Photo Platform: Am I Overweight (no donuts) ?

[rickc]

I have developed a loathing for GoPro cameras in general, and have been trying to throw together an alternative platform for still photography (primarily archaeological sites) without much money and few technical skills.
My first attempt, trying to add a second camera in the back, off the accessory bay, was not a great success.
My second attempt, using purely brute force methods, involves replacing the gimbal, etc. with a GoPro to tripod screw adapter, off of which I hang the camera, attached to an intervalometer which hangs off the bottom near the accessory bay I set up the camera to take images at 1/200 sec, shutter priority, f-whatever, continuous autofocus. auto ISO,
Then, i hook it to an intervalometer set to take an image every 5 seconds or so. I start it, and let it run.
I can see where I am going by hooking the camera up through the HDMI connector.
I usually run wide-angle through the Zeiss zoom lens.
The still images are light-years better than GoPro crap, and so I am living with all these limitations.
I think I am also really close to being over a reasonable weight limit:]
The camera is about 290 gm, the Intervalometer in about 90 gm, a cable and misc. about 40 gm. So, that is a total of about 420 gm.
It seems a bit sluggish but flies OK.
*** What happens if I take this rig up to about 6700 feet? ***

 

[andrew.baker.142]

What camera are you using?
With *most* Canon point and shoot cameras you can load CHDK with the intervalometer built in (no extra hardware weight). I've also heard that some Sony cameras can take a software intervalometer.

 

[just_bruce]

I have developed a loathing for GoPro cameras in general, and have been trying to throw together an alternative platform for still photography (primarily archaeological sites) without much money and few technical skills.
My first attempt, trying to add a second camera in the back, off the accessory bay, was not a great success.
My second attempt, using purely brute force methods, involves replacing the gimbal, etc. with a GoPro to tripod screw adapter, off of which I hang the camera, attached to an intervalometer which hangs off the bottom near the accessory bay I set up the camera to take images at 1/200 sec, shutter priority, f-whatever, continuous autofocus. auto ISO,
Then, i hook it to an intervalometer set to take an image every 5 seconds or so. I start it, and let it run.
I can see where I am going by hooking the camera up through the HDMI connector.
I usually run wide-angle through the Zeiss zoom lens.
The still images are light-years better than GoPro crap, and so I am living with all these limitations.
I think I am also really close to being over a reasonable weight limit:]
The camera is about 290 gm, the Intervalometer in about 90 gm, a cable and misc. about 40 gm. So, that is a total of about 420 gm.
It seems a bit sluggish but flies OK.
*** What happens if I take this rig up to about 6700 feet? ***

Depends on what your MSL elevation is now, but it might not even get off the ground at current weight. And if you do, expect the control response to be even more sluggish and possibly erratic. Density altitude will get us all...

 

[rickc]

Depends on what your MSL elevation is now, but it might not even get off the ground at current weight. And if you do, expect the control response to be even more sluggish and possibly erratic. Density altitude will get us all...

I am going from sea leavel to 6700'

sure would be nice to see a table or graph of payload vs. altitude ...

 

[rickc]

What camera are you using?
With *most* Canon point and shoot cameras you can load CHDK with the intervalometer built in (no extra hardware weight). I've also heard that some Sony cameras can take a software intervalometer.

The Sony RX100 M3 will run "apps" but the Timelapse app will NOT AUTOFOCUS in between exposures. This is a killer for me, which is why I am hanging an intervelometer on the bottom as well.
Yes it is ugly ...

 

[just_bruce]

I am going from sea leavel to 6700'

sure would be nice to see a table or graph of payload vs. altitude ...

Unfortunately it is more complex than that. Temperature, humidity, and atmospheric pressure all play a part. It's really about knowing how dense the air is in comparison to sea level at STP. Once you know that, rotor efficiency is essentially a linear relationship (i.e. a direct ratio)

See here if you want to calculate it (about midway down the page under Altitude)
Density of air - Wikipedia

 

[rickc]

So, using the ol' Engineering Toolbox, and all else being equal,

I would expect a 22% drop in air density going from 400' MSL to roughly 7,000 ft.

and if rotor efficiency is the most important parameter and if it is indeed linear with air density,

So so, if payload capacity is 500g (user manual) then the payload capacity at 7,000' should be around 416g,

So so so, my Sony RX100M3 + intervalometer + stuff = 420 g

So so so so, I should be barely OK ???

[Now I remember why I stopped being an engineer, lo so many years ago ... ]

 

[andrew.baker.142]

Don't assume that rotor thrust is linear with density altitude.

 

[yt lee]

The thrust will decrease as battery voltage drops.

 

[andrew.baker.142]

The thrust will decrease as battery voltage drops.

Not true.
The motors will use the same power as the battery depletes. The current will increase to make up for the lower voltage. Remember Power=current X voltage.

 

[yt lee]

for brushless motor, rpm is a function of voltage, thrust is a function of rpm.

 

[David Boulanger]

What is the All Up Weight of this Solo.

 

[David Boulanger]

for brushless motor, rpm is a function of voltage, thrust is a function of rpm.

That's all theoretical. Motors don't run at maximum efficiency to begin with. Volts drop and Amps go up. Its all about Wattage. Being that a properly built quadcopter should hover at around the 50% throttle area the voltage drop of a battery has nothing to do with anything other than the Amp draw will go up.

 

[just_bruce]

Don't assume that rotor thrust is linear with density altitude.

Hey andrew... care to help my aging brain on what would cause a non-linearity in rotor thrust reduction as it relates to density altitude?

Rotor thrust is essentially a displacement-with-velocity of air molecules (F=1/2mv^2), and the number of air molecules reduces as density altitude increases. The velocity the rotor is able to impart is pretty well fixed for a given RPM on SOLO's fixed pitch, so that only leaves the mass of air available for displacement as the variable.

What am I missing?

 

[David Boulanger]

Lets not over think this to much. If the Solo weighs less then 2000 grams you should be good. Read the Site Scan Specs. I believe the Site Scan Solo is 2000 grams.

 

[just_bruce]

The Site Scan Solo specs don't specify service ceiling. (https://3dr.com/solo-drone/specs/ ). Also, I wouldn't call consideration of temperature and density altitude overthinking. Seems like the beginning of a responsible flight planning process. But maybe that is just me.

 

[David Boulanger]

I thought I saw something about a recommended 8000' ceiling on Site Scan. Not Sure.

 

[andrew.baker.142]

Hey andrew... care to help my aging brain on what would cause a non-linearity in rotor thrust reduction as it relates to density altitude?

Rotor thrust is essentially a displacement-with-velocity of air molecules (F=1/2mv^2), and the number of air molecules reduces as density altitude increases. The velocity the rotor is able to impart is pretty well fixed for a given RPM on SOLO's fixed pitch, so that only leaves the mass of air available for displacement as the variable.

What am I missing?

Bruce,
My Master's Degree in helicopter aerodynamics is over 2 decades old so the brain is very rusty, but one thing that sticks in my head is that there isn't ANYTHING linear when you talk about helicopter aerodynamics!
Using simple momentum theory (see attached screen shot) you can see that air density (Greek letter Rho) is in the denominator under the square root symbol. As density decreases the power required increases non-linearly.

 

[andrew.baker.142]

For air breathing helicopters the power available tends to decrease with altitude more quickly than the power required goes up so that tends to be the limiting factor. What is actually a big issue at altitude for a soft in-plane rotor system at altitude is the dynamics to the rotor system itself, but this isn't an issue for a multi- rotor using propellers.