Bang for Buck Boomerang

[BuggyDad]

1 hour ago, Twinfan said:

CVAs, as per the kit plus an extra short one up front of course    Built as per the Supershot so no chassis bottom out at the front.....

Gotcha. Thank you. I aim to do similar but experiment with mounting positions a little. And I've also got a range of yellow shock plastics now so I might end up doing something a bit different if the opportunity emerges when I offer things up. 

[BuggyDad]

1 hour ago, ThunderDragonCy said:

@BuggyDad I used the m05 58.5mm shafts with spacers at the front. You need to dremmel clearance into the bumper rib because they stick out so far. At the rear RC Channel do a dedicated set of shafts. You can order them direct from Taiwan off their website.

Ah ha. Thanks. Yes, I'll get a set of those. Might get two actually because I reckon bracing the rear will get near enough to that. Any idea the length of the other shafts in the set? I might get the rear tops out of that too if the mid length pair in the set is long enough. 

[Andreas W]

22 minutes ago, BuggyDad said:

 More cars doesn't really necessitate buying more running wheels after a point. 

You are right about that. If I were smart a couple of years back I should have standardized and ran JC Pepper Pots all over. But that did not happen, when I immidiately fell in love with the JC Hotshot wheels and was too lazy to look carefully enough on the description only to realize that they did not have 12mm hex attachment. 

 

I am looking forward to what you'll come up with for the nice and humble Boomerang. Take a look of this, if you want to make the body lower and get a more Hotshot oriented look. 

 

https://www.tamiyaclub.com/showroom_model.asp?cid=87027&id=9813

[BuggyDad]

21 minutes ago, Andreas W said:

Take a look of this, if you want to make the body lower and get a more Hotshot oriented look. 

https://www.tamiyaclub.com/showroom_model.asp?cid=87027&id=9813

Oh I like that! Lowering the body is a great idea and it hadn't occurred to me. I will definitely look into doing that. I can't see exactly what he's used there but I probably would go my own way with 3d prints and a homemade tower anyway. And I will assemble these elements stock first. 

[BuggyDad]

Back to the Tamiya club's most disorganised build this evening.

I have quite a few options to consider. 

Front suspension I'm starting down the track of essentially a Super Hotshot setup but RC Channel has a nice simple and perhaps more modern arrangement with the shocks in front and a little laid down. I could make the tower for this easily but it'd require different lower arms and quite possibly shorter shocks. Then again, the Super Hotshot arrangement has to clear (or remove) the ARB mount points on the Boomerang upper arms or use Super HS arms, and leave space for steering. I haven't really got into my steering plans yet. It all looks quite tight in there. I should have variables I can move around because bell crank pivot placement is down to me, but there are other constraints too. 

At the rear, I'm starting stock. However, @Andreas W's slammed body idea raises a new question: to drop the wing lower, do I move it to behind the shocks, or do I move the shocks to the rear, a la Super HS? Behind the shocks can probably be done with just a 3d printed wing mount. The tidier in appearance Super-HS layout looks like it requires a heap of different parts, so most likely I'll do the former because "bang for buck". Well, I'll maybe mount the body at its stock height first, but I do fancy this. It might end up looking a little "different". 

In terms of build progress, not that much more. I fitted front and rear ends to the kit chassis just to mock a load of stuff up, and I 3d printed (all the orange bits) a few pieces as dimension checking placeholders for pieces to be cut out of CF or GRP. Printing is fabulous as a method of making mock-up sheet parts because a 2mm thick flat part is very fast to design and print. It's entirely useless for running but that's not the point. Some parts look funny because I'm also using them to test some print settings. 

 

 

The front suspension has loads of wheel travel. I can't tell from this why the Super HS doesn't get to chassis bottom out - mine does, with plenty of down travel. They're the same shocks I'm pretty sure. 

Left and right towers are different here - testing different shock positions mainly to enable as much space for steering as possible.

It might seem a bit "cart before the horse" to deal with these details before I design the chassis deck and sides but I thought it sensible to familiarise a bit more before I go piling in.

Assuming I can get my CNC machine running on CF sheet well enough, this method of 3d printing parts to test and then cutting them by machine is quite exciting. I can see so much scope for it. 

[BuggyDad]

On wheels, anyone feel the need to fit foams in HS series oval blocks, before I fit the rear tyres? I don't think the fronts warrant it. 

