Register To Comment
Page 11 of 18 FirstFirst ... 910111213 ... LastLast
Results 101 to 110 of 171

Thread: [FW] Tracked 4WD Lifter: Aegis

  1. #101
    No notable progress since last update, but I have been thinking. As you might know, I'm converting an already-existing linear actuator for my lifter, and I'll be using a brushless motor. One of the problems I'm facing however, is limit switches. I'm pretty sure the way the current limit switches in the linac work is that when depressed, they divert the current through a diode, meaning the motor can only run the opposite way until the switch is released again. This is obviously fine for a brushed motor, but since a brushless motor has three leads which require the timed input from the ESC, I can't use that. Basically I want it so that when the linac reaches its limit, the motor stops, and can only run in the opposite direction.

    Now the idea I came up with today was to create a separate little board which switches two of the input wires to the motor (with a FET or something) when either switch is pressed. As far as I know, this should make the motor run in the opposite direction until the switch is released, and then switch back. I'm unsure about this for a couple of reasons though. One is that this will probably make the linac jitter at its limits, depending on the switching frequency, positioning of the switch, etc. This wouldn't be so bad on its own, because all I really need the switches for is stopping the gear system or motor from being damaged, they'd just be a safety measure in case I didn't take my hand off the transmitter in time. But the other thing is, when this 'jittering' is happening, would the quickly changing current fry the board and/or my motor? Otherwise, does anyone know how to integrate this kind of one-way limit switch behaviour for a brushless motor? I don't quite want to go to the lengths of making a custom ESC just yet, this is still my first robot after all. I also don't want to have my actual ESC turn off at any point, since there's a startup time in which the weapon would be inoperable. Has anyone got any ideas?

    Cheers guys.

  2. #102
    I'm sure I researched this very thing, and what I discovered was that reversing two of a brushless motor's wires while it was spinning wouldn't change much; it would just keep spinning in the same direction until it stopped. As far as I'm aware there's no way to do it outside of using a separate microcontroller board (such as an Arduino) to modify the RC signal sent to the ESC when the limit switches are depressed. I had also considered that if the microcontroller on your ESC has unused pins, you could probably program some new firmware to accept the limit switch inputs on these pins and react accordingly. I would definitely be interested to hear if there's a simpler option, though.

    Edit: Found the source of what I wrote above: http://www.robowars.org/forum/viewto...dc16f453#88220
    Last edited by epicentre; 7th August 2016 at 10:49. Reason: Added source

  3. #103
    Another option is to turn the system into a giant servo by adding an Arduino and a potentiometer as discussed here: http://www.robowars.org/forum/viewtopic.php?t=2215. In this thread we are talking about using a brushed winch motor but it will work just a well with a brushless motor. You can alter the code to work with limit switches without too much trouble.

  4. #104
    Thanks for the advice guys. It doesn't sound easy, but I do like the idea of using an arduino to intercept the RC signal. Looks like I'll need to do some research. As for the 'unused pins' idea, I have the stuff to program ESCs, but I have no real idea how hex files work. I could give it a try though. I guess there's always the alternative of adding some sort of slip clutch in the gearing, but I can just imagine that breaking and rendering the weapon useless in the middle of a fight.

    -Edit:
    Found some resources, I'll put them here for later and anyone else that reads this in future. Looks like this isn't as difficult as I thought.

    https://www.sparkfun.com/tutorials/348
    http://rcarduino.blogspot.co.uk/2012...iver-with.html
    Last edited by R9000; 7th August 2016 at 17:45.

  5. #105
    Been working on the arduino stuff, getting there. It's easy enough to read the input and print it out to serial, but I'm still struggling to output and make the ESC act on that. Regardless however, more importantly is that I sort out the actual connection between the new motor and the linac. I'm not sure how I'm gonna do it. The brushless motor I have is STUPIDLY fast at full tilt, so I need some heavy gear reduction. The current linac gearbox has plenty of gearing which I think should stand up to the force from the motor, provided I get the limit switches working, however I'm going to need some spare gears if I'm going to even start connecting it. I've measured the gears inside, and on one with a 1 and 1/8th inch diameter and 50 teeth, I've calculated a pitch of 44-ish, so a modulus of 14. Does that sound correct? Thing is I can't seem to find any 44 pitch gears online - am I doing this wrong somehow? I thought about using a belt which would hopefully reduce damage if the motor is still running at the linac's limit, but I wouldn't get the reduction ratio I need to decrease the speed sufficiently in any kind of reasonable space. A really solid and compact option would be a worm gear, but the motor's kinda at the wrong angle for that. If I can finally work out a gear arrangement I can get a gearbox/mounting plate cut out of aluminium, but I'm struggling to even find gears that fit - any ideas? Am I doing something wrong?
    Last edited by R9000; 19th August 2016 at 04:01.

  6. #106
    I can't make head nor tails from your description of the gears you meassured.

    It's the Imperial DP (how many teeth on pitch of 1" diameter.) or DIN standard module.

  7. #107
    Ok, sorry let me try to be clearer. I measured the diameter of a 50-tooth gear (excluding the teeth) to be approximately 1 and 1/8th of an inch. So to find out how many teeth on one inch, I divided 50 by 1 and 1/8. This gave me around 44 for the pitch. Is that correct? Sorry if I sound clueless, this is the first time I've worked with this kind of mechanical engineering.

  8. #108
    I'm baffled how expertly you can convey confusion in this.

    Lets start.
    You need a gear with 50 teeth, and with an outside diameter of about 29mm .

    The 2 common "types" of gears are Imperial DP or Metric Module.

    if I use the WAG methode, I get these results.

    Metric
    Mod 0.5 Z50= OD of 26mm
    Mod 0.6 Z50= OD of 31mm


    DP 44, that's a non excisting size. It jumps from 32 to 48.

    2 possibilities.
    1) meassure again to get better values.
    2) it's a custom size gear.

  9. #109

  10. #110
    Daveimi:
    No. Way back when I was searching for linacs, I couldn't find one that gave enough force and moved fast enough. So I bought the one I have now, which can lift about 20 kg, but is slow, and then I built the robot around that. The distances between the end of the arm and the brackets I had cut are all set to fit the linac I have.

    Maddox:
    I was using this to calculate DP: http://www.robotpark.com/academy/LR/..._ROBOTPARK.png
    I'll try measuring again, honestly the most important piece of information there is that DP 44 doesn't exist. But if I'm working out the pitch correctly, I don't understand why I seem confused to you. A 'yes' or a 'no' to that would've been most helpful. :P

    Edit-
    I measure approximately 29mm/50 = 0.6 metric module (rounding here) for the gear. This sounds more likely. I suppose I'll try buying a cheap 0.6 mod gear to see if it meshes, just to make sure.


    Last edited by R9000; 19th August 2016 at 15:10.

Register To Comment

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •