What made a good 4wd buggy?

[Saito2]

For years, concentrating on Tamiya, I studied the design aspects that made the Egress less than successful as a competitive 4wd buggy. Hearing people's happiness with the Optima Mids that are out plus the re-re'd CAT xls and Super Dogfighter,, I'm curious what made them so successful? Where was the magic in their designs and geometries? Its easy to point out what makes a modern buggy great because, with the era of fresh thought over (except for delightfully different designs like the TD4), everything is "nailed down" design-wise and we seem to have entered an era of subtle tweaking rather than clean-sheet approaches.

Part of this question is in the actual mechanicals and geometries but there is also a "personality" or magic in the completed assembly. So, for those that know or remember, what was it about the above buggies that made them special? 

[ThunderDragonCy]

Not sure, but interestingly ny friend Barney was chatting at Tamiya Junkies track mert today about his Mids. He has his original Mid which was restored before ReRe, a LWB Mid and a ReRe mid, and he said for some reason the ReRe mid is really twitchy and hard to drive, even though it's ostensibly just a new version of his original Mid. There is a lot of subtlety going on in little cars.

[FromageTheDog]

If I were to hazard a guess -- I've got both my original LWB-converted Mid and a ReRe and while I honestly didn't notice it being especially twitchy, it isn't lost on me how much more rigid modern RC cars are vs. 30 years ago.  The graphite plates of the LWB conversion (or the FRP top deck of the stock Mid) are easily half the thickness of what modern cars use.  These cars would have been built and tuned around a certain degree of flexibility which I suspect "softens" their behavior.

Also, the LWB conversion has a huge calming effect on the Mid platform, so if he'd become accustomed to the LWB handling it's not hard to imagine the SWB ReRe feeling relatively more lively...

[GTodd]

Back in the day there wasnt publication that compared the Egress, TF, or the EVO to their contempories.  Each model was reviewed favorably by RC CarAction , with hits against the Egress for some UnderSteer and The TF due to its plastic shocks and bronze bushings.  I think they all handle great, club level itll be up to the driver.

[Anthroxoid]

Servo speed comes to mind when comparing new vs old Optima Mids. The differentials are also now oil filled, thus much more oversteer will be introduced using the wide, OT66 front tires. The ride height looks similar to me before even exploring tuning options so likely just the two aforementioned factors and then you’ve got to wonder what sort of traction level he’s comparing these all on as every one of the vintage 4WD buggies will traction roll with today’s carpet grip levels, just like the originals did on highly groomed golf courses 😇

What made a good 4WD vintage buggy for driving BITD? Everything about the chassis design and a very small effort from the rear wings. Counterintuitively, the big rear wings offered neglibke downforce where they were needed for handling, though up in sprinting speeds exerted some stabilization for jumping, then again for straight line stability. They have a proven negative impact on roll dynamics with modern racers making 5mm height adjustments for dynamic tuning of brushless modified class. They otherwise contributed to a more intuitive detriment in rolling your car over, but then aiding in its ability to self right like an old spring steel antenna’s secondary function. 
 

Straightaway speed, power delivery distribution and internal efficiency all aided more advanced designs. The more simple, belt driven cars allowed the old 540s to put more power to the ground instead of eating it in heat of huge gear meshes and far too many bearings (or worse, those plastic bushings *shivers* sapping all points of the power band). 

since dirt racing was THE thing for the vintage 4WD buggy design, its para enters naturally evolved to extend dimensionally outward in X and Y axis u til hitting ROAR legal limits. A touch of straight line stability was added by lengthening, and both cornering traction and rolling moment were improved with the wider stances. Look at how narrow the front end of a HotShot is compared to a modern buggy. There is more to that story in suspension sensitivity and the roll center tuning of long-arm geometry, so while earliest advanced designs may have short arms by today’s standards, they were constrained by the 2” wheel standard’s clearance because suspension travel in both full droop and compression needed to be quite generous. Buggies like the Avante that had hard bottoming in the front end tended to bounce instead of hooking up. Buggies like the CAT could jump and track well, and their camber was set at a factory tuned progressive camber rate but done well. When the upper suspension arms were done away with in order to allow a driver to tune their vehicle for various ride heights this was a big evolution and became an immediate standard, thus this first jump in suspension geometry design made for a good buggy because it was track tunable. 
 

Everybody had the same shock designs. They were all implemented in importantly subtle differences, however and oil retention and volume were secondary considerations beyond just making a car a good design in that the dampers could be allowed to rebound without shooting the freshly compressed suspension back up and off of a good contact pressure with that corner of the vehicle. Good shocks had long travel to aid in both long suspension travel and in progressively tightening their tension for protecting their cars from hard bottoming on the delicate components of the 80s. 