[Twinfan]

8 hours ago, BuggyDad said:

...the Super Hotshot arrangement has to clear (or remove) the ARB mount points on the Boomerang upper arms or use Super HS arms, and leave space for steering.

The Supershot front arms (top and bottom) are identical parts to the Boomerang.  Everything bolts up perfectly and works just fine with the Boomerang sliding steering arrangement.

 

8 hours ago, BuggyDad said:

The front suspension has loads of wheel travel. I can't tell from this why the Super HS doesn't get to chassis bottom out - mine does, with plenty of down travel. They're the same shocks I'm pretty sure. 

The Supershot uses CVA Short shocks up front, it looks like you're using CVA Mini shocks or taller towers?  That'll be why you've got more travel.  The shock body is the limiting factor for the Supershot setup using the stock towers.  I guess CVA Minis didn't exist when the Supershot and Bigwig were released and they came out before the Terra Scorcher and Fire Dragon as those could have been used instead if Tamiya didn't want to use taller towers.

 

[BuggyDad]

42 minutes ago, Twinfan said:

The Supershot front arms (top and bottom) are identical parts to the Boomerang.  Everything bolts up perfectly and works just fine with the Boomerang sliding steering arrangement.

Ah thanks. This is good to know. I thought maybe the Super-HS lost the ARB mount points. I'm going to build a CF chassis and fit M-05 steering so it's not the Boomerang sliding rack but that shouldn't be a problem - plenty of others have done this. 

42 minutes ago, Twinfan said:

The Supershot uses CVA Short shocks up front, it looks like you're using CVA Mini shocks or taller towers?  That'll be why you've got more travel.  The shock body is the limiting factor for the Supershot setup using the stock towers.  I guess CVA Minis didn't exist when the Supershot and Bigwig were released and they came out before the Terra Scorcher and Fire Dragon as those could have been used instead if Tamiya didn't want to use taller towers.

My front shocks are the old shorts. Two Boomerang fronts but same parts trees and shafts as the Super HS. So I think I have taller towers. That was the thing - I haven't got the SHS towers because I figured I'd just offer the parts up and make up my own arrangement, knowing there's an issue with the stock ones but also wanting to see if I can play around a little with angles. And keep the cost down of course. Reminds me, the one SHS shock part I don't have is the springs, which are available and cheap, as long as they're also the right tool for the job. 

[BuggyDad]

I'm quite impressed with the old style MK1 CVAs on this. I think the pistons are better molded than the 2s and they have shaft guides in amongst the o-rings. I fitted X-rings but everything else is stock. I guess the disadvantage is that with the guides they will have to have longer eye-to-eye length for a given stroke, by about 4mm, but they should work better for it.

And the bottom cups might be annoying. Long term something might change down there. I could print yellow removable spring cups and fit to ball end adjusters. 

[BuggyDad]

First go at a steering assembly that'll screw straight to a CF chassis plate. Should work nicely I think, just got to fit it in the right spot. May have to make my own bridge because this one is a bit long, but we'll, er, cross that bridge when we come to it (see if there's a significant bump steer issue first). 

These are the M-05 parts from RCAidong. I bought theirs this time because I noticed they include two additional bearings. They are capped on the top because I want to screw in from beneath, so I'll put nuts up there. Or maybe mount to another piece of sheet material above instead if it's useful to have one there to brace the chassis. Anyway, nice smooth movement and I left room for some shims so I can get it just so. 

Not much to show for a long evening on the CAD otherwise but I am getting there with my chassis parts as well. Chassis also necessitates a changed rear shock tower because the wide out chassis sides would foul the shocks in their stock position. Fingers crossed I should have some printed prototype parts in the morning, enough to assemble roughly and measure some gaps anyway. I find it quite difficult to take good measurements when my key points are apart in all three axes, so my method is iterative - print an early mockup so I can hold a 3d model in my hands, measure the errors and then amend the design. 

[BuggyDad]

Finished printing chassis parts overnight. The dog woke me up early so I thought I'd pop it together. I think it's all coming along quite well. 

Ignore the big holes in the chassis - except the battery one they're just to reduce material and time in these prototypes. 

 

 

 

 

It does look to me like my steering should avoid the shocks but I need to assemble it with tie rods to confirm.

At the rear I have a little anti-squat. Although I wanted to err in that direction rather than the other, and the relevant hole position was the hardest to measure of the lot so to err was likely, I need to measure the resulting angle and consider adjusted hole positions. I think perhaps I will aim for 1° rather than back to dead level. 

