3D printers and Alphadrome Members

[robothut]

So there are a few Alphadromers using 3d printers now and this might be a good place for all of us to talk about what we have learned about them or what our goals are and so on.

There were those 3d printedDing A Lings a bit back, who was doing that ? Then there is Marco and his over the top strive for 3d perfection and now me and my strive for fast and cheep custom robot production.

I can only comment on my point of view, so here goes. 

I have wanted to play around with 3d printing for some time now but the price of the good  printers and the fact that if you do not know how to design a 3D file then all you can do is print other peoples work stopped me. Then with the Jaggernaut project and a old grade school chum popping up and running a shop in town that has a 3d printer, I was able to learn from them . The 3d printed feet and legs made the robot cost effective since they would print the parts for free when they had spare time. We made 25 robots total with 4 printed parts per robot so they printed over 100 parts for our project. Too keep costs down on the project I used small 9g type servos, this limited the size of the robot. Normally the foot tip servo in a biped robot is connected directly to the feet and leg now linkage or levers or gears, but the little 9G servos did not have enough power to over come the weight of the robot as designed so I used a lever / ball bearing design to give the extra power required. My first design was to use gears but I could not find off the shelf gears that would work with out making the project to expensive, so it was the lever design. So once I got my own 3d printer I wanted to see if I could do the gear foot tip design.

I did alot of research on all the 3d printers out there. Yes most of them have so many limitations that they are no useable by me or they are crap or they are way to expensive. The Ulitimaker 2 and 2+ and 2 extended are the best for the price but at $2500.00 they were not a option for me. So weeding there all the other Mid priced printers "say $1k to $1500 range" I found the Flash Forge printers. Most of the low end printers have frames that are made of bolted together wood or plastic or alluminum. They all are a bit unstable. Flash Forge has all steel or injected plastic molded parts that are very firm and stable. The stepper motors in these printers move really fast and suddenly so if the case is not 100% stable your printer will not operate very well over time. I thought the FlashForge Dreamer printer was a good pick as the build size was large enough for custom robot projects and the price was in the $1100.00 too $1500 range. But that was still out of my reach. So I decided to look for ones that need repair. Trust me they all need repair. You can not own a 3d printer and not learn how to fix it as they all require repair from time to time, some more than others. But I found a auction for a Dreamer that was for sale and said FOR PART ONLY AS IS. Well for a few hundred bucks I thought this is for me. I can learn how to fix it and get a printer cheep. The parts would be useable for other printer repairs even if I could not fix it. So I bought it Yes on credit "the wife is not going to like this!".

good thing is the problems were  nothing to great and I had it printing great in a few hours.

[robothut]

So first off I added rear spool holders as the Deamer comes with small internal holders "for the temp control ABS thing all ready talked about" then since I will only be using the unit with the lid off the door off the side vents open for PLA printing I re routed the cable and plastic fiament feeds to the print head unit UP. This how most printers of this style do it as the cable do not get bent around so much as when they are cramped down in side sidways. The dramer is a dual extruder head unit. This means that you can have two different plastic filliments in the machine and if you set your g code files up right you can print in two different colors for example. When I did the repair work I started by taking the hot end part of the extruders a part to clean them out. I found that the out side screws on the extruders would not come out and the inside ones came out just fine. Turns out that there are two screws that hold the dual extruders to the machine are too long and when they are in they can lock a the same two outside extruder screws I was talking about. I did some reaserch and found this to true with most of the Dreamers. Easy fix put in shorted screws, but unless you understand the problem you can not take the extruder apart with out fear of breaking off the outside screws. I also found that where the plastic filiment enters the top of the dual extruders it wears a slot in the extruder top plate. To fix this I insert a small length of teflone tubing, problem fixed.

Here is a picture I just took right now. Its the foot and servo gear on the print bed of the Dreamer. The blue look is from the Blue LED's built in to the Dreamer. This is how the parts look as they are printed. In this case the support is very little, just a little on the big foot gear and a small part in the little gear. If you look back to the pictures earlyer you will see the leg on the priter bead and with what looks like branches growing in it. This is support material and is easlly removed.

