Now that the weather is starting to warm up and the days are getting longer in the Northern Hemisphere, my guess is the hype around brushless whoops like the Mobula7, Tinyhawk, TinyLeader and Trashcan will die back and out attention will return to larger quads. Typically these are 5" quads that suit racing and freestyle but also the larger quads like 6 and 7" that are better suited to long range. It's not the newest kid on the block but the Skystars G730L 7" quadcopter was released a few months back and I've had a chance to review over the length of the NZ summer. It was the first mainstream 7" quadcopter that was available at a reasonable price. Up until then all 7" builds were custom made like the Diatone GT-M7 I built in the long range section.
The Skystars G730L is available pre-assembled or as a kit that requires assembling. Neither option includes a receiver since the user will likely use a long range receiver such as the FRSKY R9M mini or TBS crossfire nano although in this case I chose a regular FRSKY XM+ (more on that soon). Specs and my comments on the specs below:
300mm frame with 4mm thick arms. Top mount with alloy camera protection
Receiver Choice and Install
Although I run TBS Crossfire as a radio link for my build, I wanted to test the limits of the standard FRSKY link with the Taranis X-Lite radio and XM+ receiver. For this I wired the XM plus in as below. Also not antenna orientation which is pretty close to optimal by my understanding.
After successfull installing and setting up a GPS on my custom long range build I consider it a must have item for long or even mid-range flight. The BN180 module is only around $10 and gives you real time feedback on GPS coordinates which offers you so much feedback in betaflight OSD including instantaneous ground speed, direction to home and distance to home, all hugely useful tools for flight duration and location management. GPS was installed as below following learnings from my custom long range build. See below for connections specific to the G730L.
Sadly one of my ESCs was dead on arrival. Although Gearbest offered to replace I simply used a spare BLHeli32 esc I had available (Racerstar PGA40 BLHeli_32 40A 2-6S). Although it has a different model in BLHeli32 suite, I was able to setup with the same parameters and have had no flight issues whatsoever. I have seen other reports of DoA ESCs so please be weary and get in touch with the retailer immediately if you find yourself in this situation.
Replacement Racerstar PGA40 2-6s ESC. Does the job without fuss
There was no real tune so to speak so I used the Betaflight 3.5 tuning guide as I always do and came up with a pretty good tune for me. Screengrabs below for more details. Note: I did use the betaflight throttle limit feature on a switch (as detailed here) so that I could run 6s without pulling excessive current since the stock motors add no real thrust above 80% on 6s, they just draw more current.
I was really please with most aspects of the FPV signal in stock configuration:
Good news is this is an easy fix. Rather than but a new longer antenna system where the active component of the antenna is kept further from the quad, see my solution below that uses all of the slack in the wire and keeps the active element above the battery using good old zip ties and heatshrink. The endstate is I get really good signal out and back now. Farthest I've been so far is 600m out (visual line of sight) with a very clear signal on 400mW using 2 x RHCP pagoda antennas on my goggles. Update: on more testing I'd go far to say as video quality and reception is probably the best I've ever had.
I was immediately impressed by the balance of the craft on first flight. Props were smooth and well balanced with no vibration and I've never had even a hint of oscillation using the PIDs above. Furthermore handling was extremely neutral, it's been a while since I've had a frame with a top-mounted battery so was really suprised how much I appreciated the different feel. Furthermore I like no landing on the battery (like you do with quads using bottom-mounted batteries) especially for batteries on larger craft like this are more expensive and easily damage due to larger capacity and weight.
To me 4s feels like this sweet spot on this motor and prop combination and I was able to get around 5-6 minutes of gentle flight on a 1500mah battery landing at 3.75v per cell. I'd expect to be able to run a bettery 3000mah to maybe 4000mah if you really want to go long range, especially at a higher cruising speed. I don't have any 5s batteries but I expect this would be the practical limit for efficient flying on these props and motors without a throttle limit. I did however run some 6s 1000mah CNHL ministar batteries using an 80% throttle cut and found I had similar flight times to the 4s 1500mah battery when flying gently. This makes sense because these batteries have the same power capacity (remember, power = voltage x current).
When flying a 7" quad with relatively light motors like this and heavy pitched 3-bladed props like this you will definitely need to be gentle on the throttle or add a throttle cut because it was draw a lot of current (amps) without adding a lot more thrust. For example I've seen 130A on 6s (equivalent power of 195A on 4s). What this means is that although this machine is very capable of freestyle, you'll need to be fairly responsible on punchouts. I'd recommend if you want to do more freestyle that you go to a lighter blade like the HQ 7x3.5x3 or even drop down to 6 or 5 inch props to lighten the load. A smaller prop will make it feel less "floaty" as well. It's good to have options available here anyway.
No current sensor :(
Unfortunately this flight controller does not have a built in shunt resistor to allow you to measure current drawn. This is not usually an issue where BlHeli32 is concerned since ESCs now often have internal current sensory that are accesible through ESC telemmetry however telemetry is not connected on the G730L furthermore even if I went to the effort to connect ESC telemmetry output to a spare UART RX on the FC I'm not sure these ESCs actually have a current sensor. This is disappointing on a 7 inch quad that is somewhat geared toward longrange flight since being able to guage how much current has been drawn from your battery (and how much is left) is a key measure when trying to maximise your flight time safely. This is personally my biggest disappointment for this quad.
The Skystars G730L is a fully featured pre-assembed 7 inch quadcopter that is well specced and in particular has and excellent FPV system, well thought out power train and all assembled on a surprisingly good frame. What makes this unique is that it is the first plug and fly quadcopter that caters more towards long range and at a competitive price.
No doubt it has it's shortfalls like lack of a current sensor and poor VTX antenna placement but these can be largely overcome with very little effort. Having built a custom 7" quad myself I know how expensive it can be so the retail price of $190 is not too bad although I have seen it on special for as little as $160.
For my own model it was frustrating that one ESC was DoA but good to know that Gearbest stood behind the product and were prepared to replace the faulty item. I guess the advantage of having separate ESCs here though meant I could just use one I already had available. I reality there is not a big difference between this and my very expensive custom build so if you are looking for some more reaxed and efficient flight plus the ability to carry a larger battery and HD cam for longer flights and range then it is hard to go past the Skystars G730L as an option.
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