Arming the motors, Running the Motors and checking their direction of rotation

First, look closely to the 4-in-1 ESC. At the point where the white cables have gone out, there are four marks S1 S2 S3 S4. These correspond to the 4 white signal cables. S1 to S3 correspond to the first three white single pin signal cable. S4 corresponds to the white cable in the 3 pin cable.

You can also see markings of M1, M2, M3 and M4 corresponding to the four motors. S1 controls M1, S2 controls M2, S3 controls M3 and S4 controls M4.

S1, S2, S3, S4 can be connected to any sequence of APM output pins marked 1, 2, 3, 4. For now, we are not going into the sequence. We just want to see whether motors are running and note their spinning direction.

Before we do that, disconnect any battery and connect USB to APM, start mission planner and disable "Pre Arm Safety Check". Since we have not connected it in the frame and don't have the GPS / Compass etc. attached at this moment, the system may fail the safety check and may not allow this testing. So we disable it for the time being. Later we need to enable it again. This is explained in http://copter.ardupilot.com/wiki/flying-arducopter/prearm_safety_check/ . Write parameter and detach USB when done.

Next connect the 3 pin connector corresponding to S4 in APM output pin 4. The black wire should be outwards and white (signal) wire inwards. Connect the battery with the ESC. The beeps and musical tones should be heard if everything is ok. Turn on the transmitter and pull the throttle stick towards bottom-right corner. This will arm the motor. Once arming is done, blinking red light in APM will stabilize. Now push the throttle up a little bit and the motor corresponding to M4 will start to rotate. Keep note of its direction. Switch off the radio and unplug battery.

Next connect another single white signal cable...say S3 in any of the pins 1 to 3, say in pin-3. Do not take out S4 because it also supplies power to APM. Now connect battery again and after the musical tone stops, switch on the radio transmitter and arm motors by pulling throttle to the bottom-right corner. Once red light stops blinking, push up the throttle and this time both the motors M3 and M4 will rotate.

Similarly connect the other signal cable in pin-2 and pin-1 and check the direction of rotation. In fact you can connect all of S1-S4 cables at once in pins 1-4 of the output at the same time and check their direction of rotation.

So the system is perfectly working. All we need to do is to
- decide which two motors would be the front motors and which two would be the back motors as per the Quad-X diagram in http://copter.ardupilot.com/wiki/connecting-the-escs-and-motors/ .  Accordingly we decide which of the S1-4 cables go to which of the APM output pins.
- adjust their spinning directions as per the diagram. To reverse the direction of any motor, we simply swap any two motor cables connected using bullet connectors.

Its best to do these two things after mounting is done on a frame. But it can also be done at the current stage.

Hardware Assembly of the internal parts of the Quadcopter



Finally, the Hardware Assembly of the internal parts of my new Quadcopter has been finished. A major part of the software calibration has also been done by connecting the APM Flight Controller with the PC using a USB cable and Mission Planner Software. The only thing that remains to be done is mounting these hardware on the frame, fixing the rotors, actual flight test and fine tuning of the parameters of the flight controller using Mission Planner software.

In this photo I have marked the major components of the complete hardware assembly which I have done so far without actually mounting it on a frame. Hopefully this will be helpful for the beginners as most of the photos and videos available on the internet show the mounted photos only, which make it harder to see what goes where. Also refer to my previous posts for details on the software configuration.

I am an absolute beginner...so my thread is oriented towards absolute beginners. APM is supposed to be difficult for a beginner but "difficult" is a relative word. No question is silly or basic. So if any beginner is interested to know anything, go ahead and ask and I'd reply within my limited knowledge.

hii ..am unable to arm my apm2.6,do i need to disable the pre arm safety check!!!its really frustrating

First you need to learn which kind of pre arm safety checks are carried out and need to identify in your quad which one is failing. These are available at http://copter.ardupilot.com/wiki/flying-arducopter/prearm_safety_check/

While actually flying you need to have those safety checks in place otherwise, either it won't fly or it will crash or fly away. In my case, I was calibrating some of the things even without assembling the quad fully. For example, I calibrated the GPS and Compass and then took it off before I tested out the motors (not actually flying...but checking the direction of rotation for example). Arming the motor was necessary for that. But due to the absence of the GPS/Compass, it would have failed pre-arm safety check..so I disabled it.

