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  1. #1
    Senior Pilot LesNewell's Avatar
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    ESCs - the need for speed

    Hi all. I have been flying tricopters for a while now and have started looking for an open source dedicated controller rather than using 4 heli gyros. The Aeroquad looks ideal for me. I have a background in electronics and programming so I like something that is very hackable. I took a quick look at the code and it looks to be pretty simple to add support for tricopters as well. M Holder's mixer table idea would work well for tris as well as quads, hexas etc.

    Anyway, during my research into tricopter stability I did some ESC tests. Most ESCs are designed for use in planes or helis where a smooth response is fairly important. Most ESCs have a low pass filter on the throttle input. This is added to make throttle response smooth and irons out any glitches but it very bad for multi rotor craft. After doing some research I decided to try re-flashing the firmware in some ESCs with the the firmware written by Bernhard Konze AKA Quax. This is specifically designed for fast response. Here is a video of my test results.



    A flight test in a strong wind. Sorry about the really odd video angle. I strapped a keychain cam to my head and didn't realize it was at an angle.



    The stability improvement is impressive. Apart from obviously having to keep flying against the wind the wind had very little effect on flight stability. Some others have also tried the gyro test in my first video on various ESCs and Turnigy plush do quite well. Castle creations ESCs do very well if you turn the throttle damping right down in their configuration software.

  2. #2
    Senior Pilot jpkh's Avatar
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    Hi LesNewell,

    Yes you are right, to obtain really good stability normal PWM BL's are not enought and some of AeroQuads are already using I2C based BL's. I have plans to upload Quax also to my Turnigy plushes, for many people hacking BL's is a bit problem and that's why I have been thinking to modify them and sell as modified to interested peoples.

    It's great to hear that you have been having good success with modified Plushes. Currently main AQ software does not support I2C bus for BL's but like I said, there is already few who are flying quads/hexas with I2C BL's so including that to main AQ software should not be a big problem. It's up to Mikro when it happens... and well naturally us all, we can do mod and Mikro just refines it to main code branch.

    And that difference what you did show on video.. well no need to comment the difference on speed

    Can you tell more about your Tri, I would like to build one by my self too...

    --jp
    Last edited by jpkh; 04-07-2010 at 10:50 AM. Reason: tyops...
    Flip, flop ummm heeeey what...

    Gadgets: 8 x XXXDuino's, 1 x Mega, 1 x ArduPilot/ArduIMU+, a lot of Gyros, Accs, XBees and other fun toys.
    Fleet: miniTitan E325 3D heli, PizyZap 100EP Secial 3D, Turnigy Piaget 3D Parkflyer, Clouds Fly FPV
    Projects: AeroQuad 1.8 with selfmade electronics, PhiHEXA 1.0 20Mhz FC, ArduCopter platform Leader
    Electronics: http://jdrones.com - jDrones, Drone & Electronic parts development

  3. #3
    Senior Pilot jpkh's Avatar
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    Btw... you should update your clock on your camera

    Try this.
    Connect it to your laptop, open main folder of it (folder where you can see DCIM folder)
    then create file called TAG.TXT .. yes in CAPITALS and make sure that it is TAG.TXT and not TAG.TXT.txt, depends on your windows settings how new file is created. Well if you use windows.

    inside TAG.TXT put following info

    [date]
    2010/04/07
    16:00:00

    and that's it, save it.. and put that time a bit in future like 2-3mins. Save it, disconnect from computer, shutdown your camera and then wait till you reach the time you put inside file.

    Switch it on, take small video and look video from your comp.. Also when you hook it up to your computer, TAG.TXT should have vanished..

    Tadaaa your clock has been reprogrammed

    --jp
    Flip, flop ummm heeeey what...

    Gadgets: 8 x XXXDuino's, 1 x Mega, 1 x ArduPilot/ArduIMU+, a lot of Gyros, Accs, XBees and other fun toys.
    Fleet: miniTitan E325 3D heli, PizyZap 100EP Secial 3D, Turnigy Piaget 3D Parkflyer, Clouds Fly FPV
    Projects: AeroQuad 1.8 with selfmade electronics, PhiHEXA 1.0 20Mhz FC, ArduCopter platform Leader
    Electronics: http://jdrones.com - jDrones, Drone & Electronic parts development

  4. #4
    Senior Pilot LesNewell's Avatar
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    These were HobbyKing Super Simple card programmable ESCs, not Turnigy Plush. They are virtually identical to the Towerpro 18A.
    I don't think I2C is really needed. PWM can easily go up to 400Hz which is plenty fast enough.
    This thread has a vast amount of Tricopter info. Tricopters use three motors for roll/pitch and rotate one motor for yaw. Stabilization can be done with one standard heli gyro per motor plus one for yaw. You use helicopter CCPM mixing to generate the correct throttle signals. This approach has a few drawbacks so I would like to have a go at doing all of the signal processing on-board.

    My tri has 3 DT750 motors mounted on 12mm CF tube arms. Each motor mount incorporates foam vibration dampers. The arms are then clamped onto the glass fibre frame using plastic blocks held on with nylon screws. In the event of a crash the nylon screws shear, preventing any other damage. For yaw the rear 12mm tube is mounted in a couple of ball bearings and is operated by a standard servo. The frame is ordinary copper clad fibreglass PCB CNC machined then soldered together. The excess copper is then etched off. This construction technique is very strong and easy to assemble.

    So far this setup has survived numerous heavy crashes with minimal damage though I do buy my nylon screws in bulk ;-)

    Btw... you should update your clock on your camera
    Yes I know. One day when I can be bothered, I will do it

  5. #5
    Senior Pilot jpkh's Avatar
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    I think towerpro 18 and turnigy 18 plush are also identical BL's. If that your Tri uses only 3+1 normal gyros, it's amazing stabile. Yes true you can easily use CCPM mixing for it..

