RiGi

[WIP] [MOC] 1:8 Ford Escort RS Cosworth

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800px-1996_Ford_Escort_RS_Cosworth_2.0_F

As a kid growing up in the 90's in Essex, this is one of those cars that you couldn't help but love :laugh: That massive "whale tail" spoiler is one of those iconic features of the time.

I started working on this MOC about 18 months ago, but it's been largely sat collecting dust for the last year or so for various reasons.  Now it's time to try and get back into it and actually finish it off! (This may still be a slow-burner of a project though...)

This is the current state of affairs:

800x378.jpg

It has a 5 speed + reverse manual gearbox and 4WD with a 4 cylinder engine at the front.

My initial focus was on the gearbox.  I spent a lot of time looking at various different gearbox designs people have created on here, but I always found them to be quite tall and I wanted to keep the gearbox as flat as possible and spread it out over the width of the car instead.  I took a lot of inspiration from how @Gray Gear designs his gearboxs to work around the rear axle and the use of slightly unconventional parts in the gear selector mechanism and came up with this:

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Drivetrain (yellow axle connects to the fake engine) :

Ford_Escort_Cosworth_Drivetrain_02.png

Gear selector mechanism - The "mechanical claw" pieces turned out to be ideal:

Ford_Escort_Cosworth_Drivetrain_03.png

Ford_Escort_Cosworth_Drivetrain_01.png

I've gone with the fairly typical use of thin liftarms to stop multiple gears being selected at once:

640x853.jpg

The mechanism works nicely, and the gearbox & drivetrain generally works pretty smoothly - the only issue is reverse gear has quite a lot of resistance, which I imagine is down to the 3 8T gears.  I'm also now wondering whether I could have worked a way of fitting a central diff in, but I don't think that will be entirely straightforward...

The front axle is frankly a bit of a hot mess... It's functional but not very elegant! Trying to fit drive, steering and the engine all together proved to be very challenging.  I'm sure there must be a neater way of fitting it all in, but I'm yet to find it!

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The suspension attachment to the top wishbone is largely based on the 42115 suspension.

Coming back to this after so long I've noticed some other things that are bothering me slightly:

  • The ride height seems a little bit too low - I think it should come up ~1 stud.  On one hand this should be an easy fix - simply adjust the top suspension mount positions. On the other hand, getting to these may be tricky...
  • I inadvertently slightly mis-scaled the drawing I was working from, and now my wheelbase is 1 stud too long...
  • The steering wheel is probably a bit too low

I'm also slightly torn on whether to make this the rally version or the road-going version.  My initial plan was to go with the road-going version from my childhood, but now I'm thinking the rally version would be more interesting with a rollcage, massive front spotlights, etc....

800px-Ford_Escort_RS_Cosworth_(280371564

(I'm not sure why this one doesn't have the whale-tail spoiler, all other rally ones did!)

Bodywork is a massive weakness for me - has anyone got any tips/advice on how to approach making the bodywork?

Thanks for reading! :classic:

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Seems already pretty complex build.

I'm afraid, that seats are also not in scale. And in this scale, it really could be more realistic, technically closer to original.

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Fantastic project of a fantastic car! 
I’d go with the rally version but with a whale tale. 
Someone on here built an rs500 a while back. It might be worth a look at some of that for ideas.

You could put a centre diff in place of the grey gear that connects to the diff if you used an old style diff in its place, though you would end up with a high shaft running through where your selector forks are so you’d have to look into that. 

Edited by MinusAndy

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9 hours ago, RiGi said:

 

800px-Ford_Escort_RS_Cosworth_(280371564

(I'm not sure why this one doesn't have the whale-tail spoiler, all other rally ones did!)

For 1997 the Escort went from group A to WRC, one of the changes was the rear wing. You could also order the road cars without the top wing (but why would you :classic:)

I'll take mine in diamond white with tiger stripes please.

 

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On 3/14/2022 at 6:35 AM, Mechbuilds said:

Please give this front axle some proper geometry.  At least caster angle and ackermann steering. 

I'd definitely like to improve the front axle for sure.  Unfortunately my knowledge of steering geometry is pretty much non-existent at this point, so I'm gonna have to spend some time educating myself!

On 3/14/2022 at 7:18 AM, Jurss said:

Seems already pretty complex build.

I'm afraid, that seats are also not in scale. And in this scale, it really could be more realistic, technically closer to original.

Yeah, I'd started to make the same realisation about the seats.  They were largely just a placeholder at this point though, so I'll definitely be changing them at some point.

On 3/14/2022 at 7:28 AM, MinusAndy said:

Fantastic project of a fantastic car! 
I’d go with the rally version but with a whale tale. 
Someone on here built an rs500 a while back. It might be worth a look at some of that for ideas.

