I was discussing different bowden/direct drive options with my friend over on the RoBo3D

(Mike Kelly) #1

I was discussing different bowden/direct drive options with my friend over on the RoBo3D forums and he had the idea of using a flex shaft, like this: http://www.dremel.com/en-us/Attachments/Pages/ProductDetail.aspx?pid=225-01 as a way of having a direct feed system without the weight of the stepper motor on the carriage itself.

In principle the idea makes sense. Obviously I have my concerns, but has anyone heard of this being done?

I figure the major limitations are:

  • Lack of torque and or torsion buckling
  • Rigid line causing issues or limited motion of travel
  • Awkward mounting


(Tim Elmore) #2

Backlash would also be a pretty significant problem, since these are basically just coil springs.


I have no experience with Flex3Drive, just know it from the RepRap forum thread:


(Tim Elmore) #4

Yup, the flexidrive looks to reduce backlash issues by putting a 40:1 gearhead on the end effector. That way 360deg of backlash slop becomes just 9 degrees.

At that point you’ve added enough weight that there isn’t too much benefit over a conventional direct drive, though. And you pay $150 for the privilege.

(Mike Kelly) #5

@Tim_Elmore1 that’s a great point. You’d definitely need a design that was more rigid.

@kongorilla Thanks for the link, we’ll look into that.

(Mark “MARKSE” Emery) #6

I think the Bowden solution (my Kossel Mini uses one) is a good one. The flexible shaft you show is good for driving drills and grinders but when it comes to precision turning wouldn’t the inner part twist too much? The less it twists the more inflexible it will be and your steppers will have to do more work moving the head around. Adding a gear head makes it more complex still.

(Tim Elmore) #7

@Erik_van_der_Zalm No, but I can read the information posted on the website. ~50 grams, compared to 150-200g for a stepper. That isn’t the whole story though, since you also have hotend mass and end effector mass. You may be reducing the total driven mass by less than 50%. You certainly aren’t reducing driven mass to below that of a bowden setup, which I thought was the benchmark here. Both the flex3drive and bowden setups will have non-zero backlash, and the bowden setup is practically free when compared to the $150 flex3drive.

I just don’t see many pros, but see several cons.

(Topias Korpi) #8

http://youtu.be/ntJsPCwG6xc Here is first prototype of my own build. Not very much testing behind, but it seems to work pretty well. It’s very light to turn, so spinning part of cable isn’t bending.

(Arthur Wolf) #9

@Tim_Elmore1 I have a flexidrive. The backlash is not the same as on bowdens : there is a lag when changing direction ( a bit of play, more than lag ), but once it is rotating, there is no recognizable lag between the stepper and the end of the flex shaft. So essentially you need to change your retract length, but other than that it is equivalent to having a stepper on the head.

(D Rob) #10

There is some work on this already. He even sells them. @ThantiK ​ is also working on a version. Thantik who was it selling them?

(ThantiK) #11

I abandoned that Avenue a long while ago. I didn’t buy my flex shift, @Mike_Smith ​ did, and I think it was from an rc hobby store

(D Rob) #12

@Tim_Elmore1 one pro is making Bowden unfriendly filaments (ninja flex) possible while keeping mass lower than a traditional direct drive setup

(D Rob) #13

@Topias_Korpi using aluminum is totally anti intuitive. That rig looks heavier than a Nema 17.

(ThantiK) #14

Honestly that’s the big one for me. I want/love bowden setups on all of my printers, for the fast printing speed. But I really want to try some ninjaflex.

(Topias Korpi) #15

@D_Rob that is just first prototype, so it will get smaller. Even now it’s way lighter than nema 17. Oh, and the part is just that thin flange behind extruder. It is going to new printer which will have lighter extruder. Aluminium still weights only 2,7g/cm3 when steel is 7,86g/cm3

(Topias Korpi) #16


(Michael Scholtz) #17

Think out the box the goal is weight reduction so anything that reduces weight would assist. How about switching from a fan and big heatsinks to water cooling. Will allow more efficient cooling. Smaller heatsinks and possibly a smaller stepper motor cooled so it can be driven harder.

(D Rob) #18

Ah but 2 hoses need to be added for water and those have resistance to flexing. More so than the mass of the fan.

(Michael Scholtz) #19

Still less than the flexible drive. It makes me appreciate for how small the ultimaker2 head is.

(Michael Scholtz) #20

So what about using the filament guide tube to guide air from a relocated fan to the prints head means bigger fan off the head and you can use it for cooling a heatsink and the print.