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SBrick Plus: Full Speed or No Movement

    • 159 posts
    November 23, 2018 4:04 PM CET

    Hi,

    the LEGO M motors are notoriously hard to drive. Try them with LEGO's own V2 IR receivers, and you'll likely get the same results.

    The problem with M motors is they have a large capacitor in parallel with the actual brushed DC motor in them. 

    When the DRV8833 motor driver chip in the SBrick Plus tries to charge this capacitor, it may go into overcurrent protection mode, and cut the PWM signal.

    This problem is not always present, most M motors and most SBricks work together just fine. If you can, please try other M motors and SBricks.

    The problem gets worse as the M motors need to supply more torque. If nothing seem to work, try using a thin silicon lubricant on the moving parts of your creation to reduce friction. You may try to apply lubrincant onto the planetary reduction gear inside the M motor, but you'd need to take it apart.

    (If nothing helps, and you _are_ willing to take the M motor apart, you can remove the capacitor, but this obviously isn't a real solution for most customers of course.)

    If you can't solve the problem, please write to info@sbrick.com, reference this thread, and ask for a replacement. You'll need to send your SBrick Plus and M motor to us, and you'll get a pair that works together better.

    We can't promise we'll be able to do this in every similar case, however we're willing to do this in yours, since you provided lots of important information we can use to make SBrick better.

    Cheers,

    Tamás


    This post was edited by Tamás Fábián at November 23, 2018 4:05 PM CET
    • 2 posts
    August 8, 2018 1:11 AM CEST

    I bought an oscilloscope now to see what the SBrick is doing. Here it comes:

    As long as the M-Motor is spining free, the SBricks PWM-signal looks totally OK.

     

    But when I use my fingers to stop the M-Motor, the signal turns into this:

    You can see that when the motor is blocked, the SBrick for some strange reason no longer delivers a correct PWM signal. I most cases I could even stop blocking the motor with my finger but it did not spin up with this PWM signal applied.

    The two pictures above have been taken with used batteries (around 7,5V). However, the situation is the same with new batteries or even when I connect a power supply.

    Furthermore, if I connect two M-Motors to the same port, they do not work at all. They make some noise, but they do not start rotating. (but 2 M-Motors on to different ports work)

    • 2 posts
    August 3, 2018 8:41 PM CEST

    Hi,

    I bought a new SBrick Plus few days ago and used it for the 42065 RC Tracked Racer. I created a simple profile with 2 sliders. However the Racer does not move at all until I push the Sliders to +100% or -100%.

    I could reproduce this behaviour with a sequence:
    When setting the output to 0.95, the racer makes some noise but does not move at all. When I set the output to  1.00, the racer moves (very fast, same speed as with the Lego IR).

    I already tried to upgrade the firmware (23) but this did not help at all. Is this something like a known problem with the SBRICK PLUS? Is there any work around? I found this youtube video in which the race is able to drive slower, so it seams to be no general limitation of the SBRICK.