INVADER - Nitro Slash drag car

[Doom!]

Good luck with production and sales, Killer product!

 

[johnnydmd]

I may have struck a deal with a machine shop, and it'll wind up being literally the same price I was paying for the CF sheets alone! I actually have a couple of others I'm talking to, but this is really looking promising, and that'll save me so much hassle and cleanup. Though I must say, I think my setup is very good and clean. One change I made after doing a vac dump/cleanup the other day, was to zip tie the internal dust collector bag. It uses an elastic band, and I noticed that dust had gotten around that, and that is why I had the exhaust covered with an N95 mask(no vent), because I saw a little bit of black dust where the exhaust was initially. Nothing was getting past that mask, but I saw an opportunity to fix a flaw. I ran it last night on a wheeliebar, and then checked the exhaust filter - there was nothing on it at all. Something else I did was put the entire vac inside a 5micron dust collector bag for good measure. I don't know what micron the internal bag is (it looks pretty thick and I'm thinking it's 5micron or less, kinda wish the actual specs were listed), but I doubt anything harmful gets past the external bag. So all in all, I am very happy with my CNC setup and it being dust free in my garage for when I do need to cut parts and prototypes, but for mass production, I definitely want to farm stuff out.

Now, this really leaves me with one thing I'm working out, and that is the 3D printed rear bulkhead. The way this thing is printed, because it's got screws going vertically and horizontally, there's always going to be some screws that are parallel to the layers - which is an issue for layer delamination. I picked up my new build with one of these by the wheelie bar, and heard a telltale cracking sound. So I redesigned it a bit, gave it thick reinforcements where it had some weak spots, and it seems strong enough - I tried to break it with my hands, and could not. I also made sure to tap the holes with a die instead of using the bolts, because that was definitely part of the problem as well. However - I still had Plan B in my head. I have a Photon resin printer, and there is a plant-based resin that I use to print fishing lures with that is considerably more pliable than standard resin, which shatters like glass. I printed one out, and tapped the holes.

This printed well - though it took several hours. It's also a little mucky to work with, you gotta rinse it in alcohol, and then cure it with UV. Also, some of the holes required re-drilling out with a dremel, but that was easy enough, though again, here we are with dust (I just went outside and did that crap with a respirator on). Being UV curable resin, this would also require that it's painted so that it doesn't become brittle with exposure to the sun.

Well, the part certainly looks better, and is no doubt stronger, so I'm thinking this will be the way forward. I'll test both out heavily to see how they hold up, but with that in mind, I could probably print the other suspension parts using this resin, it's really good stuff if you don't mind the mess and smell(or like me, have a place to run the printer that the wife never ventures into, lol).

 

[ahr43]

Welcome to the wild world of RC drag racing chassis builds. You are going to learn a lot. 3D printing brings a whole 'nother level to fabrication. Exciting times.

Built my own dragster chassis out of G10 fibreglass back '07-'11. Went through six iterations of design along the way. Some worked. Some didn't. Some won. Some lost. Wouldn't trade that experience for anything. Best of times for me in RC.

What really helped was having CNC AL parts made a fellow competitor. Good thinking on your part bringing in another set of hands and eyes. Hang in there. 'AC'

 

[Doom!]

@johnnydmd Is there a way to print the part in two pieces and dovetail them together so you can print the screw holes facing the way you want? I am just wondering, don't know if glueing a dovetail type of join would be strong enough. I haven't even set my printer up yet but trying to learn from you guys who have experience.

 

[johnnydmd]

@johnnydmd Is there a way to print the part in two pieces and dovetail them together so you can print the screw holes facing the way you want? I am just wondering, don't know if glueing a dovetail type of join would be strong enough. I haven't even set my printer up yet but trying to learn from you guys who have experience.

My experience with gluing parts together, is that the glue doesn't hold, even using a 2 part epoxy like JB Weld. I think the key to keep parts like this from delaminating, is to 1) Print them solid, and 2) Make sure there is a good amount of thickness with no weak spots. The one printed in PLA there on the right, I added some pretty beefy parts to increase that, and it would probably hold up ok, but I do think the one printed in resin, on the left, would be vastly stronger, there's no chance of delamination, only cracking if the resin was brittle. The plant-based resin is so much more pliable than the standard stuff, I really like it.

Of course resin printing is a whole other form of art(frustration) in and of itself, but the quality and detail is vastly superior.

 

[WickedFog]

My experience with gluing parts together, is that the glue doesn't hold, even using a 2 part epoxy like JB Weld. I think the key to keep parts like this from delaminating, is to 1) Print them solid, and 2) Make sure there is a good amount of thickness with no weak spots. The one printed in PLA there on the right, I added some pretty beefy parts to increase that, and it would probably hold up ok, but I do think the one printed in resin, on the left, would be vastly stronger, there's no chance of delamination, only cracking if the resin was brittle. The plant-based resin is so much more pliable than the standard stuff, I really like it.

