Proboat Shockwave RS modified to brushless

[rcevolution]

So I got everything installed over the weekend. Got the Traxxas connectors wired up to the esc to run two sets of batts. I installed a HobbyKing 36-56 2700 kv brushless motor with built-in water cooling, a Turnigy 60a Marine ESC, Traxxas Micro 2.4 RX with Traxxas waterproof RX box. I used the stock drivetrain and servo. I did have to cut about 1/4 off the driveshaft and shaft tube though since the new motor shaft was so long. Batteries are 7cell nimh Dutratrax 5000. Prop is Octura X427. I also ran some new and larger diameter water cooling tubes.

By the time I was able to take the boat out it was almost dark :( GRRRR. I got a chance to make some slow test tuns to check for water leaks both in hull (which I just resealed with tclear waterproof caulk) and in water cooling tubes. After 2-3 mins at slow speed I had a nice jet of water from the outlet and no water in hull! So then back out and I took her up to half throttle maybe about 20-22 mph. Back and forth for about 3 mins then brought her in to check temps and everything was nice and cool! So I decided to give her some more juice this time. Now keep in mind its getting very dark now and the wind is blowing away from shore so if something goes wring Im screwed. lol I roll on throttle slowly and got to about 3/4 throttle and I was doing 30 mph+ and it was handling great. Turned it around for another pass, got to 3/4 throttle and 30+mph (guessing) and I started hearing the motor revving real high and boat slowing down when it did this. Something was slipping. Maybe some or alot of cavitation but im still not sure what the hell that is lol. Next pass same thing but more spinning/slipping, kinda like the sound and auto transmission makes when its going out, alot of revs but very little movement.

At this point it was almost too dark to continue so naturally I decided to push my luck lol. The last run I gave her more juice at start up and it slipped a little but got up on plane then I floored it. Got to about maybe 40mph when she just reved up full slippage and it stopped. I was giving throttle now but no movement at all, just some splashing under the hull. GREAT...

I waded out a bit before it blew away asI was keeping her close to shore and got the boat. Brought her in and luckily it was just a set screw that had come fully loose on the u-joint allowing the propeller shaft to slid out. Thats why it wasn't moving and that must of been what was spinning/slipping during alot of the test run. Oh well, easy fix, but it was very dark now. Next time in the daytime i'll get some video. I have alot of playing around with battery placement and adjusting the outdrive. But all in all it looks to be fast, sits nice and even in the water and RAN VERY COOL!!!

Video is of second run last weekend.


Video Link Below:

Um0adaGW4yE


http://i237.photobucket.com/albums/ff10/evofan74/745074902_photobucket_14805_.jpg


http://i237.photobucket.com/albums/ff10/evofan74/745074902_photobucket_14803_.jpg


http://i237.photobucket.com/albums/ff10/evofan74/745074902_photobucket_14806_.jpg


http://i237.photobucket.com/albums/ff10/evofan74/745074902_photobucket_14808_.jpg


http://i237.photobucket.com/albums/ff10/evofan74/745074902_photobucket_14802_.jpg

[rcevolution]

http://i237.photobucket.com/albums/ff10/evofan74/745074902_photobucket_14804_.jpg

[yellowbird]

Hi RCevolution

- Looks good, and a bit faster than before then !!!!

Are the motor wires touching the motor coupling? If they are close, you might want to make up a shield - you can bend a piece of thin metal to act as a guard and use one of the two motor mount/ hull screws to fix it in place - like a P shape.

My motor wires are longer because I made up some 3.5mm to 4mm adapters to go from the motor bullets to the ESC bullets.

- yellowbird

[rcevolution]

Hey YB - no the wires are not too close. Just looks that way in the picure. You can actually stick your finger under the wires and not touch the coupler. There is good clearance but thanks!

I think the set screw loosened in the u joint because of all the cavitaion I was having. It was pretty bad. I think that x427 is just way too small. I dont 100% understand caviation but between the slipping and the cavitation creating a open area behind the prop i wast getting the thrust.

