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cambragol

Hotshot II Carbon Chassis Rebuild/Restore

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Yeah, I asked him if he’d make it and he said yes :D I use it myself on my two HS2s.

I looked into getting it made in alloy but the costs are huge.

I do also have the carbon one you posted and an unused vintage HS2 part but I don’t want to risk breaking it so it’s sat in a box!

Looking forward to seeing how the Boomerang part fits.

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5 minutes ago, Cynan said:

Yeah, I asked him if he’d make it and he said yes :D I use it myself on my two HS2s.

I looked into getting it made in alloy but the costs are huge.

Nice work. That piece in aluminum or some alloy would be great. I checked prices for it and a few other pieces, but like you said, costs are huge.

The boomerang shocks fit and look great (just waiting on glue for the sleeves to dry before putting stuff together - needs up to 48 hours), however, they are not Hotshot II. In the end, if I go with them, this will certainly be straying away from a Hotshot II. Especially considering my plans for the front end. I am thinking this will be more of a Hotshot III.

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42 minutes ago, Cynan said:

 :D I use it myself on my two HS2s.

Do you have a thread for your build of those? Or completed pics? Always interested in Hotshots.

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51 minutes ago, cambragol said:

Do you have a thread for your build of those? Or completed pics? Always interested in Hotshots.

No build thread but both are in my showroom. A vintage that I keep on the shelf and a runner.

https://www.tamiyaclub.com/showroom_model.asp?cid=137402&id=54058

Need to update the vintage one actually with the original shell and decals. They’ll falling off in places but I can’t get a vintage replacement so it’s cool… it’s the used look!

I’ve got one of the carbon chassis too which I’m thinking of putting in my runner though the weight saving isn’t really there and it would expose the gearbox… if I were to put the SHS skid plate on then I’d lose the weight saving. I also have some of those pipes on order and was thinking of sleeving the gearbox and arms like you have done.

 

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Checked out your showroom and left a comment. Blue can work it seems!

I am new to RC, so I don't really know the difference between how weight will effect things etc. Still haven't even driven anything but my son's Grasshopper!

But I like to pick up wisdom from people on these and a few other forums. As far as the carbon chassis benefits, I don't think there are any real drawbacks, and it looks great. However, I do want a more stock body as well, so the second trashed Hotshot I picked up (mentioned at beginning of thread) will get the leftover materials from this build, and will use the original Hotshot II body. That one might get some RCChannel pieces like you set up, as I have all their stuff. I think that one will get rear mounted shocks...but, if I go with boomerang shock tower here, I might have to use the carbon Hotshot II tower instead.

So far the pipes are working great. I don't know if it strengthens things (or potentially makes things weaker), but the difference as far as precision, and the elimination of slop, makes things feel very solid.

Make sure to use a drill press though...

 

To be fair to Tamiya though, when I built the re-re Boomerang I felt the arms/knuckles and gearbox pinholes were all very tight. I didn't notice any slop/looseness. These tow wrecks I got were a whole different story, and without sleeving they would have been like marionettes.

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Okay, let's get some more build images in here. 

I am waiting on glue to dry for the sleeving, so I am only mocking things up here. This image shows how the Boomerang shock tower is going to fit into the rear suspension/gearbox mix.

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So how is this fitting in? The upper suspension arms are the original Hotshot I arms, which do not have space for the shock tower between them and the gearbox (like the Hotshot II/Boomerang arms)

Well, in these images below, you can see that I have squeezed the shock tower *behind* the suspension arms. How can that be? Well, there was *almost* room for this. However, I had to file down the bracing posts about 1mm to make the tower stand vertical. It was a tiny adjustment and certainly doesn't effect the gearbox in any significant way. But it does allow us to fit a shock tower back there!

I also had to dremel down a lip that was around the edge of the shock tower where it abuts the suspension arms. No biggy.

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There is also a little gap between the middle brace and the shock tower, but that is easily dealt with by some flashy spacers.

Now, does the roll-cage fit with this? Well...it doesn't quite. I had to remove two of the four supports for the wings. I have an aluminum support that comes in from the rear that I can add in later, so the wing will be okay. I carved the pieces off with an exacto knife and got busy sanding. Can't make the plastic look all shiny again, but it will do.

