INVADER - Nitro Slash drag car

Welcome to RCTalk

Come join other RC enthusiasts! You'll be able to discuss, share and private message with other members of our community.

johnnydmd

Beer drinker and hell racer
Supporter
Build Thread Contributor
Messages
915
Reaction score
847
RC Driving Style
  1. Racing
Gonna call this update "The Good, The Bad, and the Ugly".

I knew this wasn't gonna be easy. And I knew I was using some new "tech". It actually would have worked out fine, had I known one detail.

Let's start with the good.

The headlight buckets are money. Perfect.
20220917_123805.jpg

When I paint them, you'll see how realistic they'll be - and man they are bright!

The mold for the buck came out nice:
20220917_110245.jpg


The foam was interesting. I set it up just like the videos with mold release liberally applied, and a sheet of plexiglass with three holes on top. As I poured it, I really wondered if I had enough. Oh boy. Yeah, I had enough. It rose up slowly at first, then it went nuts. It came rushing out of the escape holes at the top at a rapid rate, covering the entire sheet of plexiglass, and my hands that were holding it down. Kids - don't be like Johnny - wear gloves!! That stuff is HOT when it's expanding. Also it sticks to you like glue. Nothing like ripping off polyurethane foam and hair. Good times.

After a couple of hours I removed the excess foam off the glass.
20220917_161959.jpg


Mistake one was obvious. Three holes was not enough. Six would have been better. The foam pushed the glass off the mold despite my best efforts. For the rear half of the car, I'll use six. And maybe just stick some weights or something on the glass to hold it down.

The second mistake wasn't so obvious. I started trying to remove the molds, and they were budging at all. After some time, I just decided, screw it, and started tearing the 3d printed molds off in pieces. As soon as I peeled off the top layer, I saw the issue. There was foam INSIDE the friggin' molds! Apparently this stuff will find it's way though the tiniest holes and cracks - and apparently my molds were more porous than I thought.

Undaunted, I kept tearing it off, and then I saw the horrors. The foam was getting mutilated in a number of spots from all of this, and there were some major voids in the front of the car. (this may have been because of how the foam lifted the glass up, not sure). I got half of the molds off, and it looked pretty awful, and useless.

20220917_180234.jpg


I tore the other front piece off, and it wasn't nearly as bad on that side, but overall, this was really bad. Now, I could start over, and THIS time coat the mold with a liberal coat of Flex Seal (definitely doing that for the rear half!!!!). Or, see if there was something I could do to salvage this. I had a tub of wood putty handy, because I was going to use that anyway for smoothing the thing out. Now I'd have to use a lot of it, to reconstruct a lot of really mangled areas. Was it doable? Maybe. Definitely the front would have to be done in layers and over several days, to build it up. The rest I figured I could do without too much trouble. Back in my muscle car days, I was a Bondo Magician, so this was no biggie :)

I did the first mudding Saturday, mostly just to get a foundation and the shape back. I didn't even bother taking off the last mold piece yet, as it was a real pain, and figured "lemme see if I can even fix this" first.
20220918_080632.jpg


I let it dry overnight. After some drag racing with my team (I'll make another post in my Nova thread on that), I came home and had the choice to cut the grass, or start sanding. A lot of the front parts where I filled in huge voids were still squishy, so I focused on the top. I got it sanded using 220 to get the shape and lines, the shape looked good, and so I again mudded it up for round 2 (I expect about five or six, maybe more rounds of doing this overall).

20220918_195339.jpg

20220918_195353.jpg


Tonight I will sand all this down, and see about filling in the rest of the bad areas around the lower grill/spoiler. Mostly after that, the mudding should be filling little pock marks and such, which is painstaking, but easy. Then shaping the whole lower grill/spoiler area, and focusing on that.

Yeah, it's ugly right now, but I do see the light at the end of the tunnel. And I have time - as I wait for the rear molds to print. Two are done, two more (each takes a day). I won't make the same silly mistake with that. Either way I was going to have to mud this thing up, I just wasn't expecting to have to reconstruct busted up areas. Then again, I had to do that with my Dragonoid mold as well - that was the reason I decided against using water putty this time - that and the thing would weigh a ton and take a year to cure/dry.

Once I have this thing baby smooth, I'm coating it with some 30 minute epoxy, probably two thick layers. Then I'll primer it, and sand with 1000 paper, and see any imperfections, which I fix, then re-epoxy one last coat.

My other fear was how well this would hold up under heat/pressure. Well, with this much wood putty and epoxy, it was probably ok. The foam itself is incredibly strong. I put my heat gun on high and blasted it just to see if it would hold up. Even with the foam smoking, it didn't collapse, so I think it's fine. Just for good measure though, I won't put the thing into the vacuum former until the lexan is mostly heated and ready.

