[MOD] Koncept Mantis - Free instructions

[amorti]

Well now I am wondering if those unequal length wishbones will be happy without ball joints. I guess it will be fine when the suspension is unloaded as the wishbones sit pretty much parallel to the ground and the frictionless pins are at right angles, but I suspect it will be binding up at least a little bit at the top of its travel.

Now it looks like I've got my first "realistic" front suspension setup to build - I'm actually looking forward to that :)

[amorti]

I'm sure it would be child's play for @nicjasno, but I've just spent about 3 enjoyable but  ultimately fruitless hours trying to design something based on his pictures here.

My problem, I think, is trying to use Lego hubs. You have to use that for the Porsche wheels, but then it's very difficult to get everything in the available space (inside the wheel) without getting bump steer.

Maybe it would be easier with Land Rover wheels. With the axle hole through them, then I could just replicate the hub in those pictures.

A problem for another day, I think.

[amorti]

I'm still waiting for a bricklink order which contains most of the big frames and all the wishbones, so I can't build it all yet. But tonight I did start at building the rear module.

The way the rear wishbones were off centre to the driveshaft (CV joints 1L too high and 1L too far out from the vehicle's centre line) was driving me crazy. So I redesigned it.

I decided to try to channel @Madoca 1977's original instructions for the module: View Building Instructions (Photo Sequence)

Yes, I realised right after uploading the pictures that it's a little easier to construct if you use a 3L pin on the bottom 6536 connector like you need to anyway for the panel to clip on.

You do have to shorten the new CV joints by 1L for this to work, so if that's not for you then skip ahead :)

I've skipped the axle which drives the rear spoiler going up and down. I've had a couple of servos die on me lately, so I want to leave anything unnecessary off the steering. You'd lose some rigidity, but you could put it back in with something based on this picture, if you wanted to keep it.

The ride height will be about 1 stud higher since the wishbones will now be angled down a little. I don't yet have any thin wishbones to test it, but I tried a normal lift-arm as a dummy wishbone and it just barely touches where the sloped panel will be so I think where the wishbones are thinner it'll be fine. Once I've got to that point I'll look to see whether it's fine with the extra ground clearance, whether I fit softer springs so it has some sag (like a real car), or whether I look to get that 1 stud back in the hub assembly. I'll need to redesign that anyway so the CV joint sits in the same plane as the suspension pivot.

Next thing to try modding will be the front suspension. I think this is going to be fast enough that it'll need all the extra stability it can get, so I'd like to give it some caster angle, maybe even some kingpin inclination too although an experiment on that has shown it's not easy to avoid bump steer, and you can't easily get a brace across the ball joints either :/

Edited August 20, 2020 by amorti

[astyanax]

Thanks @amorti, it's lovely to follow your tinkering and progress!

I was going to say, be careful when changing the suspension geometry, that it remains stiff enough -- but it seems you're well aware.

I know the rear module looks a bit of an exotic jungle of connectors and frames, but the point to keep is that there's no way it can come loose horizontally nor vertically, because it'll be under a lot of stress.

One potential issue is around your white #5 connector: for the original design, you cannot use its pin hole. Consider this view from the rear:

The orange panels are actually leaning on the dark gray 1L beam, which prevents them from touching the 24-tooth gear. Space is rather tight there!

BTW, my next car (instructions nearly finished) will be an ode to the wishbone, containing 26 of them!

 

[amorti]

Thanks for the tip on the #5 connector, it would definitely have caused me a problem later on! Back to the drawing board for that.

I don't have a long career in studless Technic, having only ended my "dark age" this last Christmas, however building and tinkering on @Didumos69's greyhound and rocky MOCs have taught me a lot about form-locking and efficiency of parts usage. This rear module (both the original cut and mine!) really fit D's mantra of a pin hole empty being a waste!

[amorti]

This should solve the #5 connector for the flag. Sorry for linking not pasting the image, bricksafe does weird things when the photo is not square to begin with.

(PS: Welcome to the darkside, we have everything in every colour. That sounds fun until you realise you just spent 5 minutes looking for two of a thing in the same colour, ANY FRICKIN' COLOUR)

The rest of today's modding was less successful  but still fun 

I mocked up 4x wishbones using a bunch of 5L liftarms and 5L thin beams. First impression was, "hmm this suspension is very soft.

11 hours ago, astyanax said:

I was going to say, be careful when changing the suspension geometry, that it remains stiff enough -- but it seems you're well aware.

