WoW! much fly, little coin! January 30 2014

We now accept dogecoin here at there is no official checkout system yet, so please bear with us as we do this by hand....orders may take a few hours to process. We will email your files to the email address you use to contact us, as an attached zip file. To simplify things and give our fellow shibes a great deal, prices on all individual packages are currently 1000 DOGE , and the All gliders package is 5000 DOGE


To pay with doge, just send an email to with your order details, and transfer your doge payment to the wallet :




To The Moon!

Manta ray October 10 2013

The manta ray, here pictured with the stingray and a 12" (30cm) ruler for scale
The latest addition to the fleet is the manta ray... a 350MM wingspan bird that can be printed on a 190MM bed. It is designed to be flown by hand, or with a rubber band if a "runway" is used...flying wings are very pitch sensitive. We are especially excited about this design, as it is also the inspiration for our next "top secret" project, which if successful, will be a world first, in a class by itself....stay tuned...

extrusion multipliers and printing engineered structures - a technical brief October 10 2013

In FDM (fused deposition manufacturing)  printers like the REPRAP and related designs, the amount of filament that the extruder deposits through the print nozzle while printing is one of the most critical factors. The calculation to arrive at the correct amount of filament to feed will be dependent upon the feedstock filament size and variability, the nozzle diameter, the extruder drive wheel tension, the extrusion temperature, and the layer height (+/- any first layer corrections).


excessive material deposition caused these lumpy surfaces, most evident

where the fill ratio is 100% and there is no place for excess to go.

Sometimes, insufficient first layer height can be the actual cause

on thin structures such as this.


For aircraft and other objects where the interaction of the internal and external structure of an item works together to provide a desired function, significant deviations from optimal extrusion may cause unacceptable performance characteristics in the finished print.

Many of the aircraft designed by Handmade By Robots here at are engineered to flex in very specific ways in response to environmental factors such as airspeed, g-loading, gravity, and -especially in the case of the cumulus- even air currents and thermals (it is designed to resist the natural tendency to turn our of buoyant air by twisting at the wingtips).

The flying wing series develops its proper airfoil and reflex shape by a complex interaction of bending forces created when the dihedral clip, the wing hinge, the unhinged portions of the wing, and the vertical stabilizers / reflex formers interact in the assembled model.

Due to these design considerations, as well as cosmetic factors, it is highly desirable to optimize the extrusion process as much as possible so as to preserve the designed in flight characteristics, minimize weight, and to end up with an attractive, true flying model.


A small deficit of material causes the upper surface to fuse

incompletely, resulting in porosity and a lack of rigidity.


Assuming that your extruder is properly calibrated in the firmware, and the G-code generating program you use has good numbers for your filament and nozzle size, a reasonably midrange extrusion temperature, and an accurate idea of the actual first layer height, you should get reasonable extrusion quality barring problems with extruder drive function or adjustment.

For -optimal- printing, such as may be required for highly engineered pieces (such as functional items, or items designed to flex in very specific ways, such as aircraft) some fine tuning may be required. The goal is to deposit just enough material to provide solid fill of solid objects, without excess or voids of any kind. In practice, this can be very difficult, as feedstock filament size has some variability, and this variability is magnified and directly expressed in the extrusion process.

The "fudge factor" used to compensate for minor mis-calibration or filament variation is the "extrusion multiplier", a simple factor applied to the overall extrusion calculation, so that 1 equals no adjustment, .95 causes a 5% reduction in filament feed, and 1.05 provides a 5% increase in feed. 

In practice, a slight deficit of material is preferable to excess, which builds up on the print and can accumulate to the extent that if can cause a print head crash, ruining the print , or in less severe cases results in a globby surface. As long as the deficit is just enough to compensate for filament variability, and the filament is also reasonably uniform, any deficit or voids in the final piece will be negligible.  On the other hand, if the material deficit is excessive, flimsy prints, unclosed surfaces, poor bed adhesion, and porous structures may result. 


Insufficient extruded material caused these voids. In this case,

it was caused by insufficient tension on the extruder drive wheel springs.


One way to determine the proper "fudge factor" for a given combination of filament, nozzle, and extruder is to print a solid object at 100% fill. gradually increase the extrusion multiplier (by .02-.03) until the print starts to develop surplus material, which will typically be evident at the edges first as the print becomes more "messy". Then retry while reducing the multiplier by .01-.02 until the print is once again uniform. This should be close to optimal, although filament variability may cause you to back off another .01-.02 if excess material occasionally appears.

At this point you may have to readjust your first layer height multiplier to reflect the inverse of your extrusion adjustment (for example, if you -increased- extrusion by 3%, you will need to make an equivalent -reduction- at the first layer adjustment.

Having a correct extrusion calibration / multiplier will help you to make clean, high quality engineered objects that fit together and provide the performance characteristics with which they were designed.







Snap together! September 30 2013

An exciting new development in our design process is the addition of snap-fit models. The glueless construction simplifies assembly, but requires pretty clean dimensional performance from your printer. If your printer is well calibrated and makes pretty good corners, these should work for you.





On models that use a dihedral clip, it is helpful

to attach the clip corner first, while holding the 

dihedral hinge tightly closed, then slide the clip

all the way forward until it stops or clicks into place.


