Larsb tow build, Bremote LR and dual motor steering

[Larsb]

I’m starting my tow build, been thinking about it for some time but didn’t find the time really
Thanks @Jesserosco, @rttn, @Etiennebzh, @ludwig_bre and @jenz for the build info and help so far!

CAD status:

It will be a differential steering tow with dual (cheapest ) 6384 motors and water cooled x-cross 120A ESC:s. I bought the ESCs a long time ago, with the recent x-cross failures they seem pretty sketchy, but i hope they’ll last some months at least.

For the board I adapted a board plug i had already, I originally made the plug for an efoil but didn’t like the shape:

I’m aiming for a low center of gravity and to be able to move the motors freely, so the bottom of the board is plywood, overlayed with some cheap UD carbon.
I cut holes for the motor wires and designed a passive water cooling intake:

I also started on electronics I uploaded a connection diagram here: Bremote connection for dual steering ESC + BEC - #4 by Larsb

As there are only two holes used on the PCB and three pins on a servo connector I’m cutting one header pin off at the bottom and bridging the pin header for the dual steering connector on the PCB here:

I wish i had the skill to change the PCB layout to make it a dual steering PCB without mods, any chances of this happening, @ludwig_bre?

I soldered terminal blocks to the BECs to get a more clean and robust connection:

I also designed and printed a custom box for the bremote Rx and the two mateksys 12s pro BECs:

For the connections i simply used two short Y-servo cables, they were really cheap so wasn’t worth it to buy a servo connector kit.

It feels like this was the complicated part of the build, maybe except for building the Bremote LR, i hope that the rest goes easy

[Jesserosco]

Dang! Looks like it’s gonna be an awesome boogie!

[Larsb]

Thanks! I really hope it will be Your first tow video is what inspired me, it looks like so much fun! I hope to be able to improve my foiling a lot with it.

[nekitesurfing]

This looks great. I’m very keen to go this route too having built a number of foil assists. I’ve learnt to build battery packs as I knew this would be a major cost to the project and will also go down the route of two motors and a Bremote with differential steering. I’m really looking forward to reading your build posts. Keep them coming and good luck

[seagull_nz]

This is great, nice and clean. What’s the black square at the bottom left of your custom BEC/Rx box? A heat sink?

[Larsb]

It’s a tie wrap mount for the cable stress relief.

[Larsb]

Started to build up the box contents: battery, brackets, bms etc. I designed the battery clamp so that i can move the battery in 25mm increments if i need to adjust the center of gravity.

[S_Roger]

Nice that you can keep the EV battery module in its original housing like that. Often they are just too large for something like this

[Larsb]

That’s not my experience, I’ve had a few different in this kind of size, often the large modules are built up of these smaller ones internally.

[Larsb]

Wired bms tonight, these are great cells, they’re around 5 years old and voltage is still within 0.004V balance.

[Larsb]

Wired everything in the box, escs and cooling

Then started with the bremote build, got some issues with the magnet covers jamming the magnet rotation. I tried sanding the minuscule epoxy drops that had escaped and got decent rotation - but in the end I decided to redesign the magnet covers to get more clearance. I added some steps in the cover, matching the component heights on the PCB and this removed the issue.

[nekitesurfing]

Looks great. What waterproof box are you using and what qivalent power does your battery have (I.e 12s8p)?

I see your escs will be externally cooled. Is it just passively with the movement of the boogie sending water through the tubes?

Many thanks.

[Larsb]

Box is bud PTQ 11072
battery can do 10c, it’s 12s 37Ah so about 15kW

The ESC:s are cooled by the natural water flow, this works well on my efoil. If i get issues i’ll add a small fan on the heatsink on the other side of the esc:s, but i’m not worried, I think the setup will work well.

[Larsb]

Finished long range bremote😄

Build was pretty straightforward, great design work by @ludwig_bre!

I made some changes to it, increased max steering angle to +/-45 degrees and designed a steel spring setup, it’s got a quite nice feel to it. Updated the handle to fit an 18650 battery, which I had already (instead of the original 14500 that would have had to be ordered). I’m not sure the remote floats now though, we’ll see.

Looking forward to the first tests!

[Larsb]

I started the motor proofing. The cheap 6384:s look surprisingly good under the hood, only thing is the 16AWG wires, it’s tedious to switch the wires all the way to the stator and the last length can be a hotspot. I’ll leave it like it is for now.

I had to expand the wire holes since the wires originally exit to the side. I cut the hole with a dremel rotary file and rounded the edges with a wire brush:

Designed and printed a cover to get a cleaner look and keep wires from moving:

Three layers of high temp winding varnish on the stator:

Two coats of zinc spray on the rotor (i’m not too confident this will remain long though, it might be too powdery):

[Jimmy25]

What made you pick these coating applications vs epoxy?

[Larsb]

For the stator: winding varnish is made for the job
For the rotor: it’s more of a test, i haven’t used zinc spray there before.

There can be some downsides of using epoxy on the rotor:

• It can be hard getting full coverage without jamming the motor
• The epoxy doesn’t adhere well to the magnets, it easily flakes (and you shouldn’t sand the magnet coating)
• You risk getting an unbalanced rotor bell from the epoxy weight

[Larsb]

Got some progress:

• Soldered phase wires and phase connectors on the ESC:s
• Installed cable glands in the box
• designed, printed and laminated custom mast plates, designed spacer for the wires
• Cut and threaded mast pieces

I almost got the drives finished:

But sadly, I’m out of 10AWG phase wire. Ordered and will have to wait for it to be able to extend the motor wires. Might start board lamination tomorrow instead

[Larsb]

Oh, a question to @Jesserosco: did you leave the esc as it is and just mount the esc plate to the heatsink with a pad or did you pop off the outer aluminum piece before mounting it to heatsink on your build?

[Jesserosco]

I leave it as is and mount directly with thermal glue or thermal epoxy. I have used both and they both work great and not difficult to remove if you need to fix anything.