Testing needed on the new Dual
Update for testing.
Mark is working on the board for the toolhead interface now.
Marcio mentioned in today's meeting (5/10/18) that there is firmware to test with a single. Firmware for the dual is being worked on.
A simple toolhead interface board has been constructed and and tested on both toolhead designs. Also, both an Arduino Uno and Arduino Due have been set up and tested to drive the toohead servos. The input plug of the toolhead interface has been modified to attache to both the Uno and the Due.
As I was able to program a Due to operate the servos, I will now attempt to write test code for the Archim board to drive the servos directly. Until then, either the Uno or the Due can be used as a bridge between the Archim and the toolhead servos.
We had an actuator fail on the longevity test after being cycled 140k times. This equates to 914 dual benchy prints completed. I have contacted actuonix about the failure to see if the actuator lifetime can be improved beyond this.
At this rate, this would be 2.5 benchy prints every day for a year before failure.
Is this lifetime sufficient?
Personally i believe so, considering the lifetime and cost of other commonly replaced items. The heat bed is the first to come to mind. RAMBO, motors, pulleys, toolhead components, etc.
The actuators are easy to replace, and cost ~60$ ea direct from actuonix. So a customer could pretty easily replace them for ~120$
I would like to hear others' opinions on the matter.
I am a little concerned about that. While 2.5 benchies a day for a year doesn't sound too short, how many larger prints would that be in a day? It seems like something 2.5 times as tall with similar geometry would only be one print a day. Going to something that is more than 3 times as tall may cause the failures before the year mark at 1 print a day. With the build volume capabilities of the TAZ, I am assuming we will have a large percentage of customers in that niche.
@karrad this wasnt based on the height of the model and number of layers, it was based on the number of toolchanges in the print. So something may be 3x as tall but the number of toolchanges isnt necessarily 3x as many
@kent it was a mechanical failure as far as i can tell, there are little metal tabs for a resistance measurement that got bent and gouged the resistive pad.
from actuonix " At 140K cycles, failure was probably EOL from the motor brushes. Those contacts are the same ones we have been using for years in our PQ12 series and we have had no other issues with those.
140K cycles we would consider very good lifetime, I don't know if we will be able to coax more life out of them."
This is also dependent on how many toolhead changes are present in each print. This doesn't mean anything to a single-extruder print, but is more of an issue for a print that is dual-material/color for every layer.
Using the benchy metric, this would come out to 5h15m a day for a year. The benchy is a small but moderate tool change part - not all layers have a tool change, but most do.
Going off of the 140k number and not the benchy conversion metric, assuming a full build height print using the 0.18mm layer height PLA profile, this would come out to 174prints. I created a 290mm tall 10mm square tower, which I call "worlds_dumbest_dualprint" to get a metric for time based on a worst case scenario. worlds_dumbest_dualprint was sliced without a prime tower at 0.18 height on the polylite PLA profile and it came to 7h34m in Cura Estimate Time. Again, this is an extreme case. If you print 2 a day, this results in 87 days - roughly 3 months. This would mean it would be at worst a quarterly maintenance. To test the other extreme, I made 2 towers of 270*135*285 to try and get close to max build volume. This print, dubbed "worlds_most_unnecessary_dualprint", was sliced with the same profile and came to 16d19h43m. if you run that back-to-back for 174 prints you get 2928.42days, or 8 years.
So, somewhere between 3 months and 8 years of continuous use depending on what you are doing.
UPDATE: It turns out our initial estimate for the number of toolchanges in the benchy print was off. Originally we just searched the dual benchy g code for the number of T0 and number of T1 commands called out to determine the number of toolchanges (~150 ea), however there are T0 and T1 commands associated to temping up and down the nozzles. So originally we thought there were 300 toolchanges total in the benchy print, it turns out there are acutally about 120 total, or 60 cycles per actuator. This means instead of simulating 914 benchy's before failure, we actually simulated ~2300 benchy's. or roughly 6.3 benchy's a day for a year.
I feel much more confident about the longevity of the toolheads.
This engine print with support has about 360 total toolchanges or 180 cycles per actuator. This means we would be able to print ~777 of these before an actuator fails. This is an 11 hr print
From actuonix "We have tried longer life brushed motors, but their lifetime was really no better than what we are already using.
Using a brushless motor would require a new PCB (brushless driver) and would be a different size requiring us to make a different housing to fit. This would require NRE fees, mold fees, 1000+ MOQs plus there would be a significant price increase as brushless motors are always more expensive."
Since the motor brush lifetime is dependent on number of revolutions, and we are using the 100:1 actuator, we can likely lengthen the actuator lifetime by choosing a different gear ratio. Actuonix has a 30:1, 63:1 and a 100:1 option. The 30:1 is good for moving 15N (3.37lbs) , the 63:1 is good for 30N(6.74lbs), and the 100:1 is good for 40N (8.99lbs). We are only moving a mass of 0.85lbs.
My thoughts for choosing the 100:1 is that it will be very hard to backdrive so it likely wont lose position on a hard probe/failed probe or running over part of a print.
I think the 63:1 will work great, but i would be a little hesitant about the 30:1.