No dude, the other type of stiffness was missing from the suspension.

With the wishbones in the original position the suspension is all gone by about a 900g loading, but with the wishbones hung 1L higher up, the suspension travel is all gone by about 400g. With a 1.7kg vehicle weight that's biased to the rear where the motors and transmission are, that would probably means it'd scrape its belly the whole time. So the wishbones will have to affix in the original positions.

I also gave up trying to get the outer CV joint in line with the suspension pivot. The outer diameter of the joint collides with the only position you can mount the bottoms of the springs. It could be done with the old CV joints, but that's not an option as I've already exploded two of those in Icarus; it can literally shear the end right off the male half.

I tested a bunch of possible driveshaft configurations including the original and I'm still pleased that I could get the driveshaft to 1L longer, which is lucky because I've cut them now. In the original configuration there's almost 2mm change in the driveshaft length through the suspension stroke. It's much less after the changes. I've used a 1.9mm o-ring to take up the 1/4L freeplay and it is quite happily not squished through the suspension stroke. 

 

Edited August 20, 2020 by amorti

[astyanax]

10 hours ago, amorti said:

This should solve the #5 connector for the flag. Sorry for linking not pasting the image, bricksafe does weird things when the photo is not square to begin with.

That'll do it. To embed a vertical photo from bricksafe, click on its "800x600" link, now a horizontal cropping is opened, but just change the URL to ".../600x800.jpg", and it'll create a vertical image, which you can then embed.

10 hours ago, amorti said:

The rest of today's modding was less successful  but still fun 

Very recognizable! I also spent quite some time trying different configurations for the rear suspension and driveshaft. I would never claim to have found the optimal -- or even least worst -- solution. So I'm very happy to see what you'll settle on!

10 hours ago, amorti said:

In the original configuration there's almost 2mm change in the driveshaft length through the suspension stroke. It's much less after the changes. I've used a 1.9mm o-ring to take up the 1/4L freeplay and it is quite happily not squished through the suspension stroke.

Yeah sometimes the CV joint would slip out of the 12-tooth gear inside the differential (but only ever on one side -- clasping strength varies I guess). I solved it by inserting a small rubber band, as shown below (genuine Lego -- so purist! ). It increases the length of the driveshaft adequately, but it's squishy so it can compress as needed.

[chlego]

On 3/13/2020 at 10:59 PM, astyanax said:

 

===== 2020-05-17 UPDATE =====

New acceleration and racing footage! Finally after 2 months of corona lockdown it was possible to go out and record better the speed of this vehicle!

 

===== 2020-04-29 UPDATE =====

Free building instructions are now available on Rebrickable!

 

===== 2020-04-23 UPDATE =====

I've published a little video of my physical build.

There's a little acceleration test at the end, but more racing footage could not be shot yet, due to the lockdown where I live.

And yes, my apologies to the purists who don't like painted parts... When built in orange, 90% of the parts can come from set 42056 (the Porsche 911 GT3 RS).

Building instructions are virtually complete, currently being reviewed by the original designer of this beauty.

 

===== ORIGINAL TOPIC =====

Please allow me to grab your attention first:

SamBellCar-23 by R. Skittle, on Flickr

I fell in love with this creation upon seeing it featured on http://www.thelegocarblog.com and resolved to build it for myself. I succeeded in doing so using the photos from R. Skittle's flickr album, and a few kind hints from the designer himself. I've even given the model a speed upgrade: with 4 PF L motors propelling less than 1700g, it's blazing fast!

Moreover, I built a virtual model in LDCad (.ldr), and with the designer's express approval already granted, I'd like to have a go at making and sharing building instructions. This is the first time for me. :)

Now my request: I'd love to hear any experience, pitfalls, and hard lessons you've learned trying to produce high-quality PDF building instructions! Any and all pointers are welcome.

 

Hey, very cool MOC, have been looking at this since march, and I also saw it on Rebrickable.

Does anyone know how to combine XL and L-motors, because I own 2 of each...

P.S. @astyanax just saw you live in Switzerland too!

[astyanax]

2 minutes ago, chlego said:

Does anyone know how to combine XL and L-motors, because I own 2 of each...

I think you'd be better off just using 2 motors, either L or XL. Connect them with 1:1 gearing to the differential. Then you can simply use PF battery box and IR receiver too -- plenty of space for them in the cockpit. I expect it'll still be fast enough for indoor driving fun!

