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AC210FF, 2nd Gen FWD Competition Buggy

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So here we go... the development of a second prototype/generation FWD Buggy :)

Before I say anything more... if you are interested about the previous development, this topic may be useful for you:

TamiyaClub Thread: TRF201FF (Generation 1 FWD Competition Buggy)

Also, if you want a complete overview of the whole project (first and second prototype), this link may be relevant for you:

oOple Thread: Complete thread on FF/FWD Buggy Development

And here are some movies of the first prototype in action:


So in short... I have been working on a front wheel driven buggy for use in 1/10 Offroad racing. The reason for it... Well, out of curiosity I'd say. Prototypes of these popped up for a short period around 1990 and proved to be a very promising concept... until they were banned from the IFMAR (World Championships) for the 2WD class.

These cars vanished from the racing scene, but many regulations do allow them. I want to know if more than 20 years later, in the age of Brushless and LiPo, this concept can still be competitive. (I'm not mentioning here that I love that they're different and I think they look very cool) :lol:

So I started making a first prototype in November 2011, and by August 2012 it hit a track for the first time. It quickly became apparent that the first prototype had a promising pace (see youtube movies), but all the points to improve on were so big that it made no sense to update the car. A new car, built from scratch, would be the way to go. And that's what this topic is about: The development of the second FWD Buggy.

Without further ado, the design:



The design couldn't be much more different from the last car - I pretty much only use two parts from the last car (DB01 suspension blocks and wheels) - the rest is all new. The reason for this lies in some of the changes that the car needed (it will hopefully be self-explanatory later on). These are the main changes/improvements:

1. Team Durango DEX210 Gearbox: This gearbox has many advantages over the gearbox of the last prototype. First of all, the rotation direction of the motor can be changed by adding a 4th gear to the gearbox. This reverses the direction of the reactional force of the motor casing too. On the first prototype, this direction (3-gear gearbox) pulled the chassis out of the suspension, which theoretically means you lose grip, whereas a 4-gear gearbox layout should gain you grip when the motor pushes the chassis into the suspension. On this gearbox I can test both layouts and see what (and how big) an impact this has on performance.

Besides the 3 vs. 4-gear gearbox layout I can put a ball differential and (oil-filled) gear differential in there, allowing me to test the difference of the two diffs on the same car. Lastly, the slipper clutch assembly allows the use of an upright shock layout.

2. Team Durango as main supplier of donor parts: I hope this speaks for itself when I'm using a Durango gearbox.

3. Upright shock layout: I really liked the inboard suspension of the first car. However, the system is complicated and therefor difficult to understand. By using the upright shock layout, I take away one system that is difficult to understand so I can compare the performance of the FWD system easier and more accurately with a RWD system.

4. Driveshafts in line with outdrives: On the first prototype I tried to get the weight balance further forward by moving the gearbox further to the front. This put the driveshafts at an angle. Fact is, the greater the angle of a universal shaft, the more inconsistent it's rotational velocity becomes. This causes a loss of grip because your tire speeds up and slows down constantly (even when you're holding the same amount of throttle). Therefor, putting the driveshafts in line reduces this problem as far as I possibly can. It also moves the motor further to the axles. It might not be ideal for the weight balance, but it certainly does help to reduce the diving/dangling nature of the front end on bumpy surfaces (much like it also occurs on rear vs. mid-motor on bumpy surfaces) - not speaking of the reduction of digging into the ground on bumpy tracks or bad landings.

5. Shorty LiPo across width of chassis: I noticed in the tests that the forward weight balance doesn't seem to affect jumping much - as long as you have extra throttle to play with in the air. Also, the rear end didn't seem to need much weight on it. However, forward traction is always welcome. So by rotating the LiPo battery 90 degrees the car gets a weight balance that is further forward despite the fact that the motor is further to the back because the driveshafts are now in line.

6. New chassis layout: On the last car I didn't take into account where the ESC, Receiver, Transponder and wiring needed to go :lol: This time atround I have, and there is enough space behind the battery for all electronics. Alternatively, electronics can also be placed on the top chassis deck.

7. Updated Ackermann and Bump-Steer Geometry: This geometry was far off on the last car - and it didn't have enough of a steering angle in general. This problem should be largely solved on this car - and it can be shimmed and adjusted a lot to try out different settings.