You could put a centre diff in place of the grey gear that connects to the diff if you used an old style diff in its place, though you would end up with a high shaft running through where your selector forks are so you’d have to look into that. 

Thanks! I'll have to check out the RS500 thread.

Yeah, thinking back to when I built the gearbox, I think I sacrificed the central diff because it fouled on the gear selector mechanism.  That said, if I go for the rally version, I don't need to worry about fitting in rear seats, so could rework the gearbox without worrying about the self-imposed height restrictions... Decisions, decisions...

On 3/14/2022 at 9:02 AM, ukbajadave said:

For 1997 the Escort went from group A to WRC, one of the changes was the rear wing. You could also order the road cars without the top wing (but why would you :classic:)

I'll take mine in diamond white with tiger stripes please.

 

Ahh, that would explain it! Thanks! :classic: (I totally agree with you on the top wing - why buy the Cosworth without it?!)

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22 minutes ago, RiGi said:

I'd definitely like to improve the front axle for sure.  Unfortunately my knowledge of steering geometry is pretty much non-existent at this point, so I'm gonna have to spend some time educating myself!

You should visit @nicjasno's discord server and discover the wonders of lego technic geometry. 

Here's an example of radical geometry for a drift car:
r8ORgB3l.png
It has:
-Kingpin inclination (helps with return to center steering. Great for heavier mocs to reduce stress on servo)

-1 stud of caster angle (Increasing the amount of positive caster will increase steering effort and straight line tracking, as well as improve high speed stability and cornering effectiveness. Positive caster also increases tire lean when cornering (almost like having more negative camber) as the steering angle is increased.)

-Negative camber (Camber angle alters the handling qualities of a particular suspension design; in particular, negative camber improves grip when cornering especially with a short long arm suspension.)

-Ackerman steering (Better performance when turning. Your steering angle will improve.)



You can get ackerman steeringsimply by moving the connection point of the steering link by 1 stud more closer to the chassis from the pivot point of the wheel hub's connection point.
Camber can be achieved by moving the upper control arm by 0,5 studs closer to the chassis than the lower control arm. 
Caster can be achieved by moving the upper control arm back by 0,5-1 studs or moving the lower control arm forward by 0,5-1 studs. 
Kingpin inlcination is a bit trickier. You'll need to build a wheel hub in a way that the upper control arm's mounting point is one stud closer to the chassis than the lower control arm but still having the hub straight. 

 

Spoiler

Since the ford escort uses macpherson suspension, you might want to replicate that as well. 

Here are some examples i've found quickly trough google: 

MacPherson | Lego gears, Lego truck, Lego mechanics

 

 

 

 

Edited by Mechbuilds

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So after much learning and tinkering I think I've come up with a MacPherson strut suspension setup that will work.

800x600.jpg

The wheel hub started off life as the one in @nicjasno's video that @Mechbuilds posted above, which I've then modified to make longer so it fits in the deeper Defender rims and gives the axle more support.  The top mount is the result of trying out a few different ideas until I found something reasonably compact that would prevent the suspension from bending under load.

640x853.jpg

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It has (if my understanding is correct :laugh:):

  • positive caster angle (I've gone with a 2 stud offset in this instance)
  • Ackermann steering
  • a reasonable approximation of kingpin inclination - the hub is vertical but the steering link and U-joint aren't perfectly along the inclination axis

I also made a dual-spring version, as I suspect the final model may be quite heavy, so this gives me some options later on:

800x600.jpg

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(Disclaimer: this is just a test frame at the moment, the finished axle will obviously look quite different! I'll also be replacing the U-joints that connect to the diff with the new 4L CV joints, but I don't have any right now)

I still need to work on the steering rack placement, as it fouls on the diff in this test setup.  Offsetting the diff is also a possible option.

Of course, if anyone wiser than me spots any glaring flaws with what I have so far, then I'll gladly take on board any advice! :classic:

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I like it! It's a much more interesting suspension than we usually see, and looks pretty solid.

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3 hours ago, 2GodBDGlory said:

I like it! It's a much more interesting suspension than we usually see, and looks pretty solid.

Yes it's definitely a major improvement on the original setup and yes these can be built really solid and tough. 


2 studs of caster is quite alot. I think 1 stud would have been enough as is. 
2 yellow shocks are pretty stiff. I'm sure with 2 gray shocks you'll get more stiffness compared to just one yellow shock and not have issues of the parts not being able to handle the extra hard stiffness. 

Kingpin, caster and ackerman will definitely improve steering and reduce stress to the steering servo by a lot. 
Make sure the CV joints can handle the extreme steering angles. I think that U joints still would be fine with this. 

I would experiment with 0,5 stud camber. to increase cornering efficiency. 

Edited by Mechbuilds

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47 minutes ago, Mechbuilds said:

2 studs of caster is quite alot. I think 1 stud would have been enough as is. 

