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.

[saleens7]

i took out the shaft and rolled it..its perfectly strait...ive put the batt as forward as possible, and it still bounces...ill try to see if i cant push it even more forward...i dont think il be able to use trim tabs anyway, there just isnt enough room.....i dont see how it just suddenly started to vibrate....same motor, same mounting position, same everything, yet only now does it vibrate...

i guess a brace would be good to help support the stuffing tube....epoxy is drying on one as i type;)

[ozboater]

if i m not mistaken i m pretty sure that you re not supposed to use epoxy on ABS... i think CA glue is the stuff to use - i could be wrong tho'... my mate recently built an OM21 and i think he mentioned that randy n suggested CA...

[Doug Smock]

Hey saleens7,
I just went back and reviewed your pics. How much shaft do you have sticking out beyond the stern tube at the transom??

Doug

[saleens7]

Hey saleens7,
I just went back and reviewed your pics. How much shaft do you have sticking out beyond the stern tube at the transom??

Doug

a tad more than 2 1/2"...

[saleens7]

if i m not mistaken i m pretty sure that you re not supposed to use epoxy on ABS... i think CA glue is the stuff to use - i could be wrong tho'... my mate recently built an OM21 and i think he mentioned that randy n suggested CA...

you can use epoxy, it just wont hold as well sicne the surface of ABS is smooth...but i sanded the hull where i would use epoxy, that way it will hold better....

[Doug Smock]

a tad more than 2 1/2"...

I would be willing to bet that, that is the source of the vibration. You need support at the end of the shaft @ the prop.;)
Also what do you mean you don't have room for tabs.:confused:

Doug

[saleens7]

on the side with the rudder, i done have room for tabs...the rudder is too low to the bottom of the hull i cant fit the trim tabs under it....i could mount them further to the side, but its too far out that they will be out of the water when the hull is on plane....

[Doug Smock]

on the side with the rudder, i done have room for tabs...the rudder is too low to the bottom of the hull i cant fit the trim tabs under it....i could mount them further to the side, but its too far out that they will be out of the water when the hull is on plane....

Can you post a pic?
Doug

[saleens7]

here they are...

http://i86.photobucket.com/albums/k87/saleens7_01/DSC00002-2.jpg

http://i86.photobucket.com/albums/k87/saleens7_01/DSC00001-3.jpg

[Doug Smock]

Yeah that rudder eats that transom alive.:eek:
You could get creative with some thin aluminum and make some tabs. If you have to tuck the right one up under the rudder and shim the top to even things up.
You can make it happen!!;)

Doug

[Doug Smock]

Make something like this.

[saleens7]

looks like ill be makign a trip to the hardware store soon....to pick up some brass tubing and some aluminum sheet metal...ive already made a strut from an old rudder mount and some of the extra ABS from the hull (the stuff you cut out from the deck, under where the hatch goes, that way you can get inside the hull when you take the hatch off...all i need to do is find some brass tube the same size that is the stuffing tube now and JB weld it to the mount...ill see if i cant make some small trim tabs from aluminum sheet metal...

[Ctonez]

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...

I've been using the colored vinyl tape from home depot...maybe it's not really "electrical" tape, I dunno...no residue though...I know the residue you're talking about it IS goopy and gross, but this stuff comes off clean and seals well.
I still prefer more traditional hatch tape though.

[saleens7]

ill eventually buy hatch tape, but ill have to stick with electrical tape for now...i really need a new prop though....this little 31mm isnt big enough....it takes like 15-20 feet before it gets on plane and it only does like 15mph...with the old prop i swear it was just hitting 20 on a fresh batt....

[saleens7]

well...turns out the only prop i have now is broken....one of the blades are chipped....(if you look at the pics i posted of the rudder a couplr posts up you can see the crack on the prop....so now i have to get a new prop to run it....

still though i really like this hull...i think i might buy another and set it up with a brushless system....

[saleens7]

well i just ordered a 33mm and 34.5mm prop as well as some hatch tape....too bad i have to wait until the 7th until its shipped out...:( ...

i wish i hadnt of lost that prop...:mad:

[saleens7]

well i got the props and hatch tape in today (thanks for the quick shipping steven).....ill put on the 33mm prop and see if i cant take a vid...

[saleens7]

sorry, no vids yet, but twice today on the 2nd run (with the 34.5mm prop) the boat stopped...the rudder would work, but not the motor....i checked the wires and they were all plugged in.....im thinking the esc might have thermalled? i dont know if the proboat esc has a thermal cutoff though...im trying to figure out whats wrong though....