[amorti]

1 hour ago, chlego said:

Does anyone know how to combine XL and L-motors, because I own 2 of each...

Bruno's C63 combines one L and one XL motor so it's possible. I can't remember if they were on different ratios unfortunately.

Depends what you want the model to do. If you want maximum speed just get the two missing L motors, reason I say that is the motor module is very well braced using pin holes which aren't present in XL motors. If you don't need so much power just use two of your existing motors.

[amorti]

Waiting for my orders from bricklink and I feel like a dog sitting waiting for the master to come home.

So, more time to fiddle and tweak with what I have to hand, then.

I have given back the shorter driveshafts. Instead, I've redesigned the transmission frame with some didumos level form locking. You can actually notice the gears spin more freely in this setup. I think it's because 5 liftarms stacked doesn't quite make 5L, but if you lock it like this, the distances between the gears are exactly right.

Apologies that the pictures are maybe hard to decipher, it's largely made of darkside bricks and nearly everything is black. Those are black 5x11 frames on their sides, form-locking 5x7 frames sandwiched together. Those sideways frames then give a good solid mount for the wishbones, and somewhere solid to put the ends of all the axles for the 24&8 tooth gears. All with way fewer small connectors and less freeplay.

There are 92907 connectors holding the top frame on, they are really solid like that. This also helps give a tighter spacing for the shocks and rear cowl.

I'm hoping the crank handles in the bottom won't be necessary once the cockpit is built up, but if so then I'll need to find a neater way to brace that section.

The rear bodywork mounts had to be redesigned, but it's all come out nice and sturdy. Bit simpler as I don't need the tilting spoiler.

I test fitted the rear cowl, it just needed the lower rear panels swapped for 21/22 panels to clear so as to the top legs of the sideways frames.

I used some different pieces for the exhausts, as I didn't like that they were only lodged on there. These ones have a 5.5L axle through, so can't fall off.

 

Really really looking forward to finishing and driving it now!

Edited August 23, 2020 by amorti

[astyanax]

13 hours ago, amorti said:

I used some different pieces for the exhausts, as I didn't like that they were only lodged on there.

I'll be studying your pictures more closely soon, but I just wanted to remark that regarding part usage, I had set myself an additional goal: to get the greatest possible overlap with set 42056. In the end I got to 90%, which I was very happy with. But if 42056 was never your starting point, then yes, surely you can find many tweaks that fit your collection and tastes!

Edited August 24, 2020 by astyanax
added link to inventory comparison

[chlego]

21 hours ago, astyanax said:

I'll be studying your pictures more closely soon, but I just wanted to remark that regarding part usage, I had set myself an additional goal: to get the greatest possible overlap with set 42056. In the end I got to 90%, which I was very happy with. But if 42056 was never your starting point, then yes, surely you can find many tweaks that fit your collection and tastes!

Did you modify the instructions on Rebrickable?

[amorti]

22 hours ago, astyanax said:

I got to 90%, which I was very happy with. But if 42056 was never your starting point, then yes, surely you can find many tweaks that fit your collection and tastes!

I guess I wasn't thinking of it as an almost C-model.

90% is really good going, especially since they're quite different vehicles.

[astyanax]

1 hour ago, chlego said:

Did you modify the instructions on Rebrickable?

Nope, still same old. No-one has ever pointed out any error in it. I did the optimization toward 42056 before publishing the model on Rebrickable.

[amorti]

To be clear: I'm not pointing out any errors here. Only different ways of making the connections.

I'm not big on the driveshafts being 2L shorter than the wishbones, but I've played about with it enough now to realise that until Lego gives us wheel hubs without a portal reduction which accept the new CV joints, 1L shorter is as good as it gets and at that point it kind of might as well be 2L shorter, if it works.

Same concept for the odd length front wishbones. In theory it should be good as it's like a real car, although without ball joints it'll be binding to a theoretical level. But then, I also don't see any better way to do it because you won't be able to brace across the ball joints of you use them.

In the end it's only a plastic toy, you have to pick the compromises you prefer, that's all I'm doing.

[nicjasno]

On 8/17/2020 at 11:37 PM, amorti said:

I'm sure it would be child's play for @nicjasno, but I've just spent about 3 enjoyable but  ultimately fruitless hours trying to design something based on his pictures here.

