Does anyone have experience with solenoids? I wanted to run this idea of using 1 motor with multiple hot ends. You have a cold end like this mendel max extruder and then you actuate the idler using a solenoid. I am not sure if you’d push down against the spring or use it instead of the spring but you have multiple solenoids, idlers, and hyena bits on the same motor which can drive multiple filaments depending on which solenoids are activated. What do you guys think? Has this sort of thing been done before?
Most solenoids at 24v and less have very little torque or holding power so good luck!
I’ve definitely seen the idea before, I think it was on the reprap forums but I don’t really remember. Never built though.
Solenoids are quite weak. One idea that comes to mind for me is a sort of cammed shaft with the idlers on it, which could be driven by a servo. Then the whole servo and shaft assembly could be pushed against the drive with springs, and you wouldn’t have to disengage the springs to switch.
What is a dual drive shaft? Do you have a link?
Thanks for saying solenoids are weak. Are servos strong? What about a stepper that engages one idler while it disengages the other? Then the electronics would support it.
What is a cammed shaft?
Thanks for the input! I really love my Mendel max extruder but I kind of want to dual extrude. 
Dual drive shaft means a shaft coming out of both ends of the motor.
Servos can be as strong as you want, however my suggestion wouldn’t take too strong of a servo I don’t think.
A cammed shaft is like the crankshaft of a car engine. My explanation above was unclear… I may CAD my idea sometime when I’m not so busy.
belle réalisation
We discussed this very idea a few months back. It’s practical I think but you might want to consider a servo or second stepper that rotates a series of cams on a shaft, each cam then actuates a specific idler for a given rotation.
@Tim_Rastall Yeah I was thinking of a set up where you had the series of cams on a shaft on a servo, and then a cylindrical enclosure screwed onto the servo around the cams so that all or most of the idlers not pushing on filament would be pushing on the cylindrical enclosure. That way the shaft wouldn’t be able to deflect so you could probably get away with a pretty cheap servo. Then if you still wanted a spring to handle small variations in filament diameter and such, you could mount the whole servo+enclosure part on springs.
Would these go into one hot head, or have a separate one for each filament?
@Nick_Parker that’s sounds viable. I guess a servo makes better sense as they don’t require a driver like steppers. You could still use the e1, e2, e3 pins off the arduino: you’d need to common them all to the same driver and then have a sub board that would rotate the servo for a given duration based upon what pins were enabled. My electronics skills suck so there might be an easier way than that.
@Geoff_Drake Probably separate hotends. You have to purge a ton of filament to really switch plastics in a hotend.
Really good idea if your using liquids like chocolate but more complex than separate extruders for filament.
More complex mechanically yes, but it saves you some steppers, which also saves you some stepper drivers allowing you to use simpler electronics.
Saves steppers but starts adding in more vitamins. And servos are not that cheap.
@Nigel_Dickinson Firstly, servos a pretty cheap (see below), we don’t need robotics grade ones for this application. Secondly, you forget the stepper drivers you’d not need that are expensive and if you were to hack the Marlin (or whatever) code, you’d be able to free up a bunch of pins as you only care about a single enable pin for each extruder after the first one. Also, disagree with the vitamin count statement as there’s bloody loads of screws bearings and bolts in a wades geared extruder. If you were to run more than 2 nozzles (and I intend to on my new bot btw) you’d just be adding an extra cam, spring, a few screws and printed parts for each extra nozzle. You could also use a single long Hobbed bolt and just ‘hob’ it every n mm for each extruder.
http://www.aliexpress.com/item/20pcs-Free-shipping-MG995-upgrade-Torque-Metal-Gear-RC-servo-MG996R-digital-servo-for-Futaba-Hitec/570595893.html
With the aid of a lever, Newtons can be infinite. The distance they are available over is not…
Steppers are just as cheap. When you add in tax and hacking the code to free pins brings us back to the fact that driver boards are now becoming under powered for what we are doing. And when you offset the cost of vitamin’s and the messing is not effective. Like I said good idea but not practical.
@Nigel_Dickinson That’s just an ill informed opinion rather than a fact so don’t present it as such. Bots are going to have more nozzles, I know of at least 1 quad nozzle in development and when you get above 2, I think there is a compelling argument to use a single-drive-multi-idler cold end. The Vitamin and electronic costs would be significantly less than having 4 stand alone extruders and although there is always an overhead associated to developing such things, it doesn’t make it impractical or ineffective. Of course this is all my opinion but I’ve thought about it a lot, I’m making a bot that would benefit from such a development and I’ve talked to people that actually make these kind of things for a living that also see it as a viable concept.
Well if that’s the case why are we going down the route we are going. And boards are under powered processor wise. Why do we need to recompile every time. Why no multi images. Adding servos is good like I say but you can make one stepper drive multi extruders by a gear boxes and clutches. Rather like a multi feed on lathes.
@Tim_Rastall I’m curious to whether the pwm input into a servo can be replaced with an analog voltage. If I understand then correctly, servos use a pot as feedback to compare the voltage of the pwm line (pwm signal dropped into a cap to make an analog voltage) with the voltage across the pot. The motor is driven accordingly based on voltage differences. Somebody please correct me if I’m wrong. If I’m right, then you wouldn’t need to send pwm to each servo, you’d only need to send analog signals which could be tweaked with a trim pot to dial in the correct servo position. You’d need a transistor and related components for each circuit, but it’d be much simpler than a pwm circuit. Then again, I could be completely wrong about the servo input