Are people thinking about rc performance all wrong today?

[proffesso]

I'd like to go more of a scale class, ie, gpi mini trophy..rhose look great

Or better yet, an open "inventor" class, like 1970's f1..6 wheels, ducted fans etc?

[DerbyDan]

This is a very interesting topic of discussion.... & kinda reminds me of the Colin Chapman philosiphy that lighter is faster - as proved in full size Grand Prix racing with the Cooper powered Lotus racers in the 60s.

With respect to our off road 1/10th buggies it seems that this theory does not quite ring true? The current (lower) weight limit according to the IFMAR rules is 1474KG.... which with a set of Nimh cells aboard is very difficult to achieve. Back when running lower powered & less efficient brushed motors there where certainly gains to be had by having as light a car as possible. But by simply replacing the sub C cells with a much lighter 2s LiPo mean't that weight had to be added just to reach the legal limit.... weight could now be added about the chassis to improve its handling.... combined with the fact that we can now buy motors with more power than the driver/car & tyres can cope with means that keeping the car as close to the weight limit as possible is not an issue, but making the car as driveable as possible is. Certainly my CR2 is much heavier with all the weight i've added compared to the XXX I raced back in the late 90s.... but it has all the grunt I can handle & has never 'dumped' the cells in the duration of a race.

Its probably pure fluke that when the weight limit was devised (with sub C cells) that this was close to the optimum weight to what a 2wd Off Road buggy should be in 1-10th scale racing over the typical tracks that we race on?

All that said the idea of what could be achieved if the weight limit lifted is interesting. The weight of our cars with all the electrics removed are pretty damn light already, the heaviest single item in the car is now the motor - so the location of this is critical within the chassis to maintain balance.... maybe a smaller/lighter motor could be used? The spring rates would have to be alot softer & damped less to allow the suspension to ride the bumps - the challenge is how to control the car's roll characteristics given that the ride height would remain the same (for clearance over bumps etc) Would we then find that our tyres gave too much grip.... or indeed not enough?..... Personally I think grip-roll would be a big problem & special tyres would need to be developed.

Chassis dynamics & engineering is probably one of the most complex subjects as it is always a compromise to contain all the forces acting upon a car whilst allowing it to be quick & driveable. Adding into the mix the extreme (at 1/10th scale) off road conditions that a 1/10th buggy is likely to encounter only serves to make things even more complicated.

[fredswain]

Out of curiosity I weighed my RC10 last night. It currently has a graphite chassis, rpm worlds suspension, and had it's wheels and tires on. No body or electronics. Those car are very light without electronics at just over a pound. Obviously a body and wing add a little bit of weight but that means half the cars weight is normally from electronics. The ROAR minimum is around 3.25 lbs or so (not 1474 kg as that is 3249 lbs!!! ). I suppose a low profile servo could be used to keep weight down and modern receivers are so small and light it's laughable. I got to thinking. What if we could keep the total fully loaded weight of a car with 1s lipo down to 2.5 lbs? Could we then use a smaller lighter 380 sized motor with a 1s lipo and get decent speed from it? Castle makes 9600kv system for the 1/18 scale cars and the speed control it comes with is tiny. With a 1s lipo the esc wouldn't be taxed all that hard. Keep in mind that a 9600 kv motor on 3.7v is theoretically capable of over 35,000 rpm but with it's smaller size and lower torque would need to be geared for a lower top speed than what a larger motor would be at that rpm. Fortunately this is where a much lighter weight comes into play. I think 30 mph is still quite doable from it which is more than fast enough for any stock class racing. As a reference when my RC10 had the tub chassis and added weight, it was a heavy 3.75 lbs. It did handle pretty well though. Unfortunately it's lack of reliability led me to start my modern frustration with the old car thread and current car rebuild. Basically if I could hold 2.5 lbs vs the heavier 3.75 lbs, I'd need to move 2/3 the weight with 1/2 the battery voltage. The difference would have to be made up from motor selection and we all know what kind of effect changing those can have. It probably wouldn't get the current half hour runtime on a battery but that's to be expected. Now I'm getting curious enough to actually try it.

[jwscab]

the only thing I would worry about is to make sure to get the chassis close to what those 1/18 scale cars weigh. taxing a little motor and speed controller beyond it's intended loading could cause premature failure.

I understand what you are trying to convey here, we have plenty of horsepower and run time now, seems you could scale back both to achieve something more like vintage races and go with a lower weight car to save wear and tear, but I think it would be a hard sell.

[fredswain]

I'm not trying to sell anyone on it. It's an idea. Besides this is America. Look at our real cars. Fat, heavy, but powerful! Then again we aren't exactly known for our great handling cars so... (those are probably fighting words!)