The best cars also included a touch of anti squat and caster to their geometries by default. Hooking up on dirt was/is complex and so the correct tire choice was a hugely important part of the hobby. Pins give good penetration and hold on loose turf but have poor longevity, so we saw every conceivable combination of pin spikes and blocks and bars offered to the racer. There was no universally good tire pattern applicable to each car. This made the driver/owner one of the very most import parts of what made a good buggy in that they learned how to hook up without fishtailing their fidgety factory differentials out the rear or pushing into the piles. But owing to the pin spikes’ good starting point for driving on loose tracks they remained the perfect starting point, so every 4WD shipped with their own take on them.

An oft overlooked aspect of old designs was polar moment of inertia. In layman’s terms this is bringing all of the mass as close to the middle of the car in order to allow it to quickly respond to changes in steering input. The advent of mid motor design helped here. This was also the beginning of a balancing act that better handling cars discovered early on and that was finding a good compromise on steering sensitivity without being too nose heavy for the bigger jumps. The heavier cars with full width front tires could float over loose tracks really well but gave up a bit of speed and agility to handle what are unthinkable conditions for today’s racers such as competing on tracks with loose sand, or simply giving the hobbyist a buggy that was capable of actually driving on beach dunes or taller turf if the manufacturers just wanted their cusomter base to have fun with that particular model, then opt for the halo versions down the catalog and get hooked on the expensive race car that I’m mostly commenting on here. 
 

Steering lockover combined with elimination of bump steer and telescopic double-cardan joints gave the final edge to a stretched and widened buggy in that it could forgive a driver (or glitch) while in the straights and also tuck the infield without compromise. The Schumachers kept that lead for a bit, then the Yokomos stripped down what you’d want in a survivable basher such as drive train protection in favor of the under-tray & shell combo and expected frequent maintenance of the owner. This was faster but the pit time was there. The first runs of these plate-elegant uglies were also the beginning of lasting, barebones simplicity of design in every RC thoroughbred to come.

Where do aesthetics come into play here? All along from and from the get go a good buggy was good if it had nice lines. In America the more aerodynamic or futuristic spacecraft shells were intentionally boxed out to appeal to a different customer base. Yokomo did that. Tamiya is to this day the preeminent expert in tailoring looks for their intended racing audiences despite no longer competing at the high end. You simply cannot overlook that the polycarbonate forms and livery were hugely important to a design’s success. Their overall mass was also a smaller factor as a tiny fraction of total GVW because we ran incredibly heavy running gear, so designers had fun and so much more scale appeal was incorporated than what is seen today.

Ultimately the ROAR limits on class weight minimums were borne out of the internal plate minimalism movement. It is probably also where the casual hobbyist looked at these cars for the first time and felt that it was no longer a model car, just a racing thing with so much of the model building fun removed. Though as with much of our hobby that will remain timelessly subjective. For racing it does not. The good 4WD buggy combined everything from good looks to suspension customization to drive train and chassis simplicity and customization; that final frontier where the hobby at its core gives every racer a feeling that their kit is now their own car. 
 

—XOID

[Wheel_Nut]

I don't know but I'd like to have a guess.  

1) Too short wheelbase for stability. 2) Not enough suspension travel and too firm suspension.  3) Suspension arms are too short, which means the roll-centre is typically too high and it also changes dynamically on bumps. 4) Front shock mounting angle will compromise grip and steering (should be more vertical).  5) Too heavy.

 

[Saito2]

On 5/2/2024 at 12:23 AM, GTodd said:

Back in the day there wasnt publication that compared the Egress, TF, or the EVO to their contempories. 

Took some digging but here's a comparo.

 

In RC Car Action's "Track Report" of the Egress, RCCA contributor and Dirt Digest column author, Bill O'Brien titled his driving portion of the article "Erratic Egress"  Granted, he was probably playing with alliteration but there was truth to it in what he found while driving the Egress with then-associate editor Steve Pond.  The word "unpredictable" at times was used to describe its composure. Mr. O'Brien focused on the long steering rod necessitated by the steering servo placement as well as the use of a standard Tamiya servo saver which was common in all Tamiya cars back then. While these factors are contributors, its issues deeper within the Egress's geometry that are at fault. The huge scrub radius and zero kick-up combined with only 10 degrees of caster afforded by the uprights led to a "nervous" handling buggy. That's not a dig at the author. Those kind of problems are pretty deep in the engineering of the buggy and probably beyond the scope of an average review. If anything, Mr O'Brien was one of the more discerning contributors than the average puff piece writer.