It's coming along, just have to remind myself to be patient!
 

johnnydmd

Beer drinker and hell racer
Supporter
Build Thread Contributor
Messages
915
Reaction score
847
RC Driving Style
  1. Racing
Those lights are sick and I can't wait to see the finished body!

I can't wait either. Have to remind myself to be patient! It's helping that the rear half of the car is still in the mold printing phase. The Ender 3 extruder crapped out in the middle of printing the second piece, so last night had to start that one over. Should have them all printed by the end of the week, and the buck casted over the weekend.

Meanwhile, I spent a lot of time sanding again.
307306948_1471971376650167_5716020064380294813_n.jpg


The lower grill/spoiler area was fully hardened, so I started on that too. Main thing with that will be getting the lip perfectly level so the splitter bolts up right. There were still some mishapen areas like the hood scoop and bits of the hood vents, that needed some more mudding, but it's definitely getting closer. So I mudded up again, but now you can see it's much smaller patches and fills.

307540989_464528218747773_9003571433616558132_n.jpg


I actually went and hit a few more areas this morning after taking this pic last night. Just some little areas around the hood scoop and grill that I missed, or just needed to wait for some drying. I will etch the headlight lines with a Dremel, debating on whether or not to etch in the hood seam. Kinda scared honestly to do that. I do need to define the lines in some areas better, but I think the hood and fenders are all pretty close, this round of sanding will probably get it near. The spoiler area will take a few more sandings and fillings yet. Then I'll give it two coats of epoxy (the first coat tends to absorb into the putty and foam, making it extremely hard). Then primer, and fine sanding to find the last of the imperfections.

This is super enjoyable and relaxing (something I need!). I told my wife last night it reminds me of being a kid with my 69 Mustang and a tub of Bondo. I told her you can literally rebuild a car with Bondo and Duct tape, lol.

I'm also going to 3D print a piece that can be put on the hood when vacuum forming that will define the cutout for the engine. This way I can make bodies with or without the blower sticking out.

On another (related to Invader) note, I was taking with a couple teammates Sunday while we were racing, about my 3 cars and which was the fastest. One of them swears my Mustang is the fastest of the three (it's actually not - best it's run is 2.6, and Invader has run 2.3). Part of his perception was probably because I was having a lot of trouble with Invader's engine that day. I think a lot had to do with putting the SH .28 carb on it, it just was near impossible to get a good tune. I don't think the carb was misbehaving, but more that it's just too much for the .25 engine. So I was gonna put the Kyosho plastic carb back on, because frankly the car was running better and faster with it. He said - "Dude, why don't you stick the SH .28-8 in there and just see what happens?". He has a good point. I have one with the same clutch and bell just sitting there in one of my trucks. It would take me five minutes to swap out the engine and see what's what. I've rattled that in my mind all year, and kinda held back because that SH .28-8 is a beast of an engine. It's a short stroker with 8 ports, so it's probably got much better top end than the KE25 actually. I can manage the launch with a throttle tune on the radio, so I think I'm gonna give it a shot once I get the Viper body ready, because I think with the adjustable wing I can create enough downforce to handle the SH's extra power on the big end.
 

johnnydmd

Beer drinker and hell racer
Supporter
Build Thread Contributor
Messages
915
Reaction score
847
RC Driving Style
  1. Racing
Another night, and got in two rounds of mudding/sanding. Got the spoiler shaped better, and smoother, that'll be the focus tonight. Then I'll put the first epoxy coat on.

308092416_10223396869693413_5758007231982947116_n.jpg


307834729_1279419542811852_7028214218413284853_n.jpg


I'm kinda at the point where some of the tiny imperfections I am not worried about because applying putty might make it worse, and I don't want to sand too much and get into the foam because it's not as smooth looking. I also don't want to fool with the shaping too much either, I feel I've got it about as good as I can get it. I still see the right headlight cover has a slight crease on the surface. Meh. The epoxy will fill in most all of these minor things, and then the shell will be hard and strong, and I can primer this, and then use a block sander to weed out any really offensive dips and stuff like that. After it's done, I'm going to drill some air holes in the areas like the grill, scoops, hood vents, to pull the lexan in when vaccum forming. They'll be tiny 1mm holes, and in spots that are covered by stickers.

If you're wondering how I'll remove the lexan after forming it, I will cut the rear area off, and it will slide forward. I'm using .040, so it'll be flexible enough for some of the things that might snag doing that, like the hood vents. The sides will be freed and flex out easily to clear the front wheel area where it's wider.