The body struggles just a little with fitment around the front shock towers and the aluminium front suspension brace, but it would sit nicely with no further cutting just a couple of mm back. So I might try a TT-02 central shaft in it, which I believe is fractionally longer, elongate the chassis at the same time to add just a little to wheelbase and aid body fitment.

Chassis sides are not tied in to the base yet. At the front I think I'll incorporate this into the steering assembly. Further back I'm considering a simple 60mm threaded tube and zip tie that down to the floor but I might also incorporate vertical fixings between the horizontal plates I need to add for battery and body fitment. Some additional parts are required functionally so I'll make them do a structural job at the same time. 

I guess it's a classic Boomerang feature but I'm not sure the wide bumper is for me. I think I'll snap it, although perhaps it'll save an arm when I do. I might look at either cutting it down (will look messy though) or fitting a smaller aftermarket one. 

[BuggyDad]

Finally got back to the Boomerang following a little CNC progress. 

This slightly lowered body position I think will be somewhere near where I end up. 

 

This 2mm GRP will be ideal chassis material here I think. No point in any additional stiffness. It's already stiffer than ABS tubs I've got and I haven't even fixed it all together yet. 

I've now also fitted GRP suspension bracing all round except the rear top of the front, which I think is one of, if not the, least important points to do it. These parts fit like a charm. Oh I did use an aftermarket aluminium piece at the top front front, because I had it.

The chassis base connection to rear gearbox is slightly out, so that needs to be changed and a new one cut, and the body mount plate wants beefing up a smidge, but what I will do now I think is fully assemble the car before inspecting everything with a view to cutting anything that either I want to change or just do a tidier job of. There are tight clearances elsewhere too so this makes sense. Plus this first go on the CNC didn't cut right through in some quite big areas, so there's some relatively untidy manual finishing gone on and the odd little bit of delamination, where this method (cnc) should really give a perfect finish. So with some small changes to machine setup it should be perfect. Shock towers will be CF, but nothing else needs to be. I've got a neat little design in mind to brace the rear tower too. 

[ThunderDragonCy]

Top job! So good for first parts.

[Andreas W]

The chassis look brilliant and the lowered body on it looks ace. I am curious about the first driving impressions. 

[BuggyDad]

2 hours ago, Andreas W said:

The chassis look brilliant and the lowered body on it looks ace. I am curious about the first driving impressions. 

In this case I think I will be both unqualified to comment, because I have no recent experience of any Hotshot Chassis car, or a monoshock, and I suspect also that I won't have made any material performance changes over another Boomerang with a Super HS dual shock setup. I'll either have to give it to someone qualified to test, or rebuild it stock myself! 

My changes are not really performance or driving oriented. Well, I suppose the steering is in a way but the Boomerang steering is probably fine in driving terms, just unappealing to me in terms of sliding parts vs dirt and the like. HS direct mount steering didn't look great to me, but that wasn't my starting point. This'll be my third car to take aluminium aftermarket M-05 steering and I think this RCAidong gear is better than the Yr set. Two extra bearings and it's buttery smooth and totally free but with no slop at all. 

Would 2mm extra wheelbase make a difference I wonder? I don't imagine it's enough to tell. I extended it just a fraction but only to give my prop shaft a little room to move as with my 3d printed mockups it was looking like just fractionally binding, although it was hard to be sure with such a flexy chassis. It's a TT-02 shaft which I understand is a little longer than stock, although some say it fits the stock chassis. 

Oh and there is a tiny bit of rear kick up, perhaps 1°. 

So tiny things really in driving terms. The big one is probably the dual front shocks but that's far from unique.

What I hope to achieve is more in convenience and resilience - steering, battery door and bracing all around the suspension pivots. 

I'm looking forward to driving it very much though. I can hear the gearbox noise and the sliding oval blocks already! 

[BuggyDad]

Slow progress but progress nonetheless. I have cut a new chassis base following full test assembly and adjustment of a couple of dimensions, and printed all the little brackets that hold it together.

I like this GRP and I think in many RC situations it'll prove a more appropriate material than carbon fibre.

I'm oddly pleased with my brackets that hold the sides to the base. They're a simple block, zip tied to the base and then screws into them hold the sides on. Pleasing because the zip tie should entirely negate z axis weakness. 