[Ranger]

 Very interesting John. Your printer looks to be a good bit of kit and from the parts you have made so far you done a great job repairing it!  I look forward to reading more about this topic.  That's what we like to hear John- "fast and cheap custom robot production"!  Better make space on the shelves for all the amazing robots you will no doubt turn out soon enough!

[robothut]

So what makes a 3d printer work mechanically. Well you need to be able to heat a plastic material, you need to be able to control its flow and you need to be able to move it to the right location. So as talked about  before a frame of case for the printer needs to be solid or you will not get good results. Some printers move the extruder units in two axes only "Left and Right and Up and Down" and then move the build beds in the third direction"forward and backward". This is not considered to be the best way since the build bed is moving and shaking, there is a chance of the part being printed moving "losing its grip on the build bed" In the case of the Dreamer and most Maker bot Clones, the extruder move Left and Right and Forward and Backward and the build plate move Up and Down. The Up and Down movement does not shake the part being printed so this worked better.

To control the plastic filliment you need a heater that is temp controlled. all the filliments have different temps that they work best at and this changes batch to batch some times. If the temp is too high then the printed part will lack definition and if the temp is to low you will get a glogged up extruder Tip and Feed tube. Taking the extruder a part to clean out a plugged extruder is no fun, so most times you print on the hot side then work your way down slowly to find the best print temp for the plastic you are using. Most PLA plastic "like what I am using" works in the 190 to 210 C range. I have been running 200C for the silver PLA used in the Alpha-Rama project. The few test parts I printed in Black PLA needed a high temp as the 200 C would plug up the hot end from time to time.

Now what controls the plastic flow rate. Well in the case of the Dreamer right above the hot end extruder there is a stepper motor with a splined gear on it, then there is a spring loaded bearing that will pinch the filliment to the splined gear. The stepper motor will feed the plastic and retract the plastic. 

The Build Plate on most printers is heated as well, this helps the plastic stick to the build plate durring the build and in the case od printing with ABS it helps keep the part from warping . I run my bed at 50c when printing PLA plastic.

Many of you may not know that PLA plastic is not made from OIL, no it make from plants. In the USA iuts made form Corn in other parts of the world Suggar cane is common.

 

[robothut]

OK so how do you make a 3d printed part.

Well first you need a 3d file. You can make one or down load one from the net. There are many file types but I am using the most common type STL. Once you have a STL file you can not print it as is , no you have to run it threw a program called a Slicer. There are lots of slicer programs, lots of them are crap, the good ones you have to pay for . The dreamer came with Flash Print slice, it is nothing special but is good for basic printing and its free. So you open your STL 3d file in the slicer program and then you can decide how you want the part positioned on the build plate. How yo put the part on the build plate will effect how the part looks in the end and if you need supports to make the part. Printing verticaly will normaly give the best finnish but sometimes its better to lay the part flat like in the picture of the Gear Feet on the printer build plate. If you look close you will see just a few branches supporting the top of the big gear. 3d printers can print with out support to about 45 degrees, anything steeper than that will need supports if you want the part to come out non distorted. There many types of support structures I used the branch type on the foot as its easy to remove. On the battery door I have a over hang that I use a linear support as it works better for that application. There is also a support called a Raft. and it is just what it sound like. If you look at the picture of the Leg on the print bed you will

see a Raft of plastic on the build plate then supports going up to the leg part. The raft makes sure that the support limbs stick to the build plate. Yes I could print the leg turned top side down and not use any raft "there would still be supports for inside hang over areas. But buy building the leg the way I did I get a very clean print in the top of the leg where the servo mounts and less inside supports.

Othere things you do in the slicer program are you can re scale a STL file. This was very helpful for me when I made the gear feet. I was able to find the Harringbone gears on Thingiverse as a free STL down load but they were way to large, so I re scaled them in the slicer. You can also cut a STL file in to parts. Lets say the part you want to make is too large for your 3d printer, you can make it in to smaller parts that you assemble . 

The slicer lets you add the supports as talked about and it lets you set printer controls like the Temp of the extruder and the build plate and if you are using both "if you have a dual extruder printer" extruders and if so what there temps might be and type of plastic. The list goes on and on. The more you pay for the slicer program the more option you get.

