Florida Build - PM Based


#1

I have finally collected all the various parts (and a few tools) from around the world. That alone was quite an interesting odyssey. One of the tools (from Prague) is a Prusa MK3 printer kit which took six weeks to get and two days to assemble. Here it is in action just finishing the thrust bearing mount (STL file courtesy of PM!)…


Reminder to all: Don’t forget to add your build profile. Details HERE


#2

Easily the most difficult step so far of my PacificMeister inspired build has been the drive shaft. Like some others, I have found cutting threads and a hole for the prop pin impossible in these 8mm chrome plated high carbon steel shafts from Amazon. So I ordered one of these 8mm stainless steel shoulder screws which was easy to drill and already had threads. However, its actual diameter is 7.82mm (the carbon steel shafts are 7.96) so the fit into the spec’d blue connector is not as tight and introduces a slightly greater wobble issue. [Update 10/17/18 - For now I’m going with the aforementioned shoulder screw and blue connector]

After reading scores of posts I see that many are struggling with the same gearbox-shaft-to-prop-shaft connection. It’s failure – both the blue one above and several other types tried by forum members – has been blamed for many seal leaks (from the wobble), slipping shafts (from the connector grub screws not holding) and even at least one lost prop and shaft (from the whole shebang disconnecting).

So what have I learned? No surprise to see many smart people here coming up with many creative solutions. My plan is to find some shaft stock that is: A) Exactly 8mm in diameter (±.05mm) and B) Of slightly softer metal making it easier to thread, cut and drill than the original shafts. I have also ordered a couple of different couplers to try. Finally I may trot that original shaft off to a machine shop and let them have a go at machining it.

When the coupler fails it’s a lot of heartache to cut the pod open and fix it. I’m hoping to skip that step!

P.S. - The ultimate solution would be a Neugart PLE40 gearbox with a longer shaft negating the need for the coupler and shaft extension. I just wrote them about this (details HERE).


#3

Finding waterproof connectors that allow you to attach/detach the wires between the ESC and motor presented more of a puzzle that I might have expected. I did extensive searches online and even shelled out $32 for an EV connector which is back-ordered until the end of the year. I gave a lot of thought to designing one from scratch. But then I hit upon this super-easy off-the-shelf solution that is readily available on Amazon. It consists of a small waterproof shell and a shielded banana plug that fits inside. Together they make a easy to assemble and use solution - one for each of the three motor wires. Tested underwater without any leakage for three hours. Not field tested yet.

Feedback encouraged!


#4

I like the idea. Where would you place these things to make the mast detachable?


#5

In my case I will place them on a short pigtail close to the waterproof battery and esc box up on the board so I can easily take the box off. I have a slot thru my board that will also allow the foil side connectors to pass thru the board if I want to remove my foil.


#6

The product description says a rated current of ≤13A unfortunately…


#7

The junction box itself doesn’t have any cables, so it shouldn’t have an effect on the overall current rating, the banana plugs determine it. As long as the box can withstand the temperature it should be fine.


#8

These couplers are made for outdoor wire extension.
So they got a 3phase screwterminal coupler inside like this:

(5th part from the left)

An this screwterminal is made for normal AC house installation.
But since you will use the xt-plug instead you have to determine those ratings.


#9

Correct. I discard the terminal connector that comes with the junction boxes and use the banana plugs instead. They are rated 150 amps continuous.


#10

The weight of the SSS motor + Neugart gearbox is a little alarming when you first slide it in the tube and hang it off the back of the mast. All the weight is only supported from one end, putting a lot of stress on the mast clamp. It appears that some address this problem by resting the prop duct on the rear foil. I wondered if that impact sthe lift efficiency so opted to design/print a bracket that snugly slides over the tube and mounts to the foil frame. CAD file available if anyone wants it. Fits the PM spec’d tube.