Brushless motors

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Paulmchurd
Posts: 213
Joined: Sun Dec 10, 2017 4:39 pm

Brushless motors

Post by Paulmchurd » Fri Mar 08, 2019 11:11 pm

Hello,

I’ve found with the brushless motor I use that if I put the motor from zero to full throttle it will stall. Then I have to bring the throttle back to zero which will allow the motor to start again. However if I raise the throttle slowly it will get to full power but it will take anywhere up to 10seconds. Is this normal?

Or with the right set up of battery and esc can you hit full throttle and it will speed up quickly?

Thanks
Paul

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GeorgeR
Posts: 207
Joined: Sun Aug 28, 2016 9:53 pm
Location: Bath, Somerset

Re: Brushless motors

Post by GeorgeR » Sat Mar 09, 2019 10:28 am

Short answer - yes and yes. It's a common issue, but with the right setup you can get a very quick spin-up.

There are two issues in play here; the first is that brushless motors can draw a huge amount of current at low speeds, and the small batteries used in ants can struggle to provide this current - causing a significant voltage drop. If the battery voltage drops low enough the esc or receiver will cut out, causing the motor to stall (esc) or the whole robot to loose signal for a second (receiver). The solution to this problem is to use a bigger battery with a higher current capacity.

The second issue is the esc being unable to calculate the position of the motor, and therefore being unable to drive it. At low rpms the back emf voltages that are used to calculate position are very small, and when lots of power is being applied the esc can struggle to pick out the back emf "signal" from the drive power "noise". The solution here is all about which esc you're using and how it's set up. You'll want one running simonk or blheli firmware, and you can tweak the settings to get the best spinup.

It sounds like you're having the second issue, but it can be hard to tell without playing around with everything. What's your current battery/esc/motor setup?
Team Zero
Zero - rambot - - Axiom - axebot - - Valkyrie - drum spinner
Vampire - horizontal spinner - - RBMK - quad spinner gyro walker

Paulmchurd
Posts: 213
Joined: Sun Dec 10, 2017 4:39 pm

Re: Brushless motors

Post by Paulmchurd » Sat Mar 09, 2019 11:12 am

Thanks for the reply, makes a lot more sense now. Yes you are right my battery and esc set up is wrong.

I have Sunnysky X2204S motor, This SimonK esc https://banggood.app.link/xRhf4YqMUU and a 180MaH 25c battery. I guess my issue is the undersized battery. I was in the process of hooking up a 300mah battery instead. Although I had to move some components around I to fit it in and managed to burn out my arduino controlling the motors by short circuit. Ops...
Once I’ve resoldered a new one in hopefully my slow power up issue will hopefully be fixed.

Cheers for the help!
Paul

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GeorgeR
Posts: 207
Joined: Sun Aug 28, 2016 9:53 pm
Location: Bath, Somerset

Re: Brushless motors

Post by GeorgeR » Sat Mar 09, 2019 1:45 pm

Yeah, I definitely suspect the battery is the culprit in this case, those 180mah ones will struggle in a spinner, especially with a powerful motor like that 2204.

I use the 260mah 35c ones in Vampire and Valkyrie, and a 300mah 45c in RBMK. Despite the higher power lipos Valkyrie is the only one I can actually slam straight to full power, the other two require some form of gradual power up (1-2sec), but then they are both at the more extreme end of antweight spinners.
Team Zero
Zero - rambot - - Axiom - axebot - - Valkyrie - drum spinner
Vampire - horizontal spinner - - RBMK - quad spinner gyro walker

Paulmchurd
Posts: 213
Joined: Sun Dec 10, 2017 4:39 pm

Re: Brushless motors

Post by Paulmchurd » Sun Mar 10, 2019 6:13 pm

Spin up time drastically decreased with 300MaH battery. Can go half speed instantly now.

Thanks for the help.

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