I’ve been using the Drotek SDP33 airspeed sensor for years now as it has two advantages:
Requires only one initial calibration and does NOT require you to “zero” calibrate before every flight
It’s accuracy is insane, unlike previous sensors that fluctuate between 0 and 10 mph this sensor does not
It is accurate starting at 1mph on up to its maximum which makes it perfect for VTOL transition needs
My question is this:
It has become difficult to find these, Drotek does not have them in stock and I can’t seem to find more of them. What is the “next gen” sensor and who has it? I need a replacement for the SDP33.
For slow VTOLS with low transition speed, I also find the SDP33 to be the first choice. At higher speeds, the measurement inaccuracy at standstill no longer really plays a role, as the pressure difference increases with the square of the speed. For example: measurement inaccuracy of 5 m/s at standstill corresponds to only 0.8 m/s at 16 m/s airspeed.
VERY NICE!!, so, I would need a cable that had a cube orange GH connector on one end that connects to the I2C port and the other end I can hand solder to the sensor itself. I would then need to print out a housing and mount the sensor and then attach the pitot tube, is this correct?
Yes, you can connect directly to an Ardupilot FC as shown in the diagram.
If you unscrew the Drotek, you will see that there are still some passive components on it that may improve the signal-to-noise ratio. I think Drotek once wrote that Sensirion had calibrated the SDP33 especially for Drotek ? I can’t say anything about that, as I only had the sensor on the flight controller as a test.
I do remember when they first came out there were two versions and then one day there was only the 33 version. Maybe that’s what you picked up on. So it seems I can make my own but maybe it would be subpar to what I have been using which scares me a bit considering I have thousands of dollar tied up into the numbers that that sensor puts out.
If you don’t need to measure speeds below 10 m/s, I think you can use one of the pressure difference sensors without any problems. I flew the MFE Fighter today, which has 2 airspeed sensors.
Here the difference better ‘no difference’ in flight. An MS5255 is mounted on the left wing of the MFE Fighter and the SDP33 on the right. In flight at 61 km/h = 17 m/s cruising speed it makes no difference. When the quad motors are switched on, the different turbulence naturally results in larger measurement errors on both sensors.
Most excellent comparison! It does seem like the MS5255 sensor has more sporadic readings of the airspeed when below a certain Km/H. The SPD33 seemed to handle the low speeds better. This is trait I am looking for. However, you are spot on when it’s measuring higher speeds (in the flight it was 67 Km/H on both sensors, plus or minus like 2). So for fixed wing flight the MS5255 sensor is fine. I’d still like the SPD33 if I can find one and this is why.
If you have an airspeed sensor that is inaccurate below a certain speed then when you set the airspeed in ardupilot that allows the transition to be considered complete then it MUST be above that accurate/inaccurate threshold. If you have an airspeed sensor that is accurate at all speeds then you can set that transition complete airspeed to the actual stall speed (plus 20%) that any given airframe actually has. In your case your airframe is large enough that it’s stall speed is well above the inaccurate/accurate airspeed of the MS5255. I bet mine is too but I’d rather not mess with that. Plus (and correct me if I am wrong) the MS5255 requires you to zero the senor before every flight, no?
I did some more digging, the SDP sensor comes in three DIGITAL flavors. These versions have a connector that is not suitable for tubes:
SDP31 which has a max 500 Pa
SDP32 which has a max 125 Pa
SDP33 which has a max 1500 Pa
The SDP33 has a max airspeed measurement up to 50 m/s (112mph).
I think the SDP33 is the one you must of been talking about where the manufacturer made a custom version.
The problem is the the version I linked have the SDP32 and 31 in a version that does like tube fittings but the SPD33 is the ONLY one that we as UAV users need and is NOT available in a tube friendly fit. I am beginning to suspect they stopped making those and that’s why Drotek stopped as well, I’m not sure on this at all though.
I can say that Drotek has never responded to me and has over the years taken three orders of them (as in they took the money) and never shipped me anything.
As of this posting, this company has some and with more options than Drotek had!
They come from Portugal and South Africa, cost to ship two was $30 DHL and was the cheapest option. I bet you could get more than 2 shipped for the same price but I don’t need more than two.