[Anthroxoid]

13 hours ago, Wheel_Nut said:

I don't know but I'd like to have a guess.  

1) Too short wheelbase for stability. 2) Not enough suspension travel and too firm suspension.  3) Suspension arms are too short, which means the roll-centre is typically too high and it also changes dynamically on bumps. 4) Front shock mounting angle will compromise grip and steering (should be more vertical).  5) Too heavy.

 

When looking at point 2, it’s really curious how differently the pace of elongated arms was introduced so slowly, or erratically by various manufacturers. We were stuck with caster in the front end being locked to what was shipped, though some models allowed you to flip the knuckled upside down for different angles. 
 

I think most everything by 1988 was being supplied with various shock and arm positions for then aiding progressive spring tension, or for easier tracks in letting your car ride lower for all of the benefits this brings, though ground clearance was gigantic compared to even what early 90s vehicles ran. I recall that Yokomo seemed to be the first to say with their designs to ‘surf the undertray, let it slap the landings, because we’re going to have you run low on all tracks because the lower CG and roll centers regardless of all other factors helps so much.” Everybody else had the shotgun perforations in their shock stays and ball link locators and this is also where again, the drivers become a crucial part of the buggy design in the pits. You could most definitely build your car wrong for any race, and people did so and lost despite having good gear. Setup sheets I think did not arrive as a shared part of racing until after ROAR91 standards. Please correct me if you recall this earlier where you ran you cars. 
 

We can likewise expand on the similar note of tuning and maintaining rebuildable motors. There was a huge ecosystem for lathing commutators and incredibly volatile sprays available for cleaning your motor in order to get it as close to new again. There were voodoo brush compositions available with close to pure graphite composition without much binder that resulted in high conductivity and low friction but ate themselves at alarming rates, giving yet another edge if the racer chose to spend and break in those parts. getting your gearing right for what you put together was and is still crucial, so I’d call this latter point manufacturer independent, but part of good motoring skills. 
 

People went fully down the hop up rabbit holes for their chosen vehicles. If there was a good ecosystem by the manufacturer or aftermarket support this made the vehicle I here fly more attractive in a sense that beyond replacing broken suspension parts the racer at the very least felt that they had a better version of their base model. I think that this is a pretty important part of what stood above ordinary mass production. There were entire walls of custom, fine pitch/modulus gears for pinion and spur, elimination of more moving mass, and lightening other components and strengthening adjoining pieces. BITD, the race buggy was half hobby shop and tuning and half good starting point. We could collectively likely begin a thread here and never get to the end of rediscovering all of the bespoke parts offered even between ‘85 and ‘90.
 

By 1990 the 4WD buggy scene was immensely popular I think as much in part to this as the newer tech hitting the scene that brought in more racers and casual hobbyists as well. You could buy factory balanced sub Cs, or buy boxes of SCR1200s and make your own killer packs. Deans came along and said stop melting your battery contacts —those are wasted electrons thst could give you the edge in competition, too. Remember all of the various battery top up tricks that were employed such as trickling right up to the race? It was part art and science as people developed refined techniques for maxing out their cells’ potential. It was also incredibly expensive as we destroyed batteries so quickly compare to today’s durable NiMH and the well made LiPoly offerings. 

I’m probably forgetting a million other things and also do not have firsthand knowledge for the vast majority of buggies that were driven early on in 4WD, so I guarantee that there are some points that I also simply never have known. That’s what the community is for just like BITD—sharing knowledge to keep things fun and collective wisdom learned and shared. 

—XOID

[Wooders28]

Back then, racing was alot was about efficiency. 

If your car was more efficient, you could run taller gears and /or lower turn motor, and your battery would last the race.

Belt drive, is the most efficient way to transmit the power , so if you had a shaft drive, with its extra , energy sapping gears. and the belt cars ,having more top speed, better acceleration ,a shaft drive car had the odds stack against them from the off.

So when you looked for a new car, a shaft wasn't considered a race car 🤷‍♂️

With modern lithium batteries and efficient brushless motors, it's just not even a consideration these days, I think it's just Schumacher that still use belts in their 4wd?

[Sir Crashalot]

On 4/28/2024 at 1:56 AM, Saito2 said:

For years, concentrating on Tamiya, I studied the design aspects that made the Egress less than successful as a competitive 4wd buggy. Hearing people's happiness with the Optima Mids that are out plus the re-re'd CAT xls and Super Dogfighter,, I'm curious what made them so successful? Where was the magic in their designs and geometries?