8. Reducing anti-squat/kickup to zero: The first prototype had anti-squat/kickup on the front (like any buggy has on the front, but then a bit less). However, it became apparent that the reducing the anti-squat helped forward traction a lot, so this prototype has zero anti-squat/kickup.

9. Less Parts and smarter construction: This is for obvious reasons... It makes the car quicker to build, easier and more fun to work on, cheaper to manufacture, and with less parts there is less to break down :)

I've already made a first mockup of the new front end:





This mockup is to check if my CAD models of the existing parts are accurate with the real parts - to prevent getting a headache when I have expensive parts made that turn out to not fit. I can confirm though that all parts fit as expected :D Also, in the flesh you can spots some things you wouldn't on the screen with the CAD file in front of you.

For example, I do find that the front end is kind of narrow - I knew this might be an issue and it indeed is. I am going to look at different driveshafts that might be a better fit. However, if that doesn't work I already have a setup that mostly works. There are also some other small mods, but not really worth mentioning ;)

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First thoughts/reactions:

- I like the use of the 4-gear gearbox for the reasons you stated.

- I like the shorty lipo and how that moves the weight forward. I also like the idea of gaining more in-air correction capability with the throttle due to less rotational inertia around the front axle.

- Inline driveshafts are good. You're using CVDs instead of dogbones, right?

- The upright shocks should lower your CoG a tiny amount. Fewer parts is better for sure.

I hope you don't mind if I speak my mind a little... The rear suspension bugs me a little. Here's why:

- The rear suspension arms introduce camber angle changes that are related to their angle of departure from the main chassis tub. There doesn't seem to be any way to tune the camber gain without affecting the track width in the rear. It's not extreme like a Grasshopper, Mad Bull, or Lunch Box, but the effect is there. It looks like you can adjust the camber gain in the front with washers under the ball connector.

- It would be nice to have the option of a rear anti-roll bar just in case you want to loosen up the rear end a little more. I'm assuming you have the option to install a front anti-roll bar as well.

- It would also be nice to have just a touch of active steering at the rear to swing the rear out in a turn.

This is what I'm imagining for the rear of the buggy:

- The short chassis tub becomes T-shaped in the rear so that multiple suspension arm mounting points are available. A combination of mounting block shims set initial camber angle and a choice of mounting block positions set camber gain.

- The rear bearing hubs become steering knuckles with turnbuckle connections to the main tub. This compensates for the multiple rear suspension arm mounting positions, but it also provides opportunities to dial in some rear steering to swing the rear out in a turn (http://en.wikipedia.org/wiki/HICAS). You can also dial in some initial rear toe for stability.

- The chassis tub and suspension arms could include features for an anti-roll bar. If mounting locations become a problem, check out the shaft/blade approach used in the Associated TC6.1 WE.

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Thanks for the comments and suggestions :)

To clarify: The car indeed uses CVDs (Tamiya 64mm WO Uni's from the TRF201) - I do need to put larger pins in these driveshafts (the ones that go in the outdrives) or add 'sliders' that you also see on touring cars.

There are two main reasons for the very (very!) simple rear suspension system.

The first is that any weight savings on the rear contribute to a lot of extra forward traction - and the only thing I had to play with on the rear on the last car were tires, spring rate and droop. With a 'static' setup like this you want minimal grip on the rear without losing traction. This can be achieved by first choosing the right tire - it's better to stay on the side of 'too much' grip, as it's very easy to take grip away but hard to add it. Once you have the tire, you can chose the spring. Finally, you could adjust the droop to add or remove bite. On a well and truly smooth surface like tarmac the droop can be as little as 1mm without losing the rear end - on the last proto anyway ;) The new one will use 2WD and 4WD front tires and a different weight balance.

The second reason is that setup changes in the front should make the most difference on the car: You have the drive, the steering and the majority of the weight at that end. There is a lot to discover and develop on the front end, and I would like to learn to understand that first - plus the basics of a simple rear end structure. The inboard suspension on the first proto shows how much an unusual design feature can become like a blindfold in finding the points on where to improve the car - it became harder to read whether some of the behaviour of the car came from the inboard suspension or the front wheel drive, and this seriously slows down development on the main point of the car - the front wheel drive. When I understand the front end and the basic rear end I will definetely try out some more unusual things - like the return of inboard suspension on the car, and a HICAS-inspired rear suspension - about the HICAS by the way, you can do this not just for toe, but also for camber - like the Yokomo YR-F2:


There is one last concern with a passive steering system on the rear of the car... On bumpy tracks, the rear end may be all over the place. On smooth tracks it may work very nicely (indoors on tight tracks it might even prove essential) - To test all that it will need to become a system that I can easily enable or disable on the car (so it can be tested head to head).

