FWD/FF Buggy

[Origineelreclamebord]

A mould/custom shell I will consider, it doesn't just look cool, it allows a good, tight seal of the chassis - something the previous car lacked. And I admit it, I'd love to make the car look good! I pulled out one of the many designs I made for an FF Buggy bodyshell from the archives and decided to try and make the design work for this chassis. The result:



I'm very happy with how it turned out I experimented a bit with the servo/steering layout on the car. It's now possible to swap the servo from left to right to move the steering linkage between two settings: the center of the chassis or near the edge of the chassis. I don't plan to run more than a receiver or PT on the top plate, so I'll run the linkage in the center of the chassis.

Why is this relevant? Well, running the steering linkage down the center allows a much lower profile bodyshell. The sidepods are up to 10mm lower, and the cab is, too. It did need a higher piece up front because of the steering rack, and a protruding piece on the right side for the servo horn.

[Gayo]

Man, your project is so cool! Kudos
Loving your shell design

[RC-trix]

Muuuuuuch better than the hacked K1

[ruf]

Originally Posted by Origineelreclamebord

Wow, what a response guys!

@Typpo: That amount of info on the Kyosho CVDs is very interesting, thanks for sharing! I will do some comparison work in Photoshop between different pictures and what shows potential will be sourced.

I did find a slightly better option in the meantime than the Tamiya CVDs, being Tamiya's Universal Shaft wheel axles (not WO Universal/CVD) with the 65mm Durango DEX210 bones. It fits as if Durango copied the geometry of Tamiya's U-joints Ok, Tamiya's '64mm' shafts actually seem to be 64.5mm, so I only gain 1mm of width, but it is still 1mm wider, plus, the outdrive pins now have the perfect diameter.

Nonetheless, my search continues. There is room for improvement, hence no reason to stop searching!

PS: I'll also share the pictures of the Xray XB4 vs. Tamiya 201 CVDs to show you why the Xray axles are interesting and the bones are not suitable for my project.


@optiman: Nice B44 truck! My guess is that that car too will have some acceleration issues with only front wheel drive, but it's an easy and fun test Every time a 4WD buggy's drive on the rear breaks down I'm closely monitoring how it gets around the track, and to be honest for something that just happens on the spot they do pretty well


@smokes: A double cardan shaft may work very well - in fact, there are so many 'constant velocity' solutions out there that are interesting to have a look at... I'd love to make a Rzeppa joint for an RC car (the one in the center):



This does require too much customizing or even machining from scratch. Even the D-joint from Durango is a bit complicated to work with for now, but these things are worth thinking about (especially the double cardan joint because the availability of the D-joint or putting two CVD systems together)

I take it you've seen the Kyosho TF-6 drive shafts? Similar design, but at the diff outdrive interface.

[Origineelreclamebord]

Thanks guys, I'm glad you like the shell I've got tons more designs, but many aren't even do-able with a plate+post chassis design

@ruf: I've never seen these before, but I really like what I'm seeing I can imagine the load on that system is much better distributed around the head of the dogbone and on the outdrive - and it should be pretty smooth (though on a tourer I can't see much benefit of that on the outdrive end, as the suspension barely moves).

For now I'll keep it at existing driveshafts. When the FF shows potential to make rear wheel drive eat it's heart out (without being banned from the 2WD class of course), I'll definetely look into 'alternative' driveshafts. A good place to start would be to test the different settings on a touring car chassis, Double Cardan and even Rzeppa Joints are already available for some 4WD tourers It shouldn't prove that hard to convert these systems onto a FWD tourer as long as the driveshaft fits in the outdrive.

[TryHard]

For Driveshafts... LiteModz used to make a proper scale CVD for RC... not sure if the company exists anymore though..

http://www.redrc.net/2010/07/litemod...ty-driveshaft/

[mattr]

Those sort of joints don't like large angles and lots of off axis torque.
We have a good number of problems with them during development in 1:1 applications.

