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Topic-icon Free Rolling BLDC Motor on Scooter - No Regen?

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1 year 3 weeks ago #29532862 by eilewot

Hello,

I'm using the SBL1360 to control a custom brushless hub motor scooter I'm building.

I've gotten the control and microbasic to function mostly as intended, but one thing that's stopping me from developing it further is the resistance in the wheel I feel when there is no throttle on the scooter.

I believe this is because of the regenerative braking feature because when the controller is off, there is no wheel resistance. I've looked at the Roboteq articles on regenerative braking, and am not sure of what type of circuit to use to turn it off.

Do you think this is a regen issue or perhaps a closed loop speed issue? (I've tried turning all PID values to zero and changing to open loop and it doesn't help)

Any suggestions and help is very appreciated! :)

I can email my xml file if needed!

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1 year 3 weeks ago #29532864 by eilewot

I think my issue is due to regen based off of this article: dev.roboteq.com/dev1/index.php/forum/14-...eration?limitstart=0

I'm using a 7S battery on a ~250W 6.5" hub motor

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1 year 3 weeks ago #29532865 by blake

What you observe is normal. When you the controller is given a zero command the bottom mosfets of the bridge are closed, closing the phase leads to gnd. You can observe this same resistance on the motor if you detach it from the motor controller and touch any two of the motors phase wires together and then turn the motor with your hand, you will feel that same resistance.

The only way to not have this and to free wheel the motor is to completely open (float) all of the mosfets. This is done when the controllers Emergency Stop is enabled. With your controller connected to Roborun+, click the Emergency Stop in the upper right corner and you will feel that the resistance is gone in the motor when you try to turn it by hand.

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1 year 3 weeks ago #29532867 by eilewot

Thank you for the response!

I would like to eliminate resistance at times in the code, especially when the command is zero.

Is there any risk to enable and disable the E-Stop repeatedly in the microbasic code?

Is there any other way besides activating the E-Stop to get the same effect?

Essentially, I want to replicate the feeling of standard scooter motor controllers - not sure why they don't have this feature?

Thanks!

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1 year 3 weeks ago #29532868 by roboteq

The problem with cutting the mosfet is that when you will turn them on again, there will be potentially a big mechanical jolt.

A much bettter approach is shown here dev.roboteq.com/dev1/index.php/component...-sensing?Itemid=1208

Essentially, the idea is that when you want to frewheel, you apply the PWM level that will make the motor rotate at the current speed (ie no pushing nor braking)

This allows a very smooth transition between traction, freewheeling, braking.

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1 year 3 weeks ago #29532869 by eilewot

Yes, I believe this is exactly what I'm looking for! I had seen the article before, but didn't realize it applied to my situation.

I will do an in depth read and try it out tomorrow. After a quick scan, I didn't see any mention of closed vs open loop mode settings. Will the micro basic script at the bottom work in closed speed mode?

Thanks!

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