INVADER - Nitro Slash drag car

[WickedFog]

I will most definitely write a guide and post some video. I would hope to see this widely adapted, it's another big nitro selling point for drag racing, something that cannot be duplicated by an electric car, given how they "brake".

So that is awesome. I can't wait to see a trans brake in action in an RC car for the first time. Very cool man.

 

[johnnydmd]

So that is awesome. I can't wait to see a trans brake in action in an RC car for the first time. Very cool man.

Thanks! The parts are coming Saturday, other than the horn, which I do have some cheapo plastic ones I could use in the meantime to get it set up. My Noble NB4 came last night, so I played around some with settings to make sure the concept would work and it still did. The NB4 has a really cool "idle up" feature too, which will work perfectly with this I think. So it should be nearly identical to how a 1:1 works. Stage, engage trans brake, hit the idle up button, release trans brake as you hit the throttle. Hoping the micro servo has enough power to hold the brake, it's the strongest one I could find at 4kg. I have one on my 1/16 MT, and it feels pretty strong, guessing it should be enough to hold at a reasonable high idle speed.

 

[johnnydmd]

Okay, so this thing is built, and working - though needs some tweaking to get it perfect.

Though the mount I bought actually would work fine using a piece of CF, I wound up printing out a bracket. I probably will cut the CF plate and use that, as the 3d printed one has a tiny bit of flex, but I'll get to that later.

This is probably "good enough". And it'll make it easier for others to follow the build plan.

Looks pretty slick and clean IMO. Would it work?

This is how it operates:

Pretty straightforward. My only concern was that the brake grip wasn't all that strong. More on that later.

So it's pretty cold and nasty here. Just so people don't get the wrong idea and think I ran the car indoors:

Just LOL. Hey, you gotta do what you gotta do. It ran ok, maybe a little rich from added backpressure, but enough to test the trans brake *Note to self - make sure to dump the oil out of the copper tubing after running the car so you don't spill it all over the floor

Here's the test. This shows that it works, but it's also illustrating why it needs more work - as this was the max RPM boost I could give it without it moving forward a little - I bumped to 8% throttle here.

My brakes have some minor issues. First, I'm using a vented fiberglass disc - and it's pretty smooth other than the vent holes. The brake pads also have holes which I assume creates a little friction. However, though these brakes are silky smooth, they don't have much stopping power. It's not that the brake lever isn't getting pressure(common Jato issue if you don't have good brake adjustment), in fact the lever has more room to move, and it's even flexing when the micro servo engages. Bottom line is the stopping power of the brake system is weak. So, with that in mind, the first thing I will do is try out the rough stock disc and see how it does. If that does the trick, and I can bump up the RPMS to say 15% (which is pretty high actually), then I'll leave it as is. If it cannot handle that amount, I will switch to a dual disc system. I think though that the single, rough disc will get the job done. If you notice in the running video I also moved the linkage to the micro servo arm in one hole to create more torque - I actually could go one hole in further if I make a new linkage with the loop reversed so that it's to the rear of the brake linkage, getting even more torque.

All in all though, this is working as I'd hoped, and while I couldn't really test a launch, I did note that when blipping the throttle from those higher rpms, it was super responsive compared to coming from a standard idle.

 

[Doom!]

Very slick!

 

[johnnydmd]

Last night after dinner I spent some time making some tweaks to the trans brake system, as well as the brakes themselves. First, I scored the brake pads which gave them significantly more grip.

I'm sure this will wear the disc faster, but I'm ok with that! (I will make my own CF discs anyway). This little "mod" made the brakes vastly better - in fact so good that I needed to re-program the transmitter to prevent possibility of flipping the car at the cooldown if hitting them a little too hard. I did try the stock disc, and it was actually less grippy than the CF one (I think because the CF disc has holes that are there for creating friction).

Next I noticed that my linkage was sort of backwards in where the loop was that slides over the brake linkage, so I fixed that, which made a huge, huge difference in the power the servo was able to put on the brake.

Now it's a much straighter pull, and I noticed that there is now no flex in the 3D printed servo mount, so I'm going to stick with that. I'm sure I'll find a use for the mount that I bought, lol.

I didn't fire the engine up to test - I don't even think it was 50 degrees in my garage, probably 40 - and it was 17 outside! But, I did test the brake strength while engaged, and the regular brakes locked the wheels solid, pushing the car by hand, the tires stayed locked. The trans brake was nearly just as strong as the regular brake as well, with the wheels staying locked when pushing the car.

So, I think this should easily hold a pretty good throttle bump, say 15% or more. I can tell you that a 20% throttle bump is a LOT, probably far too much. Between 10 and 15% will be about right for most people.

