposes....i think the CoG is at around 35% from the transom now and it still does it...i think it may be time for some trim tabs...

[Doug Smock]

Hey salens7,
That is a down side to straight shafts, all you have to adjust is cg. Trim tabs will help you settle it down some, but don't use more than you need.
Take your shaft out and roll it on a flat surface, it may be bent causing the vibration.
Glad you're having fun!!
Doug

[Jeepers]

you also may have some play in your stuffing tube, it may be flexing the hull a bit, try putting a brace on it nearest the motor.