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Thread: Brushless driven beetles

  1. #1
    Greetings! Scott here. Long time stalker, first time poster. I am interested in building a beetle weight robot and I wish to use brushless dc motors to drive it. This will be my first beetle weight robot but I am under no illusions on the challenges I will face.

    So anyway, my first point of call is finding a suitable motor. Around this forum I have seen forum I have seen Turnigy SK3 motors mentioned a few times. Im going to go ahead and assume that its a 2118 type? Probably these:
    https://hobbyking.com/en_us/turnigy-...ner-motor.html

    These seem a good choice and I do not doubt that these motors would be very capable at beetle weight. But there is this nagging voice in the back of my skull, which says "what would happen if I used more powerful motors?" There are definitely bigger BLDC motors out there that a beetle chassis could accommodate and I could still make a bot within weight limits if I used some. For an example, why not use these NTM 28-26 types:
    https://hobbyking.com/en_us/ntm-prop...00kv-252w.html
    Provided that I used these motors with a suitable gear box, I don't really see to much of a problem in using them.

    I suppose that it maybe obvious that I am also interested in the latter motor due to its ridiculous price tag. However, I also aware of the old adage of "buy cheap buy twice". I would love to know peoples thoughts on this. As well as if im correct about my assumption that the SK3 I've link is one used in beetle weight.

    Cheers

  2. #2

  3. #3
    Thanks for the response! That sound pretty reasonable, I would likely use gearboxes for those 25mm brushed motors. This would require that I either turn down the NTM motor shaft or widen cog hole that attaches to the motor. I don't relish the prospect of either of those. I would also have to find a way to mesh the gearbox to the motor, all an expense that will quickly erode the price of the NTM motor.

  4. #4
    Hey there everyone! An update to my bldc drive activities. After some deliberation I desided to go with the Aerodrive SK3 2122 2100kv motors. I will use these motors in conjunction with some 25GA 500rpm motor gearboxes. Here is one I have assembled.

    It was suprisingly easy to assemble, the gear on the dc motor was a bit tricky to take off. It went flying in my room to land and perfectly camoflage on my floor! Everything i used to assemble it came with the gear box and motor, with exception to some epoxy glue and m2 washers.

    I placed the m2 washers underneath the gear on the motor shaft in order for it to engage with the gearbox. I epoxied the gear onto the motor shaft, the gear was a bit loose around the shaft but after i assembled everything i spun the gear box shaft as a crude way to centre the gear on the motor shft before the epoxy dried.

  5. #5
    On a different note. I found that these motors are very thirsty. I pluged one of these motors in to an afro 12A esc and enabled bi-directional control. I found that at about 50% throttle I was drawing about 7A on the DC side. I didnt see if it could go further, mostly because I didnt have a power supply that could go any higher. I am finding this a bit odd because im essentialy running this motor with no load, so I was expecting a much lower current draw.

    Perhaps I should reduce the ability for the motor to draw current on the ESC. Is anyone familiar with the BlHeli suite? I believe that i would have to reduce the motor gain? im not entirely sure.

  6. #6

  7. #7
    hmm. worth checking for sure. luckily i have 2 motors so i can do a comparison. Mind you though I was seeing this on the esc DC link and my ESC was getting incredibly hot. It's heat shrink sleave was melting off!
    Last edited by Scottie; 29th October 2017 at 20:27.

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