    Looks like I need to order more BL's and few small gyros

    I2C is good because then you don't need to have so many PWM outputs from your main MCU and can use all free PWM pins to other things like drive tilt/pan servos for camera etc. For I2C you only need to wires + gnd and can have multiple devices connected to the bus.

    From where you buy those nylon screws? I've been looking for some time a good eShop to provide nylon boltds, nuts and also vibration dampers.

    --jp
    Flip, flop ummm heeeey what...

    Gadgets: 8 x XXXDuino's, 1 x Mega, 1 x ArduPilot/ArduIMU+, a lot of Gyros, Accs, XBees and other fun toys.
    Fleet: miniTitan E325 3D heli, PizyZap 100EP Secial 3D, Turnigy Piaget 3D Parkflyer, Clouds Fly FPV
    Projects: AeroQuad 1.8 with selfmade electronics, PhiHEXA 1.0 20Mhz FC, ArduCopter platform Leader
    Electronics: http://jdrones.com - jDrones, Drone & Electronic parts development

  6. #6
    Senior Pilot LesNewell's Avatar
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    Quote Originally Posted by jpkh View Post
    If that your Tri uses only 3+1 normal gyros, it's amazing stabile.
    Thanks. It uses HobbyKing 401b gyros in digital mode. I think they update at about 300Hz. They are pretty sensitive to vibration in digital mode.

    Looks like I need to order more BL's and few small gyros
    You can never have too many toys

    I2C is good because then you don't need to have so many PWM outputs from your main MCU and can use all free PWM pins to other things like drive tilt/pan servos for camera etc. For I2C you only need to wires + gnd and can have multiple devices connected to the bus.
    One slightly worrying thought is that if you have a failure in one drive it could quite possibly take out the whole bus.

    From where you buy those nylon screws? I've been looking for some time a good eShop to provide nylon boltds, nuts and also vibration dampers.
    I get them from RS components as I have an account. They have branches all over the world but I don't know how much they would charge for postage to a non account holder.

    I tried some from eBay and they were rubbish. They were more like wet noodles than screws.

  7. #7
    Administrator AeroQuad Founder Mikro's Avatar
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    Thanks for sharing LesNewell, looking forward to seeing your progress. I keep hearing about Quax's mods... does anyone have a link to his work? I'd would be interesting to see how one would convert a Plush into an I2C ESC.

    @Jpkh, I find to SO hard to keep momentum going with further software development. I love the fact that you are potentially willing to offer modified I2C ESC's (if it works out, let's talk if you want to offer it in our store). Just a warning, once you start offering something for sale, the time you spend for manufacturing, support, shipping does take away from the fun stuff, R&D! Hmmm... but sounds like you can hire people in your area to do such work?

  8. #8
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    Quote Originally Posted by Mikro View Post
    ...I find to SO hard to keep momentum going with further software development...
    My heart just skipped a few beats reading that. I/we need you big time to keep this train moving.

    Quote Originally Posted by LesNewell View Post
    ...Most ESCs are designed for use in planes or helis where a smooth response is fairly important. Most ESCs have a low pass filter on the throttle input. This is added to make throttle response smooth and irons out any glitches but it very bad for multi rotor craft.
    Is 12c faster than the analogWrite PWM we're using. The Aeroquad appears to be quite stable with it.

    I think 12c is a great idea as well. I like the idea of having multiple options since each one has it's own up and down sides. 12c ESC's are a little on the expensive side but probably prefered if you need super duper stable camera platforms and don't mind the price hit.

  9. #9
    Administrator AeroQuad Founder Mikro's Avatar
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    I remember battling this issue when we first were on the Quaduino thread (I2C vs PWM). That was when people thought PWM ESC's were not suitable for multicopters. It was fun making a point that I can make a stable quad with just driving the ESC's at 120Hz. We are now able to drive them at 490Hz (but with reduced PWM waveform resolution). Fortunately the Turnigy ESC's only see 128 steps (from RC Groups) so we are OK there.

    I2C is definitely faster at updating the ESC's, but we could get good stability (as demonstated by you guys) without those update rates (1000Hz). I have a half suspicion that maybe that's an issue we have with accel stabilization... maybe we need the faster I2C's? At this point I really don't know, but it would be good to see if we can run Stable Mode with I2C ESC's any better.

    Having the AeroQuad store is fun, but it is a LOT OF WORK. It's a challenge to keep everything stocked, making sure things ship out quickly and provide customer support. I remember reading up on a new non-profit multicopter venture, which was a bit hard for me to believe. Having to do this much work in a non-profit environment for an extended period of time would seem to de-motivate those workers eventually. Hey but who knows? Maybe they are more efficient in their workflow? But overall, this has been a blast to be part of this community and am looking forward to seeing what you guys can cook up!

  10. #10
    Senior Pilot LesNewell's Avatar
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    I think most of the problems with PWM driven ESCs are due to the built in low pass filter on the throttle. There is no point having a 400Hz update if the LPF has a cutoff of 5Hz. With a fast ESC I don't think much over 200Hz will make any real difference. How fast does the rest of the Aeroquad firmware run? There is no point updating the ESC any faster than the main loop cycle time.

    Having the AeroQuad store is fun, but it is a LOT OF WORK. It's a challenge to keep everything stocked, making sure things ship out quickly and provide customer support.
    Please don't give up. Just a thought - would it be worth looking into getting a batch of boards built for you? If you can't find a local business to do it there are plenty of Chinese companies offering board fabrication and building. Of course it depends a lot on how many you can sell.


 
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