Of course resin printing is a whole other form of art(frustration) in and of itself, but the quality and detail is vastly superior.

If you can find this plastic weld, which is not sold in the US now, it is phenominal for gluing PLA.

Other than that, @Doom! Told me to try Weldon 4 by 3M. I have yet to try it.

 

[johnnydmd]

Struck a deal! They actually were able to really cut my costs down. Put in an initial order of 3 full chassis. Gonna put them together over the next week and get them on eBay.

 

[five9dak]

Might I suggest you outsource the 3D printed component to a service bureau with and use GF reinforced ABS ? Home gamer materials won't really cut it, IMO.

 

[WickedFog]

I dunno. If you design the parts properly, and your printer is setup right, you can print some really durable stuff.

 

[johnnydmd]

Might I suggest you outsource the 3D printed component to a service bureau with and use GF reinforced ABS ? Home gamer materials won't really cut it, IMO.

If my testing shows that the two 3D printed items (bulkheads) won't hold up, sure. However, I seriously doubt either of the bulkheads will fail, and I don't think ABS is nearly as strong as the resin that I'm using. This stuff is incredibly strong, and has a flexibility to it that standard resins don't have. I ran the car last night hard, and inspection saw nothing was cracked, still rock solid.

The other 3D printed items (throttle servo mount and flywheel guard stub, have zero chance of breaking, they are very low stress items.

I dunno. If you design the parts properly, and your printer is setup right, you can print some really durable stuff.

Plus, it's a drag car, not a basher. Those parts you printed are more than strong enough for that.

 

[WickedFog]

If my testing shows that the two 3D printed items (bulkheads) won't hold up, sure. However, I seriously doubt either of the bulkheads will fail, and I don't think ABS is nearly as strong as the resin that I'm using. This stuff is incredibly strong, and has a flexibility to it that standard resins don't have. I ran the car last night hard, and inspection saw nothing was cracked, still rock solid.

The other 3D printed items (throttle servo mount and flywheel guard stub, have zero chance of breaking, they are very low stress items.


Plus, it's a drag car, not a basher. Those parts you printed are more than strong enough for that.

Yeah, since the arms are under the body, only a big crash is going to break them. And that would break oem parts just as easily. And it's a matter of pushing a few buttons to make a replacement if that is the case. Much cheaper than buying from an outside supplier.

 

[five9dak]

I understand the appeal of design and print at home. I have a commercial grade machine I run at work. If OP wants to sell a finished good on eBay as a kit, with female threaded holes, it needs to hold up. The situation changes when you talk about marketing it. Service bureau shops open up a whole world of new possibilities for proper engineering plastics.

 

[johnnydmd]

I understand the appeal of design and print at home. I have a commercial grade machine I run at work. If OP wants to sell a finished good on eBay as a kit, with female threaded holes, it needs to hold up. The situation changes when you talk about marketing it. Service bureau shops open up a whole world of new possibilities for proper engineering plastics.

Ok, I appreciate your offer, but I'm confident that my parts will hold up. Those resin bulkheads are more than strong enough, and I manually tap the threads, no screws are going to strip out. There really is no reason for me to farm anything out. There are four parts being used here:

1. Front bulkhead - printed in pliable resin.
2. Rear bulkhead - printed in pliable resin.
3. Throttle servo mount - printed in PLA - low stress item that does not require much strength.
4. Flywheel guard mount - printed in pliable resin, also low stress item.

Why would I farm any of these out? There is no way any of this stuff is breaking unless like WF said, you crash at 60mph, and OEM plastic parts would break in that scenario as well. You have to understand, I'm running cars with these parts and testing heavily. I'm not going to sell anything that won't hold up. IF, and only if, these parts don't hold up, would I consider farming them out.

 

[five9dak]

Another consideration is your time. Traxxas designed these parts to be molded with pilot hole sizes and the screws to cut their own threads for a reason. By the time you print, paint, cure, manually tap dozens of holes per kit, what hourly rate are you really making? Ideally you leverage the same design philosophy and spend your time designing more cool stuff.

I design, print, and injection mold plastic components professionally for jobs ranging in batch size from 1 to hundreds of thousands. I was just offering up some advise. You do you.

 

[ahr43]

Good reasoning on parts survivablilty, johnny. Beyond driveline components, everything else is low stress. . . until a crash. Then CF is the first to suffer. Splintering in the 60mph range. Shattering at 80mph plus. Really can't build in crash resistance without really adding a lot of detrimental weight.

