SANDY CURTH
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Extruder v1
This system will push clay, concrete or other earthen
material to the end effector through a linear actuator.
System Components
See diagram at right.
04 / 04 / 21
-Assembled the extruder system
-Cut standoffs for the motor/gearbox connection.
-Milled a flat on a 8mm shaft so we could couple the motor to
the gearbox
We found the standoff s to be a less than ideal solution as the motor still vibrated off axis slightly. Zipties helped but we have moved on to a printed PETG solution to be tested soon.
04 / 07 / 21
-Testing revealed the system worked but was a bit leaky around the nozzle connection.
-We also discovered the seal on our plunger was a total bust.
-Clay extruded (very slowly).
We are now working to improve motor control and seals.
04 / 10 / 21
I have been curious about why pushing clay through a 3" diameter tube is no problem for our nema 23 motor but the 1/2" ID 2' length of vinyl tubing broke our first acrylic tube setup and put us right at the torque limit on the new system with a motor with far higher torque.
Assuming the softened clay to be an incompressible Newtonian fluid in laminar flow I applied the Hagen–Poiseuille equation. The pressure drop relative to tube diameter found with this model explains the challenge we were observing clearly. Even moving to a 3/4" ID connector tube will significantly reduce our torque requirements.
04 / 13 / 21
Inserting a flared cap on the output end of the extruder tube has significantly improved the flow rate. A second version of this addition includes an o-ring to prevent any clay leakage. By making the step down from the 3" ID pipe to the 3/4" tube has reduced the pressure drop at this constriction.
There is still some clay escaping past the plunger. We suspect this may have to do with the relatively low tolerance of PVC pipes.
04 / 13 / 21
Inserting a flared cap on the output end of the extruder tube has significantly improved the flow rate. A second version of this addition includes an o-ring to prevent any clay leakage. By making the step down from the 3" ID pipe to the 3/4" tube has reduced the pressure drop at this constriction.
There is still some clay escaping past the plunger. We suspect this may have to do with the relatively low tolerance of PVC pipes.
04 / 28 / 21
We were finding the extruder motor was still stalling out even with a reduction of the tube length from 3' to 2'. We revisited the control system and found that we were only sending 1/2 current to the motor through the driver. We were also sending a the lowest setting. By adjusting the driver we increase the current from .5 A to 4.1A. The result was a motor that got very warm, didn't stall, and drove the lead screw right through the PETG plunger. Essentially getting clay to the auger is no longer an issue but pushing it through the barb fitting into the mixing chamber is requires more force than the plunger could withstand.
We are now remaking the plunger in aluminum with a seal in addition to two O-rings.
The other obvious next test is running significantly softer material through the whole system.
We have updated the nozzle le interface to accept various size brass barb fitting with a 3/8" NPT connection. Having a larger nozzle should significantly reduce the force on the plunger.
We are consider shifting away from a Bowden tube system entirely (right) as that has been the root of our issues for a few weeks and is inhibiting our ability to test mixing.