Printing with PET

I tried some PET filament over the weekend, it is reputedly stronger than ABS and easier to print so I thought it may be better for my quadcopter parts. It prints OK but I was not too impressed. The part I printed warped a little, which could probably be stopped by experimenting with the bed temperature (I used 60 deg), but shows that it does not have a significant advantage in that respect over ABS (so it is not easier to print with IMO). The infill started to break up at a print speed of 60mm/s so I slowed it down and it was fine - again a bit of experimentation with hotend temperature would probably cure that (I used 210 deg). It prints with a very shiny surface finish, so may look better for ornaments etc. I happened to have a rejected (slightly warped) motor arm printed in ABS, and so I printed the same item in PET so as to compare strength and rigidity. Flexing the parts by hand did not reveal any noticeable difference in rigidity, and bending by hand to destruction needed about the same force for both ABS and PET. The PET delaminated easier than ABS, but that could be due to less than optimum print temperature. Weighing both parts however showed that PET is significantly heavier (more dense), which makes it worse for use in a quadcopter given that there are no significant strength or rigidity advantages AFAICT. PET is more expensive than ABS, which is exacerbated by its higher density (less filament length per kg reel).

Dave

Thanks Dave, that's some useful information. I considered to try out PET a while ago but didn't see any real advantages over ABS (except perhaps its shinier surface finish) so I haven't collected any experience with it yet.

I also have a spool of Nylon left which I'll use for parts that need to deal with higher temperatures (such as my custom heated bed parts), although I find it quite difficult to print with as it shows way more warping than ABS for example.

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dmould
I tried some PET filament over the weekend, it is reputedly stronger than ABS and easier to print so I thought it may be better for my quadcopter parts. It prints OK but I was not too impressed. The part I printed warped a little, which could probably be stopped by experimenting with the bed temperature (I used 60 deg), but shows that it does not have a significant advantage in that respect over ABS (so it is not easier to print with IMO). The infill started to break up at a print speed of 60mm/s so I slowed it down and it was fine - again a bit of experimentation with hotend temperature would probably cure that (I used 210 deg). It prints with a very shiny surface finish, so may look better for ornaments etc. I happened to have a rejected (slightly warped) motor arm printed in ABS, and so I printed the same item in PET so as to compare strength and rigidity. Flexing the parts by hand did not reveal any noticeable difference in rigidity, and bending by hand to destruction needed about the same force for both ABS and PET. The PET delaminated easier than ABS, but that could be due to less than optimum print temperature. Weighing both parts however showed that PET is significantly heavier (more dense), which makes it worse for use in a quadcopter given that there are no significant strength or rigidity advantages AFAICT. PET is more expensive than ABS, which is exacerbated by its higher density (less filament length per kg reel).

Dave

Dave

I have had some success with pet and found that Bed temps were lower than that needed for either PLA or ABS think I used 40 but that the hotend needed to be about the same as ABS in fact think I used 245 and it was fine at that. (I also use Kapton Tape on my bed)

I had no warping or delamination and I could not bend it at all. (It was a fairly small part mind)

I must admit that I haven't done much with it but I do have 3 rolls of ESUN PETG to go at.

Doug

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dougal1957
Dave

I have had some success with pet and found that Bed temps were lower than that needed for either PLA or ABS think I used 40 but that the hotend needed to be about the same as ABS in fact think I used 245 and it was fine at that. (I also use Kapton Tape on my bed)

I had no warping or delamination and I could not bend it at all. (It was a fairly small part mind)

I must admit that I haven't done much with it but I do have 3 rolls of ESUN PETG to go at.

Doug

Yes, the symptoms were consistent with a low nozzle temperature with my print and as I said, I am certain I could get prints at least as good and fast as ABS with a few adjustments. I used a bed temperature of 60 degrees as that is the glass transition temperature for PET, and I found that information and a recommended nozzle temperature of 210deg on [www.makergeeks.com] - but as you say it certainly needs a higher print temperature.

I could not however discern any difference in the strength needed to twist & bend the part compared with the same part printed in ABS (a 200mm long quadcopter arm). I was hoping to be able to use its reputed extra strength to make lighter parts - but I had not realised that PET is 50% more dense than ABS so it would have to be considerably stronger before I could use the strength to design a lighter part (in fact in this application strength is not the main issue, rigidity is more important to prevent the arm bending and twisting as the motor power changes). The ABS arm weighed 45g but the identical arm in PET was 67g. Of course, in different applications the extra weight could be an advantage. The filament supplier I use sells by weight (1kg spools), and so my reel of PET is 30% shorter in length to a reel of ABS, and cost £24 as opposed to £18 for ABS.