As for camber and toe adjustment... Camber gain can indeed not be adjusted without changing the design of the rear end. however, camber and toe-in can be adjusted on this car. The suspension blocks can be shimmed up and down, tilting the suspension arms. I expect this to have similar effects to anti-squat. To adjust the camber and toe-in, the rear suspension arms have blocks on them that hold the axles. These are removable and symmetrical, so you can swap them between right and left - and by turning them 180 degrees, you can add or remove 2x the camber that is built into the block (so for example from +2 to -2 camber). If you don't turn them 180 degrees you'll have toe-out (which you really don't want). For completely different camber (or toe) settings extra blocks can be 3D printed - and I think toe-in will actually become one of the more important tools on the rear, besides tires, springs and droop.

The option for an anti-roll bar is a very good one. I'm still working out a bit how to make the shock towers+wing mount work, but once I have that solved I'm sure there is space for an anti-roll bar. There may also be space for it at the front, but I don't expect to need it there (the upright shocks are very... upright - and this combined with the narrow chassis should reduce roll considerably compared to the last car).

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Totally off topic, have you ever looked at the suspension design on the Awesomatix touring car? It's a neat idea with the rotary dampers and clock springs. The main idea is to lower CoG even more. Something to file in the back of our heads for future inspiration...

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Yeah I have seen it - I love the design of that car! :D The rotary dampers are very nice - if a littl emore complicated to understand how they work. That doesn't matter too much though, if it works well (which it seems to) it has the potential to be more intensively researched.

Things like this are indeed very much something to remember - for developing this buggy, or in fact any RC car :P

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Update time:


I updated the design of the shock tower (the new design is the more curved/rounded one) - The bigger curves and thicker portions of the tower should help reinforce the tower by spreading the load better. Geometry of the mounting positions of the dampers are mostly retained.


I also updated many other things on the car. For starters, the rear shock tower and wing mount are done. I might edit them a bit, but the basic principe will stay the same. The two small rear shock towers mount to a block. This block is mounted to the chassis, and mounted to a plate. This plate extends further to the rear, on which the wing will 'float'. The plate also extends to the front, where it is mounted to the chassis with a small block, so it is not just a wing mount, but a reinforcement of the rear shock tower.

The chassis has become 15mm longer, and the wheelbase a bit shorter. The longer chassis allows for more room for the electronics, as well as shortening the rear arms (making them cheaper to replace if they break or are subject to replacement by an updated version). The wheelbase has been shortened because the 285mm might just be overcooking it a bit. I can play around with the rear toe-in after all.

The front suspension arms were also updated. They are reinforced around the suspension shafts, and the damper mounting is also more solid now. I also changed some other bits and bobs visible on this imagine, but that's just tiny stuff really :P


And lastly, I decided to design another body for it - I didn't like my original design that much. By moving around the servo, servo horn and steering linkage I managed to make it possible to lower the sidepods by 10mm - and I lowered the cab by 10mm as well. I'm quite chuffed with the result. I don't know yet if I'm actually going to make a bodyshell, though I would love to :)

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Wow. This should be amazing like the previous builds. Are you using the same printing material as before? Or have there been any new developments in 3D printing recently?

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There are plenty of developments in 3D printing, but in the case of getting ever stronger materials, they are often still expensive. For me, I've switched to a different printing method and material (SLS printed Nylon instead of FDM printed PLA). The nylon is somewhat stronger and the printing direction has a lesser influence on part strength (3D printed parts often have different strength values in the X, Y and particular Z direction (Z=between layers/height of the part). Also, there is the option to print glass and carbon reinforced nylon parts. The nylon is affordable in general, the composites are expensive when done at a company... luckily I've found a sponsor who has access to such a printer and these materials :)

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Any updates? How did testing go?

Sorry for the late reply! :lol: But to answer your question, testing has gone great! I have built and run a third prototype, and with this I have recently won a championship! What's even better, I've won the championship from TLR team driver Wesley van Helmond - he was the Junior European Champion in 2013, so when that happens, you know you're going quick!




I'm currently working towards making a conversion kit for the DEX210, so other drivers can enjoy this kit too! :) More information is available on https://www.facebook.com/orbracing

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