But if you are finished with everything and plan to arm the motors for flying, then you should not disable pre arms safety check. If it fails, you should try to find out why its failing and address the problem. If you are sure that the safety check is failing due to issues which won't affect your quad's security, only then you can disable safety check fully or skip some of them.

@Shyam, what is the failure shown during prearm check ?

there isn't any failure showing in the hud.with the usb plugged in when i try to arm it says non rc receiver and failsafe!!

Could it be that Radio failsafe is triggered due to some reason?

See http://copter.ardupilot.com/wiki/configuration/throttle-failsafe/

By the way, did you try without USB plugged in?

yes i tried without usb but no luck.is there anything to do with radio showing "set  throttle idle"

Could be. When you move the throttle up/down, does the message go away at any point? When you pull down the throttle to its minimum position, does it still show "set throttle idle"? In that case it might need calibration. Which radio do you have?

no..the message is only shown during start up rest is fine

Did you disable prearm check and then try?

I hope radio is set at Mode 2 and not Mode 1.

Which is our radio ?
And do check the radio calibration screen to see whether the bars respond accordingly to the stick movements.
If it says " set throttle idle " that indicates a bad calibration, so try redoing the calibration procedure, before that , let me know which is your radio, so that I can help with setting up the radio options.

In which step are you stuck ?
Have you done accelerometer calibration and radio calibration ?

it says throttle not idle and am using 9xr

Make sure your Channel order is - AETR - , And Mode 2.
Better off starting with a new model memory.

at last after 4 days i got my motor armed!!! but after increasing 5-10% power  throttle moves to full. i dint get it!!!

Maybe calibration is required.

Mounted the components on a frame. This is just a makeshift mounting to test whether its able to fly.



Made some mistakes which I'd rectify in the final build. But its also a learning process.

- Tried using a long M3 screw which impacted the coils and damaged a motor. Always be careful about the length of the screw you use in a motor.
- So I had to get a new motor. But identical ST360 frame motors are not available. I got a similar ST2210 motor from http://www.quadkopters.com/product/brushless-motors/st2210-1050kv-brusless-motor/

The problem is that mismatched motors can cause issues. The exact specifications of the motor which comes with the ST360 kit is not fully known. It is said to be a ST2210 motor. I have seen videos which show quads flying with dissimilar motors..so I guess it will not be a big issue. But ideally, all motors should be the same. The new motor has a different shaft size. It is better because the original kit motors need prop adapters to fit the props. Those tend to become loose and fly off unless carefully tightened. The flipside is that one prop could be at a lower height than others with adapters. In my case, the height seems almost the same.

However this new motor requires M2.5 screws. The ones that came with it are too short and won't reach through the ST360 arm holes. So I had to scour Chandni Chowk area in Kolkata and found that only one shop (Kali da's shop within the market) had such screws of the right length.

- I mounted the vibration damper for the APM in the wrong way. I should have installed in along the forward direction of the frame (two yellow arms). So I chose to mount the APM FC vertically on the damper and mounted the receiver alongside. Alternatively I could have mounted it along the damper and assumed a different "forward" direction. But this may lead to confusion .. so I didn't do it. Another option is to mount APM in any manner as you choose and then set the direction offset through Mission Planner to compensate for direction. This is probably what I'd do when I finalize the build.

- The 4-in-1 ESC took all the space and since I did not attach the battery strap before mounting the ESC, now I have to think of another way to mount the battery  

Anyway, these are not big issues. Careful planning and a bit of experience will make it easier.

The next problem I faced was that quad would not lift even at full throttle.

If this issue happens, this is easy to solve. Connect APM with Mission Planner and check the THR_MAX parameter. Most probably its set to 80. Change it to 1000. And the rotors will generate enough thrust to fly the quad. If it still doesn't, there could be other issues like fixing props in the wrong direction etc.

But my quad does not fly yet. It flips over. Its a common problem and there could be a host of issues involved, including the issue of one mismatched motor in my case. I hope to resolve the issue as well. Some of the probable causes are mentioned at http://copter.ardupilot.com/wiki/common-appendix/troubleshooting/#Copter-tilts-flips-over-or-wobbles-crazily-when-I-try-to-take-off.

