Thanks for the information. I need to crunch some numbers to see if those bigger batteries might work in my application.
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20700 are the best size vs capacity and weight but they are still a bit expensive
I tested the same ( not on a efoil) in 18650 size : GA , good capacity as long as you stay around 8-10a discharge constant rate i think
Don’t Forget that the capacity start to drop to much if the 18650 cell is used a high discharger amp , at a low rate 5a , with GA i get a better capacity than 30q , 25r , vtc5 for sure , but after ?
Yes, they are not cheap. All in I think the battery box is going to be right at $1,000. But it should last for a long session on the lake. Esp. while I’m learning and up and down a lot.
My plan was to build another pack so I could swap packs mid-day, but that’s a phase 2 thing as well.
Rev 2 of the receiver board. This one has the tilt-pitch-roll sensor and is very likely the one that will go in Phase 1. I will add a bluetooth receiver for Phase 2, but that’s just too much code for now.
This new board also has hardware to drive the alarm, and that tested fine as well. It’s painfully loud, but once it’s encased in the battery box it won’t be nearly so bad.
I also tested out the basic functionality of the display board (IE I lit up some LEDs) and it looks like it will work fine (the LEDs light up). I worked through all the information that has to get to this board and encoded it into a packet format. So the next task will be decoding the packet, and lighting the appropriate LEDs.
I was originally going to have the limit logic in the display board, but now I think that’s totally the wrong way to do it. Because I will need to act on some but not all events on the Receiver board I might as well just do all the limit logic on that board and then have a very simple packet that just tells the display board which LEDs to light up at any given point in time.
There is still a lot of thought to go into under what circumstances the machine should shut down, and how exactly the shutdown process is going to happen for each circumstance (I don’t want to just go to zero throttle instantly because that will toss me off the front of the board and really annoy me, so I’d rather it throttle down slowly).
At this point I think I’ll just have a beep and a red LED warning but not shut down for most warning events (battery box temp, driver box temp, coolant flow, etc.). The only events I’ll shut down for is excessive pitch or roll (in which case it does need to cut throttle immediately); lower battery limit and remote signal lost (both of which throttle down slowly). The rest will be some combination of beeps and lights but I don’t want it to be shutting down all the time.
Seems prudent to have another battery limit at which it throttles back, limits you to half-power to allow you to pooter back to shore. Limp-home mode.
The final rev of the prop extender is off to the 3D printer and I machined down the prop so I could bolt it on.
The only other really big 3D printer project is the nosecone, which I was going to print, but the printer estimated 1 Day and some number of hours. I might have to do the nosecone in segments.
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Hi Doug, what mill is that?
I haven’t checked in in a while - mostly because I’m predicting a very early spring and I’m trying to get all my esk8 upgrades wrapped up before the weather warms up; and there’s a ride through the new waterfront tunnel that esk8’s are allowed in and I don’t want to miss it.
Anyway, I’ve been working on the battery pack. I did learn double-sided CNC milling. It’s not that difficult if accuracy isn’t too important. In my case being 10 thousanths out is ok. The trick is to drill mount holes the size of the cutter, then use them as registration holes for the other side.
So my battery cages are going well.
The bad news is because I had so much room in the battery box when I was doing 12S7P it didn’t occur to me that 12S9P would use up so much more space. But it does. Now I’m concerned that I won’t be able to get the rest of the components in the box.
I knew I should have modeled the whole thing before I started cutting stuff up, but I never thought it would be this tight. I might not make it. Might have to go down to 8P.
The mast is almost part complete except for the one giant 3 day 3D print that I’m afraid to start.
Oh - and I have a sort of an unfortunate distraction. The last few times I’ve used my battery welder (Sunkko 788H) it hasn’t been able to put down a good weld despite my dialing everything up to 11. So I’m headed two directions. First I want to see if @Mac’s strategy of buying the 220V 709A works, in which case I’ll follow his lead.
But I’m also assembling parts for one of those simple lead-acid-starter-battery-Meets-Arduino welders, which appear to work quite well. I’ve got some copper bar in, a starter solenoid and a battery scavenged from my dead (but not irretrievably so) scooter.
