Motor specs and amp draw

I’m rigging up my current sensor to an Arduino right now and will be doing current, voltage, PWM, etc for the whole flight. Will post results when weather become flyable

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Does anyone know if these motors can handle 14s voltages? It sounds like everything else can in the system. Apparently going from 12s to 14s would reduce the amp draw by 16%.

Looking forward to batch 4 and helping solve some of these issues.

Hey guys!
I just joined the forum here. I LOVE this product idea and want one for myself!

I will be meeting with our battery engineer and going over cell options for a 12S system, and if someone can confirm the BEC, ESC, and motors can handle 14S (motors based on manufacture show they are 12S only but I hope I am wrong), if we can do 14S I think that would make for a great solution without the need to change motor KV in my opinion. Maybe the creator of this product has tested 14S already?

14S is a nominal 1300 RPM different, something you would learn and adjust your throttle finger to easily within 1-2 flights. I would be slightly more responsive nothing significant though and in fact, it may feel and be better. It should also lower the AMPS as when volts rise, amps/heat will decrease.

My focus is 100% on my Electric Hydrofoil Surfboard - EFOIL but I want to make a battery and switch solution for this cool OpenPPG product before I buy one for myself later this year. I have dealt with enough Lipo cells that I just simply will not fly with one strapped onto my back that I cannot get off me if flares up.

Has anyone thought of installing thin stainless or aluminum plate behind the battery packs as a firewall of some sort?

So, if I can get detailed stats/specs or the ESC, Motor, and Full throttle AMPS and Average Cruise amps, along with a diagram of how the power switch is wired into one battery pack I will see what our engineers come up with for the battery and high current switch.

What AH size packs are people thinking? 35, 40, 45, 50Ah?

Also, what switches have been used here that have been failing so we can review what does not work as that is half the learning curve, knowing what does not work well.

Cheers!
Chris V.

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Thanks for joining the project, looking forward to your input. The ESC and motor can both handle 14s. The BEC and voltage sensing PCB we designed for 14s (up to 60v). As for a firewall, the two plates of CF are very good firewalls in my opinion, there was a question in the forum earlier about it. A few people have made metal battery boxes if you look around.

The ESC are 80a 4-14s, the max current is 320a ±10. I think a 45Ah battery would be best.

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Thanks Pdwhite!
What is the sensing PCB? is this part of the BEC meaning if I can get a 14S BEC all would be good or is the sensing PCB separate?

What minimum volts is required for the sensing PCB? can the BEC power it?

The only reason I mentioned metal firewall is that I don’t like the idea of holes for heat/battery fire to get through if there ever was a flare-up. I actually have custom fireproof battery bags for all our batteries. This would actually work well in flight because its light and will ack as another firewall. Could cause the battery to get a little warmer if under full throttle for while but nothing significant.

Anyways, Ill look into 12S custom high current and 14S and see what we come up with.

Any insight on power switches?

Nice to have you on board with us Chris! Your experience and solutions will be valuable to us for both reliability and safety.

Here is a thread that talks about the PCB:

Just to clear some things up

We designed the system to be compatible with up to 14s (60v)
The BEC in batch 3 is built into the sensing/voltage divider circuit.

Here are the capabilities and specs

  • Voltage divider - 60v = ~3.3v
  • ESC signal splitter - PWM in from throttle goes to 4 PWM out connections
  • Switching BEC - (Up to) 60v input will produce 5v out at 1.5amps. Needs at least 12v in.
  • Power light - LED to indicate board is safely powered
  • 5v accessory pads - used to connect future accessories that consume 5v power @ < 1.5 amps
  • Overvoltage protection - inputting higher than 60v will cut off the voltage divider and BEC to protect other sensitive electronics.

Also the mounting holes are standard 30.5 * 30.5mm M3, the same as used by drone flight controllers

PS We plan making most of the electronics available for individual purchase soon and we’ll have the above info and more on those pages.

EDIT: updated that linked threads original post with the version of the PCB that we are shipping with batch 3.

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I finally had the opportunity yesterday to fly with my new amp meter.

Based on my amp and volt readings during flight it takes about 1500 watts (per motor) to maintain level flight. Watts=Amps*Volts so with 50V the amps at level flight is 30A. When the batteries discharge down to 42V the amps go up to 36A which is still 1500 watts. So in this scenario amps increase when voltage drops.

Full throttle is a whole different scenario because as the voltage drops the RPMs drop and therefore watts drop. So full throttle with depleted batteries does not give you the same climb rate. In this case the amperage actually decreases as the voltage decreases and my testing confirms this. The relationship between volts and amps at full throttle is linear with the following data points:

0V = 0A (motors off)
42.5V = 73.5A (discharged batteries)
50.4V = 87A (fully charged batteries)

The equation for full throttle is Amps=1.73*Volts

Notice we are going over the 80 amp rating of the ESCs. I haven’t had any trouble with mine nor have I seen any complaints about them burning up. Perhaps this is due to good airflow because of the ideal placement on the arms.

