Bang for Buck Boomerang

[BuggyDad 5329]

My plan for this is to really work to make it the best performer I can but in ways that are not throwing money at it (although there will be some of your traditional hop-ups if they are just by far the best way to achieve something I want to achieve). So I think that means quite a lot of homemade parts and trying to come up with innovative modifications. Or maybe not that innovative since there will be so many modded Boomers out there, but certainly there'll be my own interpretation. 

To that end, plan so far is:

1. Homemade chassis out of GRP or CF, which will get rid of the battery door thing and enable bellcrank steering; quite likely I'll go for GRP over CF for a little flex (so may be both a lower cost and a higher performing option)
2. Dual front shocks, loosely in the Supershot configuration although I'm wondering whether to angle them in a bit if that helps chassis bottom-out and/or any other geometry considerations
3. Homemade chassis sides could also potentially alter the wheelbase if I fancy that and find a longer driveshaft and assuming I can work body fitment around it
4. The holes in the chassis sides for the rear gearbox also define anti-squat, so a change there is an option and the gears look to me like they'll create squat
5. I have the scope to make all sorts of suspension mount strengthening braces, which is a mod I tend to like where arms are mounted directly to gearbox halves
6. I could model and print or make arms too if I see a way (and a reason) to introduce camber adjustment at the front
7. Query sway bar options
8. And because it's heavily modded it'll be box art*
9. Any other funky ideas that come along... 

*I realised that my box art preference is contrary. If I'm just building a kit pretty much stock I'll tend to go my own way, while if I'm modifying it heavily, or what's underneath is not what it first appears, then I like it to be box art. It's just me. See also Super Falcon.

[BuggyDad 5329]

So where are we so far? Not very far is the answer.

I assembled the gearboxes then disassembled the rear to go hunting for some roughness/resistance in its movement.

I found that the back of the metal diff bevel gear actually touches the side of the spur, and it has some casting imperfections, so I polished them back with a fine file. That seemed to make a small difference but still this gearbox has more resistance than I'm used to and it is not constant, so something is slightly out of true. Similar is true at the front. However I think also these might be as free as I can get them, and they should free up a ittle over time I hope, so I've left them alone otherwise. 

Then I decided not to fit any arms because I want to consider suspension pivot shaft lengths (and bracing). So I started looking at the chassis to make my first measurements to CAD model the important dimensions. I've got the gearbox holes in, front and rear, and a rough draft outline for the chassis sides.

Oh, and in a break with tradition I had already painted the body.

Pearl white then white, so just half a shade off box art.

[Marchie 92]

Looking forward to following this thread, to state the obvious you clearly know your stuff.

Having just built one and so far having found it pretty good out-of-box, I'd be interested in knowing (in layman's terms) what you see as the biggest areas for improvement for this car?

 

[Sir Crashalot 265]

4 hours ago, BuggyDad said:

This gearbox has more resistance than I'm used to and it is not constant, so something is slightly out of true. Similar is true at the front. 

 

80's Hotshot racers would place 850 bearings in the outside of the gearbox casing to support "BA18". This reduces the outdrive wobble.

 

[BuggyDad 5329]

3 hours ago, Sir Crashalot said:

 

80's Hotshot racers would place 850 bearings in the outside of the gearbox casing to support "BA18". This reduces the outdrive wobble.

 

Interesting. The outdrives on these rere gearboxes seem slop-free. I guess the big E-clip and bearing setup is a pretty night-and-day change from the original, which looks like a plastic part and a thrust washer retained just by a little spring c clip. Looking at the old manual I'm glad of that change. It's pretty tight, if anything I'd say it adds to the resistance. 

But in other areas I think the gearbox is a bit "of its time". One thing I note is a number of instances of same tooth count gear pairs, so wear might be concentrated. And might any out-of-true-ness be worsened? I guess I could go through a long process of disaassembling and reassembling for best fit, but that sure isn't my way! More likely I'll see if it "runs in". 