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Here is the rollcage put into place (by hand). As you can see, things are tight, but actually fit quite nicely now. 

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Went a little further with putting the rear gearbox/suspension setup together.

Aside from fitting in the Boomerang shock tower, I went with the dt-03 suspension arm and reversed Hotshot I upper arms to give a little more space between the arms and the motor, in order to house some really fat Traxxas Slash shocks. Things have worked out and everything fits with about a millimetre of clearance all around.

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Here is a little close up on the spacing I was trying to free up for these big shocks. The shocks and arms move up under compression (and a little from the weight of the car), so the actual clearance will always be better than here:

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While I was at this I decided I had better check out if the dogbones are going to work. I haven't looked into Universals yet, but I am sure I will eventually. For now I have the standard re-Hotshot dogbones, so I will start with them.

My experience on the Boomerang build showed me that there were some issues with 'binding'. I also read here and there about similar problems on both the front and rear of the hotshots/boomerangs, and I didn't see any really clear resolutions with that. I even installed the recommended Tamiya df-02 (I think) universals and they were binding too.

Anyways, while trying to relieve the binding issues I experienced, I found a trick to help a little. Mainly, the effective (needed) length of the dogbones can be tweaked by using different sized bearings around the knuckle:

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I have a bunch of bearings that are 1mm thinner and 1mm thicker. By putting the thinner one on the inside, and the thicker one on the outside, I can accommodate a dogbone that is 1mm too long. Or I can reverse this and accommodate a dogbone that is 1mm too short. Anyways, I am sure everyone knows this. I did use this technique to make the re-hotshot dogbones fit in my setup, as they were too long.

Now they fit, and there is no binding throughout the play of the suspension arms. Here they are at bottom droop and top compression:

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At maximum compression there is *almost* some binding. Hard to tell. But I see some space in that pic above, so I am going to say no binding.

With this setup the range of my suspension is also determined by the shocks, which is good I think. The original Hotshot arms had places where they were prone to crack, because, so I have read, the arms were determining the range of motion, not the shocks. This range I have here is a lot larger than the original (I believe), so perhaps there is a chance of bottoming out. I think only a tad though, depending on the size of the wheels.

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Alas! A miscalculation on my part. 

I had measured things assuming the dimensions of the original body. However, the carbon fibre body does differ in the way it mounts to the rear gearbox. At the rearmost mount point it protrudes outward about an extra 6mms. This puts it right into the zone occupied by the shocks. 

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The result is the shocks can't lean inward enough to reach the outermost mount points of the shock tower. So these shocks, or this layout, will not work with this carbon fibre body.

But, I have a plan...

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So I searched for a carbon fibre shock tower that might align with the metal boomerang tower, and provide a little more width to the shock mount points. It is not easy getting exact sizes, but I managed to track down a  couple of candidates from 3Racing that might work:

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The one on the left aligned nicely. I slapped it onto the metal shock tower, and now everything lines up! Hooray!

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This original Hotshot II came with a rear 'sway-bar' hop-up of some kind. I am wondering whether to include it in the final build or not. I don't know much about the benefits a sway-bar would provide. I kind of thought that when you have two independent shocks, sway-bars were unnecessary. Or at least provided very little benefit. 

Any other hotshot fans who might weight in on this? I plead ignorance here.

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Never heard of this hop up before.. at least not an official Tamiya one.

I was only aware of:

- bearings

- Technigold motor

- 8.4v racing pack

- two front shocks (as seen on the SHS)

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I've seen it a few times before. I even saw it in a package once, but I can't remember the brand...CRP, Trinity, Paranoia, something old school. Cannot recall.

It seems to provide a little more leverage than the standard sway bar...I think. The way it connects to the suspension arms leaves it sticking out rather oddly, like the bar is too long. I am guessing that is part of the increased leverage or ...torsion? I don't know.

Seems a bit of a waste not to use it though.

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Time to start work on the front end. I surfed the web looking for inspiration here, as I didn't really want to go with a completely stock look. I really like the look of the double 'forward' mounted shocks, and am not so keen on the 'Supershot' style front independent shocks (though they don't look so bad, and likely perform better).

These cars inspired me:

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So I am going to try something along these lines, but with my own spin. Maybe using some of those random pieces I picked up at the 100 yen shot at the beginning of this thread.