Using the above equation, if we use a 14S battery battery without changing the Kv of the motor we would expect to see the amps go up to 100A at each ESC. However, if we also change the motor from 180Kv to 154Kv then we will see fewer amps: 74A instead of 87A per ESC. That’s how we achieve lower amps with the same power output.

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That’s a lot of amps! Appreciate you doing this test for us all. Do you need full throttle to climb at a decent rate, or is there enough power at say 75% throttle to climb? If so what is the climb rate at a lower throttle setting vs full throttle?

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Interesting - I think probably it is being still in the power rating band overall that counts.

The OpenPPG has plenty of power so there is really no need to ever push the amps above 80. It’s only the first few minutes of flight when the batteries are fully charged that it will even go above 80. My son and I have climbed between 250 to 300 feet per minute with it. He weighs a little less than I do and can climb a little faster with the same wing. Here is an example from one of my flight logs of a 1500 foot climb in 6 minutes followed by a 6 minute glide back down. Notice the later climbs with low batteries are equally as steep:

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The esc are rated for 100A burst and 80A continuous draw. I do have some 160kv motors if people want to try them or convert to 14s. Its just 7s batteries are a bit more rare.

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what does the M10 on the motor specs mean?

Its just the naming for that size motor.

I will take the 160kv motors with batch 4 order once available. I’ll use 14s li-ion pack as long as everything else is compatible with that voltage.

I gathered more data for voltage vs amperage at full throttle and modeled it in excel. I found the relationship to be a power curve. I recorded the voltage in two ways (Open Circuit Voltage and Load Voltage). I performed measurements with 2 and 4 Bonkas (12S1P and 12S2P). Here’s a chart of the data after which I will explain what it all means and how I collected it:

First we need to understand that a battery is NOT an ideal voltage source. The voltage at the terminals will drop when a load is applied. This drop in voltage occurs because of the resistance within the battery itself. Here is a link if you want to learn more: Measuring Internal Resistance of Batteries - SparkFun Learn

Those who own an OpenPPG will be very familiar with the fact that increasing the throttle will drop the voltage (and the battery percentage). But did you know that doubling the number of batteries in parallel will cut the resistance in half resulting in a smaller voltage drop? This actually increases the voltage to the ESCs and motors and gives you more power (watts). This increase in watts comes from an increase in both volts and amps. The ESC is rated for 80 amps so we should be careful not to run higher than that.

Those who are flying with 8 batteries need to be careful at full throttle because that resistance will be cut in half yet again and supply even higher volts resulting in even higher amps. I’m already drawing over 80 amps with 4 batteries while with 2 batteries it barely reaches 80 amps. Remember though, that flying with fewer batteries puts more load on the batteries which can be dangerous. So more batteries is better as long as you are careful at the top end with the throttle as to not draw too many amps.

Back to my data. “Open circuit voltage” is the voltage of the battery before applying a load. I recorded the voltage, then applied full throttle and recorded the amps. You can see a clear difference in amps when using 2 vs 4 Bonkas because of the way the voltage drops more under load when fewer batteries are used (Fewer batteries=more resistance=more drop in voltage=less amps).

“Load voltage” is the voltage during throttle up. To collect this I recorded a video of my amp meter and voltage meter (throttle controller). Then I stepped through the video and recorded the values.

According to this data model, if you actually delivered 50 volts to the ESC you would draw 110 amps! However, because of the resistance of the batteries you would never get there but high quality packs with low resistance and/or multiple packs in parallel could put you well over 80 amps which is already possible with 4 Bonkas.

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Thx for all your diligence on data collection - very much appreciated :heart_eyes:

So can we set a max current draw on the esc’s when we know we are going to fly 4 or more bats. Full throttle = 90% for 4 bats – 80% for 8 bats.
I know I can program my GoldenMotor bike motor to set max current draw! Not easily but I never change the packs.
I figure I would be doing 4 max on foot launches , 8 or 12 on a trike. So having a fast way to set current limiting on the esc’s would be nice!!!

Cheers

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Chis said that their ESCs are fully programmable and can be set to a max current. They are much more expensive though and we would need four of them. If you do it based on current you wouldn’t need to adjust it between battery types or quantities. I don’t think ours can be programmed like that. However, my son and I are planning on tweaking the PWM code in the throttle controller to adjust throttle percentage to allow us to convert to 14S without getting new motors. It won’t be based on amps though but that’s ok because we can use my amp meter to get it tuned just right.

We could limit the physical travel of the controller but I don’t want to lose that much resolution. Specially since it would need to be limited by about 70% to convert to 14S and would make the throttle very sensitive and touchy. But adjusting the PWM would make it feel and respond the same as it does now.

For just flying with 8 Bonkas you could install an amp meter like I did and just keep an eye on amps when the batteries are full. Then when they are low you would still have access to full throttle.

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I’m liking this idea of controller PWM adjustment the most.

Do you know how much more expensive? Great work on the tests, graph etc. I’m wondering if using 6awg wire would help to reduce the voltage sag, would be less resistance. Are you using 8awg? Anyone out there build theres using 6awg?

Perhaps Chris can chime in on the esc’s. Cost as well as if they would be suitable for this project? If they were not much more expensive might be good alternative for some.