Category Archives: Engineering

3d printing Patents

Came across some interesting pattents that are still held by Stratasys regarding 3d printing and heated chambers.

Heated chamber to be between 70 and 90 deg C.

Tailoring strength of infill material in 3D prints

In an effort to try and control the internal fill material of a part (both direction and amount) I’ve been experimenting with some ideas. (I am using a PP3DP UP! Plus printer, but this applies to any 3d printer)

If the generic cross pattern is either not strong enough for you, or you want to tailor the direction of strength a little better what you must do is model some features in your part that the slicing software can use to put material where you want it.

The simplest method I’ve found is to model internal “cuts” or “slits” in the part. For the UP printer, the slicer software will do the 2 walls around the opening, but if the cut or opening is modeled narrower then 0.1mm, the opening never really materializes (is not present in the internal structure of the print) since the material from both sides will fuse together when being printed. I’ve been using 0.05mm for the slit width.

So if your complex geometry part needed to be stronger in one direction then in another, you could model some “slits” in the direction you want more strength* and less (or no slits in other directions).
* More strength in comparison to the generic fill of the slicer software.


This method can not only generate strength in desired directions, you could use it to just create thicker walls (more around the perimeter, more walls if the slicer software gives no control of that like the Up! Plus software)
Another thing this method can create (which is not currently possible with the UP software) is a solidly filled object. Just create offset surfaces of the outside perimeter surface (towards the inside of the part) every 1mm or so. Then turn those offset surfaces into “cuts” into the part. At each one of those location, you’ll get another set of perimeters.

A few things to note:
– With ABS, I found that walls shift slightly when more material is deposited due to the extra material the “slits” introduce. On my Up! Plus walls shift about 0.15mm to 0.2mm. I can compensate by adjusting the CAD model to account for this. Your millage will vary so do some testing.
– With PLA I’ve noticed a lot less of this wall shift. I haven’t done any extensive testing, but from the few parts I’ve printed I’d say under 0.1mm of wall movement is observed.
– Depending on how smart (or not so smart in the case of the Up! Plus) your slicer software is, it may not know that

I think the best part of all this the ability to internally “truss” a part in the Z direction with solid material. Normally in the Z direction the only material that can resist breaking is the strength of the inter-laminar bonding of the plastic fibers(deposited filament). And really only the perimeter 2 layers, since I would not count on the infill to resist much when stressing the layer bonds.
Imagine printing a tall (in the z direction) skinny tower. If you try to snap it, it will break at the layer bonds.
Now I can make internal diagonal solid pillars (reinforcements) that can resist forces in the designed directions.

More on this as I do more experiments.

Project and Task Management

After watching a short 2 min video, it dawned on me that I can make better use of my time if I pre-planned in detail most of my hobby projects.
A lot of what is mentioned in that video I felt applies to me, so I’m going to make an effort to streamline how I approach my hobbies.
Often when I have some energy to tackle a task in the evening, I am am grasping at straws for what to do mainly because I don’t know where to start or which project to work on… and for the most part this turns into procrastination. A little bit of youtube, a little bit of facebook… and the night is wasted.

I am going to pre-plan all the tasks I need to accomplish for all/most my hobby projects going on at the moment. The hope is that when I have 15 or 30min available, I can just pick up a short task, and complete it without having to look at the big picture (in the moment). Just get the task done and move on.

3D Printing resolution

With FDM (Fused Deposition Method-printing with a filament) 3D printers there’s always a question about the accuracy or precision of the print.

I read a great description of the misconceptions of how accurate 3D prints using this method can be:
“Clarification: the precision of the printhead in the horizontal plane (X-Y direction) is about .011mm (about 2300dpi). However, this number is a little superflous because we are extruding ABS plastic through a relatively larger .35mm nozzle, and all ABS plastic oozes a bit. So a more realistic & practical estimate of resolution in the horizontal plane is about .1mm. And to be crystal clear – this creates great prints. Trying to define the resolution more accurately than this is similar to trying to define the position of a garden hose nozzle to within millimeters – it’s essentially meaningless since the water is going to expand anyway.”