The molds for the rear portion of the car are 50% completed. Looking like this weekend I'll have that casted and ready to do all of this all over again, though this time it should be a lot easier now that I know the pitfalls.
 

johnnydmd

Beer drinker and hell racer
Supporter
Build Thread Contributor
Messages
915
Reaction score
847
RC Driving Style
  1. Racing
Last night I vowed to make it my final round of sanding/patching. One last time...

I was satisfied that it was shaped well enough, and that it was ready.

306606513_392103196448204_9126953439480259103_n.jpg


I mixed up my 30 minute epoxy. Started brushing the top of the car and the sides. I only did a little on the spoiler and grill area, that I'll do this evening with the nose pointed up so that it pools in the grill and vents some.
20220921_224507.jpg


Well looks like it's only gonna need one coat of this stuff! Any more, and it's going to lose all the detail. I'll do the grill and touch up the rest tonight, but this morning I was looking at it, and I don't think there's any need to primer it and re-sand, I don't think I can make it any smoother honestly. The pic doesn't really do it justice due to the uneven color, etc, it's really, really smooth, and the shape, while not perfect is definitely "good enough" for me. I still have nervousness about how the first pull will go. Will it be durable? I think so. It's got a higher "softening" temp than PLA, and I used PLA for my dragonoid head and wing forms with no deformation occurring. The only time I ever had deformation with PLA was when I printed something out and the honeycombs inside were far too big and I had no epoxy on it, and it sagged in the open areas. This foam is of course vastly denser, so I don't think there'll be an issue. And also that time I had the form sitting there under the heat lamp along with the lexan the entire time (doh!). I've since learned to not put it in until it's ready to drop. Also, this epoxy is a really thick shell, should shield the foam enough from the warm lexan like it did on my PLA forms.

The rear half is at 3/4 done, and printing out the last piece. I hope to get to work on that this weekend at some point.
 

johnnydmd

Beer drinker and hell racer
Supporter
Build Thread Contributor
Messages
915
Reaction score
847
RC Driving Style
  1. Racing
You have more patience than me...can't wait to see the final result :)

Dude, I'm really running thin on it, very anxious to do a pull and start painting! I'm really hoping the rear half comes out much cleaner and I don't have to do anything other than the epoxy coat, and maybe minor filling/sanding. Theoretically that should be the case, I guess we'll see!
 

WickedFog

Starter of too many projects
Supporter
Hospitality Award
Build Thread Contributor
Messages
8,002
Reaction score
9,246
Location
Terre Haute, IN
RC Driving Style
  1. Bashing
  2. Crawling
  3. Scale Builder
Dude, I'm really running thin on it, very anxious to do a pull and start painting! I'm really hoping the rear half comes out much cleaner and I don't have to do anything other than the epoxy coat, and maybe minor filling/sanding. Theoretically that should be the case, I guess we'll see!
Dude, have you ever seen a show called Face Off? It is a movie makeup show, and they do a lot of mold making, vacuum forming, etc. You should check it out.
 

johnnydmd

Beer drinker and hell racer
Supporter
Build Thread Contributor
Messages
915
Reaction score
847
RC Driving Style
  1. Racing
Dude, have you ever seen a show called Face Off? It is a movie makeup show, and they do a lot of mold making, vacuum forming, etc. You should check it out.

You know, I think I remember watching that once. I could probably have saved myself some pain, and trial and mostly error :) I do think the rear will be a much easier process now that I know the 3d printed molds need to be sealed first.

It'll be nice working with .040 poly again. So much easier than the .060-.080 stuff I'd been using in recent years.
 

WickedFog

Starter of too many projects
Supporter
Hospitality Award
Build Thread Contributor
Messages
8,002
Reaction score
9,246
Location
Terre Haute, IN
RC Driving Style
  1. Bashing
  2. Crawling
  3. Scale Builder
I am just wondering if the vacuum is going to try to pull all the air out of the foam and crush your mold. Have you tried this on a test piece yet?

If I were going to try this, I might try hydrocal instead of foam, and print the mold out of TPU, with a PLA block formed to the outside of the mold to help maintain the shape of the mold. With hydrocal, it's not too hard to shape and smooth it, and it has minimal shrinkage.
 

johnnydmd

Beer drinker and hell racer
Supporter
Build Thread Contributor
Messages
915
Reaction score
847
RC Driving Style
  1. Racing
I am just wondering if the vacuum is going to try to pull all the air out of the foam and crush your mold. Have you tried this on a test piece yet?