OK the main function of the slicer program. It slices the STL file. If you have seen a 3d printer printing then you know it lays down layer after layer of plastic, how fine you make this is the resolution of the print quality and how freeking long it will take to print. I am using the standard medium setting. My feeling is that I would rather print out the part in a descent quality then if if need be sand and paint it to a higher finnish than wait days for the part to print in HQ. But thats just me.

So the slicer slices up the STL file then 3d printers do not print STL files so the program saves the sliced file and the printer setting as a G code file.

Yes now you can load the G file into the printer  and GO.

My Dreamer can print from a USB connection "but that means you tie up your computer the time that its printing" or you can load it to a SD card "thats what I do" or you can send the file by WIFI to the printer "I do not know how to do that so I just use the SD card". 

I also use a UPS power back system on the printer so that if there is a power line glitch I will not lose the print that is in progress.

[nasa]

Congrats John on your 3d printer......glad it was an easy fix for you.....I am also fascinated by this technology......enjoyed your post so far.....keep em coming and have fun!

[robothut]

A few other setting that have to do with quality would be size of the extruder nozzel. The most common size for the hobby printers is a 0.4mm. Yep thats a tiny little hole for the plastic to come out of. But I think Marco is printing with a 0.2mm for his wonderful HD prints. Also you can set the infill amount. For example the body parts on the Alpha-Rama are 1.5mm thick but thats with a 15% infill. They are not solid plastic. They could be if I set the infill to 100 % but thats crazy in most cases. The slicer will make a infill pattern in my case hexagons and put a solid top and bottom surface on that. It makes for a very strong but light weight part.

[roboz]

Nice explanation John , for someone that doesn't want to invest the time in learning CAD type files 

Can a 3D scanner work to just scan existing parts & generate print file  ? Though I would imagine even those would need tweeking

& obviously that limits custom designs 

Also what's the size limitations L  &  H ? 

[WJN]

Thanks for the great write up John, very interesting. All of the 3D printing I have done was with UV curable resin. Instead of an open table, the printer had a tank- Uv curable resin is pumped in thin layers, & the laser traces the "slice" and cures it. More resin is added & the process repeats. Parts all came out clear/translucent, and then were dyed to whatever color was needed by dipping. We mainly used it for checking fits/interference before prototyping parts in the machine shop, and to build mockup assemblies for our customers to handle during proposal meetings. Resins were very expensive, and we had to account for every bit used, so I had little opportunity to "play" with robot parts.

[robothut]

Yes, Stereolithography is what we called it back in the 1990s when I used it at the music company I worked for to test plastic parts before paying the big bucks for injection molding hard tools. They do have hobby version of these laser / resin printers out right now but they are not getting very good reviews. The expencive ones do get good review, but you pay for it. Also the new ones print about 10 X faster that plastic filliment printers

[robothut]

Here are a few pictures that show the steps of a part being printed. The pictures are not very good but they were on my camera so why not share them. The plastic is a red translucent. So the first pass the machine lays down a outline of the part and then fills it in. This is a shell. Then it makes the infill, in my case this was only 15% so there are large hexagonal shapes built up. Then it caps it off. This makes a lite weight part that still is strong. If the part needs more strenth then you sellect a higher infill percent. 100% would be solid plastic, and zero would be a hollow part.

[Morbius]

Thank you John for the information provided, I've learned more about 3D printing in the last few days than I have in the last few years, quite an edumication.

[roboz]

Question for our resident 3D printers , Can translucent or tinted translucent Domes be printed ?

I'm not asking because I need a Green tinted translucent dome for my lightning Jeep !  

[Andyman]

Cool stuff, John. What's the print time on those two claws?

[robothut]

The two claws are for the Alpha-Rama bot take about 18 minuets. The leg part that holds the two servos take about 1 hour per leg, same for the feet with the gears.The body back part with the battery box and speaker mount and all that takes about 2 1/2 hours as I recall. I will time each part out on the next robot I build so that I know what it take to make a bot.