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How do I stop or freeze the large motor in a fixed position? I have a forklift type attachment that will lift to the precise height, but will not stay in position due to the weight of the attachment.

I know I can use a worm gear to solve this problem but wanted to see if there were any other solutions before redesigning the attachment.

I have tried using rotations, seconds, and degrees with a STOP at the end. Occasionally, it will stay in place but usually it drops to the mat surface.

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    Can you share your program? Mar 4 at 17:36
  • what motors are you using? can you show photo of build? i dont understand anything Mar 4 at 18:07
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    Whatever you are lifting is just too heavy. Once stopped, motor doesn't use current to keep the position. And the weight of whatever you have just lifted overcome the internal gearing and turn the motor back. As an alternative to worm gear solution I'd suggest reducing the weight of the item you are trying to lift.
    – Alex
    Mar 4 at 20:16
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According to the official documentation you could use

hold()

which

Stops the motor and actively holds it at its current angle.


Note: My assumption here is that you are referring to this

enter image description here

as "large motor". If you are using a PF Large Motor:

enter image description here

then this advice is useless, as those can't be controlled with such precision due to the lack of an internal rotation sensor.

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  • This response assumes the OP is referring to Python on EV3Dev (which is not official documentation).
    – MindS1
    Mar 10 at 18:57
  • @MindS1 I considered it official, as this site is linked from the LEGO EV3 Support site as "Go to the online Documentation and Example Programs".
    – zovits
    Mar 12 at 8:56
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I am overwhelmed by the support everyone has provided. I really did not know if I would even get a response and to get so many suggestions was wonderful. I sincerely thank everyone for taking the time to help me.

To answer some of the questions in the thread, I was using the "Large Motor" and not the "PF" Large motor. Also, since I am using the block programing tool, I do not believe the HOLD() is available. Using the HOLD would have been my desired option.

I went with Alex's suggestion and changed my attachment to use a Worm Gear with the Medium Motor (instead of the Large Motor). The result was exactly what I needed - very precise movement using motor degrees and hold the load without any problem. Here is an image of the attachment with the medium motor and worm gear:Medium Motor with Worm Gear.

Again, thanks to everyone who contributed. I truly appreciate it.

Dave

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  • Glad you were able to work this out! Consider selecting this response as your answer since you solved your own problem.
    – MindS1
    Mar 10 at 18:56
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I know I can use a worm gear to solve this problem but wanted to see if there were any other solutions before redesigning the attachment.

Without knowing the full details of your design, it would be a bit difficult to recommend anything very specific.

Is your motion of the motor limited in direction? If so, a ratchet system can be extremely effective, even a small brick can support a lot of weight. Is it possible to use a counterweight to balance the load of the weight you are lifting?

Consider adding friction to your lifting mechanism to support the weight. This could be constantly applied (in which case your motor may struggle a bit more) or applied manually or mechanically to support the weight when the motor has stopped. Most soft LEGO Technic tyres or the Technic, Axle Connector Double Flexible are appropriate for this.

enter image description here

I have also covered a few more solutions which may be of help in a similar question 'How can a Mindstorms robot lift something very heavy?'.

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