I don't think it could, I haven't tried on a test piece (ugg, shouldn't have thrown the excess away!). The thing will be sealed in epoxy - but I had planned on putting some holes for pulling tighter on some details, but now I'm totally rethinking that! Thanks, I hadn't even thought of this. The foam is extremely strong though, but who knows, I don't want to cause a problem just to get a slightly tighter pull. And really those holes aren't necessary for .040 pulls anyway. The bottom of the thing has a "skin", but I think I'm gonna spray some flex seal on that to make sure there's no possibility of air getting sucked out of the form. I'm gluing strips of wood to the bottom too, so that it'll sit up off the former and allow air to flow around it.
 

WickedFog

Starter of too many projects
Supporter
Hospitality Award
Build Thread Contributor
Messages
8,002
Reaction score
9,246
Location
Terre Haute, IN
RC Driving Style
  1. Bashing
  2. Crawling
  3. Scale Builder
We ran with 9" to 15" of vacuum, which isn't much at all. I mean I think you hit that trying to suck a DQ milkshake through a straw 🤪 But it was enough to slightly crush spray foam we used to fill gaps around molds.
 

johnnydmd

Beer drinker and hell racer
Supporter
Build Thread Contributor
Messages
915
Reaction score
847
RC Driving Style
  1. Racing
We ran with 9" to 15" of vacuum, which isn't much at all. I mean I think you hit that trying to suck a DQ milkshake through a straw 🤪 But it was enough to slightly crush spray foam we used to fill gaps around molds.

Yeah for sure I'm going to be very diligent and make sure the form is 100% airtight, I really don't want to take any chances here!
 

johnnydmd

Beer drinker and hell racer
Supporter
Build Thread Contributor
Messages
915
Reaction score
847
RC Driving Style
  1. Racing
Also, with that all in mind, I should trim the form BEFORE finishing up the epoxy coats. I was thinking of really smoothing out the portions beyond the body, but now that I think about it, a little uneven bit there will help with sucking the air out between the form and the poly and get a tighter draw. I think that this will form ok without the need for any holes drilled (had been thinking of holes in the brake vents, and on each side of the lower grill). I'll definitely do a pull first without them and see what happens.

20220921_224507.jpg
 

johnnydmd

Beer drinker and hell racer
Supporter
Build Thread Contributor
Messages
915
Reaction score
847
RC Driving Style
  1. Racing
Alright, the rest has been epoxied. Tonight I'll trim the excess off, then I'm going to mask off the "finish" areas and douse it with Flex Seal. This morning I put my palm on the top, pushed down as hard as I could, and there was no compression, so I think with it sealed, it'll be fine. It won't be under the lamp long enough or close enough to get soft, not to mention I think if the foam got sucked out it'd leave a big ole epoxy shell, lol.

308235614_388363213462674_9100698673521513760_n.jpg


307872367_587646386435083_8054195665077435493_n.jpg


Pretty happy with how it came out. It's not perfect...but I can live with that - it's close enough. Meanwhile, the rear half molds have finished printing, so I'll prep them and assemble that this weekend.

The cutline for the front half of the body after it's formed is here. It will slip over the rear part of the car which goes up to just before the front wheelwells.
cutline.jpg

Another thing I'm doing that I didn't mention yet, is experimenting with some aerodynamics. The scoops in front of the front wheel wells, I've been thinking of opening them up and have internal passages that vent out of the fender vents (those you'll see later, they are 3d printed and get glued into holes I will cut there) - to create downward force on the top of the front of the car.
 
Last edited:

johnnydmd

Beer drinker and hell racer
Supporter
Build Thread Contributor
Messages
915
Reaction score
847
RC Driving Style
  1. Racing
Well, I got it all set up, and ready to do a pull... (this pic was actually after, I didn't have the form in there when heating). Also, hard to tell from this pic, but I did coat the exposed foam areas heavily with Flex Seal. Also glued some rails on the bottom so that the vacuum holes wouldn't get covered up.

308504726_890418699002878_5949202241168582082_n.jpg


As I was heating the "polycarbonate" (I quoted that for a reason), something started looking weird. I don't know WHAT the hell they sent me, but that was decidedly NOT polycarbonate!!

308187860_1403102240178993_477835596892560825_n.jpg


It turned white, and also it was taking forever to soften. Sigh. Live and learn. Ordered some new sheets from a buyer I used before with success. Little pricier, but at least I know I'm getting the right stuff.

New sheets come tomorrow or wednesday. Meanwhile the rear half molds finished printing, so I'll get started on prepping them in the meantime.
Also, I did a thing :)

308712799_2846602308817293_1628741975600045064_n.jpg


Been curious to see how this engine might perform, it was already running the same clutch/bell, so just a quick swap. Was raining out so I didn't get to test. Hoping it doesn't break anything, lol.
 
Last edited:
Top