Mikrokopter Precision I2C to PWM converter

[RTRyder]

Do you like Mk flight controllers but don't like being locked into using I2C controllers with it? There's a great way to fix that problem for not a lot of $, http://abusemark.com/store/index.php?main_page=product_info&cPath=1&products_id=3

After building my X8 project using standard Turnigy Plush ESCs I wanted to try flying it with an Mk controller but there was no way I was going to spend the $$$ for 8 BL controllers. While surfing other sites I came across a thread on the Precision converter as well as one from a website in France. After a bit of research it looked like the Precision was the better board and it certainly cost a lot less as well so I ordered two of them, came to less than $35 delivered.

Today I finally got a chance to set it up on the X8, pretty simple really. Solder wires with a servo connector to the I2C pads and ground on the bottom of the MK F/C, set the converter for the number of motors by bridging pads on the bottom similar to setting the address on a MK BL, then connect all the ESC wires to the converter (power to the converter is supplied via the BEC on the number 1 ESC). Use a Spektrum bind plug on the converters I2C connection on the first power up to calibrate the ESC's, power down and connect the I2C lead from the F/C and you're done, that's all there is to it.

Seemed too easy to me so I made sure to take all the props off and give to a thorough bench test before attempting to fly but it appeared to work perfectly so I put the props on, went out in the backyard, started the motors and lifted it in the air. Worked exactly the same as any Mk, I couldn't see any difference in how the motors ran or how it flew. Only thing I did notice was some of the motors stopped spinning after landing before I did a shutdown. That concerned me a little so I restarted the motors and lifted off again, of course all the motors stayed running on the next landing! After a couple tries I was able to reproduce the motors stopping on their own so before using the motor shutdown sequence I gave it some throttle and the stopped motors spun up again so I don't see that as being a problem at all.

Overall this may just be the best $15 I've ever spent on an MK!

Ken

 

[Bartman]

Ken,
Could the brakes on the esc's be set to on? I'm sure you're familiar with brakes but for everyone else, many standard ESC's have a brake function that will stop the motor from turning when the throttle is set to idle. It's very handy for electric powered motor gliders where you'd want to stop the prop from spinning when the power is off and you're just gliding around.
What would be considered a top quality ESC that is also affordable to use with an MK and these converter boards?
Thanks,
Bart

 

[RTRyder]

No brakes on the Turnigy Plush ESC that I'm aware of, I think its probably just a quirk of how the converter interacts with the MK. If you land a bit off level with the thottle at minimum the F/C may send a signal that's below the start point of the esc to try and get the frame back to level by varying the motor speeds just as it would if flying. Since you would never encounter this situation while in the air I don't consider it a problem. Setting the minimum gas setting a bit higher would probably cure it and I may do just that next time I take it out to see if it does.

This particular coverter board was designed around using Turnigy Plush ESCs and their various incarnations (Hobbywing, RCTimer, etc) though it should work with just about any ESC of similar spec. Generally if the board can be programmed via a card or through the TX it will most likely work fine. I certainly wouldn't use anything more expensive than something like the Turnigy's if you get into the $50 PWM ESC range you might as well just use the MK BL 1.2 unless you need the current capacity of the 2.0 series.

Ken

 

[Bartman]

Thanks for the quick reply Mr. Ken. I'm not in love with the idea of Turnigy anything anymore. I'm considering my options for my new Okto and as much as I'd like to save money on parts, I don't think I'd trust it to turnigy stuff. I guess I could just shop around and see what good quality 40A ESC's are going for and compare that to the MK 2.0's.
Thanks for posting about that board.
Bart

 

[RTRyder]

Thanks for the quick reply Mr. Ken. I'm not in love with the idea of Turnigy anything anymore. I'm considering my options for my new Okto and as much as I'd like to save money on parts, I don't think I'd trust it to turnigy stuff. I guess I could just shop around and see what good quality 40A ESC's are going for and compare that to the MK 2.0's.
Thanks for posting about that board.
Bart

Well then, you may want to look into these, they've been reported to work fine with the Precsion board too! http://www.hobbypartz.com/volcano-40a-brushless-electric-motor-speed-controller-esc.html

I've done a fair amount of business with Hobbypartz lately and they've been great. Located in California you don't have to worry about how long it will take for the order to be delivered ( I order on Monday and it arrives on Friday ) and they're price competitive with anything HK sells so you won't be overpaying. I've bought a few of the Blue Lipos and so far they work as well as any other lipo I've bought, and I'm now using the Exceed Alpha series motors on all my KK quads. The motors have worked well so far and that includes stuffing them into the dirt a few times...

