FWD/FF Buggy

[Phil Channon]

My car had zero rear toe-in as standard, I added 1 degree to each side.
I also use to change the front and rear track to add/remove grip.

I did try adding weight to the rear of the car, both at the back of the chassis and at the end of the rear suspension arms. All it did was make the rear get out of shape quicker.

The one thing I found was to try and not focus on what the rear is doing and just keep the front of the car pointing in the direction you want it to go in.
Easy to say but not that easy to get use too.
To help I ran black wheels and a dark colour on the rear of the bodyshell to reduce my focus on it.

[Origineelreclamebord]

Wow, thanks for the details, awesome!

Interesting things that you mention... Especially on the driving style. I was already driving differently with the FF and some changes to that really help already, but what you're saying is that I should not react to the oversteer with countersteer at all, but should let the drive straighten the car out again?

[Phil Channon]

Some countersteer might be needed, but applying full power will pull the car straight. There is a subtle balance, but with practice you will find it.
Have fun!

[Losi_110]

Hi i'm loving this build. It's awesome seeing someone do something different have you got any pics with the body on? So how much of the dex201 parts does it actually use as i can't see many.

[Origineelreclamebord]

Hehe, the body I used in the test is not anything like the one I modelled: I found a small ice cream box which fitted perfectly around the chassis It looks horrible but it was good enough for a first test. I'll be looking into a mould soon - after I've met some project deadlines for the uni.

Meanwhile, I'm afraid body-on pictures look like this:




I know it's literally a box on wheels at the moment I promise though, things will get better. These pictures are from the first track test that it had last Sunday. Here are some more pictures and two videos:

Test Session Photo Album
Video 1
Video 2

The car performed really well. At first there were some problems with a loose rear end and the car bottoming out too easily, but they were quickly solved. The track became quite dusty by the end of the day, and where all RWDs were struggling this car kept going strong!

So strong in fact that it became second in the vintage race I entered it in (and I am NOT a driver to end up that high usually). It scored by far the best and most consistent lap times of the class. Ok, it's against vintage cars, but it still leaves a very good impression for it's first track test day!

Durability seems good so far as well... I've crashed it a couple of times and the car did break down... but they weren't 3D printed or carbon parts. The 3mm Polycarbonate bumper I made broke, I lost a driveshaft pin and I wrecked a wing (I have to change the mounting spot a bit).

And Phil Channon, After dialing in the rear end a bit better, countersteer was indeed rarely needed. I ran ProLine Calibers (M4) on the front and tried ProLine Calibers (M4) and ProLine 4-Ribs (M3) on the rear. The Calibers offer more rear bite and feels safer to drive, even if the oversteer is a bit more snappy (it just rarely occurs). The 4-ribs offer so much steering that you can even slide the rear-end on power. It's funny though, the oversteer in general is controllable - yet I think it might slide a bit too much for an actual gain in lap times (for many people).

[Burty248]

Fastest ice cream box i have ever seen. Has anyone else driven the conversion, like a pro driver or top club driver other than yourself. If they did what did they think of it?

[Origineelreclamebord]

Three other people haven driven it last weekend, all three more experienced and quicker drivers than me:
- Arjan (Janus_77): A six (or seven?) time Dutch-Belgian Championship winner.
- Tom (Tomboo_91): A Dutch-Belgian Championship driver who drives A-finals or high B-finals.
- Koen, An onroad driver who won the F1 B-finals of the 2013 ETS in Apeldoorn (and has a very impressive list of wins on his onroad portfolio).

Arjan (posted in this thread):

Originally Posted by janus_77

Ok, I've seen it a couple of times now. Even got to drive a few times also. Untill this point it was a nice novelty project, but now it's really starting to come together.

It was entered into a vintage race today driven by the designer Paul Dijkstra ( as a really bad replica of a Kyosho Maxxum FF ) and it was pretty quick to start with, and Paul was messing around with a few things during the day. Some worked, some did not. But by the time the qualifications were over it was keeping up with the fastest of the Losi XX's and RC10's. It was just that Paul was sometimes in the wrong place at the wrong time.

