Hi everyone,

I'm new to these sort of projects, and I'm trying to prepare all the components I need to build a hexacopter. I'm looking to buy the jD-Simplex Hexa (RTF) from jDrones, with the upgraded motors, ESCs, and the 12x45 props. I'm also planning on purchasing the radio set with it. However, I'm in a dilemma about the battery I should get and what the flight time will be. I've read almost everything I can about how to select a battery and how to calculate the flight time.

With the upgraded motors and ESCs, I'm thinking I need a 8000 mAh 3S1P 30C battery, because  8 Ah * 30C = 240 A, and the ESCs run on 30 A (so 30*6=180). Can someone clarify this selection for me?

Also, if I calculated correctly, this copter at 75% throttle will have about 4.5 minutes of flight (with the 8000 mAh battery). Does anyone that has experience with this drone have a longer flight time than that?

Thanks so much,

Kate

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Hi Kate,

A few things to clear up: When we say an ESC is '30A' that means it is loosely rated to control current draws that high without overheating or otherwise failing. It does not mean that it operates at 30 amps. Your hex will draw much much lower currents than that in almost all situations. The current, or better power, required is purely a function of the load placed on the motor, not the ESC's rating.

There are some online tools that can help you select the battery and power system. I use this one as it is simple and free: http://rc-calc.com/en/copter

It is unlikely that a properly setup multicopter would hover at 75% throttle. Most aim to hover at 50%. The above tool will help you know what you should select.

Good luck,

Jonathan,

Thanks for clarifying about the ESCs and sharing the calculator!

As far as the throttle... I have a 793.33 g thrust per motor requirement. The motor that I'm looking at gives a 690 g thrust at 50% throttle and a 1290 g thrust at 75%, so that's what I assumed would be needed for takeoff. At 50%, will the hexacopter even leave the ground?

Kate

When flying a multirotor, you want the craft to fly in a stable hover (no altitude change) at 50% throttle. If you want the craft to climb, you increase the throttle, and descend when you go under 50% throttle. So no, the craft shouldn't climb at 50% throttle, but that's how you want it set up.

Hi Kate,

Do you intend to eventually use the hexacopter for FPV or aerial video? The reason I ask is twofold: because the gear you need is dependent on the payload it's eventually got to carry, and because if it's FPV, then there are much larger communities such as FPVlab where you can find more specific help, examples and perhaps some experienced people in your area willing to help you in person, which I'm pretty sure won't be a problem with your magnetic profile photo.

I'd also go for higher cell count LiPo packs in general (more voltage = less current for the same power). There are just so many variables involved that it's much easier and likely to live up to expectations if you start out by copying someone else's rig that you like the performance of, and then proceed/learn further from there.

Gotcha, thanks for the clarification!

Yes, I'm planning on putting a GoPro camera on there for aerial video and the hexacopter will be able to hold it. I haven't really looked too much into FPV... I'm thinking just manual and mission planning? I looked on diy drone's page for local groups and there doesn't seem to be to much activity in my area, but if needed I'll try to contact someone!

As far as the cell count... this an arduino-based copter and I've read something about how it doesn't support 4S yet? I could be wrong there, but I'll have to double check. Upgrading to 4S would definitely be helpful. Thanks for the advice!

Most things (except the power system) won't support 4S. But that's no problem, because that's where 12V step-down regulators come in. The advantage of that is that you then get a consistent and clean 12V power supply for the rest of your system, but if you're not doing FPV then perhaps you don't need 12V anywhere anyway. If you mean APM or Pixhawk by Arduino-based copter, then the 3DR power module will supply a clean 5.3V to the controller independent of your battery choice (from memory I think the power module supports up to 6S).

Another thing to note: with higher voltage batteries, you'll either need lower KV motors or smaller propellers.

I think a hexacopter is overkill in terms of power (and unnecessarily expensive) for carrying just a GoPro. Besides if it's a forward looking GoPro, you're very likely to have props, motors, and landing gear in view. There are many quadcopter and tricopter frames with good vibration isolation out there that can easily carry GoPros without props in view. 3DR Iris is one of them, but in my opinion H-frames (e.g. Flip FPV, QAV500, Discovery Pro, etc)  are better for aerial video since having the camera upfront with short or no landing gear gives it an unobstructed view.

The only real advantage I can think of for a hexacopter is the redundancy (if that's even supported in Arducopter firmware), which is partially negated by the increased possible points of failure (ESCs & motors & props).

By searching for videos in Youtube, as I did when I started out, you can easily find something that fits your needs and priorities, and then just copy that or base your choice on that.

My personal priorities (for example) are:

1. Unobstructed and smooth GoPro HD video quality

2. Safety (heavy frames are more hazardous than lighter ones when something goes wrong)

3. Crash damage resistance (lighter is usually better here)

4. Value for money (smaller is cheaper when buying and crashing)

1 & 2 are often in opposition, but generally standard sized quadcopters offer the best compromise for me.

Kate, you need to choose the battery with the weight which equals to the weight of your vehicle without the battery. In this case, you will have the longest flight time. Select from the batteries which have the best power / weight ratio. It can be calculated as follows: Voltage*Capacity / Weight. Take a look at Maxamps batteries if you need to fly really long (but they are expensive). If you need something cheaper, select from Zippy (better than Turnigy). 

Hope this helps.

I'll have to look into that power module... the hexa is APM controlled. So, if in theory I did get a higher voltage battery and the power module then I maybe wouldn't need to upgrade the motors or propellers? I guess it all comes down to more calculations.

We chose this hexa because of the APM, and in contrast to the quad it has a higher payload. The GoPro camera is just the first of a few things I'd like to add on to it, later on maybe some other sensors but I can't imagine they would weigh that much. Thanks for the tip on the forward-looking camera view though, I'll have to keep that in mind.

I unfortunately don't have access to YouTube at work so I'll have to find some videos when I get home! It's a good idea to get started. Thanks!!

Kirill,

I've been looking at the batteries from Zippy... I'm a little confused at your wording about the weight though? So the hexacopter without the battery is 1.6 kg and the battery that I've been looking at is 0.644 kg. Voltage*Capacity/Weight = 11.1V*8Ah/0.644kg = 137.89W/kg. So how does this correlate to the 1.6kg?

Thank you!

A tricopter can easily carry a GoPro, APM, and eventual APM sensors and telemetry radio, and still have a relatively long flight time of 15 minutes on a 3000mah 4S with 9 inch propellers and 900kv motors. A 3D gimbal will be slightly pushing it, but a quadcopter can easily carry that too. My choice of propellers and motor RPM is not the most efficient (slower and larger props are more efficient), but this is a good compromise for smoother video and better control.

I've got both APM based tricopter and quadcopter videos in youtube (same alias) that demonstrate flight durations and video smoothness. Mine are DIY though, so if you're looking for something RTF, then I think that there are probably RTF solutions for QAV, Flip FPV Pro, and Discovery Pro frames.

P.S. I don't recommend the standard Discovery frame because it has no vibration isolation and poor work around solutions.

That's a great news :) more girls here, try FPV is just amazing :).

I have to put a profile photo :)

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