I can probably cowboy something together over the weekend and do some test welds to see if it really works.
Anyway, piccies this weekend hopefully. Unless the weather’s really nice in which case I’ll be testing my esk8 upgrades.
I love esk8 too. Got my Unity sitting in a box waiting to get used in one of my boards but I’m soooo close to having my efoil ready!
I too have a battery problem. I am probably going to buy the 2 6S batteries that pacificmeister uses since it’s proven. But man, I would love to build a battery pack but the work seems overwhelming.
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One of my boards runs a Unity. So far it’s a really nice driver. The mountain board had 2 flipsky’s but one of them died, so likely it’ll get a Unity as well.
I originally planned on the LiPo packs, but it didn’t seem like they were going to give me enough run time.
I’m hoping with the 9P of 20700’s that two people can spend a couple of hours learning - which means most of the time in the water rather than on the water 
If, after that, I can get an hour of time on foil then I’m perfectly happy.
I have 20700’s in two of my skateboards. I am actually using 10S4P of the 20700’s for my efoil testing. I have heard people mention to me before that the 20700’s didn’t put out enough discharge or something, but maybe that’s because mine are 10S. I would LOVE to put together a 12S 20700 battery pack, seems kinda expensive though!
The 20700’s I have are 15A max, so I can see why people are concerned about discharge current. On your 4P you max out at 60A, which might not be enough to get you on foil. I read somewhere that it takes 80A. But presumably that can vary widely with the efficiency of your drivetrain.
There are some beautiful 4200mAh 21700’s with 45A capacity, but they are really expensive.
I have 20700’s on my MTB, but I haven’t been able to test them much because about the time I was building that pack was about the time my battery welder was dying. So I’m suffering bad welds.
Yes, definitely not cheap. But I think battery prices are going to start coming down soon - hopefully before I want to build a second pack.
How do you get the calculation for the amp output out of curiosity? I do have other 10S battery packs I could put in parallel as well, but they’re 18650-based and I heard that’s bad to mix 20700’s with 18650’s.
Like I said, I was just going to drop $1K for two of these packs:
https://www.amazon.com/dp/B017NJTHJU/?coliid=I1YUS3JXB3JIS&colid=3L47M1OOIPEFK&psc=0&ref_=lv_ov_lig_dp_it
Oh and these are the 20700’s I’m using, from Meepo:
For 1k, I would build my own battery pack. My 14s14p battery pack should cost me less than 1k and it is made from Sony VTC6 cells with a 150a smart BMS on discharge. The 42ah of autonomy should give me around 1hr of ride time. It is a lot of work to build your own battery pack so that’s the trade off I guess.
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I don’t know how to build battery packs or else I would do that too with Sony VTC6 or Samsung 30Q. Just never mastered that art.
I buy all my cells at the same place and the ratings are in the description.
Here are the Samsung 30Q’s, 20700’s and the 21700’s I really really want to use on an esk8 build except for the price.
No connection to this company, but I really like their products.
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I didn’t know anything about RC systems or battery packs 3 months ago. I don’t think it is that hard to build a battery pack. However, you should make sure to be very informed before you start putting a pack together. There are a lot of videos and resources out there. There is also a lot of people with experience building packs on here. If I were you, I would take on the challenge. It is a good skill to have these days haha!!
I agree. I just wish I knew someone locally that I could have help me since it’s a little nerve racking the first time around! haha.
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Ok, so afraid was I to attempt to do a 3-day print that I decided to break it down into 3 1 day prints.
If you recall, here is the mast assembly:
And here is the nosecone:
I broke it up into a nosecone tip:
A center Section
and the two tails
each print takes about 8 hours.
Note that the center and the tails interlock. I would have done the same with the tip and the center except I already printed the tip.
What layer hight are you printing at? I Printed a similar part and it took 13h with 0.4mm nozle, 0.3mm layer hight @60mm/s, printed in asa-x.
Layer hight 0.3mm seems ok for this part.