My previous quad designs have all had extruded aluminium arms, which is probably the best material for the job, but I like having a 100% printed frame (apart from the fasteners). I see there are now filaments with various embedded fibres available, and I may give one of those a try. This one (sold by 3dfilaprint) is designed with ESD in mind, but the datasheet shows a superior flex strength to plain ABS - though sadly the density is not given [dzmlsvv5f118.cloudfront.net] It is however very expensive (more than 3 times the cost of ABS).

Dave

Edited 1 time(s). Last edit at 04/27/2015 01:06PM by dmould.

Dave

I have some ESUN PETG which is 18.99 EUR per Kg

and this is a photo of the label on the reel



HTH

Doug

The information on the "makergeeks" site is probably incorrect. When one person finds the ideal temperature to print at, they often pass on erroneous information due to the fact that few people bother to calibrate their nozzle thermistor, so the temperature they are really printing at is not the same as the temperature they have set (and think they are printing at). So while finding the best temperature by trial-and-error will give consistent results on that particular printer, it may not be the correct temperature to set for another printer. I have used a thermocouple probe & thermometer to check my temperature accuracy, which I therefore know is within 1 degree of its set temperature between 200 and 230 degrees on my Ormerod, though its accuracy decreases below that range.

Dave

Dave

Totally agree with you on that.

Doug

I'd thought the main advantage of PET was that it was easier to source in an FDA approved 'food safe' form. I haven't tried ABS or PET yet, but I've looked around a little bit. I know polycarbonate is very strong, and very hard to print (need thermocouples, all mettle hot ends, printed parts probabley need to be replaced with Polycarb as well)


However, if you're finding that part strength is insufficient, you might want to check out this recent research study [journals.plos.org] it's on PLOS ONE so free access for all.

The authors look at increasing part strength by printing with a low/no infill and then drilling a 1mm hole (with possibly some vent holes) into the part and then injecting various epoxies into the voids. Depending on your part this may or may not be practical.
They also admit that current infills aren't ideal for this, and that a new infill pattern should be developed. Another possibility for even better strength to weight ratios is to have 'channels' inside the part so that the epoxy only goes to the parts of the part that need it. But our current (open sourced) softwares aren't made with this function in mind, so it could be a bit of work.

Yes, epoxy infill is certainly something worth bearing in mind. I have been using various types of epoxy since the 1980's, mainly as a high-strength wood glue and filler for boat-building and other carpentry projects. Two wooden beams or stringers can be butt-joined using epoxy with a cotton or asbestos filler, and the join is stronger than the planks! (Though I always scarfed such joins just to be safe). It is a fantastic material that was the main fastener and protective coating for the 10m yacht I built, and protected it perfectly from rot and borers over a 5 year trip around the East and West Atlantic. Not a single join or coating showed any sign of deterioration (the coatings were painted with a UV protective paint). Unfortunately a few years ago I suddenly developed a pretty severe skin allergy to uncured epoxy (or maybe the formulation of the epoxy changed), and I must now take extreme care not to get the slightest drop of the liquid on my skin, or even expose my skin or eyes to the fumes for very long. It is surprising how difficult it is to protect against such a thing without resorting to a full hazmat suit. Fortunately I can handle the fully cured plastic all day with no ill effects.

Dave

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dmould
I tried some PET filament over the weekend, it is reputedly stronger than ABS and easier to print so I thought it may be better for my quadcopter parts.
Dave

I've used both PLA (Purple) and ABS (Pink) for my Quadcopter.
I think the ABS is a better material for this job as it's more flexible.
I've had a few crashes and both materials seem to stand up OK.

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Jon Steward
I've used both PLA (Purple) and ABS (Pink) for my Quadcopter.
I think the ABS is a better material for this job as it's more flexible.
I've had a few crashes and both materials seem to stand up OK.