I'm a bit worried about gearbox resistance just because I've read it many times and also after chatting to someone at Tamiya Junkies the other week about theirs, which was very noisy. 

3 hours ago, Marchie said:

Looking forward to following this thread, to state the obvious you clearly know your stuff.

Having just built one and so far having found it pretty good out-of-box, I'd be interested in knowing (in layman's terms) what you see as the biggest areas for improvement for this car?

You're too kind! I don't really, I just feel my way. Yeah, I think it is good out of the box. Others more knowledgeable than I say so. I guess what I'm really doing is seeing whether, with the marching on of time and adding in my ownership of a bit of 2020s manufacturing technology, I can have some fun updating it and "making it mine". 

[ThunderDragonCy 8116]

Looking forward to this one! Regarding gearboxes, unless a Hotshot series veteran can advise otherwise, i think they are just a bit rough and draggy. My Hotshot2 is by far the least free of any of my buggies and i could figure out anything obvious to make it nice. I think it's one of the reasons motor choice and gearing is so tricky on Hotshot cars. The drivetrain generates a lot of heat in a motor.

[BuggyDad 5329]

1 hour ago, ThunderDragonCy said:

Looking forward to this one! Regarding gearboxes, unless a Hotshot series veteran can advise otherwise, i think they are just a bit rough and draggy. My Hotshot2 is by far the least free of any of my buggies and i could figure out anything obvious to make it nice. I think it's one of the reasons motor choice and gearing is so tricky on Hotshot cars. The drivetrain generates a lot of heat in a motor.

Yeah I have a feeling it might push me to mild brushless. Or even to a slightly faster brushless and a smaller pinion, to reduce the load on the motor (and counter the resistance with a bit more torque). Superstock first though. I'm quite looking forward to my first (modern) go at faster brushed. 

[Wheel_Nut 365]

Is it possible to add 0.1 or 0.2 shim on one side of the diff to serve a dual purpose of tightening the mesh of the bevel gear and also adding some clearance away from the spur gear?

[BuggyDad 5329]

1 hour ago, Wheel_Nut said:

Is it possible to add 0.1 or 0.2 shim on one side of the diff to serve a dual purpose of tightening the mesh of the bevel gear and also adding some clearance away from the spur gear?

That is a very sensible idea. Thank you. I will give it a try. If there's clearance enough for a shim or two in there it should help with this issue. 

Gut feel is the bevel gears for the central drive shaft might be another culprit for being either a little tight or a little out of true, and being all same tooth count. 

[toyolien 5491]

Subscribed to this one. I do love a good Boomerang build. Really interested to see what twist you put on it. 

I'd also be interested in a sway bar kit for the Boomerang if you manage to come up with something.

[BuggyDad 5329]

1 hour ago, toyolien said:

Subscribed to this one. I do love a good Boomerang build. Really interested to see what twist you put on it. 

I'd also be interested in a sway bar kit for the Boomerang if you manage to come up with something.

Thanks! Do you think your 4 shock Boomerang would benefit from sway bars front and rear? The front could presumably be stock (or with smaller diameter wire but same attachment points). The rear might require a 3d print but it feels doable. 

[ThunderDragonCy 8116]

8 hours ago, BuggyDad said:

Thanks! Do you think your 4 shock Boomerang would benefit from sway bars front and rear? The front could presumably be stock (or with smaller diameter wire but same attachment points). The rear might require a 3d print but it feels doable. 