[DerbyDan]

The ROAR minimum is around 3.25 lbs or so (not 1474 kg as that is 3249 lbs!!! ).

Ah yes - I forgot the decimal point

[fredswain]

We can add weight for performance but I think that was a bit extreme!!!

[longboardnj]

this reminds me of my super lite buggy idea.. run a b4 with a 380 brushless motor and small lipo battery..

[fredswain]

I think it's got merit.The 1/18 scale Slash weighs 2-1/8 lbs and hits about 30 mph with a 3800 kv motor on 7.4v.

[Bongo Fury]

One thing to work on for the lightweight approach is unsprung weight/mass. Mainly the tires & rims I assume. In general as the sprung/unsprung mass ratio goes down getting the suspension to work becomes more problematic. Since all performance depends on those 4 little contact patches it might be challenging.

Regards

[fredswain]

It wouldn't really be all that bad. A lighter car needs a correspondingly softer sprung and damped suspension. It's all about tuning. Tires is going to be an issue. Obviously people add weight so the tires grab better. You can have all the tire in the world but with no weight to hold it down it's going to slide so compounds and foam would be a bit of a trick.

One big issue I thought about with a 1s lipo is amperage. We don't have a lot of voltage so if the motor needs a lot of punch from the battery then it needs amperage. That means a high C rating on the battery. I'm not sure if the current 1s lipos would be able to supply enough.

As I said it's all an idea and not an actual project. It can probably be done but there are several things that need to be thought of differently.

[losiXXXman]

Great discussion going on here. I think the idea of 380 brushless, has actually come up before a few times. I know I broached it once on the forum. Whenever I end up with enough extra $$, I definitely want to try it. I think for a budget minded individual, you could always try it out with a non-lipo, 1/18 NimH pack too. Those little packs can still have 7.2v, and 2000 mAH. (I haven't yet made the switch to Lipo. Again that budget issue.) I ran a Lunchbox on a stock 380 closed endbell, and it still had good power - for messing around (of course what else do you do with a LB).

One thing I didn't see mentioned, don't you have to run a receiver pack when using 1s? That's a little weight going back in - not much, but something to remember..

[fredswain]

That may make it a worthless idea since the whole point is to keep it light. Then again you can get a 2s lipo with a low mah rating without a hard case that is pretty darned light so maybe a 1s isn't necessary.

[Jirka]

I think that adding weight will make the car easier, safer and smoother to drive now when we have "unlimited" power. I see that human can not control RC cars no more if they by some technical development as a result could be made something like 2-seconds faster per lap. Reaction time etc will go beyond humans capability. By adding weight will make RC car predictably on a limit just before it loses traction. Light cars don't warn, they loses traction too fast. Also offroad cars makes little jumps all the time on rough terrain. These small jumps are more shorter and car will go over them smoother when cars are heavier.

I see that future of cars like 2wd offroad cars will make cars practically easier to drive and stronger, if tracks don't change; fast they are already.

Jirka

[fredswain]

We've already been through the whole make your car into a fat heavy race car thing to help handling. The point of the thread is an exercise in removing, not adding weight. I already know the benefits of adding weight to performance, which is completely counter-intuitive. Now I want the opposite because I feel that many use added weight as a bandaid rather than a tuning aid. Most people can't tune a car to save their lives yet most people today are adding weight. If most people do it that tells me that it may not be as good of an idea as it seems. I disagree with most people in case you haven't figured it out yet. For any benefit added weight gives, it also brings a severe disadvantage. Less weight is far less energy to dissipate in a crash, something my half pound heavier than stock RC10 could attest to considering it pretty much fell apart screw by screw at the track. It handled good for the 1-2 laps it wasn't too weak to stay together but has not run since then since I yanked the electronics out of it to install in my reliable tank of a JRX-Pro. The fact that we have near umlimited power is exactly why I'm thinking this way. It doesn't mean we have to use all the power that is available to us. A nice benefit of these high powered motors of today is the fact that they are far more efficient than they used to be as well. Let's take advantage of it. You don't need big or heavy to be fast. Smaller motors have far more power than they used to as well. Stop thinking more, more, more. This is not an exercise in more. It's an exercise in less. Once you get to a certain point, more is not better. It's just a waste. I want to get away from the American, give me more power logic, and take a more balanced give me a better design approach. I want to see how we can take full advantage of modern technology to improve a cars performance by not by throwing gobs of weight and power at it. Anyone can do that. Thinking backwards from the mainstream is usually a good thing. At the very least, a lighter car will be more reliable bashing around the neighborhood and that in itself is a benefit.