Hey guys, I’ve just started to transform my foilboard. And was looking for a motor.
But it’s been quite overwhelming going through all the threads on this forum. People are talking about different motors, but all seems to be not sure whether their motor is sufficient or not, whether it’s cost saving enough.
After days of searching, here’s some of my humble opinion on what kind of motor we should be looking for, what critia, and how should we navigate to the ideal motor.
We are all here to DIY, so cost saving is one of the priorities. That is, we should be looking for the cheapest motor that is sufficient of our mission. That is we don’t need an expensive super motor. The motor should have parameters that are ‘just enough’.
Sufficient parameters to power the hydrofoil.
motor parameters: (help me priortize)
a. RPM
b. Torque
c. output Power
d. Voltage rage (works with the most commonly used 12S)
e. Amp at work (would like to keep it low for safety reason)
f. KV (almost equivalent with RPM, for given Voltage at 12S ?? )
g. dimension (fits the Al tube, natural water cooling)
to navigate to the right motor parameter, we need to think about this sport itself.
a. how much Thrust (in Newtons?) do we need at launching stage for person of different weight (say 100kg)
b. how much Thrust (in Newtons?) do we need in cruising for different weight (say 100kg)
to find the relation between Thrust and Motor Parameters (RPM, torque, Power), we should look at the parameter of the propeller. (seems unavailable?)
That’s what I think so far… But It seems I am stucking at finding the thrust…
A lot of the German DIYer riding succesfully with an APS 64100.
There are making some changes to be waterresistand.
Big plus, good power with less watts.
I am also a owner from that motor, i will make those changes in the summertime and can see the differences to my Flipsky 65161 dircetlic.
Motor
If you want a cheaper DIY outrunner, get the 63100 140Kv motor and waterproof it.
If you want a motor that’s pretty much done and ready (some open and coat the inside with corrosion X for extra protection), get the 65161/65162 (depends on reseller) 120Kv motor with a motor shaft that takes a prop pin and nyloc nut.
ESC
Get an esc that can handle 200A and 14S battery config.
Battery
Stick between 12S to 14S. 14S will reduce the amount of current needed and also give you a higher top speed.
The maths has been done a long way back (almost 3 years ago). So unless you doing it for a project or design, there’s no need to re-do it.
For a specific speed your power requirements will stay the same. Therefore increasing the voltage will lower the current at that speed. It’s simple maths…
A higher voltage also gives you a higher top end rpm, which in turn gives a higher top speed for your motor if the ESC can handle it.
Thanks for these info!
And you are right, I am trying to do the math here.
If it has been done before, can I have a link to it?
I think it’s too important to be left behind.
math = theory is of course important. But you can only calculate something if you know the values that you have to use. there are no universities where you can learn how an e-foil behaves in water. or how to program the esc. who should teach the students if this development has only been taking place for a short time? these are all diy and companies that have been writing something here for years, those with the specialist knowledge. you can learn from them. just read the posts. see which e-foil the author of the lyrics has built. then you can be sure that what he says is true. someone writes an unbelievable amount of theory and never shows pictures or videos you know that he only thinks up on the pc. the more someone writes he could do everything much better than others who already do it, the clearer it is that it is fake. the physics is the same all over the world. everyone can only cook with water as a basis.
That’s not true.
Starting from full throttle, the same motor and the same prop, the motor current also increases, the speed only increases when the motor has enough torque.
Only with active speed control, i.e. in the part-load range of the controller, does the current drop at the same speed if a higher voltage is present.
But then the load on the controller is higher due to the switching losses.
I think for the best performance , the setup needs to run at full duty , @voltage at the maximum desired speed , just need to find the best combo between kv and voltage , assuming the motor isn’t undersized
I think the question is :
A 100kv at 14s would work better then 120kv at 12s ? ( same prop and all )
basically right. “A 100kv at 14s would work better then 120kv at 12s? (Same prop and all)”
basically it is so we say “the hotter / more kv a motor is wound” the more power it can assert. example from my flying sport: if i have a motor with max rpm 2300. i need a propeller (little pitch) that fits up to 2300 then i have 50 kg thrust. if i use a motor with max rpm 2000 i can also use the 2300 series propeller. then have only 42 kg thrust. I have a very efficient setup because the 2000 he engine can fully turn off and has no high phase currents. if i use a 2300 motor with a 2000 propeller (high pitch) the motor will try to reach the speed. however, it has too little torque, so the phase currents will increase very sharply. it may reach 2200 but it will be very hot. therefore: the setup motor and propeller must be able to fully rev up to the maxiamle speed without getting high phase currents. for the e foil with the maytech motroen i built a device for a kayak to measure the performance. my mgm hbc outputs everything to telemetry via the can bus. I have now milled 8 different solas propellers in all 4 - 8 mm diameter stages. then i drive in the water and see what values i get. where is the best ratio between speed and torque requirement. for foiling I stay one level below as a reserve. (different water temperature and other maximum speed are taken into account.) conclusion a maytech with 100 kv can be used as well as a 120 kv if the propeller is adjusted correctly. I would use the 120 for more top speed. the 100 kv is more ideal for baic and a lot of standing power to start off because the propeller can be larger. as soon as the season starts in april i will start to show the telemetry data in videos with dashware. then you can see everything I’ve told you now. regards
In my opinion motors of the same size and different kv have the same torque. The only difference is that a lower kv motor needs higher voltage and lower current to reach the same rpm has the higher kv motor.
100kv at 14s can be more efficient than 120kv at 12s because higher voltage and lower current is less heat loss. Max rpm and torque will almost be the same.
