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Newby RPM question

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dirkske
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Newby RPM question

Hi all,

Before ordering a VESC based ESC, I'd like to know if it can be used to drive a brushless with very low startup rpm.  Use case would be an RC tug boat which would benefit from really low RPM to full RPM (voltage x kv).

I'm hoping the VESC can transition from stepper motor driver like behavior (for really low RPM) to regular brushless ESC. Typically a DC motor is used, but I'd like to know if VESC could provide an alternative.  Edit: I'm looking for a mix between regular brushless ESC and something like: http://www.rovertec.com/products-bgmc2.html

 

I hope the above makes sence to you guys.

TheFallen
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If you gave us a link to the motor that you're thinking of using that would be great. The current sensors in the VESC are suited to motors that pull some current, small quadcopter motors are likely too small.

For low speed (0RPM) control you would be best off attaching a quadrature encoder with index. This will allow the VESC to very precisely vary the speed as well as give plenty of torque at these low speeds.

dirkske
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Regarding the motor I was considering something like this, or slightly higher kv: http://www.faradaymotion.com/parts/8-65-faraday-motion-lightspeed-6364s-63mm-motor.html#/44-key-yes
Mainly due to fairly low kv and build in hall sensor.  I'd like to run it around 12V. Although I'm not sure if the hall sensors would be usefull at low speed. Especially since you're talking about an encoder.

TheFallen
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To get the rated 2.8kW you'd need to run it around 10-12s, so 12V or 3s would not be very efficient.

Hall effect sensors ought to give low speed control in the 10s of RPM quite well.

dirkske
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I'm having a hard time locating < 500W with around 250kv brushless motors with build-in hall sensors. Hence the oversized one. 

I do have the following motor at hand: https://hobbyking.com/en_us/turnigy-trackstar-21-5t-sensored-brushless-motor-1855kv-roar-approved.html?___store=en_us

But given it's high kv value, I doubt it'll be usable for my purpose.  I could try though, providing I don't wreck the VESC (must restrict ERPM I assume).  Would it's hall senors be plug-compatible with a VESC4?

I've decided to take the plunge and buy myself a VESC4, to doodle with it and see how things go.

 

TheFallen
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ERPM would be your limitation for that new motor, but it's hall effect sensors will be okay, just have to make sure you connect them up properly.

TechAUmNu
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If the rpm is too high just put it through some pulleys/belt to get it to the speed you require...

Here is a sensored motor that fits your requirements https://hobbyking.com/en_us/turnigy-sk8-5045-150kv-sensored-brushless-mo...

Or a 240kv one https://hobbyking.com/en_us/turnigy-sk8-5045-240kv-sensored-brushless-mo...

dirkske
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Thanks all for the hints and tips. No doubt I'll be back for more info once the VESC arrives

As for mechanical reduction, that's exactly what I'd like to avoid by using a VESC (noise, extra maintenance/point of failure etc...). Although I realize I'll likely be running not as energy efficient (to big of a motor).

Note: I'm seeing too many odd use cases for a VESC, not good, too much ideas compared to time to invest...