Nimbus Tricopter VTOL

Hi Greg:I got the params all changed, everything seems to work,except the Rudder so i arm it,only the rear motor starts and then i use the throttle and now all 3 motors are running, then i place it in QHover and the tilt motors seem to move forward to 70 degrees , then FM FBWA motors go down to forward flight but all three motors are still running ? then i reverse that back to QHover motor tilt goes up to 70 deg and then back to Q stablize motors back up to 90 deg throttle down left and right motors stop, but the rear motor will not stop till i disarm Humm what do you think? thanks B.K

Greg i;m getting ready to order CF Props what size for front and rear ? along with 8-26v SBEC for the tilt motors, Thanks B.K

Need some help to figure this one out:

Pixhawk 2.1 Cube (Black)
Firmware 3.9.10
MP version 1.3.68
Nimbus 1800 VTOL airframe
Using an I2C expansion board
Using Here GPS
Using Motor/ESC combos that Foxtech uses (version 2 setup)
Mauch PL series current sensor with Mauch BEC (which is also giving me problems)
Power supply is a 6S 8000maH 10C
It’s not fully configured and it has never hovered or flown yet
GPS, Radio, Magnetometer and Accelerometers are calibrated and work fine until I try to use this sensor

Full Parameter File Here: Nimbus VTOL V1.param (17.0 KB)

Problem: I have an SPD3x airspeed sensor that will not work (will not report any airspeed changes)
What I’ve diagnosed so far:

  1. I used a multi-meter to confirm pin outs on both nose and body and those appear to be lining up correctly as follows: Nose side - + D1 D2 match body side - + D1 D2 and the pin outs of the SPD3x are - is Positive Volts, + is SCL, D1 is SDA and D2 is Ground.

Color scheme is as follows:

  1. If I use a regular JST-GH connector (like the one that comes with the SPD3x and plug the SPD3x directly into the I2C port on the PH2.1 (and thus removing any possibility that it is a body to nose cable problem) IT DISABLES the GPS! By disable I mean it looks like it is browning out the whole HERE GPS unit and no GPS gets to Mission Planner. Again, this is by doing a direct connect with a normal connector shown below that I bought a 10 pack of back in the day:

  1. Due to the airframe design I am unable to have the SPD3x connected during bootup and I do not know if that is a problem or not.

  2. In case it matters I hooked up the ESCs and servos according to this and I have not proven if it is correct yet as I want everything else to be working first:

It is configured as shown below:


And shows this on the HUD:

I have used this sensor before on a previous VTOL build and after changing the ARSPD Bus variable to 0 it worked perfectly. A comparison of the parameters between that working airframe and this one reveals no help.

Here she is so far:

I’m stumped!!


Use QSTABILIZE mode to do your ground testing. What you described sounds ok. If you don’t want the motors to spin when armed at lowest throttle then set Q_M_SPIN_ARM to 0.0.

As for prop sizes, I don’t remember what you are using for motors. Most of us are using the 13x8 Wood Prop Set from FoxTechFPV on the front motors because you need the higher pitch for forward flight. I’m using a 16x5.5 carbon t-style prop for the rear but that size depends upon the motor you are using. Refer to the posts above or follow the FoxTech setups.

Hi Chad,

Great color scheme!

Let’s focus on this issue above first. I don’t have a PH2.1 but connecting the SDP33 directly to the I2C port should not brown out the GPS. Your parameter settings look correct, however, I would keep ARSPD_USE set to zero until you have verified and calibrated the sensor through a flight.

Try disconnecting the SCL and SDA lines so that only the +5v and GND lines are connected. Does the GPS unit (which is fed by the PM) still brown out?


Just for check: Here is the pin assignment of the sdp33: New SDP33 Airspeed Sensor and Ardpuplane

Thanks for the help Greg!

I’ve been refining that paint job for a very long time :slight_smile: This version also has a 3mill laminate on wings and rudders to help with the degradation that foam in the field incurs :slight_smile:

  1. The SPD3x guys say the airspeed sensor does not require calibration at all, is this not correct?

  2. I fired her up as is to verify that the problem still exists (I swear they can magically go away), it does still exist. Further if you unplug the sensor the compass/gps unit does not come back.

  3. I manually cut the data and clock wires and after the PH2 stabilized from bootup I plugged the sensor in directly and the HERE module did brownout as before…reversed power wires???

  4. I rigged up a connector (using the white striping to orient the connections) so I could swap the power leads individually:

  1. I noticed that the connectors are one “up” and on the other side they are one “down” which might explain the brownout issue as the connectors I bought are both one “up” on each side so when you plug that cable in the pinouts are reversed!

