Always Upside down

[Dbx]

I've just recently built a VTH kit (for my son you understand) and am loving it.
This is the girl before we started wrecking it:

I'm more used to playing with buggies, so have been really struggling with the handling. I'm probably using it 80% bashing, 20% crawling. As soon as you get half a lick of speed up, or hard accel, she's away off into that tree stump, or has generally just flipped over. I'm learning to drive around the short comings, but the high centre of mass seems to be a real handicap..... As an automotive designer by profession i could see a better way. I did some measurements and calculations. The centre of mass is about 11mm back from half way between the axles, 2.5mm to the right, and a whopping 33mm above axle height.
So i'm moving the battery down into the very bottom of the chassis, steering servo over to the right, upright front shocks, bell crank steering, esc in between the rear shocks. I'm hoping this will put the centre of mass more errr.. central, and LOWER! I'm hoping the VTH will then keep up with my lad and his vintage Tamiya Boomerang!
This is the new front layout i'm getting 3d printed in nylon:


And i even did some FEA load analysis (bringing my work home again) to get some confidence in the structure. Some.:

I hope it'll be worth the effort! What do you guys think?

[fr8cture]

Looks pretty cool. I'm not all that confident in 3d printing myself though. I would have a welded steel version made.

[CODYBOY]

Welcome to the world of the Twin Hammer... Most of your observations have been addressed some where in this forum. Moving the battery to the front of my rig is one of the first things I did with my hammer way back when. An other would be running open diffs in the front and rear if you want better handling at high speed. Instead of lockers we are running 500-1000wt oils in them. Check out my build on here, I will cover some of these things, and a few more.
Herbie the "THUG BUG" Baja style

[Dbx]

Originally Posted by CODYBOY

Welcome to the world of the Twin Hammer... Most of your observations have been addressed some where in this forum.

Thanks Cody - i'd been reading, well before tkit arrived. Thanks to the guys here - this is the main source of any 'ideas' i've had.

I'm running 500k oil in the front diff, locked at the back. Maybe n open diff in the back is something i should try if these other mods don't get the results.

I'm running the turnigy waterproof 3520kv setup. Could be that it's overkill and i just need to get more sensible with the throttle.

The rear sway bar (medium at present) is really inefficient. The first, and most important part of the stroke has no effect, and just rocks the main link bar. This is a really poor design, an top of my list for a better solution. I've not seen anything on here yet - am i missing a fix?

As for the 3d printing, i agree - it's never going to be as nice as a fabricated metal affair..... But for me its cheap and not too time consuming to prototype. I've been using SLS stuff for years at work. If there are insurmountable issues with strength, i'll consider a metal/sls solution later.

[89redranger]

People often mistake the term "3D printed" for the low resolution and low strength parts printed by FDM (fused deposition modeling) type machines. SLS printing (selective laser sintering) is a new world, and totally different. The resolution is almost flawless, there are no layers to peel apart or "delaminate", and the materials as a whole are much better.

Don't let the pessimists get ya down (Lol...). I design a lot of my own stuff, and there is a reason my files go straight to Shapeways. The SCX10 transmission adapter I use in my personal car is printed by Shapeways, and is actually stronger than the tub, top plate, or even the stock Axial trans case I'm using.

[fr8cture]

Originally Posted by 89redranger

People often mistake the term "3D printed" for the low resolution and low strength parts printed by FDM (fused deposition modeling) type machines. SLS printing (selective laser sintering) is a new world, and totally different. The resolution is almost flawless, there are no layers to peel apart or "delaminate", and the materials as a whole are much better.

Don't let the pessimists get ya down (Lol...). I design a lot of my own stuff, and there is a reason my files go straight to Shapeways. The SCX10 transmission adapter I use in my personal car is printed by Shapeways, and is actually stronger than the tub, top plate, or even the stock Axial trans case I'm using.

I agree the shape ways printing seems much better. Guess it all depends how much you abuse your rig.

[amorton94]

I'm extremely interested in your progress! This is awesome! Wouldn't mind if you through some files my way for my printer too ;) haha

What is it you do for a living? I'm pretty close to my associates in mechanical CAD, actually sitting in my boring Solidworks class right now. Wouldn't mind sitting around and bsing with ya.

Sent from my LG-H901 using Tapatalk

[Spunkybob]

How much would this cost to have printed? I'm keen for one :P
Must be heaps cheaper then the upright ones for sale (talking over $150 shipped to Australia for $20 worth of bent aluminium.)

[Dbx]

I was hoping the 3d print would be a lot cheaper too, but due to the size, it's actually pretty pricey too. I'll see how well i can get it working before drawing any conclusions on printing to sell.
I've been away the last few days at the coast with the family (=rc fun at the beach)


The Hammers is desperately poor on the beach. My lad would not give it the time of day, and i got really tired of going and turning it back over. It couldn't get near the Boomerang on the circuit we made. Horses for courses i suppose. The Boomer is very much designed for this sort of thing.

I really can't wait to do he planned mods and see how much they help. I found out what all the fuss over poor steering was about too. With a little sand, the steering mech was almost locking up. Odd really because the Boomer has a very similar sliding rack steering, and works perfectly. Tamiya must know a thing or two that Vaterra don't.

I'm thinking i'll need a different set of whhels and tyres (lower profile?) any price friendly suggestions for beach and a bit of hard surface?

