Taking Stock

I've now decided on all the specific parts of the drone.  A big thank you to the eCalcs website in helping me with all the calculations!

So the decision:

Motors: 
High torque is good for efficiency.  I learn electric motors are measured in turns per volt, so a nice low kv motor will be fine :)  This is complicated only by the number of manufacturers out there! The good side is healthy competition so these great motors are not too expensive!

It's a bit "suck it and see" however the eCalc website tells me the Turnigy Park450 motor is good.  It's on the higher price side $16.45, that's OK as I'd rather have a good flight time and reliable motor!

Battery:
Here's the compromise already.  In a previous post I'd decided the battery.  On reflection I think two 5000mAh batteries are too heavy, so then I looked at 4000mAh.  Great, I looked at my lovely spreadsheet and found the right battery, wrong.  The 4000mAh battery was out of stock as was the 5000mAh battery :(

The compromise, I've gone for two Zippy 3700mAh batteries.  What does that mean?  Roughly 1.5 mins less flight time.  Never mind, at least I'll have the batteries soon for development rather than waiting.

One thing to note, the Zippy brand from Hobbyking are the lowest quality so will give up at around 100 charges ... but they are the lightest!

Electronic Speed Control
These control the motors from my Gadgeteer board.  It needs to respond quickly to powering up the motors, with a low internal resistance to save power and avoid overheating.

I've chosen the Hobbyking Blue Series 20A, motors go up to 14A.  Why this model?  It's meant to be a fast responding ESC and light weight.  We'll see.  It's on the higher price side at $10.37 however this might just keep the drone from crashing!

Propellers 
Easy one.  The eCalcs says for my drones weight with the particular motor I'll have that 10" propellers are best.  Ideally I'd like black propellers however they were out of stock, lovely bright green ones instead.  I'm sure I'll get used to it!

Best Battery!!!

I love maths ... some calculations have just more than halved the battery cost for the same performance, enjoy the post :)

I ask myself, which battery has best capacity to weight ratio?  Out comes the spreadsheet!

I went through all the 3 Cell batteries on the Hobbyking website, found the lightest for each mAmp and divided by the weight to give mAmps per gram.

The Comparison 

There a big difference between the best and worst batteries!  The best battery when compared to worst battery is 34% better, like for like that gives an extra two minutes of hovering flight.

FYI, interesting the best overall battery is in the model speed boat section.

Ultimately I'm looking at time in the air.  So what about the 6100mAh battery? It's has a worse mAh/g however it holds a third more power.

According to the eCalc website site, it estimates the best 4500 mAh battery 17.4 mins in the air where the 6100mAh battery gives 19.4 mins in the air!!!

Do we have a winner?  I thought so except a school boy error ... I forgot the cost!!!

The Cost of Power

6100mAh battery is $100 USD and the 4500mAh battery is $58 USD.  Both are a lot for a battery!

Perhaps one day I'll buy these batteries however I want to constrain the costs.  The 5500 mAh battery $96 however the 5000 mAh battery is $27 USD.  Much more like it!

My Winner

I think we have a winner!!!  It gives me more air time at 17.6 mins and half the cost of the "best" specification battery.

More interestingly this battery is light enough to parallel which that gives 24 mins of hover time with thrust left over for maneuverability.

Battery Investigation

What an amazing website this one is: eCalc

It is fantastic, all the aeronautic calculations for you!!!  It's been a big help and homed my design ... I'll write a bit more about it on another post :)

Batteries!  What to choose from?  I know I need a 3 cell battery for the right voltage yet with hundreds of 3S battery it's difficult to decide.

Lots of people on their quadcopters are using 2100 or 2500mAh.  Yes why not use that! :)

Oh dear, on the calculation website only 10 mins of hover time and about 6 mins of high powered flight :(

I need time in the air, therefore a big battery.  What's the largest 3 Cell battery on Hobbyking?  How's about a nice big 8400 mAh?

It's a beast of a battery at 640 grams yet that gives me about 21 mins of both fancy high powered flight and hovering.

One thing that was bothering me was the heavier the battery the more power needed to make the drone hover.  The more power need to keep it in the air the less we have for accelerating forward and maneuverability

Ummm, we could have a drone with a long hovering time yet not able to keep up with me.  Ummmm.

I was thinking, is this the best battery?  

The above battery is the lightest 8400mAh for that capacity and is the best (on Hobbyking) battery in terms of mAh per gram.  Are there batteries with less capacity with a better mAh per gram?  

Then I starting thinking, if I optimise the mAh per gram then this reduces the weight and we have more flying time :)  Yea!!!

Then I remembered my basic physics, I find the best mAh per gram battery and then put them in parallel !!  could then have the correct voltage and lots of power!!!  Why not 10000mAh?  Yes, this could be excellent!!!  

Time to create a spreadsheet to find out :)

Power to the People

I've been getting a bit side tracked with all the sensor issues.  Time to learn about batteries :)

Lithium Polymer, LiPo, is where it's at ... better than Nickel Metal Hydride yet cheaper than Lithium Ion.

There's a huge range of batteries from Hobbyist websites, so let's investigate what I need:

• Light weight ... postman will love me however it's for the drone's benefit
• Large energy capacity ... fly forever!
• Small size
• Cheap ... not cost me a fortune :)

I want everything!  I can't have everything :)

Something I've learned is the important of the battery "C Rating".  It stands for also how quickly you can safely drain the battery without damaging it.  Great little guide here!

What does that mean for me?

Four motors for me and lets say 20 Amps motors each = 80 Amps Continuous Discharge.  So I need a battery that will have a large capacity multiplied by"C Rating" = 80A continuous discharge.

Let's say the batteries I'm looking at have 2000mAh capacity, I therefore need it to have 80A / 2000mAh =  40 C Rating.

Voltage and Power

How much voltage do I need?  This relates to the type of motor I'm going to use!

Interesting, first to decide which are the right motors and then you'll know how much voltage you'll need.  Once you know that then you'll know which are the right batteries for you :)

So which motors?  Haha, that depends on how much power I need and that depends on the weight of the drone!

To add extra dimension, the more dynamic responsiveness I want the drone then the more instant power it'll need.  how dynamic I want the drone to move?  Plus also the money factor :)

Time to make an estimate of the drone weight!