[Origineelreclamebord]

@TryHard: Last week their website worked just fine, but today it seemed offline. I sure hope it's just a problem they're having with the website, not with their business. I liked the CVS Driveshafts, and I quite liked the pictures I saw of their touring car...

@mattr: Could you tell me more about this? What you mean with off axis torque (plus, what the result of this phenomenon is on handling, durability etc), what angles you can use it at all, and without off axis torque problems, what other issues you might be facing and lastly, if there are any solutions to this that you could share with us?

[mattr]

When you get to higher angles, the balls on the outside/inside of the bend come out of their groove, or at least, don't engage enough to transmit any torque with out damaging the balls/grooves. You end up transmitting the torque thro the balls to the left and right of the bend. Concentrating the load.
Also, all the shuttling in and out wears the balls/grooves very quickly. We have to use special, modified CVDs for XC type vehicles, at huge expense. Not sure exactly what the threshold is, but 18 degrees is sounding alarm bells.

[Origineelreclamebord]

Originally Posted by mattr

When you get to higher angles, the balls on the outside/inside of the bend come out of their groove, or at least, don't engage enough to transmit any torque with out damaging the balls/grooves. You end up transmitting the torque thro the balls to the left and right of the bend. Concentrating the load.
Also, all the shuttling in and out wears the balls/grooves very quickly. We have to use special, modified CVDs for XC type vehicles, at huge expense. Not sure exactly what the threshold is, but 18 degrees is sounding alarm bells.

Wow, that sounds really troublesome! I really thought they could handle more than those 18 degrees and were more consistent (though I did read about raised wear levels).

Still, I'm interested to give them a shot later on in the project - in fact, I'm open to a lot of suggestions on this one. Jimmy mentioned he seemed to have a bit more traction with his Tamiya DB01 using dogbones rather than universal shafts. I find it surprising (I'd say upgraded parts should enhance handling), but I don't doubt his judgement. It's worth trying The same counts for Rzeppa joints (if possible), CVDs (both the type with the cup on the axle and the type with the cup on the dogbone), and something I'd fancy to investigate further is rubber driveshaft couplings like the Lotus Elan have from the factory. A simple mechanical solution, I believe it's a constant velocity solution, it offers some give in the drivetrain (VERY desirable on a front wheel driven car I'd say, even if this makes the feel of the throttle a bit more vague and slingshot-like).

[ruf]

Originally Posted by Origineelreclamebord

Jimmy mentioned he seemed to have a bit more traction with his Tamiya DB01 using dogbones rather than universal shafts. I find it surprising (I'd say upgraded parts should enhance handling), but I don't doubt his judgement. It's worth trying

This is a known phenomenon in offroad RWD. CVA, CVD, universals, sliders, and dogbones all have different effect on rear traction as the mating surfaces interfere with suspension travel under load, and thus affect weight transfer. In addition, the angle also plays a large role, hence the idea of spacing the gearbox higher. Also fore/aft angle has an effect, especially notable in touring cars as the front arm/caster block is spaced back and forth. Wheelbase is only part of it.

[mattr]

Originally Posted by Origineelreclamebord

Wow, that sounds really troublesome! I really thought they could handle more than those 18 degrees and were more consistent (though I did read about raised wear levels).

It may well be more than 18, i was only involved very vaguely as it's not my area of responsibility. I do know that different designs behave differently (greater or lesser angles possible) but that one looks very simple, so likely to have a lower angle before "issues" occur.

[Origineelreclamebord]

All in all the science of these driveshafts is pretty complicated - which makes it all the more interesting!

I really appreciate all the ideas, suggestions and information coming in! All this input (in general, not just he driveshafts) has really helped to develop the car more quickly and find potential ways to make the car perform better before it even hits the ground And it also gives points for improvement for the longer term.

