Practical 3D printed parts

With the recent addition of 3D printers to the FIRST Choice store are team has been wondering what parts can be made more efficiently on a hobby 3D printer than traditional tools (lathe, mill, CNC mill etc)?

The only practical thing we’ve come up with is rough spacers, particularly ones with tapers.

3D printers are great prototyping tools. A part can be cranked out on the machine with no oversight required. Parts that may not be make the final robot can be made and tested this way.

In addition to the miscellaneous plastic parts that can be made, definitely look into resin and urethane molding, or even aluminum casting, using the 3d printer to make the mold masters or mold halves themselves. Parts of pretty significant strength can be made this way.

This is more of an FTC application but I designed and printed our flag turner on a 3d printer. I think for the majority of FRC it may not be as practical but there are possibilities.

I’m currently, with the aid of some members of 449, checking out the feasibility of printing GT2 pulleys, which would be a huge cost-saving measure and allow a lot of flexibility over COTS aluminum pulleys. I’ll report back on how it goes, if you’d like.

Spacers, plastic gears, and plastic inserts to reinforce sheetmetal (see pictures linked) can be useful parts made by a 3D printer.

https://fbcdn-sphotos-d-a.akamaihd.net/hphotos-ak-ash3/548975_478807028814715_571422371_n.jpg

https://fbcdn-sphotos-c-a.akamaihd.net/hphotos-ak-ash2/531460_478807125481372_499420493_n.jpg

The bright orange plastic parts were 3D printed. They were used kind of like spacers between the sheet metal of the bridge appendage, to support them so they didn’t cave in.

I believe 4334 3D printed some pulleys for their 2013 drivetrain, but I’m sure Joel/someone else from them can chime in.

In addition to the above suggestions, encoder and other sensor mounting brackets are another common use.

Also, remember that objects that are 3D printed via the FDM process (where ABS/PLC plastic spool is melted and extruded into the printed object) are weak in between the vertical layers. There are two ways to deal with this: 1) accept this and design/layout the parts with this in mind; or 2) design hybrid parts that use other parts or hardware to reinforce the 3D printed parts.

One final note: FDM process 3D printing is generally pretty slow. It might take 12-24 hours to print some parts. Some parts may actually be much faster to make via drill press/band saw/lathe/mill or purchase as COTS parts. Make sure you balance your resources. You don’t want to design so many 3D printed parts that it takes 7 weeks to print them all. :ahh:

That’s interesting, I’ve seen people cut HTD pulley profiles on a CNC but GT2 pulleys have curves that would be difficult to cut without a 4th (or even 5th axis). It would be interesting to know how they obtained the proprietary GT2 profile.

It looks possible to print the pulleys easily, http://www.thingiverse.com/thing:16627 but they would need to undergo some testing before use on a robot. What would help teams though is that they could print out the pulleys and use them if the part they want gets back-ordered. I am also wondering about any teams that used 3-D printing with gears for low load applications to see if they held up.

I pulled the CAD of bbman’s website, with the hope that the profile is correct (or close enough to correct that it’ll work, the fact that their CADs have different profiles for HTD and GT2 pulleys seems to indicate that they’re not just using a single erroneous profile for all of them).

I had heard that other teams had successfully machined pulleys from CADs obtained this way, so it seems worth a shot.

If it doesn’t work, I’ll check out the parametric pulley link nicholsjj posted (thanks for that, by the way) - though I don’t have OpenSCAD on my computer right now.

See attached picture. Material is ABS. No idea what the specs were when they were printed…whatever our sponsor had set up for whatever they had recently made.

I copied the GT2 profile off one of the websites (sdp-si maybe? it’s been so long now I don’t remember) and the printed pulley meshed very nicely with a GT2 belt. Just haven’t had the ability to test the strength of the pulleys on a drivetrain yet. The printer I have best access to is an FDM…great insight mentioned above. For a drive pulley (off a gearbox) my plan was to mate an AM hex hub to the printed pulley (similar to what AM currently lists on their website for the 2013 chassis). I would add another circular hole pattern to drill and tap for #10-32s on the AM hub. The wheel pulleys I was planning on attached to a WCP dead axle hub. The side you can’t see (resting on the table) has a bore for an R8 bearing. An R6 bearing would go in the WCP hub. No chance to test these yet to see what breaks…hopefully soon.