I've also been using the Exceed ESC's on the small quads since last summer and they've been more reliable than than the Turnigys, I've had a couple Turnigy go bad and zero Exceed go bad and I certainly beat the H**l out of them on the KK's.

Ken

 

[Bartman]

the nice thing about wiring up my own esc's is that i can build in true redundancy with the batteries going to the power harness. as it is with my Okto II, i have dual batteries but they feed to a single point on the power board. There's no safety built in if that solder connection ever breaks loose.
Thanks again Ken.
Bart

 

[DroneBuilder]

Only thing I did notice was some of the motors stopped spinning after landing before I did a shutdown. That concerned me a little so I restarted the motors and lifted off again, of course all the motors stayed running on the next landing! After a couple tries I was able to reproduce the motors stopping on their own so before using the motor shutdown sequence I gave it some throttle and the stopped motors spun up again so I don't see that as being a problem at all.

Ken -

The designer of that i2c converter has built-in an ESC throttle calibration routine. It is remarkably simple:
1) Disconnect your SDA and SCL lines from the FC to the converter.
2) Connect a "Bind plug" (you know, like is used when you are setting your receiver into 'bind' mode) in the place of where the SDA/SCL lines go into the converter. That is, short SDA to GND.
3) Power up the ESC's (with the battery)
4) You will hear the ESC's (since they are Turnigy Plush) go "beep beep . . . . . . . . . . beep".
5) Reconnect the SDA/SCL lines from the FC to the converter.

If you have already done that, there is one other trick to insure the motor stopping thing does not happen. Using MKTools, use the "MotorTest" and slide the throttle (on your PC screen) up a little. Default MK min throttle is 8. Most of my Turnigy Plush ESC's need a min throttle of 15 or 18 to insure that the motor actually starts spinning in the motor test.

Once you have established the correct number that successfully starts each motor every time, then set that as your minimum gas number and click on 'write' in MKTools.

You correctly report that it doesn't really seem to create any problems having the motors stop spinning, but it is discomforting to see, and seems like it could create a problem. So the min gas trick should solve it. I have a few of TC's i2c converters, and also a few of the "flyboards" from FlashRC. They both perform similarly, but since TC's has the built-in ESC throttle settings (and since it is 1/3 the price, and since he ships it cheaper and MUCH faster than FlashRC) I would strongly his converter over the other.

Also, TC releases user-updateable firmware from time to time, one more reason to buy his. I say this since I had to wait over six weeks to send my flyboards back to FlashRC for an upate after they found a flaw . . .

 

[Macsgrafs]

Where does one get the TC from?

Ross

 

[zorba]

Ken, I have these converters also. Like DB says you have to calibrate the motor startup.
Whatever value all motors start you use this +2. Mine are set to 15.
Also TC has firmware update on this post. http://www.rcgroups.com/forums/showthread.php?t=1399162
Also you have to calibrate the max and min throttle range.
Unplug the power from the FC. Turn on your Tx and put throttle stick all the way up. power up the esc's. You'll hear the beeps and cell count after 3 seconds lower stick to min gas then you will hear the confirmation beep. Now your throttle range is set.
Bill

 

[RTRyder]

I did the calibration when I installed the converter, read through all of the relevant discussions over on RCG. The only time I see the motor stop behavior is if the X8 lands off level, haven't tried it yet but I believe setting the min gas setting a little higher will fix the problem. Otherwise you'd never know there was anything different about it from flying, works just like an MK with BL controllers.

Where does one get the TC from?

Ross

I posted the link to them when I started the thread, here it is again... http://abusemark.com/store/index.php?main_page=product_info&cPath=1&products_id=3

Ken

 

[Macsgrafs]

Thanks Ken, I did add the link to my favourites, but I have so much in there that I'm confusing myself!!! I even read ALL that thread from start to finish, am now a touch more enlightened

Ross

 

[DroneBuilder]

you'd never know there was anything different about it from flying, works just like an MK with BL controllers.

Ken -

Would you be willing to post video of your X8 flying? Also - what frame, motor, prop and battery combo are you using on your X8? I have a keen interest in this because I have an X8 that flies like a wounded duck, and I need to get it back to soaring like an eagle!

 

[RTRyder]

Ken -

Would you be willing to post video of your X8 flying? Also - what frame, motor, prop and battery combo are you using on your X8? I have a keen interest in this because I have an X8 that flies like a wounded duck, and I need to get it back to soaring like an eagle!

