Thankyou guys for all the awesome feedback! Really happy to see derfrickler here in the thread. Thanks so much for your low voltage documentation on this FC mate, great work!

Voltage drop across the battery tabs and a something that I’m aware of and it’s good to point that out. I will stay with the battery trays for now and then remove them later if I need that extra amount of juice in the can to get that last bit of flight time.

So I was working on the vtx setup tonight. I’m going to use a matek 5V BEC to power it. I did some testing on the low voltage cutoff using a bench top power supply, recording how the matek BEC reacts when Vcc changes from 8.4V down to 5.5V. These two voltages represent the starting (4.2V/cell) and flight-ending (2.75V/cell) voltages for a 2S li-ion battery pack. Remember I nominated 2.75V as the minimum I would safely accept.

I’m not a fan of FC 5v regulators, I’ve had my fair share of them die on me.   I’ve lost quads over this and have had a tendency of late to use a separate BEC to power my vtx. I don’t know but I reakon that the high current hogs vtxes can be (compared to cams, rx,gps etc) is the reason for most FC voltage regulator failures. I dunno, my 2 cents lol.

From 8.4V down to 5.3V Vcc the matek BEC outputs 5V.
When Vcc goes below 5.3V the matek BEC outputs Vcc less 0.3V. 
When Vcc goes below 4V the BEC shuts off.

This is great news. Effectively it outputs 5V when it needs to and I can be sure it will stay at that voltage even at the flight end voltage of 5.5V Vcc (2S li-ion pack at 2.75V/cell).


One note on this test is that I had to have a load on the output of the matek BEC to be able to measure the output voltage. The load I chose was a frsky rx, hardly the same load as a vtx outputting 300mW+ but we shall see what the real world tests show.

Most VTX are fine at 4.5V anyway, so the BEC should work without problems.

(28-Apr-2021, 07:19 PM)derFrickler Wrote: Most VTX are fine at 4.5V anyway, so the BEC should work without problems.

Ok that's good to know, thank you. :0

So I tried printing the frame in ABS and I've found the angle of the rear GPS holder failed to stay together without any supports.  I want to try this frame in ABS so I will update the design to include some self made supports.

Thinking about the voltage drop across battery contacts and the whole fact that one still needs to attached an external 18650 battery tray to this design - I decided to incorporate the battery holder into the design.

I found this cool 18650 holder on thingyverse with a spring loaded element built into the design.   Here's a test print I did in ABS just to get an idea of how it works.   The left side of the battery holder in the pic below is actually disconnected from the main assembly and slides forward and backward to allow you to insert a battery and then have some pressure against the +/- terminals.   How cool is that!



So I remixed the hotdog frame again to accommodate this battery holder for a 2S li-ion setup.   I'll hopefully print this soon.  Need to get this thing in the air with FPV electronics on it so I can start getting an idea on the flight times and LVC behaviour.



I had to loose one front set of 16x16mm stack holes but I was able to keep the FC relatively centered.  I like the idea of a pure 3D print and including the battery holder in the design.

That's really cool! How much does the battery holder weigh?

Ya, that battery holder is a cool find!
I'd also like to know what it weighs.

What do you plan to use for contacts?

It weighs 8g for 1s. I am planning on using some brass standoffs, I might add solder to the brass ends where they will make contact with the battery terminals.

So I ended up getting the hotdog in the air 





I decided to confirm the specs of the vtx and found the unify nano can operate down to 3.5V so I decided to run it off Vbat instead of through the 5V matek BEC.

In my haste to get it up and flying I forgot to add a cap to the power terminals on the FC/ESC.   The video is a bit shoddy for it.   I'm not worrying about it now as I'm printing another revision of this frame in my quest for 30mins.  

I've tested out a few pairs of li-ion now.   I'm finding the Samsung the best performers so far.  I have Panasonic li-ions as well but the voltage drop when flying at the start is considerable.   Remember this is a 2S rig so the demand on current through the batteries is higher, they don't have the luxury of being put in parallel, lol. 

Dry weight is now at 93g.   Add a set of 2S li-ions and it comes in at 185g.

On this revision of the hotdog my best flight so far is 15 minutes, 16 seconds.   Just half way there.

Here's the flight, all thumb aching 15 minutes of it, not sped up for your pleasure.



Some things to note as this is an incomplete build.

• no gps installed yet
  
• no cap filtering
  
• wobbles, PIDs - how do they effect current consumption? do higher PIDs lend to greater current draw?
  
• Motor PWM & ESC firmware updates - should I try rpm filtering and/or higher frequency PWM options?
  

ph2t.

Looking good! I like it, and the name too Do you think you could mount larger props for increased efficiency? Seems like there is some space left, maybe with a small modification of the arms you could easily go for 4"?

Thankyou FSOT, yeah I'm planning on a 4inch at the moment and a few other things as well.

On another note, a new concept: catastrophic ejection, lol...

are these 3000mah cells? how did the voltage recover after that flight? was you able to get them empty?
these would be nice cells: http://www.molicel.com/products-applicat...y-product/


"wobbles, PIDs - how do they effect current consumption? do higher PIDs lend to greater current draw?"
the perfect locked in feel isnt the most efficiency tune, i believe higher pids lend to greater current draw. overall a good tune is efficiency.
i believe the frame stiffness can cause vibrations, as its on the heavy side with 2s liion, probably some additions would be needed?
pids and esc settings might be both important for flighttime, as its not that usual combination. it might need different settings? i would try an increased startup/rampup power about the wobbles
24khz befor 48khz esc firmware could be a reason about the wobbles too.
probably the wobbles are pid related only :-) but i would mention about the settings i named while tuning process, if there would be an issue there wont be an improvent with pid tune

i like 4inch but would this match? its not the lightest settup at 2s, the stiffness of the frame might be on the edge between flyable and vibes additional 1103 might struggle to spin a 4inch blade and would provide decreased effiviency - i believe the bearings will go noisy very soon i would like to see the truth about 4inch but seems not promising to me.

Hi ph2t,

Use Velcro Cable Ties, they are light weight and can be cut to length.
They are the only thing I use for battery straps. They work.

Also, the 1103 motors will spin 4 inch props, but it is not efficient. A 1303 motor will spin 4 inch props just fine.

Thanks for the replies hugs and ifly- appreciate the insight.

I’m thinking 1204 at 5000kv with 4inch biblades, designing a new print for it now.

Due to the sheer weight of the two batts, 1103 has bugger all authority on 3inch. I was able to tune some out by upping the pid multiplier slider value to 1.2 and up filtering sliders to 1.4.

Next revision of the hotdog is currently being printed - the 4" dog...



Prusaslicer approximates 30g of filament used.  I have incorporated the 2S li-ion version of that spring based battery holder I found into this design.

This version of the dog will be 4" bi-blade running some 1204 5000kV motors.  I think it could work.  I was running 1103 10000kV at 70% throttle on 3" bi-blade.   Given that I'm going up in prop size, dropping to 5000kV motors with no throttle scaling this time around should be similar dynamics around making this flyable!   I'm such a hip shooter, lol, no ecalc here.