TOPIC:

HI!... I'm modding a buddies boat. I need a diff outdrive that the set-screw side fits a regular brushless 540 style motor shaft (3MM?)I have a dogbone that comes up to the motor but no way of connecting it to the motor. If I could get a dif outdrive that would slide over the motor shaft, I could just slip the dogbone in and be done. Any help on this would be greatly appreciated! Mabey some of the boat guys could chime in. Never owned a boat so my knowledge is limited with this.

HI1... This is basically what I need but to fit a 3mm motor shaft.

Sleeve it with some brass or aluminium tubing (Or rod if the I/D is still too big) - most model shops sell the stuff. A snug fit in the drive cup hole would be best (5mm O/D?), then drill out the new hole 1/8" to suit the motor spindle. You might also have to pop the grubscrew hole through too if it won't just squash the tube (2.5 max so you don't damage the M3 thread)

Other option would be to mod a pinion - drill part way down the centre, same size as your dogbone ball, then run a hacksaw across the top for your slot. What's on the outside doesn't matter, as long as your ball-hole, slot, & motor spindle hole are there/right

Most boats I've seen have a gearbox anyway, the propshaft isn't usually connected directly to the motor unless it's a much slower 5-pole one (Otherwise the prop spins too fast & you get cavitation, ie lots of stirring & not much forward motion). Because of the lower speed they can get away with using cheap UJs (Huco) or stiff rubber pipe to connect the propshaft

Oh, & Tamiya tractor trucks use a drive cup very similar to that pic, & they're definately 5mm I/D (The one on the end of the 3-speed gearbox)

HI!... Well all the fast boats around here are all direct drive off the motors. A few buddies have the Traxxas Spartan. It's direct drive and does 50MPH. NO cavitation. I think I found my solution. I'm using a vintage Hotshot gearbox input drive. It's female hex fit perfectly over the prop shafts hex head end. I will then shorten that Hotshot shaft and bolt on a Traxxas female diff outdrive. Then run a BigWig steel axle shaft with one of it's ball ends cut off. Then I'm going to run a 3MM brass coupling. One end will connect to the motor shaft with grub screw. The other end will slide over the cut BigWig shaft and also tighten down with a grub screw. Man I luv fabrication. lol!

Yep fabbin is fab!
The motor spindle will be 1/8" (3.2mm) so you might have to slightly enlarge your brass coupling hole to take it, assuming it's exactly 3mm bore.

What motor is the Spartan running?
I'm no toy boat expert, but I know my outboard will just thrash the water if you overrev it, the boat's quicker if you throttle back & let the prop "bite" into the water. I spose the size/pitch of prop & shape of the hull would play a big part in what rpm you can get away with

HI!... Well this is the stock boat's gear box :

That's before I shredded it with the brushless on 11.1. LOL!

Final drive ratio is 1.35. So my EZ-RUN 4000KV motor on fully charged 7.4 (Actual is 8.42 volts) spins at 33,600RPM. So go through the gearbox the prop would be spinning at 24889RPM. Sounds about right. On 11.1 (Actual is 12.60 volts) the motor spins at 50,400RPM. Through the gearbox the prop would spin at 40,000RPM. So basically with going to be direct drive it will go almost as fast on a 7.4 LiPo as it did on the 11.1 LiPo.

This was the set-up that puked the gearbox. Remember this is a $49 boat from COSTCO. LOL! It originally went 8-10KPH. That was with a 19.2 volt NiMh battery. Like here :

Then I put the brushless in it. This is on 7.4 volt LiPo.

The issue now id the boat pulses on the water at high speed. I figure this is due to it not being a 100% "V' bottom hull. It's on a "v" 60% down and then the bottom is flat. So I think once it gets up on plane it's trying to ride on top of the water instead of cutting through it like a "V" bottom boat would do. Again this boat was NEVER designed to do what were making it do. lol. Hey it's winter time, I'm laid off from work. What else are a bunch of 40 year olds going to do? LMAO! My whole life i've made things go fast that were never meant to.

Anyway my thoughts are to try to get some plastic and make a smaller "V" bottom on this boat. Something like the size of a Toblerone candy bar, and mount it down the middle of the flat section of the hull? Thoughts?

Non-existant user wrote:

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Then I put the brushless in it. This is on 7.4 volt LiPo.
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Nice

This is my Vosper RTTL - 7.2NiMH, I forget what the motor is exactly, something 540 sized and brushed ... it's enough to show a bit a wake, but I did think about putting something else in there to make it do more like 40 knots ... not a scale 40 knots BTW - a real 40 knots