3-D printed pulleys.jpg


3-D printed pulleys.jpg

Art’s First point is probably one of the most important things to keep in mind while printing parts. Depending on the exact geometry of the part, printing in the strongest orientation (the layers do not want to pull apart from one another) is not always the orientation that will most accurately produce the part. There are some interesting ways around this, either splitting the part into multiple parts where each sub-part is optimized for geometry or strength, or as Art said, you can make a hybrid part where some other component reinforces the weakened area.

I used your method exactly in Decemeber-ish of last year to make a prototype pulley (ignore the versa keys…) and the profile was pretty darn close to perfect.

https://db.tt/WT0HnkDQ

https://db.tt/Wd92gCkg

From what I saw, the printer ran a few thousandths over while making the teeth, so if I were to make that exact pulley again, I’d probably remove a couple thou from the tooth profile and see if it cleans up with tooth engagement at all. All in all, wasn’t a bad final product, IIRC, the teeth being a touch big was only noticeable once the belt wrapped more than 120* or so.

Also, as far as I can remember, the pulley was surprisingly strong, we clamped the belt in a vise and beat the pulley up a bit and there was little to no permanent damage. It’s worth noting that the pulley was printed from Ultem (polyethermide) which is something like 2.5-2.75 times stronger than ABS in the same machine. Odds are, ABS should hold up just fine, but if I were using ABS, I’d make sure that at least one wheel was directly driven from the transmission or something.

While we’re on the subject, here’s a picture of one of the larger print runs done for last season’s robot:

https://db.tt/tqhDMaaS

If I remember correctly, that build took somewhere around 11 Hours to print from beginning to end, including warm up time. Starting from the left most side:

-(4) parts with rectangular holes were servo brackets that were printed a touch too thin to hold up to handling before the servo was mounted,

-(2) spacers to offset a sprocket from our shoulder joint - they had the standard 1.875" hole circle printed into them, along with a 1.125" OD protrusion on one side to pilot into a bearing bore, and on the other there was a 1.125" ID bearing bore to hold an FR8 Bearing,

-The large clam-shaped parts on the right side were a spacer for our shoulder’s pivot. There were (6) Hexagonal pockets printed into the spacer to hold 10-32 threaded inserts along with some neat cutaway geometry to allow 25 chain runs through the pivot to our climber. I stood on one of the shoulder spacers to see what would happen, and it didn’t move a bit.

Also, here’s one of the encoder mounts made over last season - initially, this was the ‘standard’ mount used on both our drive and shoulder although the shoulder’s final encoder configuration was a bit more complicated (cooler) than this: https://db.tt/kJqK0kE3

We have a uPrint SE that we love to prototype parts with and we made some spacers that we used on our 2013 robot. Some of the things that we made were custom shaft attachments/couplings for the window motors.

This year we are working on our 6 wheel tank drive with 5mm HTD belts. We were looking at using the VEX Versa Hubs with the 42 tooth HTD pulley from Andy Mark. We decided to combine both parts and we now have an integrated pulley with hex drive that attaches to the VEX traction wheels. We are pretty excited about it but we will continue to test for strength.

We spent a lot of time researching how to create the actual 5mm HTD profile for the pulley and it took a few attempts to get it right but this 42 tooth profile is perfect now.

I see no reason why these will not be on our actual robot this upcoming season.


photo 1 (3).jpg




photo 1 (3).jpg

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Great thread, thanks for starting it!

Here are a few ideas of what we have printed over the past couple seasons:

-Our 2012 shooter wheel was custom molded to give us the exact shape/diameter we wanted on a wheel with almost all of its mass on the outside rim. To make this wheel we 3D printed a mold, machined a hub, and poured the urethane around the mold. Oh yeah, and we embossed ‘125’ in the wheel, because why not? (See attached images)

-Also in 2012, we 3D printed components to center the ball as it went up our lift into the shooter wheel. This ensured we caught the ball in the same place on the wheel each time.