I have like 6 diff props to try from 27mm to 35mm with 1.4 and 1.5 pitch, will be interesting to see which is best. And also the best battery placement is, more fore or more aft.

I work 10 hours a day and it gets dark so early now so the soonest I can test is Saturday :(

Which prop did you end up using YB and did you have any cavitation probs?

[yellowbird]

My pond is frozen so the earliest I can test is March :crying:

There are 2 causes of cavitation:

- With a prop near the surface, sucking down air that means the prop loses grip - I have a mini-C which does this on start-up until it picks up some speed

- When a prop spins too quickly, so the low pressure behind the blade becomes so low that gas bubbles dissolved in the water can escape and cause the prop to lose it's "grip" on the water.

In your case, because the prop is turning so fast (40k+ rpm) it may be prone to the second cause on start-up. Once you are running it will be OK, and if you "roll" into the throttle you can reduce it. A larger prop would naturally spin a bit slower and may be less prone to "propspin" but would increase the current drain and would stress your ESC more.

I use a Octura Y535 (35 x 1.5 pitch) copper prop on 2S with my 2900kv motor and a plastic X431 (31 x 1.4) or Y531 (31 x 1.5) on 3S for about 33k rpm. Because the plastic props are only rated for 25k rpm or so, I accelerate fairly gently with them to avoid breaking a blade and so have not noticed any problems with cavitation.

According to my logger, on 3S the ProBoat motor is generating about 800W with these props so the current draw is higher than your Turnigy motor (according to the specs I found online). I ran it briefly with the Y535 prop on 3S but the power consumption peak was over 1100W.

What is the next size up prop that you have in a 1.4 pitch?

[rcevolution]

great explanation on cavitation thanks, still doesnt make sense LMAO! It never will I guess :) Yes I am goign to try some diff props. I have some glass filled/plasctic props from here OSE, in 1.4x30mm, a 1.4x32, and a 1.4x35. Then i have 2 Octura X431 plastic props. I also have a metal 32mm from OSE but I dont knot the pitch. The model # is OSE-80705. Then I also bought two Aquacraft Power Vee plastic props (stock props for that boat) they are 31.5mm, pitch???

I guess i dont have any 1.5 pitch although It looks like these AQ Power Vee props have more pitch, they might be 1.5, i dont know.

No that i think about it, I think I was having alot more cavitation than set screw slippage. Ive never had that kind of caviation in my other boat Traxxas Villain EX, so i am new to that. Ill try the x430 then step up to x432 and finally x435 using those slighty stronger glass-filled/plastic props.

BTW how since you have a SW26, how far should the stern of the boat sit into the water in relation to the bow? Should it be nice and level or the bow be pointed up some? Just trying to figure out how far forward or back to slide these heavy-ass batts. NO IM NOT GOING LIPO :)

[yellowbird]

Hi RCevolution

The Villain EX uses torquey, slow-revving brushed motors with a ~2:1 gear drive to turn relatively big props at probably 5-6000rpm - that's why you didn't notice any cavitation before.

Stepping through the range of props you have make sense - just try to keep an eye on the ESC and motor temps if you don't have a logger or access to one and be aware that the plastic props could break if you are too aggressive on the throttle.

To balance the boat, normal rule of thumb is that the center of gravity should be 30% forward of the transom (vertical back of boat). For the SW26 that is about 8.75 inches from the back of the boat. To check, rest the boat on something like a smooth pencil so you can roll the boat backwards and forwards until it balances (hanging the back end over the edge of a table helps here). Then measure the distance from the top of the pencil (pivot) to the bottom edge of the transom and adjust battery position until it balances at the 8.75" mark. Typically the batteries will need to move 2-3x the distance the CoG is off (e.g. if the CoG is 0.5" out the batteries may need to move 1-1.5" to get to balance).

Good luck!

[rcevolution]

ok great description - thanks again Yellow Bird

[forescott]

ooooh! nimh is heavy! Lipos would gain mph and lose weight. That thing would be a rocket!!

[rcevolution]

i know i just dont like lipo - had a bad experience with them before.

[rcevolution]

Updated 1st post with VIDEO