I do wonder whether I am overloading the thread with pics though...

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First step in my crazy plan, is to put two 5mm thick spaces in the empty space for the upper anchor of the top suspension arms:

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What? Why?

Well, I am going to *gasp* drill two holes through the upper anchor, through that spacer nut and out the other side. This hole will hold two pins I picked up at the 100 yen shop.

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Next I will use these cheapo L-brackets to mount the bottom of the shocks on the lower suspension arm (Yes, they are just generic L-brackets):

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Like so:

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Hopefully this is strong. I have another piece I can slap on the bottom to provide extra support, but this feels okay. No worse than some of the third-party hop-ups...I think. Though mine is further down the arm, where it is narrower...

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Okay, drilled through the upper suspension arm anchors, and put the 100yen shop pins in. I had to drill 2mm into the 5mm nut on the inside, to allow the pins to go in far enough to hold on the far side. I heated them before I put them in to make a nice clean thread out the back.

I then used, again, 100yen shop prizes to serve as supports for both the suspension mount points, and this shock anchor I am building. The outside one will be trimmed and smoothed with a dremel shortly.

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All my suspension pins are temporary. I will go around at the end and fit nice sized ones with eclips.

Oh yeah, I cut and fit a 12mm piece of steel pipe between the two supports. That`ll keep `em in place. Hard to see there.

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Okay, things coming together now. Trying out one of the shocks. These are huge Traxxas shocks. I think 95mm.

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I did test out this setup with some broken suspension arms and a smashed up front gearbox. So I am not completely reckless with the drill. It took a bit of experimenting, a bit of drilling, etc. So what I am making now is the final version based off that 'draft'.

Here it is now with correct wheels and springs, attached to the chassis:

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And here it is, completed, with the final custom brace added at the front, held on with e-clips:

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Need to hook up the steering properly next, and find dogbones that fit.

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Nice work... That being said, this placement of shocks reminds the Kyosho Optima/Javelin, and it was probably one of the most modified thing on those in the eighties, basically to get the shock anchor points at an higher position so they work better...

Looking forward for the next posts of this build... 

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6 hours ago, silvertriple said:

Nice work... That being said, this placement of shocks reminds the Kyosho Optima/Javelin, and it was probably one of the most modified thing on those in the eighties, basically to get the shock anchor points at an higher position so they work better...

 

Thanks! Kyosho's Optima and Javelin are probably my favourite looking buggy's outside of the Hotshot/Boomerang combo, and certainly I have a few shots of them in my 'rc inspiration' folder.

I actually built it this way to get a bit of a 'lower' anchor point for the shocks. I wanted to have a full range of motion for the arms, and full compression of the shocks at the end of the motion. Maybe not good for performance, but I like that it works that way. Then again, I suppose higher anchor points accomplish the same thing...It looks funny though. Like the engineering for the shocks was done after the design of the entire buggy. Which is the case.

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Not much going on with this build. I am opting not to go with stabilizer bars, as I am not going to be racing this car. Just running it everywhere else. Currently I am awaiting some suspension pins of the correct size for the front and rear, as the ones I have are too long.

I always liked the original dogbones on the original Hotshot. Look at this:

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They just look so badass. Big, beefy, the thick part highlighted etc. However, the Hotshot II comes with some really anemic dogbones by comparison. Even the Re-Hotshot's dogbones are relatively thin. And they are also boring grey.

So, for fun, I took the re-Hotshot's dogbones, threw them into my drill, then hit them up with some sandpaper. Iterated through the grits, and voila! They look a little better, and certainly evoke the original Hotshot dogbone better. Here is a before and after, and an assembled view:

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Got some stuff in the mail that let me get back onto finishing the chassis:

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All titanium bolts! They aren't that expensive, so why not?

My modifications to the rear suspension required an odd length suspension pin of 38mm, hence the Kyosho. The body mount isn't quite as high as the original, but lets me bolt from underneath, to allow clearing of the main shaft (as the hole is misaligned on this body). 

Also got a sweet main shaft from a TT-02, in red, thanks to @toyolien

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Mounted the bell crank that I de-anodized previously:

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Then put it all together. The Chassis is pretty much done:

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Next will be on to electronics, motor, and the body shell! Time to spend some money I think...

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