Some people following this on FB asked about clutch wear, etc. While it's going to cause some wear, I don't think it's significant, and certainly less than what you get from normally running around, starting and stopping often. Besides, it's a drag car, you're only running a few hits, and it's not like you'd have the trans brake engaged more than a couple of seconds anyway. Also, being a drag car, wear and spare parts are a part of the game! In 1:1, a trans brake is hard on the torque converter, and those have to be replaced regularly.

I think we might hit the mid 30's later this week, and my garage will be warm enough for me to test (I don't like running under 50 degrees generally).

 

[johnnydmd]

I have started on my custom lower chassis, this is kinda rough yet, but I do have the upper chassis aligned (and superimposed in this image). Like the upper, it'll be in 2 pieces held together by a brace. My new bits came in this weekend, so I'll run some cuts this week and get the Mustang build started.

There will be some changes/tweaks to the design, this was just to get the overall layout started. It will be built for using Jato transmissions. I haven't yet put the holes in for the engine mount, need to get more measurements, and the holes in the rear aren't measured out yet, just guesses.

 

[johnnydmd]

Weekend started good - got my big block mount set up, and put a "mule" big block in (A Kyosho KE25). Everything fit pretty easily, and I can very quickly swap my big block out for a small block, in minutes. Just waiting on my Reds 2113 on-road exhaust to arrive, and maybe some warmer weather, lol.

It's crazy how much more intimidating this car looks with a big block! I did have to do some minor mods to the RCR mount in order to fit the rotostart (as in cut the front piece off completely). Also had to cut out a little of the lower chassis plate for that as well. My focus for this car will be solely locating steel trans gears. It sounds like they are due to arrive in March.

The KE25 should be a good starting point for testing (and I'll still test that against the OS .21 tm small block). I was pretty set on getting an LRP .32, but not set in stone yet. I'm strongly considering a Force .38, which has a bit more top end, believe it or not, and well there's no replacement for displacement That being said, throttle speed/curve programming is going to be important. My friend is running a Nova .28 in a nitro Slash (somehow he crammed it in there using the stock single speed Slash trans), and it has so much power that the car literally spins into a cyclone and cartwheels when he punches it - even if it's near the top-end. I've never even seen brushless drag cars do that. So far more power than I can utilize, but it's better to be overpowered and dial it back than underpowered.

I then started testing my new router bits, and that didn't go as well....

I set up on my back porch, got the fan blowing the dust and chips (and I really need a smaller, more focused fan/blower for this), and it was doing pretty well at first...

I only had one piece of CF left, so I made sure to mark the starting point in case I wanted to stop it and start over - which I had to do twice after the bit jammed and got off track. I stopped it before it cut anything badly. The third attempt was looking great, so I went in the house to watch some football and let it do it's thing. It was humming along nicely, then I heard it stop, so I went out, and it was jammed, sadly this time it damaged the CF too badly to re-use. Sigh. I've since modified my speeds to be as slow as when I was making my small parts, which always finished without issue. I'll get some more CF in a few weeks and try again. I will say that these new bits made really nice, straight vertical cuts though. It's just going to take two hours for each piece - but I should be able to just leave it alone and do other things while it's going.

Here's my fail piece, lol.

 

[WickedFog]

Awesome stuff. Sucks on the failed cut, but you'll have that. I am surprized you done have a vacuum table setup to hold your parts down.

 

[Doom!]

Why do things like this tend to jam when your in the home stretch?

 

[johnnydmd]

Awesome stuff. Sucks on the failed cut, but you'll have that. I am surprized you done have a vacuum table setup to hold your parts down.

Hmm, would that be strong enough to hold them in place? Or do you mean to hold the parts that get cut out down?

 

[WickedFog]

Hmm, would that be strong enough to hold them in place? Or do you mean to hold the parts that get cut out down?

We used only vacuum tables to cut every part. I think it was only 9" of vacuum that held the parts in place. They are quite strong. I even machined aluminum molds on the vacuum tables.

Here is some info. You can actually buy tables fairly cheap if you look around.

http://www.cnccookbook.com.s3-website-us-east-1.amazonaws.com/CCCNCDIYVacuumTable.html

This was held with vacuum, and as you can see, it is a diy vacuum table, only made from high end tool board....

 

[johnnydmd]

Interesting. I might have to build something! Only issue I think is that when I'm cutting CF, it's going to probably score the surface as I usually need to go a half mm deeper than the material to get a full cut.

 

[WickedFog]

Interesting. I might have to build something! Only issue I think is that when I'm cutting CF, it's going to probably score the surface as I usually need to go a half mm deeper than the material to get a full cut.

What you do is use a tooling board as a fixture. The tooling board has a couple holes drilled through to let the vacuum through. Then, in the face of the tooling board, you cut a groove around the inside of the part profile, but offset about 5mm. This is where you insert the vacuum seal (round foam strands). Take a grinder and grind grooves in the board like a spiderweb that extend from the holes you drilled. Grind them just like scratches in the face reaching out towards the seal. You need this foam seal around any holes you drill too, unless you drill the holes last, and you don't put any grinding marks where they intersect a hole. But with this, you can cut as deep as you want around the profile and you don't lose vacuum.

