Alpha feedback

[dave_k]

Quick question for my alpha... the manuals say to NOT move the motors manually as they can feed back into the board and fry some silicon. Does that also apply when there is no power to the machine? Say I pushed my y axis about a foot to make room for something in my shop, when the machine was not turned on. Could that do any damage?

[bill1]

It is my understanding as long as the power is off you are ok.
Bill.

[jseiler]

Motors when turned generate voltages. When I did a motor upgrade, just for fun, I connected 2 stepper motors together, and by turning one, I could get the other to turn. Never thought that steppers would drive like that.

With that said, the voltage that comes from those motors is proportional to the speed you turn them. If you have gearheads, those motors might turn pretty fast. If you have to move the motors with the control box unpowered, certainly you would want avoid high speed moves and jerking them from a stop.

John

[gpari]

I have pulled my gantry about 6 inches every morning, before power up, for almost 2 years. Always pulled slow and was never too concerned until I put on my 3:1 gearboxes. Now I pull REAL slow. My next mod to ease the stress is a cam-over lever to engage/disengage the pinion gears on the x-rails so I can push and pull with no worries.

[richards]

Stepper motors act as generators. When the shaft on a stepper motor is turned, the motor generates electricity. Depending on how fast you spin the shaft, the motor will generate more or less electricity. The stepper motor driver may or may not be designed to handle that generated electricity. Some stepper drivers can handle generated electricity better than others. In any case, it is best to move the motor slowly and only for short distances - unless you know exactly what you are doing.

[ryan_slaback]

David,
I bought my alpha in June of 06. I had to call in to Shopbot for some tech help one time and mentioned my fear of manually moving it. I was told by tech support that moving by hand was a problem on the prts but not on my alpha.

[dave_k]

Thanks Ryan and others that have chimed in on this. I removed the aluminum table on my BT32 alpha in the process of moving it down to my shop, and I didn't want to disconnect the stepper motor for fear of getting it back into alignment correctly, so I slowly pulled the table off (no power to bot) but wondered if even that was not a good thing. Also when uncrating it, at one point I sortof leaned into the crate, and in doing so put my weight on the z axis and it was not secure (as the x and y were with bolts) and it moved down a few inches. Thus this post asking about this. As I don't anticipate many times where I will have to move an axis by hand, I will still be careful to keep that at a minimium even though SB apparently says for an alpha it's not as big of a problem. Thanks again folks.