3D Printed Electronics Sled

[ecarson]

I've absorbed quite a mass of information from this forum in the few weeks I've been a member. The search function is quite good at finding pertinent results quickly. I flgured to return a bit of it in some small way.

A couple of months ago, I decided to return to the world of rocketry and attempt to get my Tripoli Level 1 certification before the end of the year. I guess they call guys like me "born again" or something like that. I launched several Estes kits back when men were walking on the moon on regular basis. The bug got me again for another few kits during my college days, and it was all quickly forgotten when I entered the work world. Now being retired a couple of years, the bug has returned once again.

Last year during a major project of mine on an aircraft simulation project, I acquired an inexpensive 3D printer. An Anet A8 of the Prusa i3 configuration. Only about $150. Several upgrades were made. Frame reinforcements, Z-axis limit switch adjuster, fiberglass core belts and belt tensioners, bed leveling improvements, MOSFET power relays for heated bed, and a few other things. The machine is a whole other hobby by itself, as I had to build the thing from a thousand separate pieces, but that was quite a fun learning experience.

This following posts are about a 3D printed avionics sled I am designing in the early stages. After attending my first local high power launch a couple of weeks ago, I saw an alarming number of ballistic crashes due to recovery system failure in the high power arena. I immediately resolved to try and minimize the probability of that happening to me for my Level 1 attempt. I also remember losing several rockets during earlier years to high winds aloft, and when I read about the dual deployment method, it seemed a great solution to that dilemma.

This is basically a 3" diameter rocket, which will have an avionics bay or "avbay" coupler for the fore and aft parachute compartments. I am building as much as possible from scratch. I already have a few nose cones printed, using a design I found on Thingiverse. An elliptical nose cone, of three sections that thread together. It fits a standard 3" heavy duty mailing tube quite perfectly.

I started with a plywood section electronics sled, and thought that a 3D printed sled would be better. I wanted a better symmetry across the rocket long axis which I call Z. The avbay has two threaded rods, 1/4"-20 made of 6061 aircraft alloy. They are on what seems to be a 2" center standard. This is the main structural connection of the avbay bulkheads. Avbay tube length is about 9". (I actually using millimeters for most of my design work, and I'll explain that in a bit.)

Last year, during my simulation project, I used the free open-source program "Blender" heavily. I got fairly comfortable with it. I attempted to use FreeCad for parametric design, but no traction yet on the learning curve for that. I realize Blender is considered mainly for artistic use, but I have found that is has powerful capabilities for engineering 3D printed components. It seems as if many folks find the learning curve on Blender a bit too steep as well, but I got along with it pretty quickly.

Blender works best for me using millimeters I have found. Numeric fields purport an accuracy of .00001 millimeter on position and size. More than good enough for any 3D printed work. This works smoothly on export to STL file, which comes in right on the money into Cura 3D print slicer without any scaling necessary.

The following two photos show screen shots of my sled in the Blender quad-view, and the export to Cura (also free) slicer program. Of the slicers I have used, I like Cura the most, and have always had acceptable results writing the g-code to my 3D printer.

 

[ecarson]

Continuing on:

The gcode is copied to a micro SD, and transferred to the printer computer. I'm using black PLA from Hatchbox, as it seems to be fairly consistent in quality. Temperature parameters are 195 C nozzle temp, and 50 C bed temp. Blue painters tape over the aluminum bed for print adhesion. This has always worked quite well for me. 30% infill on a tetrahedral pattern, between 0.8mm side wall thickness, and 1.2mm bottom and top thickness. The main reason for that, is the acceleration loads were no doubt most severe at launch and of course main deployment (that is if everything works OK). 0.2mm layer height, at 50mm/sec main print speed, and 60mm/sec infill speed.

I always use a brim for bed adhesion of 8mm. The electronics raft is 160mm tall, so compared to the base dimensions I wanted a solid bed adhesion. The structural improvements I made to all axes of the printer would prove beneficial at the highest end layers. Another reason I printed like this, is absolutely no internal or overhanging support structures were required. The only material removed at finish was to peel away the brim. Finished weight 42 grams.

First photo is just starting. First layers are critical during 3D printing. Second photo is the completed print, which took a bit over 4 hours start to finish.

 

[ecarson]

Continuing On:

I was quite happy that the finished sled fit over the threaded rods perfectly, with only a slight amount of friction resistance. The whole avbay system fit perfectly, so the center-to-center distance was right on the money, as well as the rod diameters. I am using nylon 1/4-20 nuts to secure the sled along the rods.
Another result of this design, is that the rod and bulkhead structure is stiffened quite a bit, with increased torsional rigidity. If you twist either end opposite each other, only a slight amount of deflection.

Two nine volt batteries, are placed on gusseted "shelves", on either side of the sled. My plan is to fasten an Adept DDC-22 on one side, and then an EggTimer on the other. There will eventually be dual ejection canisters on both ends of the avbay. If one system fails for whatever reason, then the other will be backup.
Small cards cut to the size of the planned circuit boards, are taped just to see how they will fit on each side. The systems are currently on order.