 

[johnnydmd]

The design of the lower chassis is mostly complete. I still need to add in the slots for both the small and big block engine mounts. Otherwise, the holes are all there, measured, re-measured, re-measured, re-measured! (yeah, at 20 dollars per 100x250 sheet, can't afford any more mistakes!).

Meanwhile, waiting on my Reds 2113 exhaust system (L manifold). Also waiting on functional parachute system Also waiting on Winter to be over so I can test all this stuff!

 

[WickedFog]

The design of the lower chassis is mostly complete. I still need to add in the slots for both the small and big block engine mounts. Otherwise, the holes are all there, measured, re-measured, re-measured, re-measured! (yeah, at 20 dollars per 100x250 sheet, can't afford any more mistakes!).

View attachment 141418

Meanwhile, waiting on my Reds 2113 exhaust system (L manifold). Also waiting on functional parachute system Also waiting on Winter to be over so I can test all this stuff!

Don't you have a 3d printer as well? If so, why don't you test your designs with it first?

 

[johnnydmd]

Don't you have a 3d printer as well? If so, why don't you test your designs with it first?

Not sure if the 3D printer g-code would translate to CNC g-code in a useful way(and vice versa), I've never tried though.

 

[WickedFog]

Not sure if the 3D printer g-code would translate to CNC g-code in a useful way(and vice versa), I've never tried though.

I meant 3d print test parts to see if everything fits. That is what 3d printers were designed for in the first place. Rapid prototyping.

 

[johnnydmd]

I meant 3d print test parts to see if everything fits. That is what 3d printers were designed for in the first place. Rapid prototyping.

Oh, right, well I already have the prototyped parts, Invader is the prototype This is all built off of that car's dimensions. I guess I could make some kinda model out of the g-code (not really sure though) and print out and line up against the original just to make sure I didn't muff up any of the measurements.

 

[WickedFog]

Oh, right, well I already have the prototyped parts, Invader is the prototype This is all built off of that car's dimensions. I guess I could make some kinda model out of the g-code (not really sure though) and print out and line up against the original just to make sure I didn't muff up any of the measurements.

If you have dimensions, i can model up an STL for you to print in just a few minutes.

 

[johnnydmd]

A whole lotta stuff came in Saturday, actually much to my surprise. I was supposed to be doing work around the house. Well that didn't happen

The exhaust was a perfect fit -

It wasn't warm enough to run the engine though. I wish I had some real specs of the KE25 SP, but I guess it's around 3hp and 35k rpms. Some people say they're good engines, others say not. Mine barely got broken in before I swapped it out of my MT.

The big block fits under the vette body without the need for trimming (either the body or the cooling head). I'm debating on whether or not to even use the cooling head, but for now I'm keeping it on.

I also bought the AJC functional parachute system. Given that I have strengthened my brake grip, even though I've got it programmed to be gentle, I still had my eye on these for some time. There was no way to mount this thing on the open ended Corvette body, and honestly I don't think it's even a good idea to mount it on a closed ended body (and really nobody should be running closed end bodies anyway for various reasons). I found a pretty good (I think) spot on the STRC wheelie bar. It's a little more tucked under the body this way, and it has just enough upward trajectory to get the chute into the air flow when it deploys (my theory, anyway). I may however move it the attachment point to the next rung forward/up. AJC said ideally it would be in line with the top of the tire, although, in their example pic, it looks inline with the axle, as I have it. (and I have noted that most of the 1:1 cars seem to hook it even with the axle, so maybe it's more correct where I have it).

To do this, I just needed a couple of 5m standoffs, a couple of 2.5m washers, and m3 bolts. Drilled mount holes, and it fits snugly, with the washers clamping tightly on the wheelie bar. The chute lanyard attaches to one of the wheelie bar braces with a carabiner. I got some good advice from people using this system about trimming the chute, etc. I'll test this at lower speeds first to make sure it doesn't lift the car - but I think it'll be ok, as my car is now back up to just over 6lbs running the big block and having the four or five ounces the chute assembly weighs.

This is their example pic, btw.

With my body on, I think it's a pretty good fit overall. I'll have to test at various speeds and work up to top speed just to make sure it isn't too strong and lifts the car.

My only complaint is that the micro servo they sent with me, for whatever reason, just spins when connected. Fortunately I had another, nicer one, and it worked. The other complaint is that the trap door needs a little filing down on the hinge, as it's far too tight and doesn't open smoothly. Otherwise, pretty cool mod I think, that is totally functional!

I'm also designing a front body support system specifically for the Corvette bodies, to keep the nose from bending down at high speed and hitting the front tires or ground. It will bolt on the front where the bumpers for the Slash used to be.