My problem, I think, is trying to use Lego hubs. You have to use that for the Porsche wheels, but then it's very difficult to get everything in the available space (inside the wheel) without getting bump steer.

Maybe it would be easier with Land Rover wheels. With the axle hole through them, then I could just replicate the hub in those pictures.

A problem for another day, I think.

Got some pics of your current setup?

 

[amorti]

On 8/20/2020 at 12:11 PM, astyanax said:

[snip] next car (instructions nearly finished) will be an ode to the wishbone, containing 26 of them!

 

I just saw it - looks amazing!

I guess once I've finished Mantis and played with it a bit, I'll be ordering 11 more wishbones and some buggy motors :D

[astyanax]

7 minutes ago, amorti said:

I just saw it - looks amazing!

I guess once I've finished Mantis and played with it a bit, I'll be ordering 11 more wishbones and some buggy motors :D

Though I'm afraid its driveshaft will offend you even more...

[amorti]

@astyanax Yebbut, pushrod suspension

15 hours ago, nicjasno said:

Got some pics of your current setup?

 

I don't have any right now. I built a test rig then stripped it for parts.

Basically it was the original (it's complete by step 45), but with a 5L wishbone slipped in between the bottom wishbones, and a shorter liftarm inside a 6L wishbone for the top wishbone. There seems to be slightly more space in the front of the wheel housing, so I favoured moving the bottom ball joint forward a little and leaving the top in the same alignment. That might change when all the parts are in, and I can see where any space really is, or isn't.

Two main problems came up:

1. building a wheel carrier with the Lego 3 pin hub which would fit inside the wheel and not have bump steer (Land Rover wheels might solve this but they'd only be connected by friction on one axle, which might not be enough to hold.
2. not being able to brace across the ball joints. The model is 1.7kg and will be pretty quick, it needs that part braced for sure. Part of this was I don't have any 5L steering rods, only 6L. Doesn't need to be right on the ball joints I guess, which might make it easier.

I will come back with pictures when my bricklink order gets in!

Is there any argument that just caster angle is enough and KPI isn't necessary when using the Porsche wheels? The steering centre is pretty close to the middle of the tyre anyway, much more so than with the older wheels.

Edited August 28, 2020 by amorti

[nicjasno]

Caster is a must, i recommend 3-5 degrees. KPI is recommended but i guess you could get away without it. It'd add more feel to the HoG steering.

[amorti]

8 minutes ago, nicjasno said:

Caster is a must, i recommend 3-5 degrees. KPI is recommended but i guess you could get away without it. It'd add more feel to the HoG steering.

No HOG, this is an RC model.

The benefit I'd be looking for is helping it to track straight as it gets up to speed.

I'll come back when I have pics :)

[nicjasno]

7 minutes ago, amorti said:

The benefit I'd be looking for is helping it to track straight as it gets up to speed.

In that case you really want caster. I'd go with 5 degrees, and a very slight toe in.

[amorti]

It's finished in white!

Yes, there are lots of Chinese bricks in there. No, it doesn't fall apart when you touch it.

See all those white pins? They're there waiting for you on the darkside 

The "03" see stickers may not make the cut. The colour works but they were originally on doors and aren't oriented right for this.

I deleted the airbrake. Decided I'd rather make the spoiler a little more sturdy. The exhaust pieces changed too.

You can also make out how I modified the rear bodywork to suit the reinforcement of the transmission area. It's very tight for space around there.

I've done a fair few mods tying panels together to make the wheel arches a bit sturdier. It's nothing anyone couldn't figure out with a few basic connectors so no pics unless anyone asks.

Front suspension modded, gives a softer suspension that should be effective outside, and about 1 stud more ground clearance; as standard it has just under 1 stud which seems tight. The steering angle is marginally reduced, but it's still plenty and shouldn't stress the servo.

Rear hubs modded using 5L axles with stops. Holds together better than originally designed.

It's running with 4* Chinese +30% L motors, a Lego servo, and a MouldKing lipo battery box and digital remote. Only 8.4v but it's about as quick as a pair of buwizz and normal L motors on fast setting. Battery doesn't last long for outdoor play, so I may put an RC lipo in there, there's loads of room.

Edited September 4, 2020 by amorti

[amorti]

On 8/27/2020 at 10:38 PM, nicjasno said:

Got some pics of your current setup?

 

Yes, now I do! However, it feels like this is a new thread, rather than clutter @astyanax's thread.