Camera independent pixel-shift possible?

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mawyatt
Posts: 2497
Joined: Thu Aug 22, 2013 6:54 pm
Location: Clearwater, Florida

Post by mawyatt »

rjlittlefield wrote:
mawyatt wrote:Here's an example of the Ti DRV8825 I mentioned, note how bad it misbehaves even without a load!!
Heh! That looks pretty much like a StackShot in low precision mode. There, the nonlinearity appeared when the drive current was set too low, for "holding torque". The solution was to increase the minimum drive current, which is why high precision mode also makes noise and the motor gets warm. I have no idea what driver was involved.

--Rik
Rik,

My Stackshot does make a lot of noise when in Hi Precision mode, and more current does increase holding torque. The Stackshot I have is old, maybe ~2010, so wouldn't have these newer motor driver chips.

Motor parameters like inductance & resistance can play into the controller performance, as well as usual mechanical details. A low inductance motor will have a much faster rate of change current in the PWM mode, and may exceed the set limit. I suspect different controllers have different behavior when the current limit is exceeded when used in a PWM mode. A high resistance can cause significant heating due to I^2R loses. The little THK KR15 will get pretty warm at higher currents due to the high 5.6 ohm coil resistance.

If you read in detail the site I mentioned and followed some of the comments, the Ti parts seem to have their bad behavior with various motors and setups. Most wouldn't even know about this, since it's related to micro stepping, and hidden amongst many other factors which usually limit performance, but I just chalked my 5 DRV8825 modules up to learning experience :roll:

Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike

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