Looks nice! My first designs were completely enclosed and used aluminium tubes for the arms, but my current design is similar in construction to yours (no photo available right now). The plate carrying the battery (lower plate) hangs from the arm-carrying plate by 6 anti-vibration balls rather than being bolted. The weight of the battery gives the plate inertia which kills all vibration and allowed me to mount a camera on the battery plate for jitter-free video (absolutely zero "jello" rolling shutter effect). I'm presently designing another similar quad that has the controller also mounted on the top of the battery plate - isolating the controller from vibration should give smoother flight characteristics without needing to perfectly balance the props (which is a pain). My present design has the controller mounted on its own anti-vibration balls on a higher plate, but because the controller has very little weight (inertia) the balls do not do as good a job as they do on the battery plate.

ABS is considerably less dense than PLA and so makes a lighter frame (=more flying time between charges). Flexibility is not however desirable in the motor (propellor) arms. I have a previous unsuccessful design where I made the arms too thin. They were plenty strong enough, but their ability to twist and bend made that design almost uncontrollable. I spend far more time designing & building than flying them - I have yet to master the art of FPV flying though the last couple of times I tried shows that it is definitely a superior experience!

That's interesting Dave.
This is my first attempt at Quadcopters and you're right about the difficulty flying these things.
The design I've used has the battery Velcro'd to the underside so the weight is low down and feels stable.
Once I've got the knack of flying I'll brave to mount my Gopro on the top. Crashing would be 'eye wateringly' expensive!

Yes, my present design also has the battery attached by velcro straps to the lower plate (it is loosely based on this design [www.thingiverse.com]) - , though surprisingly I found over various designs that a lower C of G does not make a great deal of difference to the stability in flight. The PIDs need to be set up carefully on the controller, and always use "stability" mode (for MultiWii that's "Horizon" or "Angle" mode). Trying to learn to fly a quad in acro mode is very difficult.

Dave

That is an impressive looking Quad. Two camera's too!
I'll aspire to that one next. Mines definitely an entry level option.
Good fun though.

There is a considerable difference between PET and PETG. PET seems similar to PLA but PETG is way superior having almost zero warp without a print bed cooler and being a lot stronger from my observations without scientific testing.
I print PETG at 245C hotend and 100C (85 at glass top) bed for best results whereas PET prints at similar temperatures to PLA.
I received a couple of rolls of eSUN PETG from reprapworld a couple of days ago and have been printing quadcopter parts. I very much like it.
For a lower price, similar quality, infinite colour options but with a longer delivery time I would order direct from China: [www.ecoreprap.com]

Edited 1 time(s). Last edit at 05/21/2015 05:21PM by Ralph.Hilton.

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dmould
Yes, my present design also has the battery attached by velcro straps to the lower plate (it is loosely based on this design [www.thingiverse.com]) - , though surprisingly I found over various designs that a lower C of G does not make a great deal of difference to the stability in flight. The PIDs need to be set up carefully on the controller, and always use "stability" mode (for MultiWii that's "Horizon" or "Angle" mode). Trying to learn to fly a quad in acro mode is very difficult.
Dave

I am just starting out with Quadcopters. From basic physics lowering the CofG is going to make the copter less manageable. As gravity is a minor factor compared to acceleration the optimum CofG must be central on all axes.
I'm working with the version at [www.thingiverse.com] as I use Openscad and it is easier to modify.

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Ralph.Hilton
I am just starting out with Quadcopters. From basic physics lowering the CofG is going to make the copter less manageable. As gravity is a minor factor compared to acceleration the optimum CofG must be central on all axes.
I'm working with the version at [www.thingiverse.com] as I use Openscad and it is easier to modify.

An excellent choice sir - that's my design! (uploaded shortly after posting about it here). If you downloaded it a while ago, check again because I later added a text file containing a list of the parts that I used (not that you have to use those particular parts of course, but they are the ones that fit without modifying the SCAD and are all available from the UK HobbyKing warehouse). Check that your motors have wires coming out in the correct direction for the mount holes - if not simply swap the two mount hole variables in the Scad file. The motor bolt length variable is important to match to the bolts you will use - if you use longer bolts than that variable you may damage the motor (by screwing a bolt into its winding). I did not include the ESC or battery connectors & wires in the parts list - I soldered bullet connectors for the ESCs directly to the power distribution board (lying flat on the pads). Let me know if anything is not clear regarding construction.

Using F5 in OpenScad instead of F6 to render after making changes is faster, but you will need to increase the max number of elements rendered. That parameter is found in the latest version of OpenScad under "Edit">"Preferences">"Advanced">"Turn off rendering at nnnn elements" Note that F5 does not always render accurately, often displaying bits that should have been subtracted but it's fine as a quick check of the effect of changes.

Dave