The problem with ST360 frame (and many other frames) is that there is a lack of mounting space. Moreover, the 4-in-1 ESC that I used took up all the centre space. A battery hanging from a battery strap is not a safe proposition. If you hang the battery below the quad, there would be hardly any space left for mounting a camera, telemetry, FPV etc. Moreover, with the battery mounted at the bottom, the landing gears won't reach the ground and quad would land on the battery and would never remain horizontal.

A cheap jugaad undercarriage can easily address the problem. I took a "Lock and Lock" lunch box which are sturdy and have four locks on the sides which won't open accidentally. I mounted the base plate of the quad frame on the cover of the lunch box by making two M3 sized holes using heated M3 screws and then used M3 screws and bolts to attach the cover of the lunch box.

Then I heated up my soldering iron and made a square hole on the side of the box to take out the battery connector. I also made three slits below the box. Two would have been sufficient but adding a third gives the option to place the battery on both of its sides. Then I placed the battery within the lunch box and using the "bumblebee" battery strap provided in the ST360 kit, I fixed the battery with the base so that it won't slide within the box while flying (and shift the Centre of Gravity). That leaves lots of space inside the lunch box on both sides of the battery as well as on the upper cover of the box to mount telemetry and camera in the future. The box itself is also large enough to act as a stable landing gear. A bigger sized lunch box can be selected, if needed.

Now, I have a landing gear cum battery holder with space to spare for future connections. 

Check the attached photos.

Finally, the quadcopter flew. The joy was short-lived with the news of the passing away of Dr. APJ Abdul Kalam coming in. Just yesterday I posted about writing a letter to him regarding the issue of the DGCA ban on UAVs.

Dedicating my quadcopter to Dr. Kalam. He always inspired me.



Managed to find out why the APM Copter was flipping over. The reason: wrongly connecting the ESC signal cables to the output of the APM flight controller. Please ignore the connections of the ESC with the APM output which I mentioned earlier. The diagram above shows what actually needs to be done.

In case of separate ESCs, the connection is simple. ESC from Motor-1 goes to output pin-1, ESC from Motor-2 goes to output pin-2, ESC from Motor-3 goes to output pin-3 and that from Motor-4 goes to pin-4.

In case of 4-in-1 ESC like this one, it would be like as shown in the diagram. Since I placed the ESC with the red side downwards, the motor connections were as follows:

Quad Motor-1 with ESC M1
Quad Motor-2 with ESC M3
Quad Motor-3 with ESC M2
Quad Motor-4 with ESC M4

Now the signal cables on ESC, S1, S2, S3, S4 corresponds to the Mark on the ESC M1, M2, M3, M4
APM pins are marked 1,2,3,4 where connections from the Quad X motors are supposed to go.

So, connections will be as follows:

Quad Motor-1 <=> ESC M1 <=> S1 <=> APM Pin-1
Quad Motor-2 <=> ESC M3 <=> S3 <=> APM Pin-2
Quad Motor-3 <=> ESC M2 <=> S2 <=> APM Pin-3
Quad Motor-4 <=> ESC M4 <=> S4 <=> APM Pin-4

With these connections, the quad hovered without any problem. Tested all the controls and they worked perfectly. Even with a dissimilar motor, no issues were noticed.

Next I'd start fine tuning the APM settings.

@santanucus

Good to see you finally got it working! 

I'd like to apologise for some of the curt replies earlier. Sometimes we forget we went through the same phase. I replied to some of your queries in a hurry, wrongly presuming the context.

Do share with us your next flight video!  

No issues Thanks.

Here are some pictures of my "Flying Tiffin Box"  

Outdoor flight is difficult due to the rains. Moreover lots of fine tuning remains to be done. Hope to get some outdoor videos after fine tuning.

Before I go for adding FPV capabilities to the quad, I organized my "tiffin-box" quad and tightened up the loose parts.

- added a foldable GPS/Compass mount
- used zip tie to organize the cables from ESC to Motors
- added a plastic casing to protect the APM FC and the Rx from direct impact. This is the case from a 50 CD spool which I already had at home. I had to cut it along the 4 arms of the frame and made a hole to insert the GPS cable. It is not made of strong plastic and is flexible type. So wrapped it with some cellotape to strengthen it up a bit. It was a perfect fit - not too small and not too big.  Too big a casing would increase the chance of impact from the propeller.

So far it flies well, although its getting heavier. I haven't weighed it yet. Hope it would be able to fly with FPV and all. Here are some pictures.

Is that ST360 kit from QK?? the one that comes only with motors and frame.?