Wednesday 10 April 2013

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!

Wednesday 3 April 2013

Airframe Arrived!

Oh yes yes yes!!!

The airframe for the drone arrived yesterday!  I'm so excited to assemble it.  

Sadly I have a few late evening for work and I'm away at the weekend.  With a bit of luck on Sunday evening I'll start assembling it :)

Below are some lovely pictures of what I have to play with :)

Arms
The drone has 25cm arms, it will have four arms plus four spares just in case any crash damage!

Landing "Gear"

Center Hub
The center hub of the drone which the arms attach too!

Monday 1 April 2013

Captain: Signal the Motors

How to get the Gadgeteer signals to the ESC to control the motors?
The ESCs need Pulse Width Modulated (PWM) signals to then control the motors.  PWM is relatively easy to understand and there's a great webpage on Wikipedia.

The Gadgeteer board I have gives outputs PMW signals so life is good :)  Apart from the usual problem, not enough ports on the Gadgeteer board!

Along comes my friend!  Pulse InOut from GHI Electronics.
What's lovely about this board is that it can support eight input and output PWM signals!  

I only need the four output PWM signals however I'm thinking perhaps the inputs could be used for ultra-sonic sensors to help automated landing and/or obstacle avoidance.  That'll be for later on in the project :)


Wonderfully, the Pulse InOut board indepently generates it's own PMW signals from a command rather than forwarding on a signal from the Gadgeteer board.  Why is that cool?  

If the code on the Gadgeteer board hangs then the motors still get their signals!!!  I love this fail safe(ish)  approach!!!

Safe Landing
Perhaps I might (later on) code for the chip in the Pulse InOut board for the case if the Gadgeteer board code does hang.  

I'm thinking along the lines if the Pulse InOut does not receive any PWM commands from  the mainboard for say 10 seconds then it gives equal power to the motors to hover and then slight decrease in power to enable landing.

Buying Time
I can't wait to get the board and start coding for it!  I placed the order with Proto-Pic a few days ago and being Easter there will be a few extra days wait.  Hopefully it'll be here before the weekend!  Yea!!!