INVADER - Nitro Slash drag car

[Greywolf74]

Oh man...now I wanna buy a CNC router

 

[johnnydmd]

Grrr - steel gears not coming. Seller cancelled the sale - said they didn't have any. WTF? Why list 1000 pieces for sale then? I suspect these were meant for distributers and I guess they will show up in a few weeks at various outlets. I do see that there is a steel 1st gear available. I wonder if that's the common failure point since the first gear's input gear is also steel (probably was another failure point, explaining why that one gear is steel in the stock trans). I might just get that gear and see what happens. I have some Fast Eddy ceramic bearings coming, so I was planning on rebuilding the thing with those anyway.

[edit] - Seems that *all* of the Hot Racing steel gears are also sold separately - but it was just the 1st gear that's available. I also see that I had it backwards regarding stock - that the second gear is the steel one. I got confused because the HR ones are designed backwards from how Traxxas does it regarding the sleeves. Looks like Feb for the arrival of the full sets. Meanwhile I'll just run the stock ones with the OS .21 tm for now when I get warm days to test. La Nina is gonna help out with that in my part of the world this year, so I'm hearing.

 

[Doom!]

Grrr - steel gears not coming. Seller cancelled the sale - said they didn't have any. WTF? Why list 1000 pieces for sale then?

I hate that!

 

[johnnydmd]

I am designing a new upper chassis plate out of CF. Partially because of aesthetics, but also to make room for the big block mount as the left rear corner post is ever so slightly in the way. This will provide a mount for the tank, as well as the on/off switch. I decided to do it in two pieces as one, the assembly is larger than my 250 x 100 x 3.5 CF sheets that I have, and two, it's probably a little bit too long for my router - I mean, I think it would fit, but it's cutting it a little close for my tastes. This is the rear section and the coupler that will connect the front section.

The front section is much simpler, basically a 2x6x3.5 piece with 7 holes. I will though strategically cut out material to reduce weight as I've done with the rear half.

This also allows me to use a sweet, lightweight receiver box I had laying about that was for another project that it didn't work out for -

This is the reason for the second set of 3m holes near where it joins to the front half. You may ask, why not just use the holes at the edge that are for the posts? Well my friends, it had to be moved slightly back because otherwise the servo arm would not clear it. Also, given that I want access to the receiver without having to remove the bolts holding the posts (which is a pain to do without having to use pliers and scraping up the posts), this makes sense - plus it has a nice cutout between the attachment holes and antennae holder where the post bolts can nestle. This allows me to also keep my steering setup completely intact and not have to move the servo/bellcrank assemblies around to make clearance.

I'm replacing the existing steering servo mounts with a pair of lightweight alloy ones -

They'll bolt onto the front section that isn't designed as of yet. I needed to make a few more measurements but need to disassemble some stuff to get them.

At some point gonna replace the stock crappy Traxxas servos with some low profile ones -

Lastly, I'll use some small L-brackets to make a hump-pack holder that uses a rubber strap on the front section.

I'm thinking it might be a good idea to test the cut with a piece of lexan to make sure all measurements are correct before cutting the expensive CF sheets. provided it doesn't melt, lol. Maybe at slow speed it'll be alright.

 

[Doom!]

I'm thinking it might be a good idea to test the cut with a piece of lexan to make sure all measurements are correct before cutting the expensive CF sheets. provided it doesn't melt, lol.

No Melting Allowed!

 

[WickedFog]

Can't wait to see this chassis plate. I am so jealous!

 

[johnnydmd]

Well the lexan sorta worked, it drilled the holes, cut out the gas tank hole, then it got jammed up, but it gave me enough to see how things lined up. I had it very close, only had to move two holes by 1.75m and change the gas tank hole a little, otherwise it was spot on

The final designs are ready to cut, CF sheets arriving today. Learned a few more tricks for this, hopefully it cuts and doesn't screw up, these sheets are damn expensive!

Rear half of upper chassis plate g-code:

Front half of upper chassis plate, and coupler g-code:

Rear section takes 1 hour to cut, front takes a half hour. Afraid to leave it in case it jams up, so I guess I'll crack a beer or two and watch it go in 30 degree temps, lol.

I'm using 2.5m thick CF, I suppose if this is too troublesome, I could really do this upper plate with 1.5m.

 

[johnnydmd]

Got the pieces cut. I struggled with g-code, and had to finish all of it with a dremel. Btw, the Dremel Light, is a POS, it hardly holds a charge worth a crap. Had to keep stopping for an hour or two to recharge. For the most part the holes were spot on - other than the two in the front which seemed oddly shifted - need to double check some stuff. I also had to tweak the tank mount holes and the hole for the on/off switch a bit. I've updated my design for that, so next time it'll be right. My plates are a little ragged, but they are functioning prototypes. I needed better bits, and to adjust the g-code a little to cut deeper, but otherwise, it's pretty nice. Waiting on a low profile steering servo Tuesday, then I'll finish assembling it all.

This wound up, believe it or not, actually shaving off 25 grams of weight vs the stock plastic pieces.

 

[Greywolf74]

This is such an awesome build!

 

[Doom!]

Lookin' good, were the holes just off center?

 

[johnnydmd]

Lookin' good, were the holes just off center?

They are supposed to be centered, and aligned with the holes towards the middle that support the bellcrank. I looked at my design, and somehow the holes got shifted and I didn't notice, it would seem.

 

[Doom!]

I have to be real careful of that at work, it's easy to nudge something or not have the centers aligned. When cutting it makes a big difference whether you are cutting on the inside or the outside of a line.

 

[johnnydmd]

So after "analyzing" some when I got home, looks like I was wrong, the front holes need to be spaced wider than the bellcrank holes. I have some new bits coming this week, so I'll probably recut the front half.

