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Brushless motor jerks/cogs

Discussion in 'Newbie Q & A' started by Nairfon, Sep 4, 2014.

  1. Nairfon

    Nairfon New Member

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    Hey guys so I recently bought a Cheetah Sensored Brushless Motor
    4000kv and 8.5t.
    I've been having some problems with it and at low speeds it seems to jerk/cog up, and then will eventually stop(unrelatable but it's like it stalls like a real car, if that helps lol)
    I'm unsure whether the mesh is lined up properly but I think it is, is there a good way to check this?,
    Tk get the car up to its top speed I have tk slowly(very slowly) pull the trigger in.
    While holding the rc car in my hand with wheels of the floor I can fully accelerate it for about 2seconds then it just cogs(again like a jolt to stop or a stall/cut out)
    If anyone knows any resolution to this problem please help me out, it's really bugging me!
    And I'm concerned that my spur
     
  2. teosrc

    teosrc Studio Forums Elite
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    Cogging is normal for brushless motors. You could try gearing down, but then you wouldn't go as fast... it might help for cogging though.
     
  3. Crankbait

    Crankbait Think...
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    A sensored brushless motor shouldn't cog.
    Make sure your sensor wire is fully plugged into the motor and esc.
     
  4. Antho11

    Antho11 Studio Forums Elite
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    What rc is it? What battery are you using and specs? Is the battery fully charged? Are the connectors clean (don't electrocute yourself when cleaning)?

    You can check if your mesh is good by putting a piece of paper and turning the pinion so it gets fed through. Then once it's all the way through pull it out and check if the state of the paper. This technique works pretty well.

    Torn=Too tight
    Crimped but not torn= Good mesh
    Not crimped a lot=Too loose

    It could be that your battery pack doesn't have enough juice to power the motor. So the motor will draw more than the battery can supply.

    You can also try recalibrating your radio with the esc. Worst case it can be a faulty motor esc.
     
    #4 Antho11, Sep 4, 2014
    Last edited: Sep 4, 2014
  5. 6677

    6677 New Member

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    They won't cog alot, but brushless motors do function by incrementing the shaft in steps, that very nature does mean that fundamentally they will always cog - particularly when driven from a fixed voltage, there is some trickery that can smooth it out when running from a varying voltage or from 3 phase AC as that motor design was originally intended for but you dont get that luxury on an RC.
     
  6. Seamus_RBNW

    Seamus_RBNW RudeBoyz NorthWest
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    every brushless I have geared down has eliminated the cogging nearly entirely... maybe it is worth the 3-4 bucks for a new pinion to try it at least
     
  7. dna4engr

    dna4engr Studio Forums Elite
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    We really do need some specs on what you are running in the rest of the rig. A couple of the things you describe aren't just cogging though. It could be your battery(does it have enough of a C rating). Also your esc may not be able to handle that motor.

    Give us the details and we can help.

    Dna
     
  8. Y2daT

    Y2daT Over Powered RC
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    all looks like good advice to me . double check the gear mesh . 1-3 tooth smaller pinion gear will not hurt . make sure the sensor wire is connected correctly . make sure the esc is programmed for sensor-ed operation ( some sensored esc's do both sensored and unsensored . what is the battery type, MAh ? u will want something to put out around 150Amps give or take ..depending on the setup ... so if you have a 5000 mah 2S lipo it needs to be no less than 25C .
    if you are running a NIMH that may be an issue . ...
    So one thing at a time lets eliminate some possibility's.
     
  9. Nairfon

    Nairfon New Member

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    Ok so for some specs-
    The car Is a 4wd HPI Maverick Strada XB Evo
    The transmitter/reciever is a Absima(Asbima? Sorry if incorrect) it's 2.4ghz
    So the motor is the 4000kv 8.5t, this motor did come with an esc combo, it's 60a esc
    The battery I'm running is a 4700mah 7.2v
    So today I tried out the car again, with the battery above^^ and it basically would not go unless I gave it like a push start, even then it would only go slightly, since you guys mentioned the battery not being able to power it enough that does seem plausible, I will goto lipo soon hopefully.
    So the esc came with a program card and on it there is no choice for Sensored/unsensored and I saw it said it was only Sensored, so that can't be the problem right?
    Is it worth taking it in to an rc specialist shop? There is one near me so that may be worth taking it in to have it inspected and tested properly. And possibly get some advice on a lipo and testing some out to see what works. Thank you guys for the advice!

    -gotta love this forum!!!!:')
     
  10. Crankbait

    Crankbait Think...
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    You can get into the science of 3 phase ac/dc, and sensored brushless motors, but the simple fact is if they are geared right you will not perceive any cogging at all.
    There are other things that can be adjusted like the esc start up power, setting your esc for a sensored operation, ect.
    If trickery is needed to have a properly operating brushless motor you're doing something wrong.
     

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