-Again in 2012 we printed a gearbox to power our intake/elevator. It utilized 2 FP motors and the first 2 gear stages of the plastic FP gearbox. We ran through 2 quick iterations of the gearbox, and it worked flawlessly all season.

-This past year we printed ‘cable guides’ to mount over the pulleys on our lift. This prevented the sailing line we used to lift our elevator from jumping off the pulleys themselves. Again a couple iterations of these and they worked flawlessly all season.

There are so many applications for 3D printing in FRC. We’ve been using printed parts for years, and we’re always finding new applications. Keep your eyes open and dont be afraid to try something out (just make sure you give yourself enough time to implement a backup plan if something goes awry).

-Brando







Brandon,

I’d really be interested in more details of the urethane pouring process and pictures of the mold, as this is something I’ve never done. Your finished product looks good. I’m also interested in seeing the 3D printed FP gearbox if you have a picture.

Thanks.

I’ve got plenty of pictures back on my home PC- I’ll circle back tonight and post them.

-Brando

Just in this one picture there are many 3D printed parts:

  • wheels on end of arm that set floor height.
  • bearing blocks on active leading edge (inside wheels)
  • finger grippers on 3/8" round, keyed shaft
  • crowned flat belt pulley on keyed 3/8" shaft (under flat belt)
  • finger grippers on 1/2" hex shaft
  • bearing blocks on main arm pivot
  • drivetrain gearbox dust covers (near side yellow, far side purple)
  • camera/light ring mount (purple, on underside of shooter)

We’re to the point now where we’ll make just about any nonstructural part with the 3D printer rather than spending fab time to make it. Thus far, we haven’t broken any plastic parts. The bearing blocks were an experiment to see if semi structural parts could hold up if made beefy. These have lasted through two off-season competitions and at least half a dozen demos.

What material do you use?

Here’s a project my senior students worked on. I don’t have access to the printed part (at school right now and I’m home), but the second one fit extremely well to a VEX Versa hub. The original intent was for our 6 WD test bot and the driven wheels would used this design. Last year’s bot used an 8" drive wheel and 6" driven wheels, but we used chain drive. This year we want to use belt drive and we couldn’t find the tooth ratio we wanted so we started to draw this in Inventor. The tooth profile wasn’t too hard to get, but the hard part was getting the right diameter for the circular pattern of the tooth to work out in Inventor and in real life. So, this one is 39 tooth to match the Andymark double pulley, so if we use this design, wheel sizes will be common. But I’d like to cheat the driven ones to be smaller to increase the wheelbase of the bot. Therefore we redraw it with the right tooth ratio and off we go. The problem will be getting a smaller tooth profile to fit with the part. If we keep the 39 tooth drive with a 6" wheel, we need a 26 tooth driven for a 4" wheel. Not sure how that 26 tooth will match up with the Vex Versa Hub Pattern. But in the classroom that becomes an absolutely great design exercise to go through!

BTW, Project Geometry is your very good friend in Inventor. Just make sure you have the parts in an assembly, constrained correctly, and then you can modify the part you are working on to match very, very well with the mating part.





ABS is a very nice plastic and is very strong. After 3D printing technology improves enough, it will be feasible to start producing things like pulleys and other highly used parts. Pulleys should already be an easy one to 3D print as long as you use an aluminum or steel axle because the load is distributed throughout, reducing the stress on the plastic!

I have gotten many things printed in ABS. They are very strong, and lightweight and take compression forces quite well, as long as there is no sheer or bending force on it. My Stirling Engine crankshaft broke because of the high sheer force I accidentally placed on piece, when removing the building material. I should have used an abrasive instead, to get rid of the black building material.

Our school has either 2 or 3 of those Dimension 1200ES printers! Out of that, we use only one!