Starling 2 payload

Eyal

Hello,

I’m currently designing a compact indoor-use kit around the Starling 2 platform, specifically the Starling 2, not the Starling 2 Max.

I would like to add a few additional lightweight sensors to the drone, but I could not find a clear specification in the datasheet for the available payload capacity or recommended payload margin.

Could you please clarify:

What is the maximum recommended additional payload for the Starling 2?
Is the published drone weight already close to the practical lift limit, or is there usable margin for small external sensors?
Are there any recommended limits regarding added mass, mounting location, or center-of-gravity shift?
Would adding small sensors affect flight stability, flight time, or PX4 tuning in a way that you recommend avoiding?
Do you have any other compact indoor-capable drone models that may be better suited for carrying additional sensors while still staying smaller than the Starling 2 Max? (Maybe the Stinger FPV?)

At this stage I am still in the design phase, so I do not yet have flight logs. I can share the planned sensor weights, mounting concept, and pictures/CAD layout if that would help.

Thanks in advance

Alex Kushleyev

Hi @Eyal ,

The full weight of a standard Starling 2 is about 285g (with battery).
the maximum motor thrust at full power is ~185g (at 7.5V) -- single motor
this means the total max thrust for 4 motors is about 740g , which means about 2.6 thrust to weight ratio
- please keep in mind that you can never apply full power to all 4 motors due to needed motor rpm differential for control
it is a good practice to have at least 2.0 thrust to weight ratio in order to maintain good flight control. If you follow that guidance, it means that you can add about 85 extra grams to Starling 2 and it would be at 370g
- flight time (hover) will drop from ~35 mins to ~25 mins (not exactly linear due to lower motor/prop efficiency at higher thrust)
it is always recommended to try to keep the center of mass as close as possible to the geometrical center of the vehicle in order to reduce the moment of intertia and off-center mass which can affect control.
depending on where the bulk of the weight is added, re-tuning flight (attitude) controller may be needed. extra weight far from vehicle center will increase moment of intertia, so the controller will need to adjust

Stinger FPV drone is a very different vehicle and although it is smaller than Starling 2 Max, the flight time of Stinger is significantly shorter due to.. smaller propellers, heavier (more durable) frame, etc

I think it all depends on what sensors you are planning today. If you want to share that, we can try to help..

Alex

Eyal

Hi @Alex-Kushleyev,

Thank you for the detailed explanation regarding the Starling 2 payload margin and the thrust-to-weight considerations. The breakdown is very helpful for my design trade-off.

I would like to ask one follow-up regarding the Stinger FPV. In my application, flight endurance is not the primary constraint, so the shorter flight time compared with Starling 2 is not necessarily a blocker. Durability, compact size, and the ability to carry a small external sensor package are more important for this specific use case.

With that in mind, could you please provide a similar payload-oriented assessment for the Stinger FPV?

Specifically:

What is the typical all-up weight of a standard Stinger FPV configuration, including battery?
What is the approximate maximum thrust per motor?
Using the same recommended minimum thrust-to-weight ratio of approximately 2.0 for good controllability, what additional payload margin would you consider practical?
Are there recommended mounting areas or structural points on the Stinger frame for small external payloads?
Are there any known limitations compared with Starling 2 regarding payload mounting, center-of-mass sensitivity, or PX4 attitude-controller tuning?
For an indoor application where flight time is less critical, would you generally consider Stinger FPV a better candidate than Starling 2 for carrying a small external sensor package, or would you still recommend staying with Starling 2?

At this stage, I am trying to make a platform selection between Starling 2 and Stinger FPV before freezing the mechanical layout. Once I understand which platform has the more suitable payload margin and mounting flexibility, I can share the planned sensor list, estimated added mass, and CAD/mounting concept for your review.

Thanks again for the support.

Best regards,
Eyal

Alex Kushleyev

@Eyal , sorry for the delay. Here is some additional information regarding Stinger FPV:

https://docs.modalai.com/stinger-vision-datasheet/
base weight with battery : ~570g
maximum thrust per motor : 650g @ 15V, 2600g total theoretical
theoretical max thrust to weight ratio: 4.5:1, lots of extra margin, but if you add a LOT of weight, will need to check motor temps, etc.
CAD model for stinger (may be slightly outdated) : https://forum.modalai.com/topic/5180/looking-stinger-fpv-cad-models -- you can attach your payload to carbon fiber
I think that Stinger will be easier to tune up with additional payload because of more responsive and powerful propulsion system than Starling 2.
i dont know what your sensor package is so, it is hard to comment about which platform is better. Starling 2 has landing gear that offsets it from the floor. Stringer is much lower to the ground.

Alex

Eyal

Hi @Alex-Kushleyev,

Thanks again for the response, the data and the CAD have been really helpful.

A few things I'm trying to pin down before I choose the correct platform for my project:

The big one is the Ethernet question. For my setup to work I need a reliable gigabit-class wired link to the VOXL 2 Mini. Forum threads suggest M0062 is dev-only, and M0130 looks like it's keyed to the full VOXL 2 and might not work with the Mini on Stinger — what's the right path for Mini specifically?