The chassis base is still a little out but it's workable. The holes for rear gearbox attachment are <1mm out (which I could alternatively fix with a reprint of the smaller bracket) and the interface between base and sides needed to have been designed for a clearance fit rather than to exact dims, but a file sorted that. At least this time the machine cut it through as intended, so no manual finishing required. 0.3mm extra depth seems to be enough to cut through, if I keep to the central portion of the bed.

One of the changes I made was to bring the steering crank assembly forward 6mm such that might tie rods are close to parallel at the mid point. Ideally it'd come forward a little more but I'm going to have enough trouble keeping them out of the way of the shocks as it is. 

One reason for slowness is whenever I'm CNC cutting my laptop is out of action for anything else. I have spied a spare old laptop in the office that I may be able to repurpose, but I'll have to get into it first. 

[BuggyDad]

Well, things accelerated today and I'm not far off done. I got the shock towers cut and glued, a few more prints done and fitted, a couple of other little problems solved and the electronics in. Stickals finished too. 

The rear tower is two pieces of GRP glued together to make 4mm. It seemed most convenient to do it this way because it's got some 2mm deep cut outs in one side. So this way I just cut the two different shapes and glue them together. Bit difficult to measure out tiny amounts of epoxy - too small for my scales so I used a paracetamol pill packet! Seemed to work OK though. Next time I might try the convenience of superglue. The end result is so rigid I think you'd be hard pushed to tell it from 4mm CF. 

 

The front towers are slightly reshaped in an effort to help body fitment and I think they improve aesthetics slightly. They are stiff enough to be run but they could do with a reinforcing bar between them before any harder running. Or I could look at bracing down with a spine at 4mm thick - more elegant but a faff. 

 

I adjusted and reprinted two internal parts to deal with my chassis base fitment issue. It now fits perfectly. Printing can be initiated in seconds where setting up a cut might take me half an hour. And in this case it's less machining time and a fraction of the material cost too. I think it's fine for printing to be somewhat trial and error. CNC not so much, you want to get your mistakes out of the way before cutting, ideally. 

I worked on suspension and steering, mainly just assembly options for range of movement and bump steer etc. I could do a little more but I may not. The rear CVDs, it turns out, are a limiting factor in suspension travel (after I amended my tower design thinking it was that). There will still be chassis bottom out plus a couple of mm, so it's fine, but if there was a little more drivetrain give the shocks and other parts would go a fair bit further. 

At the front, the CVDs with the 3mm hub inner bearings I have fitted (necessary to avoid binding at max travel) are a limiting factor on steering throw. Not ideal, however I think other limiting factors follow right after this, and in the extremes of travel even before, so there's little point in trying to tackle it. At the front I have chassis bottom out plus about 10mm if I want it, so it's hard for me to see how the Super Hotshot won't bottom out (as is famously the case, apparently). 

I worked out a neat way to brace the rear tower forwards, mainly because there was a pair of bosses just waiting there on the gearbox. This is a very rigid arrangement, probably unnecessarily so, but I made the brace when I was using a 3d printed placeholder for the tower that was pretty soft. 

 

Finally, I'm working on a wing mount. I needed to make my own regardless, because of other parts changes, but my body is low and you can't drop the wing with it because of where the rear shocks are. Anyway, I like a lairy wing, so I'm going out behind the shocks but up and a bit more steeply angled to carry the line on but with a bit of a kick, like a sort of poor man's Top Force. 

 

I'll probably tone it down a bit from this position, which was just a roughly measured first stab. 

Full box art on the stickers. I like the Boomer body, I think it's absolute classic Tamiya with just a tiny hint of 80s Ford (Escort - the square one - Mk3? I don't know why I think this, it's probably just me) thrown in - full box art because for some contrary reason my very modded things have to be full box art. 

Oh and, of course, it's got a proper wire aerial! I need a flag to stick on the top of it don't I? I always wanted an RC car with one of those. I didn't even design my battery mounting bits for the screw position, it just fits! 

Still to do: fix and reduce (or maybe not?) the wing mount and better fix it to the tower; improve battery retention clips a little; redesign frame that supports rear body mounts, to use 3d printing, come up with a front body mount solution, maybe change ball studs and spacers around at the front for the final bit of improvement around bump steer and clearance from shocks (although it's good enough now). 