This is by no means finished and tested in flight of course. I thought to incorporate printed stand-offs for the circuit boards, but that would have resulted in overhangs of one way or the other, and the resulting support material needed for dimensional accuracy.

For now, my plan is to drill the sled for the circuit board fasteners, and to melt slots above and below the nine volt batteries that will allow use of a heavy duty plastic wire tie. The gusseted shelves (I am hoping) should give adequate support for the dual 9-volt batteries on initial acceleration. My OpenRocket sim predicts 6 to 9 G's force at launch using a few different H-motors on the lower end.

Later on, I plan to shock test this structure, by dropping the avbay from a height with cords attached to the eyebolts. Then of course, several ground tests of the ejection system before I even think about putting it up at altitude.

 

[Cl(VII)]

Nice. My Prusa i3 mk2 kit is supposed to ship next week, and the first thing I will print after the tests is a sled for my Mongoose 54. Being really new to 3D printing I was afraid to get the Anet A8 and do the upgrades. I was afraid if it didn't work I'd wouldn't be able to trouble shoot it to get it to the self upgrading stage. Did you directly solder the heated bed connection? I believe I read the connector was at risk of wire fatigue and short.

The commercially available 3D printed sleds take plenty of G loads. I have flown one with a 9V to around 50G...I like Warp9 motors.

 

[ecarson]

Cl(VII), Two things really helped me on initial assembly. First a series of videos on youtube, detailing the complete assembly. I downloaded those videos and watched about three times each even before the printer arrived. Second, an included mini-SD card with the printer has color manuals in PDF on it. I printed both the full assembly and operations manual out and put in a binder before I even put one nut on a bolt.

On the heated bed, the MOSFET relay board is highly recommended by the Anet A8 and A6 support boards on Facebook. When I first joined that group, there were only 2000 members and I picked up the clue on the MOSFET board. Now, I think it is over 22,000 and very difficult to get good advice because of the deluge of "noise". There is a quite useful files section on that board however, and I downloaded just about every file.

So, from the printer control board, two small wires connect to the MOSFET (which is only about $10 on ebay I think.) I mounted the MOSFET directly below the control board on the frame. The MOSFET has the heavy duty screw terminals, so no worries about overheat of the control board connection at all. Most of the long term users recommend the MOSFET board. In short, the control board only gives a low amp signal to the MOSFET, and the MOSFET does the heavier amperage "lifting". The connection between control and MOSFET is now static, and non-moving. I can now comfortably leave the printer to do it's thing with confidence without keeping an eye on it all the time.

I highly recommend the fiberglass belts, and belt tensioner upgrades. They were quick and easy to install. The frame braces took a lot of plastic, but are well worth it when printing at high layer counts. With each upgrade, I saw an improvement in print accuracy and overall quality.

An assortment kit of M3 Allen head screws, and spare throats and nozzles have proven a good investment for keeping the thing operational.

 

[djkingsley]

The design of you sled looks good. I would recommend that you look at PETG and/or ABS filaments. I have had PLA sleds go soft and deform while in the hot summer sun on the pad. The new high temperature PLA filaments that have come on the market may also work but I have not tested them yet. I have several designs up on https://www.thingiverse.com/Djkingsley/designs that may give you ideas. Good luck on your L1 project

 

[ecarson]

djkingsley, you gave me a good idea for testing. One reason I chose black was because of radiated heat properties inside the avbay tube. The aluminum rods might sink a few more calories than steel as well. However, Murphy always prevails it seems. PETG seems a more forgiving filament in the open, although I have plans to build an temperature controlled enclosure to use ABS at some point. Materials are in the workshop even as I type. It will probably be late September, early October before I get this all ready, so hopefully summer heat will not be an issue when I finally get it all together.

 

[Cl(VII)]

Cl(VII), Two things really helped me on initial assembly. First a series of videos on youtube, detailing the complete assembly. I downloaded those videos and watched about three times each even before the printer arrived. Second, an included mini-SD card with the printer has color manuals in PDF on it. I printed both the full assembly and operations manual out and put in a binder before I even put one nut on a bolt.

On the heated bed, the MOSFET relay board is highly recommended by the Anet A8 and A6 support boards on Facebook. When I first joined that group, there were only 2000 members and I picked up the clue on the MOSFET board. Now, I think it is over 22,000 and very difficult to get good advice because of the deluge of "noise". There is a quite useful files section on that board however, and I downloaded just about every file.

So, from the printer control board, two small wires connect to the MOSFET (which is only about $10 on ebay I think.) I mounted the MOSFET directly below the control board on the frame. The MOSFET has the heavy duty screw terminals, so no worries about overheat of the control board connection at all. Most of the long term users recommend the MOSFET board. In short, the control board only gives a low amp signal to the MOSFET, and the MOSFET does the heavier amperage "lifting". The connection between control and MOSFET is now static, and non-moving. I can now comfortably leave the printer to do it's thing with confidence without keeping an eye on it all the time.

