TL;DR need a motor for locking to parts together (like a screw) and it needs to last around at least 100,000 locks and unlocks. Will a simple DC motor last like that? my constraints are <80g of weight and a price less than 20$
long version with details:
I'm designing a tool changing printer with a very low budget. the only steppers I can find under 80-100g that seem reliable are 15$-20$ ones from StepperOnline. I rather keep that as a last step since with shipping it costs me 35$~ and I want to keep the BOM low.
firstly I tried a 28BYJ-48 and I was worried about longevity since it started sometimes skipping steps after weeks of use. I could incraese the gearing from 1:2 to 1.3 but I got scared since it was very unreliable outside the printer without gearing anyways. and heated quickly if I did a lot of tool changes. So I switched to a simple burshed DC motor with gearing. It simply keeps rotating until the tool is locked (look at e3d's tool changer or the jubilee to understand the mechanism! but basically a screw and a thread in that's very... spread out!) and I sense the current to detect a locked. so far with a some software tricks (slowly ramping the PWM down to avoid it from spinning backwards after a lock) it's working good for now. but after googling I learned that dc motors have low lifespan when frequently stopped and started and when stalled often. but how long is that lifespan? An average print might have 150 tool changes in it or even more. the reason I'm avoiding servos is because according to E3D "The old Servo was struggling to exceed 60,000 tool changes whereas the new beastly Stepper Motor can easily surpass 400,000 cycles."
so any ideas? will my DC motor last enough in this printer? something around 100,000 is what I consider acceptable. is there a way to increase it's longevity? any alternatives that aren't expensive?
also as a side note. is there any compact'ish mechanism that can break a motor when it's not moving? i can use a solenoid or something but that'd take a lot of space and an additional pin
If you need a motor for 100,000 locks/unlocks, then use a motor that is rated for a MTBF around that figure. Than eliminates all the cheap hobby motors, doesn't it
Paul
Paul_KD7HB:
If you need a motor for 100,000 locks/unlocks, then use a motor that is rated for a MTBF around that figure. Than eliminates all the cheap hobby motors, doesn't it
Paul
amythebun:
Oh i was expecting experianced maker to perhaps have experiance on these type of motors. I guess i can test it but it'll take ages!
On the other hand, how many motors as backup would you feel conformable with if the seller and the motors were no longer available for purchase? If your motor dies, how long would it take to find a replacement. We usually purchase several devices when only one is needed for a project.
Paul
Paul_KD7HB:
On the other hand, how many motors as backup would you feel conformable with if the seller and the motors were no longer available for purchase? If your motor dies, how long would it take to find a replacement. We usually purchase several devices when only one is needed for a project.
Paul
the reliability is more of a concern because you never know when it's gonna fail. I would've used a servo and my project would be done months ago if it wasn't because of this. but I don't want a long expensive print to fail because a motor failed. then again. as you said that I thought to myself, what's a single failure every single year? i mean failures happen more often because of other issues anyways (calibrations etc).
I think i'm gonna do a servo now!