Among other aspects, the front-end of the Egress lacks kick-up which the other three buggies all have. This is detrimental to bump and jump handling. A poor oversight by the designers?

 

 

[Saito2]

2 hours ago, Sir Crashalot said:

Among other aspects, the front-end of the Egress lacks kick-up which the other three buggies all have. This is detrimental to bump and jump handling. A poor oversight by the designers?

 

On 5/11/2024 at 11:09 AM, Saito2 said:

The huge scrub radius and zero kick-up combined with only 10 degrees of caster afforded by the uprights led to a "nervous" handling buggy.

All the core geometries of the Egress are derived from the Avante. Tamiya attempted to band-aid fix some of the issues those geometries caused by increasing the front suspension travel with more upright shocks, tighter ball raced steering and narrower front tires but the real problem couldn't be solved without a total re-design like the Jamie Booth Egress had.

In discussions with other members, we were able to glean some possible answers, or rather see the method to Tamiya's "madness".

First, note how, like the rear of an SRB, the front arm pivot points are in line with the diff outdrive. This was done on purpose. If you carefully listen to the Avante promo, the narrator mentions how the arms were designed not to extend down from the chassis bottom to allow good ground clearance.

Second, the lack of kick-up may have been intentional. Kick-up wasn't a new concept for Tamiya. Both the earlier Hotshot series and the then-concurrent Thundershot series had kick-up. It was surmised that the Avante was possibly developed with a smooth track in mind. The notable lack of front travel supports this theory. I believe the earlier quote on the subject compared the Avante to a sort of off-road F1 car, one that might benefit from the quick response these geometries afforded. Indeed, one of the Avante's strengths that I recall was its ability to navigate a quick hairpin turn. Of course keeping it going straight at speed on a bumpy US off road track was another matter only exacerbated by the Avante's short wheelbase (something the Egress also corrected). The large scrub radius is a blunder though that only worsened the front end's natural tendencies to be nervous.

 

 

[Sir Crashalot]

[Howards]

On 4/27/2024 at 6:56 PM, Saito2 said:

So, for those that know or remember, what was it about the above buggies that made them special? 

I wonder if the question is more around what required them to evolve in the way they did. 

Better batteries and motors increase capabilities encouraging the design of more elaborate and taxing tracks.  This in turn encouraged longer wheelbases, more thoughtful weight distribution, more capable shocks, geometry changes to help tame speed and respond to bigger bumps and jumps and the ditching of any design references to full size sand buggies. 

At the sharp end if your straight line speed wasn't at least as fast as the next person's you could not win, so efficiency drove the design of simple inline belt arrangements. These also had the benefit of being relatively cheap to manufacture compared to shaft drive.

As the cars got quicker and the tracks wilder they had to be durable. The CAT was a tank. You could smash it about all day and it just shrugged stuff off. To finish first first you have to finish and unless you were a total klutz it was difficult to stop. 

So these buggies just became really single minded. They were all tough (in varying degrees), efficient, capable machines. They all represented a form of design local maxima.

On 5/11/2024 at 10:33 PM, Wooders28 said:

So when you looked for a new car, a shaft wasn't considered a race car 🤷‍♂️

Tenth Technology Predator entered the chat.

[Wooders28]

48 minutes ago, Howards said:

Tenth Technology Predator entered the chat.

Funnily enough, they where late to the party, and didn't arrive until the mid 90's?

Battery and motor tech had moved on, and wasn't the 1200 - 1800mah nicads of the mid- late 80's with bearing motors instead of bushes (although available, really expensive before the 90's, and out of paperboy wages reach..). Batteries had more than doubled in capacity (think Nimh was out by then?), so although still critical, not AS critical, but think Kyosho still didn't swap to shaft until early - mid 2000's, with the belts are better mindset?

 

[Howards]

Yeah, they came a bit later. Developed in the early 90s and sold around 1994. Fundamentally they were up against iterations of the late 80s/early 90s models. Bosscats, ZX-Rs, Works 93 etc. These folks stuck with belts because it's what they knew and their tooling and philosophy was set up around it, but the simple shaft drive of the Pred combined with it's minimalism was just more efficient so they ran faster on the electrics at the time - and it's how they won races.  I agree that the shaft designs around the early 90s were too fussy and complex compared to the directness (in design) and reliability of a belt.

I find it intriguing that Schumacher has gone back to belts though now. I think it took designers a while to work out how to make the efficient, reliable and reproducible shaft drive but once they got there you have to wonder why they'd then want to move away from it, as boring as it might be to build and look at.