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DC actuator design

Discussion in 'Motor actuators and drivers' started by CalSim, Sep 3, 2014.

  1. CalSim

    CalSim building things

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    @SeatTime Thanks a lot for your answer. A grab screw is my first option for sure, but check the dimmension of the pulley. The hub is too big and i have not the proper tool to screw the hole. in a local mechaniser they told me that their tool would hit the flanges on the top. that video shows the basics of the idea. I've seen it lots of times :):)

    eaorobie suggested me to use a manual tap screw with a bar welded to extend it. that will be my final choice, but first the hole has to be made anyway. If the main shaft is broken due to the hole ( which i doubt ) i can buy a pair of shafts for <15€ and i will look for that tool.

    Im actually working on the pololu, wirings etc, and until i receive the shaft coupler and the pot syncro system.... cant test it

    @RacingMat I'll check that thanks a lot

    Greets
  2. CalSim

    CalSim building things

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    @RacingMat That flexible coupler is to connect the pot? on the same shaft of the motor?

    I plan to transfer the forces from motor to main shaft with a solid coupler. That main shaft has a small 72teeth pulley and the pot has a 15teeth pulley, both 9mm the smallest i found. it makes a near 4.8:1 reduction. as 50cm of linear belt movement is 1.37 turns on its pulley, (the same that the shaft) I spect 6.6 Turns on my pot.

    Thats the way i'm sensoring it, not with a flexible coupler. I've also checked the posibility of using 2x 0.8M pitch gears, but 30€ more expensive for 1 actuator.

    Whas this the reason you suggest the flexible?

    Thanks
  3. RacingMat

    RacingMat Well-Known Member Gold Contributor

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    >That flexible coupler is to connect the pot?
    yes, this way you prevent shear forces to wear your pots...

    if you mount pot onto the motors, it's less necessary (I haven't)
    if they are mounted on the plateform base, it's mandatory for durability
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  4. CalSim

    CalSim building things

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    Nop, the coupler is a 15mm x 20mm, not for the pot. on monday I spect to receive the small pulleys, then i can assemble the pot section, and show you. then you will see where my shaft coupler is and why it is solid.

    greets
  5. CalSim

    CalSim building things

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    Hi guys I got the solid coupler.

    IMG_5336.JPG

    Here is its final place.

    IMG_5337.JPG This is why i choosed the solid model, i though it was essential in that piece.

    This is an overview of the actuator.

    IMG_5334.JPG

    No electronics finished. need to fix motor to the side first, and need to open a 45mm hole on the shaft side to let the coupler introduce to the side and close down the motor to the external shell. Since i dont have the correct crown to drill it have to wait until tomorrow. Tomorrow I spect to receive the small pulleys and then i can mount the pot and show you. There is also a fan grid incomming. Imprimation paint is on the way too and im still thinking on color, any suggestion?? :p

    Dont horror about the size, think i'm planning 50cm travel, and possibility of software changes ( just limit the pot) to achieve up to 70-75cm of travel, since i have some range on the pot turns ( used only 6.5 / 10) and some space ( still to determinate )

    :grin

    EDIT: photo makes some distorsion, note dimensions are (mm): 180 x 270 x 950.
    Last edited: Oct 7, 2014
  6. bsft

    bsft

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    nice job there
  7. CalSim

    CalSim building things

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    Well some updating. I've burned 2 pololu dual VHN5019 and the third is spected to work. I have no progress until electronic works, but i've made the screws to the pulleys and installed everything, here are some photos.

    IMG_5447.JPG whe whole thing
    IMG_5448.JPG Quality belts Continental german belts.

    IMG_5449.JPG Finally made 2x m6 grabscrew holes on each pulley
    IMG_5450.JPG Some oil to avoid rust on every shaft

    IMG_5457.JPG Wiring diagram made by me, will do it with paint or something when have time.

    I think the next will be a video of the thing moving.... Not many things to show you until it works.

    I must say it actually works, it follows the target but i made some mistakes with the drivers wiring and screwed it up.

    At braking the belts are holding 40kg, Did not test any more, that was without power haha, but phisically it does not seem to fail. Lets see how the pololu handles power peaks.

    More soon
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  8. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    Nice job, am looking forward to the video.
  9. CalSim

    CalSim building things

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    Well new pololu and new wires and new procedure to make it work.

    IMG_5503.JPG Clean solder.

    IMG_5505.JPG Ready to plug.

    I tested a 7.4v lipo and the Traxxas motor. Everything was ok.

    Here is the result. I'm affraid now this is working i dont want to kill them with high values.

    What do you recommend for now?



    I was not able to stop it with 1 hand. Also did not want to trap my fingers with pulley haha

    Now:

    When the motor reaches the target, it inverts and backwards. how do I configure to use the "coast mode" ??

    I learned in the slot cars world that if you connect both terminal of a DC motor, it brakes. Is this the "coast mode" ??

    I want the motor to brake, and when the pot speed is 0 ( motor speed 0) start to reverse. I think I would have a faster direction change, since this motor is 4900rpm and gear makes 80 rpm with 60:1, and takes hard to stop it.

    I know this can be pòssible with the SMC3 util, but please show me some light on what parameters and how much to start trying.
  10. CalSim

    CalSim building things

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    Well, now, with same parameters there, 1 direction stopped working properly, just like the first pololu that I lost 1 dir on 1 channel.

    It works down, but only sometimes up, and it makes a strange noise. Also, when I run constant down, the motor does not stop and does it perfect. when the motor works "up" constant, the motor stops after a few secs, and does not work for that direction. After some direction changes on the pot(<-- with this i mean to pass over the target line manually), it works again.

    As you have seen on first test, it was working perfectly, following the motion target line. Nothin was changed and that problem arrived again.

    Waiting for some answers. Maybe a code fault? Dont know.