Speaking of such things, I've updated the rear shock tower and done the rear arms:



Gullwing arms were not an option, so I did what I think is the next best thing: Mounts below the arms. You might wonder how these arms could be symmetrical... Well, the idea is to print the arms with mounts on both the top and bottom side, and remove the side you don't need with a Dremel. That way the car uses 'directional' arms, yet if you grab one from the spares box it will fit on either side of the car (even though it may not look as pretty for the rest of the race day)

To lower the dampers through the suspension arms, the arm requires a huge opening in the center. I think it will hold just fine, but I guess I'll find out exactly how strong it is on the track. Durability concerns aside, the change allows for a much lower shock tower assembly without using very radical angles on there. It also allows the wing mount to move 5mm further forward and to use smaller clearance cutouts in the wing.

It's another thing off the list... In fact, I'm now kind of waiting for the long outdrives to find out if the car will become 240mm wide or slightly wider

[Origineelreclamebord]

Ok, time for a little update The long outdrives got in (link) - they are 1.25mm longer, and apparently the gear diff outdrives too are longer than the original 210 outdrives.

Conclusion: The car can become just a bit wider. I made it wider by 0.5mm each side - it means a safe clearance of the diff nut, and the extra distance I'm using - like Durango intended with these outdrives - to keep the driveshafts properly seated on extreme angles (and I'll have plenty of those situations in store for this car)

I tweaked the suspension stroke on the rear (it was too much compared to the front). I also made a few spacers here and there in specific shapes so when it's taken apart you can distinguish parts and you're not shimming until the world ends!

All these spacers and small bits have been ordered at a 3D printing company (I needed parts for another project) - the big(ger) parts from the car itself will be printed soon as well, and the plates will be cut from Plexiglas first (I suppose that'll do it for road testing).

If the mockup and onroad test drive shows no problems, then the car is converted straight to carbon and 3D printed nylon

As a last thing... I decided to stick with Big Bore shocks. I was planning to use SB shocks with BB springs, but it's too expensive right now to buy two sets of front SB dampers (the cheap spot I sourced - where both SB and BB dampers are less than 30 GBP new, also had only one SB set in stock).

I may need some time to understand the BB shocks as I've never worked with them, but I'm sure they will work nicely. In later testing stages I could always consider moving to SB shocks with BB springs.

[Origineelreclamebord]

I was in the mood to make some fancy pictures today











This is what the car could end up looking like This result is still a few steps away (particularly the body) but everything has been going quicker than expected on this second prototype. I can only hope the car itself also goes quicker than expected!

[RC-trix]

Pro-quality work, Paul

[Origineelreclamebord]

The design work is up to the point where the parts for the second prototype can be made - the files have been sent to the parts making parties I can't say how much time there will be between now and receiving the parts, but fingers crossed it's soon!

What I can share with you in the meantime is an image to show you how extensive the conversion is:



As you can see the car only has a donor gearbox, driveshafts, hubs, shocks and rear axles.

I'm currently working on getting all donor parts ready. The gearbox has a minor issue (the layshaft spacer seems to bind up the gearbox a bit), other than that it's going pretty well. The shocks are built and ready, I'll be making a setup sheet for the car soon for the first setup I'll be trying.

[johnnygibbon]

looks amazing quality
ive been puzzeled about your gearbox issues . wish i could help

[Origineelreclamebord]

Thanks I think the gearbox issue is just a spacer that's a wee bit too long - it is the layshaft that's causing the trouble, and it seems to happen only when I tighten the stuff and have all the parts in there: without the layshaft bearing (closest to the motor plate) in there it went just fine - probably because that means nothing could bind

Anyway, I got a bit bored of waiting for the parts after the amount of time I've spent on the project, so I kind of had to make something... Why not make a setup sheet for the car?




It immediately gives a good overview of the setup options. I think it's fun to see how much the front can be adjusted as opposed to the rear end It's funny looking back on it how little I did with those setup options on the last car, all because I was focusing on tires and the issues with that inboard shock system.

PS: Next time I will make the setup sheet in a different way... it took way too much time to make!

[tramp]

Thanks for the update, im really enjoying this thread & cant wait to see the finished product. It's great how professional this all seems! Seen as though you have all the CAD/CAM data will you be getting more components manufactured to be sold as a kit? it would be great to think that regular people who dont have the same CAD skills could own their own front wheel drive