But the last main he had a bit of luck and had a clear track, just look a his best time and the best time of the winning car ( ARRC10, was entered as a car since it was driven by muliple drivers ). The AC210FF also had a fastest lap that was about 0,7 faster than anyone else. Granted it was on the surface it was made to live on, really low grip dusty clay, but still it's starting to get onto the same pace as the normal buggies.

It will be interesting to see if it will get even better with a bit more tinkering

Keep up the good work Paul

Attached image:

Tom: 'This is really nice!'
Koen: 'It's kind of too easy to drive!'

I can ask Tom and Koen them to make their own statements as I'm not going to write down quotes that they didn't make... but overall I think I can summarize that the people who drove it, liked it

Tomboo was the only guy to jump with the car other than me, and he said it was a handful to jump...

...And to be honest, when you haven't driven it for a full day yet, indeed it is: I wasn't confident enough to jump the car over all jumps until the third heat, and until the second final my jumps were a bit inconsistent. However, I think the 14-lap result of the third final heat shows that with a bit of training and setup in the right ballpark, lap times come a long way!

The thing is, when you jump it like a RWD it will nose-dive. The trick is to apply more throttle in the air and it will remain perfectly level or even have the nose pointed in the air (and yes, I will post pictures of this soon). Also, over really small jumps (or should I say, big bumps) it might also nose-dive a bit, and a quick burst of throttle really helps there. This is why the 6.5T motor comes in handy, even with a low punch setting

Edit:
I've put some new pictures in the album, something like this:

[Losi_110]

Got to love the work in progress bodyshell Can I ask on question I think I must of missed the answer to somewhere along the way with this thread, but why do you use narrow rear tyres? Wouldn't it help with the low rear grip/ weight to have heavier rear wheels?

[Origineelreclamebord]

Valid question, and when I initially had a lack of rear traction I was wondering the same thing.

The decision was taken on several things:

1. Wide/Rear tires were required for the rear wheels on 2WDs, but they changed this to 'driven wheels' instead to prevent the FWD having an (unfair) advantage of having the freedom to pick 'any' tire up front.

Instead, it's now limited at the front like an RWD on the rear, and tire choice on the rear end as free as it is on an RWD at the front.

2. With the first prototype it didn't take long before I was trying bald rear tires, then nearly bald tires, then narrower tires with good tread left on them. The rear end doesn't need as much grip as wide/rear tires offer.

3. Narrower tires and wheels reduce unsprung weight, reduces the weight in the extremities of the car (reduces rotational inertia) and in combination with other weight savings the (incidental) result is that I can now play around with some weights on the car yet keep the car at the minimum weight.

[Gayo]

Fantastic work! Thank you for sharing your thoughts and the development with us oOplers

I have one suggestion to do: have you tried a wing in the usual place, i.e over the rear wheels? Wing shape, size and position have a huge effect on the handling and yours is really, really forward placed.
I think that in the usual position, your car should fly better and not feel so light rear-wise. Unless I'm wrong

[Losi_110]

That makes sense, seeing the work that has gone into this I thought there must be a good reason for it that I wasn't getting lol

[Origineelreclamebord]

@Losi_110: I can understand your question very well, please keep on asking them The simplest of questions can raise the most interesting points as how to improve the car! The learning curve is steep and with this (relatively) small knowledge base on these cars there are no clear guidelines on what works and what doesn't (what you do have on RWDs).

@Gayo: Thanks for the suggestions! It may indeed help, I'll try it out somewhere along the line: I need a new wing mount anyway because the current mounting position on the wing leaves it vulnerable to backwards upside down landings (for example when it flips over after a nose-dive). While I'm at it it's not a big deal to add a few more options on the mount.