   The stingray
The glueless stratos

These and more coming soon.... and don't worry, If you have recently purchased any of our "all models" sets, I will be forwarding the new designs to your emails when they are ready, free of charge!
In the mean time, the preview editions are availble at thingiverse.... and 

3D Printing airplane wings and other membrane structures May 27 2013

When printing very thin (1-4) layer structures with FDM printers, special issues are sometimes encountered.


It is often helpful to use a slightly higher (3-7 deg C) than normal temperature for the first layer to enhance print leveling, reduce nozzle pressure, and to improve adhesion. Be careful not to raise the temperature to the point where decomposition of the thermoplastic begins, as this can cause nozzle clogging and degraded print quality.


  You will need a bed surface with good adhesion qualities. It must be flat, free of skin oils, and clean. For ABS, Kapton tape cleaned with CPVC-PVC-ABS pipe cleaner compound works well. For PLA, Kapton adhesion is often poor, and can be improved by dissolving a small amount of ABS filament with the solvent swab and wiping down the bed surface with the resulting mixture. Beware that this process will result in extreme adhesion for ABS prints.

An adhesion void in an otherwise ideal 

single layer print. This small defect will

be reinforced by the second layer, so a

reprint will not be necessary in this case.

First layer height:

The first layer height must be adjusted either physically or in software to give .5 to .8 of the normal layer height. Software settings should be made in the print profile to reflect this. This will allow good print leveling characteristics. Layer height and percentage should be adjusted to achieve a print line with approximately 1.25 - 1.5x nozzle diameter, with a flat profile and straight edges.

Bed flatness:

Many times, the print bed is not perfectly flat. Compensation must be made within the first layer to achieve good quality thin prints. This imposes certain constraints on the process, depending on the relative irregularity of your print bed.


Localized sieving caused by a gap 

in the tape surface of the bed.


  Any variation in bed height within the work footprint should not exceed .5 of your first layer height (layer height x first layer multiplier). Compensation can sometimes be made by increasing your slice layer height within the available constraints. Prints can also be constrained to a more regular area of the bed, or the bed surface can be replaced with a flatter bed.

Bed flatness problems are characterized by variations in print quality depending on its area on the bed, with some areas showing surface curling or stringing while other areas print correctly. Some minor variation may be unavoidable, and often defects will be buried under a following layer if they are not too extreme.

Surface Defects:

  Surface defects include surface curling and sieving. Surface curling is characterized by a ribbon type defects along the fill print lines, resulting in a rough, higher than layer height print profile.

Surface curling indicates excessive nozzle pressure. It can be remedied by increasing the physical first layer height (adjusting the end stop), or reducing the software first layer height percentage.




Minor curling caused by insufficient nozzle height. 

In this case it was not too severe, but artifacts can

sometimes block the motion of the nozzle,

ruining the print.


    Sieving is characterized by fill that is not bonded to the adjacent filaments and is sieve like and not fully contiguous. This is regularly accompanied by poor adhesion and poor structural characteristics. sieving can be remedied by decreasing the physical first layer height, or increasing the software first layer percentage.


Sieving, here caused by a low spot on the bed. 

Nozzle height should be adjusted to give a

 workable compromise between the high

and low areas on the print bed.


The favored mechanism for correcting first layer defects is to set the software first layer percentage to .7 of your layer height, and adjust the physical first layer height (end stops) to achieve the desired print quality. Final tuning can then be done in the software setting.

Sometimes print defect types will vary over the surface of the print. This is an usually an indication of poor bed flatness or adhesion problems.

Nozzle Pressure:

It is helpful to be aware of nozzle pressure, especially when printing membranes. High nozzle pressure causes surface curling, poor edge definition, point blobbing, corner artifacts, and stringing artifacts. Insufficient nozzle pressure results in poor adhesion, intermittent voids, and sieve like membranes.

Low nozzle pressure results from excessive physical layer height, improper filament / extruder calibration, or filament drive slippage. Sometimes low temperature can mimic low nozzle pressure by causing drive slippage.

High nozzle pressure results from insufficient physical layer height for the software settings, low temperature, poor filament / extruder calibration, or nozzle blockage.

Elasticity in the printing system, especially on bowden type (indirect) drive extruders can cause artifacting when the conditions causing the pressure buildup are temporarily relieved, such as when the head is lifted.

When printing first layers on an imperfect bed, nozzle pressure will rise as high areas are encountered, restricting flow from the nozzle. System elasticity will then cause excessive plastic to be extruded when this pressure is relieved, such as when a lower portion of the bed is encountered or the nozzle is lifted, sometimes causing gobbing or poor line definition.

In some ways this automatic flow adjustment can actually be helpful, as it creates a leveling effect, extruding less plastic on the high spots, and filling in the low ones with the surplus. The goal is to achieve the best compromise of leveling and print quality, to provide an ideal foundation for the second (and often final) layer in your membrane print.

Elasticity effects can be reduced by reducing the hot area as much as possible by cooling the extrusion barrel, using low elasticity components in your drive and extruder systems, and by careful control of filament retraction parameters.