My servo came in a day early, and it fit (tightly). The arm had just enough clearance for travel, didn't need to shave any of the plate - but I do need to on the radio box, but it's very minor. The steering servo is a high torque, low speed, low profile one. I will also probably update the throttle servo to a low profile, high speed version.

The only other issue is when I bolted the tank and tightened it down all the way, there is a little bump on the bottom of the tank that's now contacting the lower plate and making it so that the upper plate doesn't rest on the posts. So I will put some foam tape around the lip and add extra rubber grommets to raise the tank some (and in the process giving it some more cushion and resistance to vibration).

In this pic you can see a trio of pockets that didn't cut through, and I just left them as is. Two of them are under the radio box (doh!), and so I've redesigned all of that area with a single, larger cutout that's closer to the tank. This was just for saving a little weight is all. I also mistakenly countersunk the hole for the radio box, because...brain fart.

Ignore the overly long bolts, I have new ones coming that will be the right length Also ignore the cut in the cutout there, this is all because of the router not cutting it all the way through and me having to finish it with a Dremel. Next pass will be sure to cut all the way through.

Pretty stoked, I should have the thing bolted up and adjusted tonight, and we have some warm weather this week (though wet), might even get a few test hits in. Hoping my Flysky Noble 4 comes in too

 

[johnnydmd]

Got it mostly finished - my new Noble 4 is coming next week or so, thus I haven't put the old receiver in, but the wires are routed.

I have a new high speed AGFRC low profile servo coming also for the throttle.

Couldn't find any orange 28mm standoffs, so had to improvise with a 20mm and 3 2.5mm spacers. For the bellcranks, I cut of the plastic insert sleeves that the M3 bolts pass through inside each pivot. Otherwise, probably would need to find some plastic tubing to achieve that. The steering is now finished, and it's nice and tight, and with that servo should be a huge improvement.

Wiring routes up through the open slot on the plate nicely. Receiver battery mounts perfectly in the front, I will mount a retainer strap to hold it. It's a great spot for that, adding weight to the nose. For the tank, I would up just putting some 5mm standoffs, and it's very stable and solidly mounted.

The last piece of it, is that I need to figure out where and how to mount my GNSS unit. Probably somewhere in front of the receiver box...

 

[Doom!]

Beautiful even without the body. A rig to be proud of for sure.

 

[johnnydmd]

Beautiful even without the body. A rig to be proud of for sure.

Thanks! I think I'll be said when it's done...which I think we be never, lol.

I guess it's possible that eventually I'll build another drag car based on this template with slightly different drive train specs, but for now I have all the vehicles I need for racing next year (my two solid axle Dragonoids, no prep and prep drag cars, the two TMaxx's for IS MT classes). I want to focus on tools and things to help improve each of these as needed. The cool thing is that my wife is really excited for the drag racing next year She plans to record a lot of it via drone.

 

[johnnydmd]

Pretty much got it fully ready to test. Now it's snowing. Figures.

Battery mounted neatly in the front. I had to mod the throttle servo mount yet more to accommodate the low profile, high speed AFRC model. I think I shall 3D print one, and make it lighter weight as well. I might be getting a little insane with the obsession over grams. Might be

The GNSS mounted nicely in the rear. It's very lightweight, so it won't affect the balance.

Spent some time on the body, re-shaped the front splitter and evened out the rear stabilizer fins (actually, have to work more on the left outer one, it's still slightly tall).

Lastly, I got an idea to install a working trans-brake! The Jato trans has a two part brake linkage, which gives me the opportunity to use a secondary servo on the linkage between the pivot and brake, and interestingly enough, the Jato trans has mount points where I could put a CF plate and some servo mounts along with a micro servo that could be controlled by a third channel.

This could be a major, major advantage on launch, just like a 1:1 drag car.

Buffed the body and put the new livery on as well -

 

[johnnydmd]

Ok, so I got this trans brake thing worked out! I found a sweet servo mount that will work perfectly -

https://www.amazon.com/Micro-Mounting-Bracket-Protector-Finish/dp/B07V4YG35X

I already have a couple of these servos - https://www.amazon.com/AGFrc-Sub-Mi...L4PH12N/ref=pd_lpo_2?pd_rd_i=B07L4PH12N&psc=1

I ordered a micro servo horn - https://www.amazon.com/Reefs-RC-REE...fix=micro+servo+horn,toys-and-games,65&sr=1-4

(I have used this horn/servo combo on my 1/16th Megalodon MT, they work great, good torque)

I did a little test setup last night with a plastic horn. I put a collar on the linkage with a piece of fuel tube and a washer, and a 1.5mm linkage with a loop from the servo horn to the brake linkage. The loop slides over the linkage, hits the washer and pulls the brake lever. Didn't need a lot of servo travel, so that's good as I was worried it might bind/bend the linkage as the arm swings, but it's loose enough that it slides nicely and pulls the brake tight. It wasn't a perfect test, as I was just holding the little guy in place with my fingers, but it was good enough to give me full confidence in this design.

The servo uses the channel 3 toggle switch, and it works exactly like a 1:1 trans brake. To use, you toggle the servo into the locked position. Then you can get the engine RPMS up (how much would depend on a variety of factors, such as brake tension, slipper clutch, etc, but I would think you'd probably not want it so high that the slipper spun). Then you press the button again and hold it until ready to launch. When you launch, let go of the button as you mash the throttle, and the trans brake releases. I've tested this aspect of the electronics, and it's flawless. It's so diabolically perfect! It will literally slingshot the car. It's almost cheating

 

[Doom!]

That stuff is all so confusing to me, sounds good when you explain it, but I would be lost if I had to figure it out myself.

 

[johnnydmd]

That stuff is all so confusing to me, sounds good when you explain it, but I would be lost if I had to figure it out myself.

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".