EEVblog #257 – Makerbot TroubleshootingPosted on March 14th, 2012 6 comments
Dave & Phil try to calibrate and print something for the first time on their Makerbot Thing-O-Matic. But as Murphy always ensures, it turns into a troubleshooting bonanza, where much hair is lost, but much knowledge gained…
The two types of bearing is to ensure the Y axis is not over constrained. The tolerance in the parts can result in variation in the distance between the Y rods.
Also, make sure you have the proper REF settings on the stepper drivers. Incorrect settings can result in reduced current through the motor and reduced torque. http://wiki.makerbot.com/thingomatic-doc:stepper-driver-ref-settings
Regarding belt tension:
For some types of belt drives, span vibration frequency can be used as a measurement to verify belt tension. If Makerbot did not specify the belt tension this way …wonder why not.
Maybe the free vibration frequency is out of a range where it could be measured easily or perhaps there is too much uncertainty of that method due to the carriage being on the belt.
The theory is just the same as a guitar string. At a certain tension a flexible string of a certain mass will have a known vibration frequency. On the belt drives I work with it is very easy to pick up the sound with a guitar tuner or by recording the sound into any recording device and do spectrum analysis in Audacity.
This could be something to try…
Dave, I’ve been where you are – you have a lot of fun and experimenting ahead of you. Believe me – YOU WILL GET THE HANG OF IT.
Tip #1 – captan tape over that aluminum, and wipe it down with acetone. It works!
Tip #2 – Make sure you have no binding in your axis’s (you can wiggle the bushings on the bars to better align them for free-er movement), and tweak the voltage settings on your steppers (plenty of docs out there on how to do that).
Tip #3 – print, print and print some more. There is a learning curve, but you’ll get to where ‘it just works’. Took me about 3 weeks of head banging to get there… But now, an education behind me, I can reliably print pretty much whatever I want. If you get in a real bind, let me know and we can skype and swap lies.
I think the stepper motor for the Y axis may be a bit on the small side.
As a rule of thumb I was taught that the maximum moment of inertia a stepper motor can drive is about 3 times the moment of inertia of the rotor of the stepper motor. Or 7 times if you use ramping to drive the stepper motor. Corrected with gear ratios, etc.
Ramping is when you accellerate the motor to top speed and decellerate when at the destination instead of immediately letting the motor turn at maximum speed.
This is likely why the disc was a success and the space invader not. The speed graph of the Y axis when making the disc is likely to be a sine wave which rules out sudden accelleration changes. The speed graph of the Y axis when making the space invades is more likely to similar to a square wave which ensures out sudden accelleration changes.
You could stick an accellerometer like for instance the one in EEV blog #181 to the table and generate those graphs to verify whether my hunch is correct.
If my hunch is correct I would try use a half sine profile to speed up the stepper motors to maximum speed and down again (ramping) to solve any issues.
Hope this makes sense,
That should be:
You could stick an accellerometer like for instance the one in EEV blog #181 to the table when making the 2 objects and generate those graphs to verify whether my hunch is correct.
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