INVADER - Nitro Slash drag car

[Doom!]

Glad to hear the trash bag method worked out as planned. Everything is looking good. I'm kind of sorry I don't need one of your chassis, they are sweet!

 

[vuduracing74]

I have a lot of pics already of the process that I need to get off my phone, but here was just a few of printing and painting the driver:

The design in meshmixer
View attachment 119893

My computer painted guideline
View attachment 119894

Printed and painted - this was supposed to just be a prototype, using my crappy little Davinci, and I broke it a few times getting the supports off, but I'll use it I guess. I really wanted to practice on this one. I might post pics of the painting process so I don't forget how I did it.
View attachment 119895

I've already done quite a bit on the bubble form which is kinda interesting, lol. Will post them later.

That freaking awesome!!!!

 

[johnnydmd]

Glad to hear the trash bag method worked out as planned. Everything is looking good. I'm kind of sorry I don't need one of your chassis, they are sweet!

Well as cool as the trash bag method was, there was a similar much better solution for purchase Guess I shoulda looked around a bit, lol.

This worked flawlessly, was quite quiet, and wasn't hard to clean up afterwards. I also bought an attachment that puts a brush around the bit that has a vacuum attachment. I didn't use it this time because I really needed the parts I was cutting and this was my last piece of CF. I'm not sure I'd run the vacuum for fear of small sections that get cut out getting sucked up, but I could try. The reviews show that the bristles must be trimmed/adjusted or the Z movement can jam. If this works though, that would make cleanup almost unnecessary. I did fashion a second, thick foam filter on the exhaust of my shop vac, and I'm confident there isn't any dust getting anywhere when running it. I guess then the issue will be emptying the shop vac which I think I will do by filling it with water and dumping that into a bucket or something or maybe a disposable cloth sack. Not sure on that yet...

The weather saturday was bad, so I was home and decided it was a good time to tear down the engine and replace the bearings with the ceramic ones I bought.

I also wanted to do some other mods with the crank, and be a little more aggressive with the sleeve ports. The engine parts were all very clean and in great shape. Then again, the run time isn't much for a drag car. I was pleased to see that the crank for this engine already had an existing scallop (some engines don't have that at all). It was a little sharp on the edges, so I smoothed it out some. Not much of a change, just something I've seen guys do to improve the flow and reduce turbulence.

Here you can also see the rod pin is hollow - this is a nice feature of the KE25, there is a spring and pin that goes in there, and it's used for a ratcheting system for the pullstart. There is(can be) a OWB, but when the engine is running, that rear shaft doesn't actually spin, and removes all of that rotating mass that a OWB normally creates.

I also wanted to ramp the shaft. This improves flow, and creates more pressure in the crankcase, and is a mod for improving the low end response/power.

I then worked on the sleeve, and wanted my port fangs to be a little better defined and bigger.

I was careful not to go into the nickle plating of the inner sleeve.

Now it was time for the bearings. The old front bearing popped right out. The rear bearing I heated the engine to 220, and it just fell out. Then the fun began! I worked on the front bearing first, and I noticed right off that the new one was tighter fit. I heated the engine up to 230 or so, got it in. Cool. Then I worked on the rear. No dice. Took it up to 250. Nope. Then 290. Nope. Not even close! I set the new bearing on top of the old, and in a "you've GOT to be kidding me" moment, saw that the new one appeared to be .5mm larger! Well that was never going to fit for sure. I wasn't about to give up though, so out came the dremel, and I started working on the outer race of the new bearing, slowly grinding it, taking great care to make sure it stayed evenly trimmed. Two hours(!) later, I was able to get it to go in with a little mild heating of the block (hoping I didn't take too much off and have it be loose). Looks like it was about perfect, as to get it in fully I had to whack the crank pretty good with a rubber mallet.

The new ceramic bearings were a HUGE difference. When spinning the crank with my fingers it spun very freely compared to the originals. My entire drivetrain is now fully ceramic bearings, and it shows.

I let the crank cure overnight, and after 24 hours of curing, took it outside to fire up. I fully expected some tuning changes, and it was as you'd expect, on the rich side. Few tweaks of the needle, and right away it was very noticeably very, very quick to spool. I will get a chance to fully test at next weekend's final TNT before we begin our cash days events.

 

[Doom!]

The new enclosure is perfect! Sounds like the ceramic bearings are going to be sweet.

 

[johnnydmd]

Took the car out on Sunday for another TNT with the team. It was HUMID. So took a few minutes, and got it dialed in. Started blipping it around the pavement. The thing has considerably more power than before, each little blip of the throttle put the front wheels up, and slammed hard on the wheelie bar. I gave it a moderate blast, maybe a 20 foot launch just to see before putting it on the tree, and had no brakes! One of the stop collars was too far up. Sigh, the trials and tribulations of changing a chassis and carb at the same time. Luckily it was heading in my direction and I had to decide to either catch the car with my foot, or let it go by and hope it slowed down enough. Chose the foot Foot was ok. 3D printed body brace was not. So I didn't want to run the car and have the nose of the body digging down on the big end and catching pavement. Meanwhile, I went to work on Hissed Off, got it tuned, and ready to go - and then the rumbles of thunder came, so we had to break down the track and pack up in a hurry.

One thing I also did was buy a corner weight system. This is such a great tool for balancing the car and tuning the shocks. I was pretty stunned to see how far off I was, and also stunned to see that the car weighed more than I had previously thought. 6.8 lbs (with a full tank of fuel)! My other scale showed it at 6.25, the full is maybe .2, so I'm probably at about 6.6 - which is still a pretty heavy car. (By comparison, Hissed Off weighs 5.4 on the corner weight scale). Given the chassis are identical, the weight difference is attributed to the big block drivetrain, all steel shafts/gears, etc. This is the tradeoff for having at least 50% more power, so it's really an interesting comparison between two approaches. (Invader, the heavier, but more powerful car is much faster).