[Dbx]

Originally Posted by amorton94

What is it you do for a living? I'm pretty close to my associates in mechanical CAD, actually sitting in my boring Solidworks class right now. Wouldn't mind sitting around and bsing with ya

Thanks. I've used Creo for this. My job is hard to narrow down, but i specialise in CAD and motorcycle design. My Mrs thinks i'm nuts when i work long days in front of a cad screen, then pour masses of hours into this on an evening. I think she has a point.

[lonleycreeper]

A couple of things that might help with handling.

I don't know where you have your links set at but the link locations make a difference in how the twin handles. I have mine in the upper hole(upper links) stock mount on axle. Front camber link is inside hole.
The ride height looks a little tall.
My shock collars in front are topped out, the adjuster is barely off the cap. The rear 10 turns from the cap.
The spare tire sits almost above roof level and weighs as much as a small lipo, if not more.
Front differential, heavy oil, 10,000 or more. I run a locker, but I break front end parts frequently.

Look at buggy racing tires, proline, j concepts, aka...


Driving style,

Slow in fast out is key to this buggy, mine steers with the throttle and I drive it that way, I think the locked front end helps with this.


Hope I helped.

[Dbx]

Originally Posted by amorton94

I'm extremely interested in your progress! This is awesome! Wouldn't mind if you through some files my way for my printer too ;) haha

What is it you do for a living? I'm pretty close to my associates in mechanical CAD, actually sitting in my boring Solidworks class right now. Wouldn't mind sitting around and bsing with ya.

Sent from my LG-H901 using Tapatalk

Thanks!
I did this work using creo, but i use other software too. Its difficult to narrow my job down, but i'm a cad specialist working mostly with motorcycles.

[Dbx]

Originally Posted by lonleycreeper

A couple of things that might help with handling.

I don't know where you have your links set at but the link locations make a difference in how the twin handles. I have mine in the upper hole(upper links) stock mount on axle. Front camber link is inside hole.
The ride height looks a little tall.
My shock collars in front are topped out, the adjuster is barely off the cap. The rear 10 turns from the cap.
The spare tire sits almost above roof level and weighs as much as a small lipo, if not more.

Thanks lonleycreeper. I'm set up pretty similar to that. I have more pre-load on the rear shocks. The springs are so soft they can't overcome the damping and weight of the car, and it jacks right down over bumps with less pre-load.
I removed the spare after this pic was taken, which Made an improvement as you suggest. I'm going to make a link truss for the rear top links as a look-see.

After closely observing the turn-over point, i'm convinced the tyres are a big part of the problem after mass height. They are the kit issue swamper variant. They are so soft, even on sand, they fold over, dig in, and over she goes.

[chopfather]

I don't own a twin hammer but if your tires are folding over then you should try some crawler innovations foams before replacing your tires They have made a huge difference in my scalers !

[CODYBOY]

Originally Posted by Dbx

Thanks lonleycreeper. I'm set up pretty similar to that. I have more pre-load on the rear shocks. The springs are so soft they can't overcome the damping and weight of the car, and it jacks right down over bumps with less pre-load.
I removed the spare after this pic was taken, which Made an improvement as you suggest. I'm going to make a link truss for the rear top links as a look-see.

After closely observing the turn-over point, i'm convinced the tyres are a big part of the problem after mass height. They are the kit issue swamper variant. They are so soft, even on sand, they fold over, dig in, and over she goes.

The tires folding over is more a product of soft foams than a poor tire. I run closed cell foam in mine.
Do you know what weight shock oil you have in your rear shocks? It could be you need a little heaver oil, that is why your car is bouncing. Preload is mainly a tool for adjusting static ride height. Hope that helps you out.

[jgrim]

[QUOTE=Dbx;5477578]
The rear sway bar (medium at present) is really inefficient. The first, and most important part of the stroke has no effect, and just rocks the main link bar. This is a really poor design, an top of my list for a better solution. I've not seen anything on here yet - am i missing a fix?
QUOTE]

I inserted shock O-rings on each side of the rear trailing arms where they attach to the rear axle. Takes out most of the free play yet still allows the axle to flex. Jerry

[jgrim]

Originally Posted by lonleycreeper

Look at buggy racing tires, proline, j concepts, aka...

My thoughts exactly. I have new Proline 2.2 Calibers that I just received. However, they will not fit any of the beadlocks that I have on hand (bead is too thick), so I just ordered out RPM Revolver narrow trac wheels. The overall width will be about 1.5 inch wider and the sidewalls will be stiffer. BTW, I run mostly on loose dirt. Jerry

[Dbx]

Originally Posted by CODYBOY

The tires folding over is more a product of soft foams than a poor tire. I run closed cell foam in mine.
Do you know what weight shock oil you have in your rear shocks? It could be you need a little heaver oil, that is why your car is bouncing. Preload is mainly a tool for adjusting static ride height. Hope that helps you out.

The jacking down is a result of too much damping. Winding up the pre-load raises the spring rate to overcome this, as well as raising the static sag point as you say. I have 32.5wt in them, as supplied. Maybe i'll get some 20 in there.
I've ordered some 96mm dia tyres, (stock is 112mm) and will load them with some firm foam as per your suggestion.

[Dbx]

Originally Posted by jgrim

I inserted shock O-rings on each side of the rear trailing arms where they attach to the rear axle. Takes out most of the free play yet still allows the axle to flex. Jerry

I've just done this mod. Seems to work pretty well. Thanks!

[Spunkybob]

Originally Posted by Dbx

I've just done this mod. Seems to work pretty well. Thanks!

Photo? I am not sure what you guys mean.