I got cheap a 1080 f-one skate wing. So I fixed all the damage what it had, bought a 65mm aluminium mast and builded a carbon board for kitesurfing out of it. Unfortunately I did not really make it riding (not that easy).
Right now is winter in the south of Germany, so I thought, let us build an efoil out of it. I was a mechanical engineer and builded a few fpv drones, so I assume I will get the job somehow done. I also have an old selfmade 3d printer, but I prefer not using it. I think it will be easier and faster to model something directly on the foil. I will go for a quick and dirty build first and if I realy like it, we will see what I will do with it.
So far all parts are ordered at Ali + Li-Ion cells from nkon. The only thing what I did not yet order is the prop. All together (including 48€ for a fliteboard prop) even including a spot welder, … I spent 599€.
The parts are the following:
-12s8p 21700 cells LG INR21700-M50L (4900mAH, 15A discharge): 2,25€ per cell => 39Ah on 12s with 120A max current (2900 Watt at 3V cell).
-flipsky VX3 pro: 98€
-BDUAV 6384: 53€
-150A flycolor flydragon ESC: 71€
-Matek micro BEC: 8€
-a randaom 6800 + a random 8900 Keramic bearing: 7€
-8AWG (Battery), 12AWG (Motor wires), 20AWG (receiver) cables: 14€
-Nickel Strip 0,2mm: 12€
-soldering device: 21€
-Antispark plug, other plugs, 2 Balancer cable, 150A breaker, glue, voltmeter, voltage beeper, … (other small parts): 41€.
So what is the plan:
-For the battery I will build 2 times 6s8p and connect it in series with a 150A no spark plug. (Reason for that is, that I have a 6s balance charger already)
-Motor I will fix to the mast quick and dirty (modeling clay or something like that)
-cables keeping on the outside of the mast and also making a proper fluid Dynamics with tape.
-I will try to remove the original cables coming out of the motor and directly connecting the 12AWG, because I have read here somewhere that those can burn down and lead to a short cut.
-motor I will either dip into corrosinX or thread it with thermal conductive resin.
-Board I will do a quick and dirty build out of styrofoam and carbon with around 120L (80kg rider) because I have the stuff for it in my house. I will put in an Acryl plate or something like that as base.
How do you think about that? Any concerns or hints (also if you think that one of the bought parts are sub optimal I would like to hear).
Hi @Petr, seems like you have it mostly planned out. I’m curious to see how the modeling clay would work for a quick and dirty motor mount.
You haven’t specified which spot welder you bought, but you do mention 0.2mm nickel. You may have trouble getting good spot welds on nickel of that thickness depending on the spot welder. Many of the cheaper options can’t generate a large enough pulse of energy to make a nice weld on 0.2mm.
I also have a battery pack with LG 21700 M50LT cells that have a 15A rating. If they are like mine that rating applies below 25degC, above that and the continuous current rating drops below 10A. You will probably still be okay, just be aware that your current margin may end up smaller than that 15A number.
Thank you very much for the hint. Then I better limit the output current to 80A and check the temperatur behavior of the battery before increasing. How many cells do you use @S_Roger combined with which motor and do you limit the current somehow?
Maybe filling the complete batterypack with thermal conductive epoxy. Then it is waterproove and I can place it in the water for cooling in case I need to max out the current.
Does someone know how often single cells needs to get exchanged? That would be the drawback what I see in case it gets molded in epoxy. Maybe also thermal expansion could be an issue. Did someone try that already?
For the welding I have ordered the following, but I assume out of the ali-page it cant be judged if it will work, or is it already clear that I nead to order a proper/more expensive one (0,2 nickel plated stripes was the plan to use)? https://a.aliexpress.com/_EIWxCdn
Can’t go wrong with KWeld. Not inexpensive but very effective. Build your packs and then resell for almost what you paid and it works out same $ as buying cheap and you aren’t getting unpredictable end product.
I have a 10S11P pack that was reclaimed, a few others on the forum bought one too. I have it connected to a Flipsky 75200 and 65161 120kv motor. It’s worked quite well and never been hot, just a bit warm at the end up a session. I haven’t seen anyone report issues with it. I think @Foilguy has one too?
I think your 12S8P will probably work out for you. If you budget 3kW for takeoff power, that would be (3000W/43.2V)/8=8.7A per cell if you assume nominal voltage. If you assume the pack is getting low at 3.3V per cell you get 9.5A per cell. So not an outrageous demand on the cells, as long as you aren’t plowing around half submerged for a long time. Amps will drop down quite a bit once you are up on foil and you shouldn’t need to worry about it at that point.
thank you very much for your data. Sounds also good to me when it is working for you and I have around 15% less available current.
The following source I also found, where they did measurements regarding heating of the cell. They measured 21A for 5 min at ambient temp of 25°C as still fine (max cell temp <70°C). Our cells have in the pack maybe a bit warmer ambient temp, but sounds to me like still ok if it is pulling 15A per cell. I will watch the current and the temp and implement a measure based on that.
I have several of the 10S11P “robot” packs and am very pleased with them.
I think spec wise the Flipsky 75200 and 65161 motor is more “robust” than what you chose so be conservative with your VESC values as those cells will supply all and likely more than you require.
At 10S (lower V than you) the rig has all kinds of start power with the 65161 motor spinning a Flite prop.
I have had new riders on it that were over 100kg and no issue with lots of repetitive hard starts.
I have already worked on several things, but I was busy with some animal documentary. So was not able to provide updates. Now that is done, so I will start doing some updates here. (who is interested, here is also the animal documentary:)
The Battery is done. I have 2 seperate 6s8p blocks created so that I can use a 6s balance charger which I already had. The blocks are coming without a BMS. All cells in parallel I have fused with cheap fusewire from alibaba. In series there is just 1 fuse behind both blocks to at least protect the battery in case I get a shortcut. After finalizing the blocks I added stripes of a sealing as shock protection before I wrapped it in pvc. The pictures are showing upper and lower side + the final blocks
Here is now also the attachment of the motor to the foil. I had another good idea, so I changed my approach. I just printed a piece of plastic and put a clamp. First I just wanted to press hot clue in a pipe to model this peace of plastic to avoid setting up the printer, but then I anyhow installed creo and set the printer back to live. It is done out of PETG. It was not perfectly matching to the foil but with a heatgun I could fix that. Over the clamp I will stick a waterresistant tape to improve hydrodynamic.
To add, the cheap welder worked somehow. I also changed my strategy from 0,2 nickel plated steel to 0,15mm pure nickel. It was not the best e.g. welder battery got empty and I needed to do often breaks to reload. also the handheld cables got always to hot to hold. Spots were also sometimes not holding very good but with checking every welding point and doing a lot of them it was manageable. So who is tight on budget can go for it. I dont know why but somehow spots on the - side of the cells were very good and on the + sides pretty tricky.
I would suggest to increase your battery terminal thickness. At the marked spots you will gett the current of your 8P over the nickel strip, which will be too much.
You could extend the terminals and solder them to the nickel between the batteries, but it would have been better to solder before spotwelding, to avoid to heat up the cells.
See here, 1. battery soldered carefullly after welding, still OK after 4 Seasons.
2nd battery was soldered first and then spotwelded.
ok, I put it into a calculation and 2 stripes are still by far to less. So I will put 3 layers of strips to get some heatsink between soldering and the batteries and then I will solder a wire on it. Thank you @sat_be, that could have ended bad.