This was the "before" weight distribution:

While the side to side weight was pretty balanced, the cross weight was not, and the rear was pretty far off. This explains pretty clearly why the car was veering left on some of the runs where I knocked the tires off. Right tire was staying hooked while the left spun.

I worked on the shocks. I know people like to bash Integy, but they make some really nice shocks, well some of them are nice. These shocks are really easy to adjust. I got the car near perfect.

It's a pretty tough balancing act, especially considering you have an exhaust pipe hanging off one side (which is why the front is near impossible to get right). The rear is dead on. Cross and side to side are pretty close to perfect.

 

[Doom!]

I really enjoy reading your threads, I would never be able to do most of what you do, but it is interesting to watch.

 

[johnnydmd]

Tested out my router with the suction system. I had 3d printed an adaptor for the hose to fit tightly in the socket, and a little duct tape to hold it in place. Absolutely flawless! Very little dust anywhere to clean out of the box. I had added a second filter to the exhaust of the shop vac, and then put a damp paper towel over that just to see if anything was escaping. Nothing was

The whole operation works well, and now I'm getting into the final tests (my shock towers and printed 3d parts).

That chassis is the OG Invader one, which still can use a Slash transmission, so I wanted to test if my rear bulkhead would work with the changes I had made for it to be used with the Jato trans, and it still works. I'll test fit all these parts and make sure they fit.

This week I'll start cutting a chassis to sell.

 

[95PGTTech]

Another one who just likes to watch. I am a fabricator for 1:1 cars and motorcycles so most think my 1:10 stuff is more custom/engineered than most and your stuff is 100x beyond my level. The technical details in the posts is impressive, and a lot could learn from you in terms of preparation for racing. The guys who are winning don’t just gather their stuff up throw it in the car show up and take home trophies by accident…on any scale.

 

[Doom!]

Looks like you've finally got it all dialed in.

 

[WickedFog]

So jealous. Now build me one! I don't have enough ambition to do it

Great job man!

 

[johnnydmd]

I started putting this thing together...

Kinda have my doubts about the 3d printed suspension, but I'll thrash it about and see what breaks or not. Can the rear arms hold up under hard acceleration? That's my biggest concern. No big deal though, I'd just swap them out for stock ones if they don't. The rest of the stuff isn't high stress, though I'd imagine a crash would probably break some things, but hey, don't crash, right?

Meanwhile, I found these beefy big bore shocks, and after some modification, made them work. I really like these and for 25 dollars, price is unbeatable.

Been struggling to find a manifold that isn't expensive, but finally found one on eBay today.

 

[WickedFog]

Looks really cool man. For A-arms, I always had this idea to print some in 3 pieces. The front and rear edge of the arms, with the hinge pin holes laying vertical on the print bed, and the center section laying flat on the bed. Then screw and glue the front and rear edges to the center section. That would keep ya from the arm separating at the hinge pins, and should be strong enough to take a bit of abuse.

 

[johnnydmd]

Looks really cool man. For A-arms, I always had this idea to print some in 3 pieces. The front and rear edge of the arms, with the hinge pin holes laying vertical on the print bed, and the center section laying flat on the bed. Then screw and glue the front and rear edges to the center section. That would keep ya from the arm separating at the hinge pins, and should be strong enough to take a bit of abuse.

I've thought about that too, even thought about cutting it from CF and using aluminum line (p) clamps, but couldn't find anything small enough.

In the end I think I'll just farm them out and have them printed in nylon (if it's cheaper than the stock parts). The rear bulkhead is custom so I was planning on that part anyway.

 

[johnnydmd]

I had been looking for splitter struts for some time with only finding these very flimsy 1/10th scale things that fell apart. So I had printed out some CV joints myself and made some, but they didn't really have any strength either and the shafts kept popping out.

I searched around for a bit, looking for micro sized CV joints, and finally found some that were light and small enough to work (they are made for RC boats actually). Got some 3mm aluminum rod and viola, very sturdy, functional and cool looking splitter struts! This should help with keeping the splitter from digging into the pavement on the big end, which it had been doing, even with the body brace holding the front up as it were.

The only issue I had was that the (very) tiny 1mm set screws required an allen key the size of a hair, so I used some of my shorty 1mm screws instead. maybe not as pretty, but they hold strong. Got both bodies rigged up last night, gonna do a little testing this weekend, but these should hold well.

 

[Chubaka]

The time and effort spent on one car is just amazing with great detail.

 

[Doom!]

Looks like your shark teeth went to the orthodontist. They look great, you always come up with great solutions.

 

[johnnydmd]

Looks like your shark teeth went to the orthodontist.

OMG, that's exactly what my wife said! I was going to paint the cv joints orange, but I kinda liked the metal look.

 

[Doom!]

I like the metal look too.

 

[WickedFog]

Looks killer.

 

[johnnydmd]

My chassis design has been finalized, and the very first of these completed and sold. This one I let go for a little lower price because one of the plate's finishes didn't quite match, and it was to a teammate, so reduced the price. It's weight comes in at a very light 429 grams.

Shown here with a Jato transmission mounted up:

Note how the trans is bolted through the shocktower (which is why I 3D printed it with the custom holes). This gives the most flexible portion of the chassis a great deal of stiffness.

Now I'm shopping around for companies that can cut the parts for me at hopefully a reasonable price. I'd cut them myself, but it's just too much work because I still have to clean up the edges with a dremel a little, and dispose of all the dust and splinters from the shop vac. I think my router will be relegated for just other custom cuts, etc. I doubt it could survive making a bunch of these.