Esk8 conversion - possible, but worth it?

Build, Repair & Mod
#1

Aloha good folks!

At the bottom of my soul a new dream has emerged and now it’s time to do some brain work to fulfill it :wink:

I’m thinking of building DIY jetboard or rifle-case efoil. Jetboard is preferred because of the feeling and shallow waters capabilities, but I guess it would be a way harder to build comparing to a rifle efoil.

But. First things first.
I have a decent esk8 gear and I wonder if the following can be sufficient to be utilized in a jetboard:
2 X 6374 170kv 3500kW
MakerX dv6pro dual vesc 100/180a
12s7p LG MJ1

I have an idea to make some gearing so the both motors would power one jet prop - so there would be some room do adjust ratio/kv/rpm/torque.

Do you think that such a setup can provide any decent speed (like 20kmph at least) and reasonable working time/range? Or it’s just not worth to convert my esk8 and more powerful battery and motors is the only way to go? My weight is an advantage here (65kg).

I’d like to achieve min. 20kmph+ (40-50 is the golden goal :smiley: ) and min. 30 minutes of fun (60 Min is the goal). Possible?

I have tons of other questions, but let’s deal with this one to start and then I’ll spam with other topics :wink:

Shaka lads and gyals!

#2

Checked some data, i think the dual motors will do 20kph easily but your system won’t work as is.

Power available:
Your pack has 882wh at 7A continuous discharge per cell, 49A out for 7 parallels so you’ll only get 2500W continuous which is too little for your speed goal.

Ride time:
With two 6374 at 3000w each your pack would get you only 9 minutes of riding so the pack needs to be 3x the size to be able to go full blast for half an hour - realistically it’s never full throttle continuously so slightly less than 3x will probably be OK.

Rpm:
12s 170kV would give roughly 6250 rpm which is probably too little for a jet drive, you might need to gear it up.

#3

Thank you, greatly appreciated!

So… that arouses new questions then :slight_smile:

If I’m getting this right - to utilize the full potential of the motors I would need… how many battery amps? Equal to motors amps, like 2x90A = 180A?

I suspected the battery is the weak element in the system, but now I realised I’m not really sure how motor amps are related to battery amps.

Now, let’s assume the same setup, but with efoil, not jetboard - I believe it’s more efficient, but I guess the runtime would be still too short, right? So maybe the greater speed, but the time?

And, hypothetically, if not that battery (and eventually motors) - what would be a recommended minimum for 20kmph+/30min+

Also, you write 6250rpm might be too little - so what RPMS are minimum?

Still not sure if go jetboard or efoil. Jetboard would more fun and better spots at my peninsula, but efoil way more efficient and simpler… hmmm… :slight_smile:

#4

It’s two different use cases efoil and esurf and i haven’t got experience in esurf. Power, batteries and these motors i’m ok in.

To use the motors to the max and have runtime i’d triple your pack as said. 12s20p of these cells would get you 140 battery amps and 7kW, that’s a fair balance to the motors and would get you the ride time for esurf. Motor amps are not the same but it seems your esc is powerful enough in theory. I think it’s likely that it will overheat in an esurf since ”continuous” in spec sheet and continuous in reality aren’t ever the same.

Jets (as far as i know) run high rpm, low load so i’d expect around 20krpm for the impeller but i don’t know where the boundaries are for an efficient jet.

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