There is just one concern I have. On the last car there was little clearance between the rear wheel and the wing. This resulted in kind of a snare for RWD cars that ran into the back of the car: They got tangled between rear suspension and wing. That's the whole reason why the wing is so far forward, and so far it seems to have largely solved the problem.

So there possibly is a trade-off between car performance and the possibility of cars getting stuck in your rear end even on light contact. That needs testing though as that was also with wide rear wheels and uprights, so... bring it on!

[Gayo]

Interesting issue!
So you need the wing support to act as a rear bumper

[Burty248]

Or have it high enough to stop cars getting caught?

If you look at page 11 the wings especialy on the hpi they seem very high. How about somthing like that?

From the vids the car does look good, it looks like you can really push the car through the turns.

[Origineelreclamebord]

Well, back then it was a trend to have the wing pretty high up, but I suppose that too may be worth a shot

The car can be pushed through turns and I don't exactly know how quick it is compared to an RWD, but not any slower. It's also surprisingly easy to do, you don't run the risk of spinning out the car as dusty as the track was, just the risk of running a bit wide.

Edit: Some awesome action pictures by fellow member Eric Hendriks:

[Origineelreclamebord]

Another update

I drove the car again today - this time with Schumacher Minispike 2 Yellow/Schumacher Cut Stagger Yellow - both sets worn but not bald - good enough for a first impression. I wanted to drive on a local (astroturf) tennis field but it wasn't free... so instead I moved to the next best high-bite surface: abrasive tarmac!

The car started out with the same setup as on clay with only a tweaked ride height at the rear - which gave it less rear droop. The car didn't seem to mind though, the rear end was very stable - in fact, the more agressively I threw it into corners, the more it understeered. I mounted the front shocks further to the inside at the top, which seemed to add a bit of roll and front bite, but still the rear end was a bit too grippy. I removed the shims I added earlier on in an attempt to lose some toe-in this time. It did help a bit, but this doesn't seem like the main cause of the issue. I guess I'll be needing a stiffer rear end on the car.

It's pretty funny how big a difference this is to clay: The rear end doesn't budge until you destabilize the rear end by braking (on which it easily overreacts as I noticed on other surfaces as well).

The similarities are also very clear though: Smooth driving work best. On clay, too agressive driving in general caused oversteer, on here it seems to trigger a load of understeer. I'm happy with the understeer though, if you push it too hard into corners it simply misses the apex (and in the worst case scenario you have to make a stoppie to evade track barriers) - that's a lesser price to pay than triggering a self-destruction mechanism with massive grip roll and a mushroom cloud somewhere at the end of the carnage trail

[Burty248]

Sounds like your making a lot of progress. Im no expert but perhaps you could change some esc or transmitter settings so that the front doesn't lock up during braking?

kind of like applying the brake slowly on a mountian bike to insure you dont go over the handle bars? It might mean that you need to brake earlier but the car would be more stable entering corners.

[rcjunky]

some radios can change servo speed, if so turn down the throttle speed, making it slower on gas and breaks, but not releasing, might make it feel more conventional.

[Origineelreclamebord]

Thanks for the advice guys I was already considering to turn down the throttle EPA in the braking direction to a point where it makes more sense using it a little.

That said, I'd like it to work and be dialled in without too many transmitter options - otherwise I'm hiding/reducing handling traits that I'm trying to find out about and then optimize in the chassis design.

Of the testing so far I find the understeer/oversteer part very interesting. The understeer that occurred on the test yesterday was really only if I deliberately pushed it too far... which also worked really effectively as a brake by the way It just kept on losing speed until the front tires found enough side-bite to change the car's direction.

Being just slightly more gentle made all the difference. I think it means that you give the car just enough time to roll a bit onto the outside front tire, shifting weight and generating the grip on it needed to move the direction of all that weight resting on the front end.

[Burty248]

Have you tried anything to do with caster or antisquat on this car? Surely as this car is fwd as apose to rwd antisquat will have compleatly different effects.