Timing belt sizing for quadrotor power transmission

Looking for info on designing timing belt power transmissions. Some sites I’ve found of interest:

The tooth profile of the FT2 and HTD belts have a much higher resistance to skipping combined with a higher power transfer.
Technical data on belts, gearing, chains.
HTD belt data sheet
ore HTD belt design data sheet
SKF “Power Transmission Belts” manual ; from page 128 onward for timing belt sizes and calculations
Gates manual for “Powergrip GT2 Belt Drives” (may have to register; it’s free)
Gates design manual for “Light Power and Precision” (may have to register; its free)


Looking for places to get cheaper timing belts:
Chinese outfit. Prices reasonable, minimum order is $25 shipping
Supplier list of timing belts and pulleys (bottom of page).


What I learned from going over the SKF and Gates design manuals for timing belts and pulleys: Belts transmit a certain amount of power. That power is based on the rpm of the pulleys. Taking the RPM out of the equation, the force on the belt is relatively constant for (for a certain RPM). The torque varies but only because the gear diameter changes. Between the different timing pulley sizes (at a constant RPM) the torque varies based on the pulley diameter. The force on the belt is relatively constant.

The force on the belt however seems to vary with RPM for some reason. Have to understand why that is. Also have to understand why the belt length affects the force transmitted by the belt.

The torque and power numbers listed in the tables is based on 6 tooth engagement. Less then 6 teeth requires a correction factor.

Going with a GT2 pulley system. It provides a much better power transfer with less skipping. Even a small GT2 2mm pitch belt at 6mm wide will be able to transmit about 70w of power. The 4mm wide belt should transmit about 47W of power.
Equation for Power: P (W) = Torque (N-m) * RPM * (2*pi/60)  (source)

Using the data from the “Gates Light Power/Precision” design manual, a GT2 5mm(pitch) belt can transfer nearly 3 times the power at the same belt width and RPM then a XL belt.

For the GT2 belts, the 3mm pitch belt can carry 4 times the load of the 2mm pitch belt and the 5mm pitch belt can carry 5 times the load of the 3mm belt. So instead of increasing the belt width, you get much more bang for the buck by going to the next size pitch belt.

In contrast with the  Trex450 belt is 2.03mm(MXL) pitch or 0.8 inch pitch, 3mm (1/8″) wide. This MXL belt can transmit about 30W of power.
From THIS POST I was able to get about 700g of thrust = 50ish W with only 5 teeth engaged on the 11T pulley at around 2000RPM. Since only 5 teeth were engaged (6 is minimum) only 80% of the possible power was transmitted, so i could possibly transmit 40ish W with all 6 teeth engaged. I was actually exceeding the design guidelines in terms of power transmitted but only by a little bit.  Going with a larger puley of 19T (see this post) I was able to get 1080g of thrust = 90ish W.
I was pushing the system way beyond its design capabilities. Likely the timing belt design data is conservative.
With a GT2 belt, I should be able to transmit WAY more power with a similar sized belt. With a 14T pulley, at 3600 RPM,

For a 3kg AUW (2kg quad and 1kg payload), I would aim for a 3:1 power to weight ratio, so need to be able to generate 9kg of thrust. Using two 250 blades (250mm long, 22mm chord) I need about 4500RPM at 10deg blade angle to get 9kg of thrust from all 4 rotors. With a 2 bladed rotor I’d be sucking down 911W. Slowing down the rotor to 3500rpm and adding 2 more blades (4 total) 9kg of thrust can be produced at 880W. Goes to show how much drag increases with RPM.
Designing for 3500 RPMs and 1KW power usage (250W per rotor)

Keeping track of projects

For projects where ordering parts is a necessity (like from HobbyKing), I should keep track of why I ordered each part and what its intended use will be.
I guess this should apply to most other projects. Keep track of progress, and just generally keep a log.

Copper CAM offset?

I notices that when milling a board who’s NC code was generated by Copper CAM, there is an offset between the drilled holes and the etching of the tracks.
Once I drill the holes, I’ll enter an offset of X-1 and then zero Mach3. That shifts the subsequent steps (etching, cutout) by 1mm to the left.
On closer examination, 1mm may be too much. I will try 0.8mm on the next board to see how it turns out.


It turns out that my mill is not perfectly perpendicular to the board. The error comes out of the fact that the end of the tool for the engraver mill and the drill is much different and when a small rotation is added to the mill head a linear difference is observed.
I adjusted the head rotation and now both the milled and drill points line up perfectly.

Limitations of the PP3DP UP! Plus printer – Thin wall sections

In designing some components I was interested to figure out what the limitations were of the printer, and figure out how it behaves when the printed part deviates from the cad model.

My first concern was how thin a wall the printer could print at different slice thicknesses, so I made a test part that integrated short pieces of different thickness wall sections. Continue reading