[saleens7]

im uploading a vid right now...its using the 33mm prop so its slightly slower than if i used a 34.5mm but its much more controllable and the motor doesent get that hot (it passes the 5 second test)

[saleens7]

oh yeah, forgot to add, the servo broke loose from the hull....(probably because i didnt sand it before it went into the hull...) well now i sanded it and the epoxy is drying...next time ill get a vid of the 34.5mm prop and see how it performs....

[saleens7]

ok here it is....sorry for the low quality....my camera has one that is high quality than this, but you can only record for about 8-15 seconds...

http://www.veoh.com/videos/v952348bngtAHgw

[saleens7]

well, for some reason, every time i run the 33mmprop the esc cuts out and i have no throttle (i still have steering though).....i think its pulling too many amps for the esc to handle....i have another esc that can handle more amps, ill give it a try...the thing is it has no connecotrs on it, so ill have to steal the ones from the proboat esc and use em on this one....

[saleens7]

well i took it out with the new controller and 34.5mm prop and it didnt stop, but it glitched alot....anymore than 20 feet from me and the throttle would turn off for half a second every other second....the motor has caps on it and the receiver has foil on it...and yet it still glitches....

[saleens7]

well, i got tired of the glitching, so i went b ack to using the old esc.....i guess the motor pulls more amps than this esc can handle on the 34.5mm prop, so i went back to using the 33mm prop....im wondering if exposed wiring could have caused the glitching with the other esc...as the wires that went to the Rx were cut by a prop and i had to solder them together (they are covered by shrink wrap though)....

anyway, since i used the connectors from this esc to the other one, i just soldered the motor wires to the esc wires...anyway, im charging up the batt now....

[saleens7]

is it me or are the last 11 (12 if you include this) posts are just mine..

am i just talking to myself or what?

[saleens7]

well i tested it to see if the esc worked right and the shaft vibrated violently....to the point were the vibrations got so bad the shaft would slow down....the shaft isnt bent (whew).....but i wish i had more of the stuffing tube i need so i can make that strut...till then, i dont think i cam run this boat anymore in rask of damaging the shaft.....

if i ever build one of these hulls again, im going to use a flex shaft.....and a brushless....and maybe even lipo as well:D

[saleens7]

well i cut the shaft shorter to see if the vibrations willl stop....they are the same as before...and less than an inch of the propshaft is exposed....

[Doug Smock]

Saleens,
Your motor isn't secured properly, flex coupling isn't straight, the shaft is bent, the BUSHINGS in the tube are worn out, or your prop is WAY out of balance.
Take the prop off and see if the problem goes away. It should be pretty easy to figure out.
Doug

[saleens7]

the motor is secured nice and tight (the bolts holding it on are tight and the motor mount is firmly secured to the hull)...the shafts isnt bent (just tested)..without the prop it still vibes, the coupler seemes pretty strait..i cant see any sight of even a slight wobble when i spin it...im...i dont think there are bushings in the tube....the inner diameter of the tube is just slightly larger (by a fraction of a millimeter) than the diameter of the shaft...

[saleens7]

ok, well i think i might have found the problem....when i rotate the shaft freely in the tube (without the couplerattached and no prop) it feels like there might be a very slight bend in it that could cause the vibrations when spun faster.....

[Doug Smock]

ok, well i think i might have found the problem....when i rotate the shaft freely in the tube (without the couplerattached and no prop) it feels like there might be a very slight bend in it that could cause the vibrations when spun faster.....

Maybe that's it!!! It has to be something, it can't be nothing. LOL;)

Doug
PS On your next straight shaft build, opt for a shaft with bushings in it.:cool:

[saleens7]

i dont think ill ever use a strait shaft again....although im considering rebuilding this boat in the future using a brushless motor and a flex shaft...probably a .098" one....

[hookedup]

i got a used OM21 hull off of RRR, i put a 19 turn motor in it and 6 cells and was pretty disappointed:( it was way slower than my SV. i am going to go brushless and lipo. i have been told the OM21 hull can go 40+ mph easy, so we'll see.

[saleens7]

yeah, mine wasnt exactly speedy either....at one point when the shaft didnt vibrate and i used the high rpm motor with the 31mm prop it was doing about 20mph....although it overheated alot and was almost uncontrollable....

im already looking at some cheap lipos at maxamps...ill get two lower mAh 2s lipos (like 2-3000mah) and wire them in parallel....im looking at a feigao 8s for the motor....ill be happy if i can get in the high 20's to low 30's with this hull...if its going to go 40+ it will probably have to be a little weighed down or else it might be too hard to control.....

although that might have to wait till later....once i get the SW36 and SV27 finished im going to save up and buy some new forks for my bike...then im looking into buying an rc car.....although im still not so sure i will buy one yet....i am looking into the red cat racing volcano....pretty cheap for a nitro truck....there is also the nitro pede and electric pede (not the VXL version...way too much $ for the likes of me)....and for christmas im going to be buying some stuff for the drifter..(probably motors, esc's, and motor mounts)....i might be able to get the OM21 hull and hardware in there as well....but i would rather wait until i have no more projects before i do that.....much easier to build/fund when you dont have to buy parts for other projects....