Though because the upper pivot is so far up, it is a smaller effect than it would be if it were lower down.

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5 hours ago, 2GodBDGlory said:

I like it! It's a much more interesting suspension than we usually see, and looks pretty solid.

Thanks! I'm only really used to the standard Lego double-wishbone suspension, so it's been pretty interesting learning about and building something more realistic!

2 hours ago, Mechbuilds said:

Yes it's definitely a major improvement on the original setup and yes these can be built really solid and tough. 


2 studs of caster is quite alot. I think 1 stud would have been enough as is. 
2 yellow shocks are pretty stiff. I'm sure with 2 gray shocks you'll get more stiffness compared to just one yellow shock and not have issues of the parts not being able to handle the extra hard stiffness. 

Kingpin, caster and ackerman will definitely improve steering and reduce stress to the steering servo by a lot. 
Make sure the CV joints can handle the extreme steering angles. I think that U joints still would be fine with this. 

I would experiment with 0,5 stud camber. to increase cornering efficiency. 

Thanks for the comments! :classic:

The caster angle works out at ~12.5 degrees with a two stud offset or ~6 degrees with a one stud offset.  I read in another thread on here that recommended ~10 degrees so I went with the two stud offset.  Although I did also read that most real cars tend to use around 3-5 degrees, so a one stud offset may be more realistic.

Yeah, the two yellow shocks are super stiff, but that was mostly for proof of concept of the dual-spring setup. I don't have any of the soft shocks right now, but I'm planning on getting the 42139 All Terrain Vehicle at some point, so that will provide me with plenty of soft shocks to play around with!

The main reason for changing the U-joints to CV joints is because I noticed that the axles tends to start slipping out of the 12t gears in the diff after a while, so I want to use them so the axles have that extra wiggle-room. I'll still keep the U-joints at the hub end for the extra steering angle.

Out of interest, as this is going to be a manual model and not motorised, would adding camber have much noticeable effect? Or is that something that would only be noticeable at the higher cornering speeds you would get with an RC model?

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Progress Update: after much tinkering I think I've finally got the front axle geometry setup just right!

Head on, everything looks to be as parallel as possible:

800x600.jpg

I managed to get a smidgen of negative camber, which is hopefully enough to have an affect:

800x801.jpg

I ended up reducing the caster angle to 1 stud as it was getting tricky to line the steering rack up in such a way that didn't create toe in/out.  Now the steering angle is much closer to being parallel with the axle and the wheel alignment is much better (the steering rack is fixed in place right now so I could check the wheel alignment more easily):

800x600.jpg

I decided to drop the diff down 2 studs to create more room to fit the fake engine in (the axle with the orange connectors will connect the engine to the gear box)

One downside I've found to my wheel hub design is that if I use 4L axles to connect the wheels, they have a tendency to slip off the u-joints after a while.  The best solution I've come up with so far is to use a 5.5L axle with stop and use a 3x3 disc as a sort of wheel cover to hide the excess axle length:

800x600.jpg

Hopefully over the bank holiday weekend I can spend some time finalising the bracing, steering and fake engine!

As always, if anyone more knowledgeable than me (i.e. almost everyone :laugh:) spots any areas for improvement then I'll gladly take on board any advice! Thanks :classic:

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Looking good! I'm a little worried about the gearing at the front differential, though. I mostly build RC models, and the bracing between the 20T gear and the differential would definitely not hold up to that. I assume this is a manual model, so forces will be lower and it might be ok, but one thing I would look into is replacing the 16:16 gearing you have coming from the differential with 12:20 gearing in order to reduce the forces on the differential further, kind of like using a planetary hub. I'm not quite sure whether gearing up or down there, but probably gearing up, so the 20T gear is on the U-joint axle, and the 12T is on the differential's axle. That way, the carrier will have lower torque, and be less likely to skip.

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1 hour ago, Teo LEGO Technic said:

This is a really cool MOC! I'm excited about the next progress report :laugh: . 

Thanks! :laugh:

1 hour ago, 2GodBDGlory said:

Looking good! I'm a little worried about the gearing at the front differential, though. I mostly build RC models, and the bracing between the 20T gear and the differential would definitely not hold up to that. I assume this is a manual model, so forces will be lower and it might be ok, but one thing I would look into is replacing the 16:16 gearing you have coming from the differential with 12:20 gearing in order to reduce the forces on the differential further, kind of like using a planetary hub. I'm not quite sure whether gearing up or down there, but probably gearing up, so the 20T gear is on the U-joint axle, and the 12T is on the differential's axle. That way, the carrier will have lower torque, and be less likely to skip.