[ThunderDragonCy]

This is fantastic. On the front tower, are they taller than stock? Reason the SHS doesn't bottom out is because it uses short shocks with a tonne of spacers to give about 10mm stroke. If you just used a mini shock or taller towers then it will happily give more travel. 

[jonboy1]

Awesome build @BuggyDad - love it! I completely agree with you about the Boomerang having one of the very best bodies, I think it's because it is a lot more angular and "muscular" than a lot of the more "flowy" ones. 

Making the body lower makes such a huge difference - have you seen this one: https://www.tamiyaclub.com/showroom_model.asp?cid=87027&id=9813

And I love the rear wing too - keep it!  

[BuggyDad]

1 hour ago, ThunderDragonCy said:

This is fantastic. On the front tower, are they taller than stock? Reason the SHS doesn't bottom out is because it uses short shocks with a tonne of spacers to give about 10mm stroke. If you just used a mini shock or taller towers then it will happily give more travel. 

I was aware of the issue only from on here, so rather than getting stock SHS parts to compare (plus they're pricey so they fell foul of the "bang for buck" brief), I thought I'd just get hold of the short shocks, which I knew would have plenty of stroke (and I knew they were stock), and just lay it all out so I'd get chassis bottom out and enough down travel. 

No spacers in my shocks. I could actually drop the tower tops a couple of mm for a bit more front droop, but I don't think there's a need. And spring choice is a question too.

These front springs are monoshock fronts, so I thought they'd be far too much for this, but they seem OK. I have a pair of SHS ones to try too. I might have a mess around, but ideally I need a Junkies meet to try it out before I refine because it's already good on the "bench drop and aaaah" test. 

I guess what surprised me was that tamiya would design those towers too short (or indeed use the long body shocks with short towers), because it seems pretty straightforward stuff. Perhaps they just didn't have chassis bottom out as a thing to go for at that time - I suspect this is the case since intuitively one might well assume that a chassis scraping the ground on an off-roader is not a positive thing. 

[BuggyDad]

4 minutes ago, jonboy1 said:

And I love the rear wing too - keep it!

Cheers! Yeah, a change is possible but this one makes me smile, and so I think most likely it'll stay. It's got a really perky, ready to pounce, kind of attitude. 

[BuggyDad]

Had a little bit of time today so I sorted out the body mounting front and rear and got the newer battery clips on. I think I can call it done. Maybe not "done done", but "done". 😉

So I took some more piccies outside. 

 

 

 

 

 

 

There's a front body mount in the box, which I imagine is for the later bodies that use some of the same parts. Or maybe it's for using dual shocks on a Boomer. Anyway, the scope to lower the front of the body more than another say 2mm is pretty much non-existent, so there was little reason to try to do anything else. In the end, I have body position very close to stock. Adding 2mm in wheelbase has changed it a little, as has wanting to fit it uncut around the front towers. 

I'm not sure my battery retention would survive track running, but I could back it up with a strap.  

And I do need to adjust front toe but I won't bother til I tinker with the ball joints. 

[BuggyDad]

A couple of things to mull over before I get back to this...

@ThunderDragonCy mentioned mini front shocks on a SHS, and mine doesn't need the stroke of shorts, they look a bit too tall and it'd be nice to raise the spring cups up just a couple of mm on taller lower eyelets out the way of the steering. Plus towers are easy to design and make and shorter ones would flex less. 

And I have a feeling these shorts could come in handy on something else. 

Hmmmm. 

Depends on how much stroke I can lose, I guess. 

Another thing to consider is the slop in the front upper arms. I think ball jointed front hubs might exacerbate it because they add no further support. The front upper pivots are the only ones I haven't added my own bracing to - instead I used an aftermarket aluminium brace on the front (which is sloppy) and there's nothing behind the arms. It wouldn't be all that pretty but I think there is just space under the body to brace behind as I have all the other pivots, and out front should be easy. I could add a grp sheet brace in front of the aluminium part but it may be neater to replace it and incorporate it with a 3d print for tidy fitment. 

It could be argued that some of this stuff is ultimately a bit pointless on a car like this but I'm finding it an enjoyable new angle to take on all this work on an old 4wd chassis as a project for learning CNC routing. And, it's almost free (if you ignore the purchase of the CNC machine, which I think we can all agree Bernie would wave through in a heartbeat). 

[Grumpy pants]

A fantastic build - 👏

[MadAnt]

Fantastic, I love it.👍