Belt-extruder d278|17
putting the extruder stepper on a fixed position to minimize moving weight.
Does it work? My understanding is that in this case the extruder reaction force must be taken by X-Y motors. So yes, less weight to move, but more demand for torque to keep the extruder pushing. Or I just don’t understand the whole concept. It seems to be a challenge on the sw side as well.
One side H-bot?
Yes and it is a development concept so i don’t know how well. My biggest concern is the asymetrical force - you could double the belt and mirror it to the other side so you have at least a parallel force.
You also could simplify this with the Prusa design so the motor will move in Z (2 motors X and Extrd would be on that Portal) and you only need to compensate X translation.
@Dont_Miyashita looks similar but it is different. You see only the extruder drive - X and Y translation system is removed. The H-Bot has the belt fixed on the carriage.
You’re depending on a belt to drive an extruder, I doubt you’ll be able to maintain enough torque without having issues. Additionally there really isn’t any firmware support for a system like this because the E motor has to account for X/Y position as well. A better method would be to use a Flex3Drive sytem.
@Adam_Steinmark If you design something new you are normaly on uncharted territory - you never have any support. But you need to go new ways to improve something (or fail) relaying on existing is not creative - Like an H-Bot (or CoreXY, Delta, or Belt-printer ) need a different Firmeware. Sure i need to write my own. Or at least a compensator script - you can use the X/Y signal to calc that pretty easy - so just a microprocessor for the extruder is needed. Also i can use Nema 21 or 34 as weight and size doesn’t matter anymore. Flex3Drive is only usefull for small printer and from a mechanical point of view not an elegant solution.
So “better” is a very subjective term 
There have been a lot of proposals to do stuff like this (remote belt drive extruder) but I’ve only seen 1 actual working implementation, which was a Mendel with the extruder motor on the Z stage a number of years ago. Firmware support isn’t actually all that hard in something like Marlin, you’re just adding or subtracting steps in the same place the CoreXY kinematics is done. (Admittedly, this does bad things to the acceleration constraint limiting code, but nobody notices.)
What’s really important here from a mechanical standpoint is gearing down the extruder drive so there’s minimal force on the belt. Like 10:1 to 40:1 gearing on a worm screw. Otherwise, you’ll get racking and position jumping from unbalanced belt forces, and risk losing XY position registration when the extruder stalls.
@Ryan_Carlyle with your info i found this https://www.thingiverse.com/thing:15132 and yes i already used the big pulley to get a ratio - wondering if you can drive the filament directly with a wormgear - but probably that causes to much friction. Despite retracts a fast moving belt shouldn’t be a big issue.
Somehow i like it to have an Idea and find out someone else already has done the work 
https://www.youtube.com/watch?v=6sF87FcMKyI
Yep, pretty sure that’s the one I was thinking of.
Worm screw filament drive has definitely been done (Stratasys has some patents, and many early RepRaps had them, eg look at the old BitsFromBytes extruder) but you run into issues with 1) the filament spinning and losing motion or 2) excess debris production from the sliding/grinding contact.
Personally, I think you’re going to want a bigger gear ratio than a single big pulley can provide, but it’s certainly worth trying without the worm screw gearbox.
Wow the belt in that video does not look it’s under much tension at all.
yeah that doesn’t look right - also it seems to be only the carriage not the extruder driven via a belt - if i understand this right. But i am using the same system on my BeBot concept but through the other axis.
It’s not so much that you need steep gear reduction. What you really need to do is reduce belt tension, and large pulleys at both ends can accomplish that while maintaining enough torque to extrude.
@Dale_Dunn fair point; you could do big pulleys on both ends and get the same benefit as a gear reduction for the goal of minimizing uneven belt loads. To my mind the gear reduction is worthwhile in itself for increasing extruder power – a 1:1 extruder drive puts the motor in a wasteful region on the torque/power curve – so there’s really no benefit to a big pulley at the motor side.
@Ryan_Carlyle , Yep, but I also wouldn’t want to have to output a wasteful number of steps at a high reduction ratio. Normal extruder reduction is around 4 or 5:1, so I was thinking this concept could implement that with larger than usual pulleys.
@Dale_Dunn Yeah. The rotating flex shaft extruder options available use 30:1 or 40:1 worm gearing and that’s about as high as you should go on a NEMA 17 before you’re heading too far down the wrong side of the power curve. They end up running pretty slow retracts, which is fine because they’re effectively direct drive, but it’s definitely an issue for step pulse generation limits.
One interesting design i remember seeing was one that used a shaped (hex?) rod across the carriage, it was driven from a fixed stepper at one end, and the extruder gear at the head rode along and was turned by the rod.
@Justin_Mitchell I know one with a square rod - but i don’t like the friction and additional weight of that bar. You probably also need a gear as higher torque probably jam the movement. You can also use a extrudet gear so there is not another moving component. A long worm drive could also work (also influenced by carriage movement) but all are only one dimensional solutions.
You’d want a fairly large step-down gear ratio at the extruder to minimize the racking forces on the Y axis. And the blue pulley is rotating on the wrong axis for feeding filament and tends to get in the way of the filament path. All of which doable, but complicates the mechanism.