Thanks for the input! This is going to be a purely manual model, so hopefully there won't be as much stress on the components than there would be in an RC model.  I was conscious of the bracing around the diff and the potential for it to sag a bit, so I deliberately used longer axles and doubled up on supporting liftarms at the ends of them to try and minimise this:

Ford_Escort_Cosworth_Diff.png

I'm hoping that this will be sufficiently strong enough for a manual model, but I'll definitely keep in mind your idea of swapping the 16:16 gearing with a 12:20 gearing.  I presume if I went down that road I would also need to apply the same gearing on the rear axle with it being 4WD?

In a worst case scenario, there's probably enough room for the engine if I move the diff back up so that it's directly connected to the driven axles and use the newer 4L CV joints - but I don't have any, and I'm trying to avoid doing too many parts orders! :laugh:

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You're right, that does look about as solid as you could get while having those 16T gears where they are, so it'll probably be fine, as long as the gearbox doesn't put up too much of a fight. The fact that it's AWD (without a central differential, if I followed the thread thoroughly enough) should help, too, since you're not really ever going to have it relying on just the front axle. And yeah, you would need to recreate that gearing on the rear axle to keep it even if you did decide to change it, but I don't think it would be too hard. (Though if you did put in a central differential, there would be no need to ensure that the gearing was the same; you'd just get torque vectoring to front or rear. I think the lower gearing on the front would give it a forward torque bias, though, which is probably not what a rally car would use)

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Thanks for the reply.  Given that I'm going for the rally version rather than the road going version now, I don't need to worry about fitting in rear seats.  That means more room available in the rear of the car, so I'm tempted to rework the gearbox to include a central diff now in keeping with the real car. 

14 hours ago, 2GodBDGlory said:

so it'll probably be fine, as long as the gearbox doesn't put up too much of a fight.

That's a good point. If I did rework the gearbox, I might change it from a 5+R to a straight 6-speed (or even just keep it as a 5-speed and lose reverse) which would help it run a bit smoother as the 3 8T gears used for the reverse gear do put up a bit of resistance currently.

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I’d go 5+r for sure. And centre diff. 
This is looking really good and far far cooler than another lamboferrariinsertpointysupercarhere.

Following.

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On 4/17/2022 at 3:16 PM, MinusAndy said:

I’d go 5+r for sure. And centre diff. 
This is looking really good and far far cooler than another lamboferrariinsertpointysupercarhere.

Following.

Thanks! 5+r and a centre diff is the ideal scenario as that's what the real car has, so I'd like to keep that if possible, but it'll involve a bit of reworking of the gearbox at some point.

Supercars definitely have their place (the 42056 911 GT3 RS was the thing lured me back from the wilderness of my dark ages...), but there's plenty of other interesting cars out there to MOC, so I'm glad to offer a bit of variety! :classic:

In terms of an update, I've made a decent amount of progress (after far too many hours of tinkering :laugh:) and I think I've finally got a front axle that I'm pretty happy with!

In order to fit the engine in I had to place the steering rack back as far as possible whilst trying to keep the bracing restricted to a pretty limited path:

640x853.jpg

I then had a choice to make for the engine position, either place it partially over the steering rack which would have meant it sitting very close to the height of the bonnet, or place it in front of the steering rack but be able to mount it 2 studs lower.  In the end I went for the second option as that way it'll give me more space to add some details on top of and around the engine later on:

800x600.jpg

In an ideal world I would have preferred it to be one stud further back, but I'm scuppered by the half stud length of axle that sticks out from crank at that end.

Finally, added some bracing and the suspension top mounts:

800x600.jpg

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(Orange axle connects to the engine, yellow axle connects to the diff, steering from the u-joint above)

So it now has decent suspension geometry (positive caster, negative camber, kingpin inclination & ackermann), drive, steering and an engine! :grin:

I suspect I'm going to have to route the steering to the steering wheel with two 90° bends via bevel gears rather than using u-joints, but that should actually make it easy to add a HoG steering knob on top of the dashboard so I think I can live with that.

Next job - try and rework the gearbox to add a central diff and make reverse gear run smoother.  I also briefly considered reworking the rear suspension to be more realistic, but after looking into semi-trailing arm suspension I realised that that's way beyond my knowledge level right now *huh*)

As always, any suggestions/critique are greatly appreciated! Thanks :classic:

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Nice going! It looks like it'll be a really interesting MOC.

I would encourage you to give the semi-trailing arm suspension a shot, though! I was just taking a look at it, and I think it would be an interesting challenge and another great touch on this already mechanically interesting MOC.

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Thanks!

Making semi-trailing arm suspension would definitely pose a challenge given my very basic mechanical knowledge and limited MOC-ing experience :laugh:  (Although it would be pretty awesome if I could manage to pull it off!)

I can only find one example online of it being used in an MOC, and that's @nicjasno's Ford Sierra RS 500.  Fortunately, his YouTube channel has the livestream recordings from when he made that MOC, so I might try and find some time to watch them to try and get a better understanding of how it works mechanically and how it translates into Lego...

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