[SJFE]

Hey ya know that I thought was pretty kewl (car wise). That HPI E-Savage with the buggy body. It looks really fun. I think thay claim 25 mph out of the box & it comes with 2 packs and a charger. It's just somthing I allways look it in the mags and wonder "what if". While we are talking about other areas of rc..I think MrsSjfe is gettin me an Efligh Bade CX2 for christmass :p. My little picoo z is getting tired. I think the lipo is almost shot.

[saleens7]

yeah, the e savage does look nice...its the 350$ price tag thats driving me away....

the nitro pede is the most money im willing to spend for a first rc car (260$)...

although im really liking the volcano SV......18 motor stock, 4WD, 30+mph stock, stable (the pede like to flip alot) and only for 220$....ive taked with people who have it and its a pretty good truck....although the traxxas is known for its durability and i think it does like 35-40mph stock....there are also many aftermarket parts for it....its just the price, lack of stability, and being 2wd thats keeping me from buying it.....

although with all of these things i need to buy, i dont know if ill be able to start on the OM21 until next year....and even then when i get a job, almost all the $ i make will be going to savings for a car and college expenses....

[SJFE]

One thing to consider with buying off brand cars & truck is parts avalability. i always looked @ the cheaper units but was worried about replacing broken stuff & upgrades.

[Ocean Racer]

I have a RTR XTM ep Excellerator 2wd its a nice car it does about 10-15 mph stock at hobby ppl its 150 bucks its a 1/10th scale. i spent around a 110 bucks and ugraded i got a new esc and modified motor. I got a Xtra Quake no turn limit esc $80 and a Method R 17x2 turn modified $20 according to them if i get a higher powered batt i can do 35mph. But im going around the mid twenty's and thats on a 6cell 1500mah Ni-Cd it comes with fully threaded shocks adjustable slipper clutch servo saver u can adjust the tires tow and tilt its a fun car to drive on or offroad.:D

[Rex R]

20-25mph is about right for the om21 with a 19T and a 31mm prop. and yes things will get hot if the boat isn't set-up right.

[FRED]

REX is straight on the button for equipment and speed and prop. Someone mentioned sv-27 comparing to om-21. No way JOSE! I was going to buy a om-21 but i would spray 3m-77 inside and the lay fibercloth on top of 77 and push in at cranies and noaks and let try. The hull may have alittle give but will be real tower of strenght. Now for a motor, a handwound 14/2 motor with .130 flex and teflon and cg at 30% and carbon fiber 631 and lipo 3850 mah, this would be a long lasting unit with hardly any maintenance. Oh yes, i would polish my flex till it shines with very little ribs to the touch and a lit touch of teflon grease. Also homemade hardware! Forgot a setup. Motor Maxx wild on 8 cells with a carbon fiber 633 or a lipo 3s-11.1 and water cooled.I have this setup in a No Step 1 and it flies for 5 minutes, good enough for me!

[Rex R]

while I don't have direct hands on experience building etc an om21...I do know my electrified is on a par with the ones I've run with (roughly 21-24 mph 19t spec class). the key for keeping these boats cool is to 'air out the hull', about a 1/4" above the water riding the prop. can be a wild ride if your turn fin gets bent :)

[FRED]

Rex, i had 2 Electrafieds with a Chameleon #2110 which had a higher rpm and a 534 prop but one bad point was the turn radius which was too long. One day some geese flew in and landed right in front of the boat. I veered and hit a water sprayer and i kept on the throttle and pushed it around enough to get it home and it was on plane, one tough boat. Right now am working on Randy Naylor Patriot little boat with a 480 speed with 1200 lipo and a carbon fiber 629. Wooden 22" boats i make seem to turn out the best of the bunch. Oops better not hijack om21 posting, sorry , carried away!

[FRED]

Saleens 7, you were running a solid shaft in the om21! I thought they were stuffing tube and .130 flex and a carbon fiber 631 and a Chameleon motor. You know what your doing and when i read where you found shaft was bent, i'd keep using the shaft since you have it already setup for the shaft. Let everybody know how things turn out. Tower has a motor called Speed Secret at 40,000 for $22.00 and best is to put good non-groove brushes in upright and let it fly. Watercool and hood cool too. I have one in each Mutineer with a carbon fiber 631 prop and you can't catch them, nope, retired here and i have 2 or 3 spares of the secret if needed. I don't pass out bull cause i like to see boaters have as much fun as i do! I'm retiring from thread as i have no further info, thanks!