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Amp Draw Calc for LARGE X8 (Pre-Flight) Need an Attopilot?

Posted by Robert Blank on July 14, 2015 at 5:47pm

Hi,

I am currently trying to determine the anticipated amperage draw for a large X8 platform that our team is using to carry a ~10lb sensor for use in the field of snow science and hydrology. It has (fortunately) come to my attention that we need to reduce the 22.2V coming from our batteries to under 18V when supplying power to the PixHawk using the standard power module, which came with the PixHawk flight controller. It seems that we have two options:

1) New power module with increased power handling capacity 

http://www.ebay.com/itm/like/251927302504?lpid=82&chn=ps

2) AttoPilot - I'm still unclear as to exactly what this would do although many other forum posts on this topic have addressed this to some degree. 

http://autonomousavionics.com/products/attopilot-180-amp-voltage-and-current-sensor?utm_medium=cpc&utm_source=googlepla&variant=727049877&gclid=CjwKEAjw5pKtBRCqpfPK5qXatWYSJABi5kTxuPNZNpBSmjE-kt1xoWP9rvDEu6f_aGYRYkDxHzfqIhoCbBrw_wcB

My question is twofold - 

1) Which option, if any is the best route to take. What specifications need to be met so I don't max out either option?

2) How to calculate the theoretical amperage draw from an X8 (sets of two coaxial motors). I have not found much material on how to calculate theoretical values for this type of configuration since the motors are 'working in tandem'? Does this matter? Help here! 

- T Motor U10 KV100 

http://www.rctigermotor.com/html/2014/Efficiency-Type_0314/198.html

- 29x9.5 CF Props 

http://www.rctigermotor.com/html/2013/prop_0805/13.html

- 22.2V 6s 25C 22,000 mAh batteries (option to run either two batteries, or four, in parallel depending on payload/configuration): 

http://www.getfpv.com/batteries/flight-packs/tattu-22000mah-6s-25c-lipo-battery.html

- Gryphon Dynamics X8 (V2) Frame XQ1400 VZX = 1400mm 

http://gryphondynamics.co.kr/product/x8-airframe-kit-new-version

- PixHawk Flight Controller

- FPV = Separate system

- Around 50lbs Takeoff Weight

http://www.getfpv.com/batteries/flight-packs/tattu-22000mah-6s-25c-lipo-battery.html

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Tags: amp, attopilot, calculation, x8
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Replies

  • Christopher Rice December 10, 2016 at 6:21pm

    Hi Shaun;

    I'm helping Robert with his X8 unit and we're struggling with power/motor/screw type, and noticed you mentioned using a KDE motor with an 8s pack. Did you do this since you posted this reply? Thx.


    Shaun Bell said:

    I'm running two 6s22ah packs in my X8 and U8pro 170kv motors.  As Rob pointed out, running all your power through one sensor is a bad idea.  Mine uses an attopilot 180 fed though only one of the two packs.  So if the Attopilot fails, I still have the other pack that's wired direct to the DB.  As for the power to the Pixhawk I run one ubec wired with attopilot into the power port.  Another two ubecs to the servo rails with a switching circuit that only feeds one at a time in case one were to fail.  Also I add a reverse zener diode across the +- rails in case of power spikes.  Only needed if your powering noisy stuff like digital servos.  One thought about your setup.  6s with the 100kv U10 may not fly so nice.  Even my 170kv has been a tough go for stability.  I'm switching up to 7208 or 7215 135kv KDE direct motors on 8s packs.  It was a pain to realize I had to ditch all my ubecs for HV version lol!

  • Shaun Bell August 27, 2015 at 11:03pm

    I'm running two 6s22ah packs in my X8 and U8pro 170kv motors.  As Rob pointed out, running all your power through one sensor is a bad idea.  Mine uses an attopilot 180 fed though only one of the two packs.  So if the Attopilot fails, I still have the other pack that's wired direct to the DB.  As for the power to the Pixhawk I run one ubec wired with attopilot into the power port.  Another two ubecs to the servo rails with a switching circuit that only feeds one at a time in case one were to fail.  Also I add a reverse zener diode across the +- rails in case of power spikes.  Only needed if your powering noisy stuff like digital servos.  One thought about your setup.  6s with the 100kv U10 may not fly so nice.  Even my 170kv has been a tough go for stability.  I'm switching up to 7208 or 7215 135kv KDE direct motors on 8s packs.  It was a pain to realize I had to ditch all my ubecs for HV version lol!

  • Rob_Lefebvre July 14, 2015 at 6:04pm

    Do not run all your power through a single resistor on large aircraft.  Period.

    You don't need amperage data that badly.  You barely need it at all.  If you really must, get an Amploc current sensor, which slips over a wire, with zero chance of failure.

    And then I recommend to use a proper UBEC instead of a no-name voltage regulator from Ebay.

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