These next-gen no-prep cars are a bit bigger and heavier than the 1/10 full-prep cars running fifteen years ago. Newer no-prep are inherently more survivable. Project is looking good, johnny. Once you get a few chassis out there on the track you can refine the design and improve the breed. Hang in there. 'AC'

 

[johnnydmd]

Good reasoning on parts survivablilty, johnny. Beyond driveline components, everything else is low stress. . . until a crash. Then CF is the first to suffer. Splintering in the 60mph range. Shattering at 80mph plus. Really can't build in crash resistance without really adding a lot of detrimental weight.

These next-gen no-prep cars are a bit bigger and heavier than the 1/10 full-prep cars running fifteen years ago. Newer no-prep are inherently more survivable. Project is looking good, johnny. Once you get a few chassis out there on the track you can refine the design and improve the breed. Hang in there. 'AC'

For sure! I have 2 cars running the chassis(one big block, one small block), and a third running the "OG" version. The fourth chassis, that I just showed is going to a teammate for testing, so I'll get some feedback from him as well. I've got three full chassis part sets coming soon, those I'll assemble and I've got buyers for all of them who will have some feedback as well.

 

[WickedFog]

@five9dak - Traxxas doesn't use any special design in their screws to cut threads. They are standard machine screws, threaded into non-threaded holes. Nothing special about them. If your pilot hole is a tad bigger than the minor diameter of the screw, they will self thread into the plastic just fine, whether it's PLA, ABS, or whatever.

It is actually a stronger thread than tapping. It works just like 'form tapping' metal components, where you run a tap into the hole, but the tap has no cutting teeth. So it removes no material. It creates a much stronger thread. Screws form their own threads in plastic exactly the same way, if the hole is designed accordingly.

I design all my parts this way. And I don't have any issues at all with screws pulling out. Check out my Carnage build in the Rock Crawler forum. The screws are all 1.4mm machine screws, threaded into holes printed at around 1mm diameter. No layer separation, no stripped holes, etc.

I too designed and manufactured parts and work holding solutions for manufacturing, but I was in the racing and Aerospace industry for 25+ years. Not mainly in plastics though. Although I machined a lot of delrin, nylon, and other plastic components, my main area of expertise was aerospace alloys. But I started in my dad's wood shop at the age of 9, and was forced into early retirement at the age of 48. So I was basically in manufacturing my whole life. And I have been following 3d printing since the first commercial grade 3d printers were shown at the IMTS show in Chicago years ago. I have owned up to six 3d printers at one time, including an STL resin printer. I still have 3 FDM printers. It's one of my favorite hobbies next to RC.

Everything in this trailer frame except the screws and bearings is 3d printed.

And with all this experience under my belt - Johnny still impresses the hell out of me!

 

[five9dak]

My comment was not an assault on 3D printing. I just suggested another material to make it preform more like the traxxas molded parts, with machine screws that cut their own threads. OP mentioned he had a female thread strength problem in his original FDM parts and was exploring other manufacturing methods - UV cured resins and manual tapping. I simply suggested another solution. Forget I said anything, I was trying to help, not distract from the work he as shown this thread.

 

[WickedFog]

It's all good man. Finding that sweet spot for threading screws into plastic is a learning process. I have had more than my share of failures. And it even varies from resin to resin. I am still adamant that using any kind of screw or tap to cut threads into any plastic, whether home printed, outsourced, or OEM plastic will create a weaker thread though.

One thing that helps is ensuring you have enough perimeters around your part to create a nice internal boss for the screw holes. For 3mm screws to thread into the plastic, I use 4 perimeters at a minimum with a .4 nozzle. And you have to make sure the infill overlap is set to around 25%. That will create a nice lug inside for the screw to get a grip in.

I really wish my slicer allowed you to select features of the part to add more perimeters to. I am sure there is a workaround, like creating an internal boss with a very tiny gap around it and the rest of the internal part. But I haven't experimented with it yet.

 

[johnnydmd]

My comment was not an assault on 3D printing. I just suggested another material to make it preform more like the traxxas molded parts, with machine screws that cut their own threads. OP mentioned he had a female thread strength problem in his original FDM parts and was exploring other manufacturing methods - UV cured resins and manual tapping. I simply suggested another solution. Forget I said anything, I was trying to help, not distract from the work he as shown this thread.

Like I said, I appreciate the offer, and I would certainly consider it if my parts fail (so far they have held up). I'm always open to changing things, based on testing. I'm not going to put anything out there that hasn't been very thoroughly tested.

The problem I had with the FDM rear bulkhead wasn't thread strength, it was some delamination when the screws parallel to the layers were threaded, and then doing a stress test (in that case, it was lifting the entire car by the wheelie bar). The resin version has held up even when yanking the car up by the bar off the ground. As far as the tapping, I could just use the screws, it's probably soft enough to do it, but it only takes a few minutes for me to tap those out and be sure that the structural integrity isn't compromised given that it's a bit harder than plastic.