Z axis Brake August 12, 2020 06:42PM |
Registered: 10 years ago Posts: 199 |
Re: Z axis Brake August 13, 2020 02:47AM |
Registered: 11 years ago Posts: 14,685 |
Re: Z axis Brake August 13, 2020 06:56AM |
Registered: 10 years ago Posts: 199 |
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dc42
You could put G91 G1 H2 Z0.1 G90 towards the end of config.g. We don't normally advise putting movement commands in config.g but in this case it seems justified.
I am looking at various options to support motor brakes in RRF. One is to assign a pin as a brake for an axis, and turn it on whenever the axis motors are enabled. Another is to add a command to power up motors without moving them.
Re: Z axis Brake August 18, 2020 04:13PM |
Registered: 6 years ago Posts: 3 |
Re: Z axis Brake August 20, 2020 05:30PM |
Registered: 10 years ago Posts: 199 |
Re: Z axis Brake August 20, 2020 06:02PM |
Admin Registered: 11 years ago Posts: 3,096 |
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Govahnator
Interesting! Thanks for sharing.
I will look further into this.
Not sure if i can use it on a Nema23 and Duet2. Also not sure if this combined with 4.7 ohm resistors will do for me.
Re: Z axis Brake August 20, 2020 10:30PM |
Registered: 12 years ago Posts: 5,796 |
Re: Z axis Brake August 21, 2020 02:46AM |
Admin Registered: 11 years ago Posts: 3,096 |
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the_digital_dentist
I tested shorting the Z axis motor in my belt lifted Z axis in UMMD before I installed the worm gear drive. Here's what happened...
The braking action is proportional to the current in the windings. The current is a function of the motor's rotational speed. If the motor doesn't spin, there's no current and no braking. So the motor spins, and the bed drops. Shorting the coils does not prevent the bed from dropping. It's progress is slowed initially, but it accelerates linearly (?) at first, and then gets to some speed where the braking no longer seems to work and it drops hard and fast. Maybe that's a function of the length of the z axis and the mass that's dropping. Maybe in a short Z axis, it will lower itself gently and never accelerate to the point that it crashes. In my 700 mm long Z axis, it definitely got to the point of crashing.
I'm not sure why you'd want to put resistors into the circuit. They will limit the current and the braking. It would be simpler to put springs at the bottom of the Z axis and let the bed drop. The end result is the same. The bed will end up at the bottom of the Z axis when motor current is cut.
Maybe you could couple the bed to some very strong magnets dropping through copper tubes to slow the drop...[www.youtube.com]