On power: working back from your published 12+ min flight time on a stock 4S pack, I'm getting hover power around ~107W. Does that line up with your bench measurements, and what does peak / maneuver current look like for the indoor flight Stinger is built for?

Thanks,
Eyal

Alex Kushleyev

@Eyal ,

I will look for an indoor flight log from a stinger. At hover, the power usage should be around 110-115W based on motor dyno tests. The peak motor current can go up to 300W (per motor), but it's not possible to have all 4 motors maxed out.

Regarding ethernet.. It is actually possible to establish a full wired interface using the same usb interface that is used for ADB. it is a lot more efficient that using something like adb port forwarding. We have some scripts that set up the full network with NAT, when voxl2 / voxl2 mini is connected to a linux host. There is one script that enables the usb ethernet in voxl2 kernel and then there is the host side script to set up the networking and tcp/ip rules for NAT (so that voxl2 can access internet via the host) -- the NAT part is actually optional.

Actually the first part (without NAT) is already documented here, you could try it : https://docs.modalai.com/qgc-via-adb/ -- this will give you a full tcp/ip connection to the linux host.

For downloading log files, we get about 35-37MB/s, it seems to be a 400Mbps link. Even with 1Gbps usb3 adapters we don't get full 1Gbps, so this may be the best you can get. Can you clarify your application for the network connection?

Alex

Eyal

Hi @Alex-Kushleyev,

This is very helpful, thank you.

The 110–115 W hover figure lines up well with my own estimate, and the per-motor peak-power clarification is exactly what I needed for the power and payload sizing.

I also went through the QGC-via-ADB / USB-NCM documentation. The approach looks clean, and the ~4 ms ping shown in the doc is well within my requirement. Latency matters more to me than absolute throughput, so that result is encouraging.

For context, my data-rate needs are modest: on the order of a few tens of Mbps total. That's a couple of compressed video/sensor streams from the drone, low-rate telemetry, and one small latency-sensitive control/data channel. Based on the ~400 Mbps you mentioned, I don't expect bandwidth to be the limiting factor.

A few things I'd like to confirm before committing to this path:

Does the USB-NCM setup remove the need for a separate Ethernet add-on board entirely? From the doc it looks like NCM runs over the same USB connection used for ADB, which would suggest I only need physical USB access to the VOXL 2 Mini, with no added Ethernet hardware on the drone. Is that right?
Is USB-NCM stable for sustained real-time streaming? The doc example focuses on QGC / lower-rate comms. Are there known issues running the interface continuously at tens of Mbps over longer operating periods?
How does USB-NCM latency behave when the VOXL 2 Mini is under heavy compute load? Should I expect latency spikes or jitter under CPU/GPU/DSP load, or is the interface generally stable enough for latency-sensitive data alongside onboard processing?

The main thing I'm trying to decide is whether USB-NCM is robust enough to be the primary data link from the VOXL 2 Mini for this application, or whether I should still plan for a dedicated Ethernet interface.

Thanks again,
Eyal

Alex Kushleyev

Hi @Eyal ,

I just did a quick test and I am getting 2.0ms ping time when voxl2 cpu is in perf mode, and about 2.5ms when in auto mode. VOXL2 is idle.

the NCM networking feature works concurrently with ADB, which is great and we also have some scripts to set up NAT if you need your voxl2 to actually use the Linux host as a "router" to access outside world. that is easy to set up as well (requires some routing changes on the linux host).

In terms of real-time streaming, it is definitely adequate for image / video streaming to a Linux host. In fact, this option is my personal favorite way of connecting to Voxl2 while developing / testing cameras and viewing multiple streams in voxl-portal. Voxl-portal uses jpeg compression, which is a lot less efficient than h264/h265 and with the NCM connection, i don't have any issues (compared to adb port forwarding, which also allows voxl-portal to work, but is about 10x slower and uses a lot more CPU, you get frame drops in voxl-portal if required bandwidth is higher than 30-50Mbps or so). I am mainly using the USB-NCM feature for development purposes (as opposed to on a flying drone), but i have not found any limitations, at least for the bench testing use case.

In terms of CPU load affecting the speed, i just ran a test stress -c 8 which loads up all 8 cores to 100% and the ping times did not change in perf mode (2.0ms) and in auto mode, the ping times reduced from 2.5ms to 2.0ms because the cpu cores are actually running at faster speeds. I am guessing that all the USB stuff is happening in the kernel at a higher priority, so it's not affected by the user applications (unless the cpu overheats, i supposed). GPU / DSP loads should not have any effect on this, since they are separate hardware.

I also did another test - stream 4 video streams to voxl-portal (live view), which added up to about 100Mbps of network traffic and ping time stayed between 1.5-3.0ms (sometimes lower than 2.0ms).

I have not observed any stability issues related to NCM being active for long periods of time (days). Make sure you are using a high quality USB-C cable (nothing fancy).

Alex