My Boomerwig ran nicely without the front bar. My Hotshot2 has a thicker front bar than stock with the monoshock that works, but the rear bar on that (its originally a Supershot) just made it worse. The dual front shock mounts of any flavour use the ARB mounting holes so you will have to make something or check things. The boomerang arb mount is different to the hotshot mount in that it has a boss instead of 2 holes. That said, IIRC I just bolted the bigwig towers straight on, so maybe Hotshot arb moubts and a custom bent bar to avoid the shocks would work. For my opinion i always preferred the look of the Bigwig front setup, but the inboard mounting of the shock made it need heavy damping and very stiff springing. If you are thinking of custom arms, a bigwig style setup with the shock eyelet 50 or 60% along the arm would be great. The bigwig is only about 30% so has loads of leverage to overcome

[Twinfan 1798]

I'm planning on using the HSII front bar and mounting brackets on my SuperBoomerShot, with longer screws to hold both the ARB and shock brackets to the chassis.  The question is then whether the Boomerang or Hotshot II bar fits or needs to be bent to clear the shocks (as ThunderDragonCy says).

[BuggyDad 5329]

3 hours ago, ThunderDragonCy said:

My Boomerwig ran nicely without the front bar. My Hotshot2 has a thicker front bar than stock with the monoshock that works, but the rear bar on that (its originally a Supershot) just made it worse. The dual front shock mounts of any flavour use the ARB mounting holes so you will have to make something or check things. The boomerang arb mount is different to the hotshot mount in that it has a boss instead of 2 holes. That said, IIRC I just bolted the bigwig towers straight on, so maybe Hotshot arb moubts and a custom bent bar to avoid the shocks would work. For my opinion i always preferred the look of the Bigwig front setup, but the inboard mounting of the shock made it need heavy damping and very stiff springing. If you are thinking of custom arms, a bigwig style setup with the shock eyelet 50 or 60% along the arm would be great. The bigwig is only about 30% so has loads of leverage to overcome

 

3 hours ago, Twinfan said:

I'm planning on using the HSII front bar and mounting brackets on my SuperBoomerShot, with longer screws to hold both the ARB and shock brackets to the chassis.  The question is then whether the Boomerang or Hotshot II bar fits or needs to be bent to clear the shocks (as ThunderDragonCy says).

If i was going to use the Boomerang ARB in its stock position I would look to make the tower and ARB mount as one piece (or ARB mount fixed to tower), since I will be making the towers anyway. However my suspicion is I will go as @ThunderDragonCy did and choose no ARBs once I have dual shocks. But I might still look at the design as to how they could be fitted to at least try them out. I think I'd just make the ARBs themselves by bending wire. 

Designing arms is certainly a possibility, although their design might be a challenge to achieve strength with home printer constraints. I'll puzzle also over whether the outer part of the arm could be a simple CF/GRP sheet part, given it's a ball mounted knuckle and a right angled steel shock mount - would just need to solve how to fit the inner hinge pin. Perhaps sandwich it between 2 bits of CF with a 3d print between just to make the hole nicely? Or perhaps CNC out of a tougher plastic? 

The very inboard shock mounting on any dual front shocked HS series models I've never understood - why put this extra leverage on a shock? But also, if there's that extra leverage and therefore reduced shock stroke required, why didn't the Supershot designers achieve chassis bottom out on such long front shocks? I'd expect long shocks inboard mounted to take away any real constraint on wheel travel. Curious. 

[toyolien 5491]

11 hours ago, BuggyDad said:

Thanks! Do you think your 4 shock Boomerang would benefit from sway bars front and rear? The front could presumably be stock (or with smaller diameter wire but same attachment points). The rear might require a 3d print but it feels doable. 

I've only ran mine on tarmac so far.

[BuggyDad 5329]

Got back to this today. Suspension pins are a bit of a question mark for me. Does anyone know of any e-clip pins in the 40mm and 53mm* (or a bit more in each case, can add spacers) range? Looking for this kind of size because I intend to add bracing in some spots. 

Or perhaps I can find a way to cut E-clip slots into stock 3mm stainless to make my own. Anyone tried that with just a drill chuck to work with? 

Some other details surprised me too.

The rear arms particularly have very little material to them, so I think even home 3d printing might produce a stronger option if I need one. I was also surprised to find the rear hubs are also hollowed out. Then again, if it ain't broke... 