I can, just not sure when at this point, rainy and windy today and possibly for the next few as well. I had it flying on altitude hold last evening and it held nicely, just need to get the GPS installed to see how well it holds position at the same time. See my X8 build thread for specifics of how its put together...http://www.multirotorforums.com/showthread.php?247-X8-build

Ken

 

[Bartman]

Ken,
If you use the converter then you don't need the I2C isolator, right?

 

[RTRyder]

Ken,
If you use the converter then you don't need the I2C isolator, right?

Correct, there's nothing that needs to be isolated without the BL's.

Ken

 

[RTRyder]

Coming along nicely

After work today I did more tweaking of the X8 and the I2C converter. Just to make sure the board has the most recent version of firmware I flashed it using the file available on the website. After that I put a bind plug on and let it do the ESC calibration routine again, then one by one I disconnected each ESC and checked the programming to make sure they were all set the same. Made a minor change setting the motor timing from low to middle. While I was working under the hood I put the rest of the Mk electronics stack in place so I now have GPS capability too.

Buttoning up the wiring once again I hooked up the laptop and got into MKtool, from there I enabled the GPS and then did a little testing of where each motor wanted to start up. The majority of the motors wouldn't start until the readout hit 15, a couple did start at 12. Most interesting part of doing the individual motor test was the how smooth or noisy each one was, the older motors that had been on the frame while it was a quad definitely made more noise than the newer ones installed in the X8 conversion.

Now that I had a confirmed setting for motor start I configured the minimum gas setting to be the same in Mktool and wrote the changes to the flight controller, the motors now all start and stop at the same time just as I expected they would. I did manage to get a short test flight outside between rain showers though it was a bit windy. GPS definitely needs to be tuned for the X8 though that will have to wait for a dry day but overall it appears to work just as well as the Droidworx AD-6 that donated the Mk electronics.

Its coming together slowly, just need some decent weather where I can spend time outside with the laptop dialing in the GPS and altitude hold settings then see how well it works on a waypoint route.

Ken

 

[zorba]

Sounds good Ken. It looks like we both sort of have the same setup.
I don't have the gps installed yet, is there a way for you to post the results of your gps settings once youre done so I can use them as a base starting point? I also like to see some pics of your rig.

Cheers
Bill

 

[RTRyder]

Ken -

Would you be willing to post video of your X8 flying? Also - what frame, motor, prop and battery combo are you using on your X8? I have a keen interest in this because I have an X8 that flies like a wounded duck, and I need to get it back to soaring like an eagle!

After an interesting day of attempting to dial in the GPS settings I think I can shed some light on the problem you're having. First, the I2C bus Mk uses to talk to the standard BL's is faster than the PWM communication you get with the converter, what that means is the reaction time of the standard ESC isn't quite what the parameters in the flight controller are tuned for. What I've been finding is the X8 either due to some unique characteristic of the coax configuration, or because of the I2C to PWM conversion, or some combination of both, is a LOT more sensitive to calibrations and parameter changes than either of my Hexas.

If you have an X8 with MK controller and I2C converter I suggest the following. Connect to the flight controller with MKtool and reset back to factory defaults. Manually change only those settings unique to things like Potis used to turn features on and off, minimum gas for proper motor start, camera settings, enabling altitude hold and GPS, etc., leave the tuning parameters at default for now.

Next do a COMPLETE calibration, accelerometer and compass, and make sure to get the X8 as level as you possibly can when doing the ACC, use a bubble level or a couple of them to make sure. I have one 3 foot carpenters level I use to make sure the surface I'm using is level and two 6 or 8 inch little bubble levels I use on the frame to make sure its level sitting on the level surface. Now do the accelerometer calibration and if you have the Navi and GPS installed then do the compass.

Do a test flight and I think you'll find its much better but still in need of some fine tuning, start with gyro stability, 8 is default, try 6, and also dynamic stability, 70 is default, try 65 first, if that makes things worse try 75. Whichever way makes things better, keep bumoing it in small increments until it starts getting worse again then back off to the last good setting.

Do one at a time and make SMALL changes, I'm finding very small increments can make a big difference in the flight characteristics. Once you find a setup that works fairly well make sure to save it to a file so you can get back there is further changes make things worse.

Ken

 

[DennyR]

Ken
I have been using the Abusemark and the Flyboard and they both do not start or stop properly, but they are ok once you get off the ground.

 

[llamatrails]

Have you set your MinGas value high enough ? I used MKTools to see what the motortest value needed to be for the throttle to start them reliably, and added 3 to set my MinGas. Problem solved.