I highly recommend the fiberglass belts, and belt tensioner upgrades. They were quick and easy to install. The frame braces took a lot of plastic, but are well worth it when printing at high layer counts. With each upgrade, I saw an improvement in print accuracy and overall quality.

An assortment kit of M3 Allen head screws, and spare throats and nozzles have proven a good investment for keeping the thing operational.

A couple questions more about the A8 as I have some friends that are now intrigued by the idea of a low cost printer, but also being entry level like me they worry about troubleshooting it through the upgrades. It is less of a concern for the second printer in a group since there will in theory already be a working Prusa to fall back on if someone breaks a part, so I think at least a couple of them are thinking about getting A8s and upgrading them.

1) Did you need to upgrade the power supply since you are delivering more current to the heated bed? 2) what is your impression of the hot end that comes with the Anet? I have read they can be temperamental compared to the authentic E3 V6. 3) I know it is a hobby in itself, so the cost of upgrades isn't as big a deal, but how much have the upgrades run you other than the time and filament cost for the printed parts? I want to give folks who ask a non-guess answer. 4) What filament types have you printed so far that worked and didn't? You give nylon a shot yet?

 

[ecarson]

Cl(VII) (by the way, love the avatar. I used to have the whole Gen. Jack Ripper "communist" speech to Mandrake memorized when I was a kid. Also, I actually got a circular slide rule similar to Stangeloves that my father gave me a few decades ago.)

1. No upgrade to the power supply so far. The MOSFET does tap off of the extra terminals of the stock one. I may go to a higher wattage when I try ABS though, but depends on how well the planned enclosure works.

2. The hot end works great, if you get the heatsink fan and finned heatsink out of the way. Another upgrade was to put that fan above the hot end, and toss the aluminum finned heatsink in the parts box. The user that came up with that, said "to have a little faith", as it seemed counterintuitive. It works quite well.

3. Really the only purchased upgrades have been a few 6mm toothed idler pulleys, 10 meters of fiberglass core belt, the MOSFET board, and a few extra assorted screws and nuts. Around $25 total, and I have lots of belt, idler pulleys, and screws left over. All the rest has been printed by the Anet itself for itself, so count about 1/2 of a $30 kilogram spool, or $15 more.

4. Just PLA, although I have ABS spools still vacuum sealed. I have been looking at carbon fiber filled nylon for another project after the rocket, but first the enclosure.

 

[Cl(VII)]

Cl(VII) (by the way, love the avatar. I used to have the whole Gen. Jack Ripper "communist" speech to Mandrake memorized when I was a kid. Also, I actually got a circular slide rule similar to Stangeloves that my father gave me a few decades ago.)

1. No upgrade to the power supply so far. The MOSFET does tap off of the extra terminals of the stock one. I may go to a higher wattage when I try ABS though, but depends on how well the planned enclosure works.

2. The hot end works great, if you get the heatsink fan and finned heatsink out of the way. Another upgrade was to put that fan above the hot end, and toss the aluminum finned heatsink in the parts box. The user that came up with that, said "to have a little faith", as it seemed counterintuitive. It works quite well.

3. Really the only purchased upgrades have been a few 6mm toothed idler pulleys, 10 meters of fiberglass core belt, the MOSFET board, and a few extra assorted screws and nuts. Around $25 total, and I have lots of belt, idler pulleys, and screws left over. All the rest has been printed by the Anet itself for itself, so count about 1/2 of a $30 kilogram spool, or $15 more.

4. Just PLA, although I have ABS spools still vacuum sealed. I have been looking at carbon fiber filled nylon for another project after the rocket, but first the enclosure.

Thanks, and that is a very thrifty way to a good printer. For $150-200 there isn't much to lose in just jumping in, and giving it a shot.

 

[Leo]

For Anet users here some improvement parts. In particular I would recommend using the Mistral 2.1a.

https://www.thingiverse.com/Leo_N/designs

 

[EricLobster]

@ecarson - Man great job and thanks for sharing what you are doing. I'm curious to know if you would recommend a filament based printer or resin based for such projects. Like according to this guide, I'm assuming it's this Form 2 version.

 

[ecarson]

EricLobster, by resin based, I am assuming you mean the laser type 3D printers where the beam traces on the surface of a liquid to cure it. Back in my working for industry days, I had a few suppliers of that sort of service approach me to prototype product designs I was working with. As far as I know, those are quite expensive (relatively speaking) compared to filament deposition type printers.

As far as suitability for use in rocketry applications, I could not say whether one method is better than another. I made my decision on my printer, after researching the outsourcing of models and parts I wanted to have made last year, for another project. After finding the Anet A8, and its low initial cost plus economy of upgrades, that made the most sense for me. I make most of my decisions these days based on close examination of value. Being retired, I now have lots of time, and limited budget. Back when I was working, it was almost zero extra time, and quite a bit of disposable income. So all I can really say, is research and evaluate based on your own situation.