  2. When hooked up the connectors to the bird as shown above no brownout occurs.

  3. I then plugged in both the clock and data connectors to this setup and turned her on:

  1. No brownout occurred and the airspeed indicator on the HUD is a rock solid 0.0 which is the behavior I saw with my previous franken-VTOL aircraft.

I blew in it and IT WORKS!! YAY!!!


  1. Now that it is reporting airspeed I did some further figuring, it turns out that you DO have to have this sensor completely hooked up before booting up the autopilot or it will not recognize the sensor. This fact played a part in the confusion I was having.

  2. One connector up and one connector down was a detail I missed and explains a lot.

  3. I now have to find a way to be able to plug in the battery and keep the sensor attached unless anyone knows of a way to make this work otherwise? I can’t see Foxtech or others not knowing about this issue.

  4. I do remember reading about this problem but I don’t recall what kind of airspeed sensor they had.

  5. Doing a pre-flight calibration does NOT make the sensor work if you did not have it plugged in on bootup.

  6. Doing a Preflight Reboot Shutdown command DOES make the sensor work. I am not happy with using this option as it means I am adding another thing that can go wrong in the field and I am booting twice while having to connect the nose cone (which is more stuff that can go wrong and is not as good as having a permanent connection)

I put the airspeed sensor in the fuselage with long silicon tubes between it and the pitot tube on mine, now it is always connected even with the nosecone off, works great.

I know that the position of the airspeed tube is important, where did you attach yours? Got a pic?

The tube is in the same position, on the tip of the nose, just the sensor has moved to under the battery tray, I also did away with the PCB and connectors.

Here is my contribution, A mount for the Pixhawk 2.1. The holes on the bottom are for attaching spacers for the Mateksys FCHUB-6S power distribution board.

Nimbus 1800 AP Bracket v3.STL (522.0 KB)

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Thanks Greg: I checked Fox Tec put a ruler on a 17.5.5 inch prop they use for the rear motor wow that would almost hit the body and the V tail wouldn’t that cause prop wash vibrations to the plane? My motors 580 kv front and 400kv rear,I do have a spare 320 kv motor from one of my heavy lift X8 Octo’s I can use if it’s needed


So, instead of having the sensor and the tubes in the nose cone and running a wire between the nose cone and fuselage you have the two silicone tubes running between the nose cone and fuselage?

Yes, just the two tubes, they nice and flexible so tuck away in the nose cone when it’s on and don’t kink.


See post #108 for my results using the 400Kv motor and the 16x5.5 carbon t-style prop. It works great!


Thanks for posting the pinout diagram.


To be clear, we have been calibrating the SDP33 setup once. Set (ARSPD_AUTOCAL=1, ARSPD_USE=0, ARSPD_SKIP_CAL = 0) and then compare the AS sensor log graph with the GPS ground speed log graph for a sanity check. If it all looks good, then reverse the settings (ARSPD_AUTOCAL=0, ARSPD_USE=1, ARSPD_SKIP_CAL = 1). Details are in the WiKi below. Perhaps @Rolf can comment further on this.

Calibrating an Airspeed Sensor

Using the Preflight Reboot Shutdown command on either MP or QGC works just fine.


For those of you using a FrSky Horus 10/12 with APM will soon be able to use a new Yaapu Widget mapping feature from Alex Apostoli. This is still experimental but seems to be working on my transmitter. Any three position switch can be assigned, in my case SA, to change between the normal main HUD, MavLink Message screen, and Map screen. Shown below is the map screen from my house which requires the GPS sensor to be discovered through Ardupilot. A second zoom switch, in my case SB, can be assigned to change the zoom from three different levels.

For long range fliers, the GMapCatcher User Wiki shows you how to set a path and then download the area maps that would be included in a visual path. Shown below is a 100km path from my flying field in Rochester, NY to Niagara Falls. Buffalo, NY is just below and Toronto, Canada is on the upper left.

I don’t think the Horus can do a screen snapshot or I would post some images from the field. The new mapping feature adds convenient position tracking right on your transmitter screen. It can be used with or without a GCS.


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Hi Greg: So everything seems good except when i switch to FBWA the Back motor does not stop in forward plane mode what param controls this function?? I ordered the props and will keep the 400kv in the rear motor with the 16.5.5 props yours looked good enough for me Thanks B.K

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I haven’t done a ground test in so long that I can’t remember what happens. Perhaps the FC is looking for sufficient speed in the plane before it disables the rear motor. It is stuck in transition mode. Maybe someone else knows…

Hi Greg well i started in q-Stab, then went to Q-Hover then FBWA throttle was in the middle i don’t have a AS sensor yet so maybe i should disable it to see if that works. Thanks B.K

Hi: Greg how or what are the motors rotate ie= CW LF, CCW=RF Rear= CW?CCW what are they supposed to be. Thanks B.K