The front knuckle ball joints have a heap of play. I think perhaps a 3d print of part E9, just with a little more meat around the ball, could get rid of this, and also just be a wearing part - it's not like it needs any strength and nor does it need to retain a screw, being sandwiched between arm and little steel sheet. I will look into this. 

*sized using the usual(ish) convention of measuring the total length rather than the clip-to-clip length which is 3mm less

[Twinfan 1798]

For info, I've just finished my SuperBoomerShot chassis build and have the dual Supershot suspension up front combined with the Hotshot II sway bar. Everything bolted up just fine 

Clearance is minimal on everything, but given the front shocks to arms gap is exactly as it would be on a Supershot I guess all is good.

[BuggyDad 5329]

And then a quick test of the 53791 CVDs which are quoted as a hop up for this by Tamiya. 

On the left it is fitted with 1150 bearings, as per design. 

On the right I have replaced the 4mm wide standard bearing on the inside of the upright with a 3mm wide version to take the axle and swing shaft outboard 1mm.

Diff is rotated so the shafts are at the worst point for binding (pin perpendicular to suspension pivot). Wheels are just sitting on the axles, no wheel mounting parts fitted, so a little pinch of salt is required. 

So I reckon you can just about get to chassis bottom out with 53791s fitted as standard but it's touch and go and probably requires a bit of tyre squish. I can very well see how, depending on shock configuration and whatever other variables, folk can have these bind. Maybe it's in running with 2.2" wheels where issues come to light? 

Anyway, I think if there is an issue it should be small enough to be solvable with thinner bearings.

I also think the bumper is massive, the oval block tyres are just marvellous and it all looks a bit too much like a tractor right now. 

[BuggyDad 5329]

I noticed these holes in the wheels.

They're at the inner and outer edges so I don't think they're intended to be vents since they're covered by tyre bead. If they're not vents then what are they? Are they for glue perhaps? 

[BuggyDad 5329]

55 minutes ago, Twinfan said:

For info, I've just finished my SuperBoomerShot chassis build and have the dual Supershot suspension up front combined with the Hotshot II sway bar. Everything bolted up just fine 

Clearance is minimal on everything, but given the front shocks to arms gap is exactly as it would be on a Supershot I guess all is good.

Nice. Well, any clearance is enough clearance I guess. What shocks and how's your chassis bottom out? It strikes me that there's not a huge amount of shock stroke required so one ought to be able to find a way to accommodate the necessary travel. 

[toyolien 5491]

6 hours ago, BuggyDad said:

I noticed these holes in the wheels.

They're at the inner and outer edges so I don't think they're intended to be vents since they're covered by tyre bead. If they're not vents then what are they? Are they for glue perhaps? 

They are holes to allow you to glue the tires on without having to remove them to get the glue in. I've seen that in a few tamiya manuals before but can't remember which kits. 

[ThunderDragonCy 8116]

@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.

[Andreas W 2175]

The Hotshot tyres are relatively large diameter,  so there is hardly any difference between them and a 2,2" tyre. Here is a Hotshot wheel on my Dictator compared to a Schumacher Full Spike (on a JC Hotshot wheel) for comparance. 

[Twinfan 1798]

7 hours ago, BuggyDad said:

What shocks and how's your chassis bottom out? It strikes me that there's not a huge amount of shock stroke required so one ought to be able to find a way to accommodate the necessary travel. 

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.....

[BuggyDad 5329]

1 hour ago, Andreas W said:

The Hotshot tyres are relatively large diameter,  so there is hardly any difference between them and a 2,2" tyre. Here is a Hotshot wheel on my Dictator compared to a Schumacher Full Spike (on a JC Hotshot wheel) for comparance. 

Yes, looking at the wheels and tyres I did wonder. They're big tyres. I love the look of them actually, to me they do just look very right. I had oval blocks on the rear of my Falcon as a kid. For some reason even then I was drawn to them. I will probably buy some JC Boomer 2.2 wheels sometime but I'm not in a rush - in the meantime I'll pinch running wheels off something else. More cars doesn't really necessitate buying more running wheels after a point.