Are people thinking about rc performance all wrong today?

[fredswain]

Everything is theory until proven of course. I can definitely see why it might not work optimally with existing car designs or by just making existing cars lighter but I don't see why it isn't a valid idea. It may just take some different design elements being applied and I think that's the key.

[minichamps11]

Been following this thread with interest....can't hold back any more:

people mention adding weight helps hold the front end down during acceleration. I see that. I could also see just allowing the slipper clutch to run a little looser to accomplish the same thing....... people complain about mid motor setups in off road due to less forward traction during acceleration. If you've got so much forward traction that you are pulling the front wheels off the ground, you can stand to lose some forward traction!

Loosening the slipper to keep the front end down on a modern 2WD car running high performance brushless + Lipo (especially on UK high grip tracks) is a bad idea as it causes the car to behave erratically. The slipper heats up excessively and either slips too much or temporarily binds up - quite often both on the same lap in my experience, resulting in no drive when you need it or wheelies when you don't. Slippers were originally designed to help keep your car pointing forward on low grip tracks with brushed motors and NiCds. Only in the last year have manufacturers started to address the issue of overheating slippers (X-Factory, Associated, Kyosho vented slipper plates)

On your forward traction comment, you seem to be confused. Mid cars are less likely by design to lift the front wheels versus a rear engined car due to their central weight distribution. The last thing Mid engined cars need to loose is forward traction!

Another idea would be to lay the shocks over quite far like the old Kyosho Optimas did up front. That would be far simpler but the weight of the shocks isn't as central.

If you're an engineer, do some research on spring progression + piston velocity versus wheel movement and you'll realise why laydown shocks are a bad idea and went away on competition buggies in the 90's.

Perhaps revisiting the laydown front shock arrangement could benefit that area as well. There is no reason why a laydown shock can't work just as well. It's all about the linkage geometry. The biggest downfall to this is the added complexity and hence weight.

If you mean "inboard" suspension like the Ttech Predator, then yes, you're right, the concept has many benefits. I don't think you'll find it much heavier than a conventional suspension system either as the additional extra rocker/ pivot / rod weight is compensated by having shorter dampers.

The solution from a weight balancing perspective is to run mid motor. The next obvious problem is that it may not hook up all that well due to the amount of weight on the drive wheels. A valid concern. However X-Factory figured out that if you run the motor in the same direction as the wheels, it's rotational inertia applies a force in the opposite direction to the chassis that helps transfer weight to the back. It's simple physics. Their solution was to run the 4 gear gearbox to accomplish this.

This helps but the 4 gear solution on it's own doesn't generate enough force to improve traction & grip in all situations. X-Factory cars in the UK run heavy. Here's a quote from Chazz himself "Most set-ups are pretty specific about the amount of weight and its placement. There is much discussion in this thread about it. To begin with, where do you race? It's quite different for different circumstances. Here in the U.S. on most dirt tracks, you want total weight between 1550 and 1650 gr. In U.K. on grass/astro, it's about 100 g more" (see thread here on oople.com http://www.oople.com/forums/showthread.php?t=76018&highlight=weight - there's loads more info on the X-Factory forum about why the X6 needs weight to run competitively.

The downside to this added weight is that the car nearly ripped itself apart in a wreck from all the excess energy that had to be dissipated. I'd never seen so many parts break at once before. It led me to nearly throw my RC10 away in the trash I was so mad at it. It was that moment that I decided that I wanted to think about this in a far more in depth way to get to the source of the problem...or rather a solution depending on how you look at it. It was time for a reboot.

I get the impression from this comment that your driving isn't up to scratch.....if you don't crash, you don't break stuff so the extra weight isn't an issue . Another (far politer) point of view is (assuming you are talking about a vintage RC10) is that 1980's /90's cars were designed back when we were running 14 - 24 turn brushed motors and 1200 - 2000mAh batteries. They had to be light to run fast for 5 minutes (4 in the USA?) so adding silly amounts of weight was always going to be a killer. I'm always shocked by the thinness of the C/F shock towers on my old cars. Nowadays we're running 4mm thick towers....... I'm a big fan of the way the Losi 22 designers deliberately added weight to the car by beefing up the components to help the car survive those 5T brushed 50C Lipo powered crashes. Personally I'd much rather have a heavy car that survives a crash unscathed than one that is 200g lighter but undriveable because it's too nimble and darty for me to drive consistently for 5 minutes.

I'm going to sound a bit arrogant in saying this but as a person whose day job is mechanical engineering and design, I don't really care about the overall opinion of someone who gets paid to drive a toy car around all day.

Yes, you do sound a little arrogant..... For all you and I know, Tebo, Cavalieri and the like could have Mechanical engineering degrees. However even if they don't, to ignore their hours of experience seems a little foolish - just because you don't understand how something works doesn't mean it doesn't...... If team drivers add weight, it's because they see it as an advantage. It's not there to make the cars look pretty.

I do agree with your comment that many people add weight to compensate for damper tuning - thinking back to my early days with my Lazer FS, I did that very thing. For 12 months I ran an extra 140g (sometimes even 200g) when I first swapped from NiMhs to Lipos. This was partly because at the time the loss of 140g of battery screwed up the weigth distribution of a chassis designed for NiMhs, and partly because I didn't have the track time to develop a whole new damper setup for a lighter car. With help from other racers, I've now got the car sorted for Lipos and only run 60g in the spine between the cells and it definitely jumps and lands better, plus changes direction quicker. HOWEVER, I still run the car heavy on occasion as the lighter car grip rolls more on high grip tracks, and when it goes over, it goes too fast for my poor reactions to catch. (Now there's a conversation to be had with a professional automotive chassis dynamics engineer - try and talk to them about grip roll and see what they have to say. I know...I've tried it....)

Also the heavier Lazer FS is usually more settled on very rutted and bumpy tracks. If I tune the light Lazer's springs and dampers to match the lower weight, there's insufficient damping to manage high speed low frequency bumps (i.e. a rolling hump on the straight) with the result that the chassis bottoms out and next thing I know the car is upside down having a 30mph crash....

I strongly agree with the comments others made about a heavier car being easy to drive as it slows the chassis's reactions down, especially as the only feedback we get about the car is behaving as we race is visually.

If you know how to balance your effective spring rates, you can compensate for anything.

Er....wrong. The problem here is that our "toy" cars have to deal with small high frequency bumps then next thing have to cope with landing from 5ft in the air. No 1/10th RC car damper can be optimised for both scenarios. Same goes for full size cars too, which is why adaptive damping systems and /or air springs are becoming common place on luxury / high performance cars. A common theme to every tuning guide, chassis dynamics book and conversation I've had with a pro driver is "suspension tuning is all about compromise".

I'm not saying I know the answers to your questions and I admire your quest to rethink & redesign the 1/10th buggy.....however I'd bet money that the many RC companies and racers around the world have been there and tried it before you, with the result that what we have now is the best compromise for the current 1/10th off-road racing scene.

[fredswain]

I'm not sure where you get the idea that I'm confused on mid motor cars. I have one! I said that rear motor cars already have so much rear traction that they can often lift the front wheels off the ground and hence can lose some of that grip and not suffer for it. That's why I said mid motor isn't as much of a downfall as many think it is. You are changing away from a format that has too much grip yet people complain because they would lose some if they went to mid. So what? You only need enough to do the job. You don't need excess and that is the problem with current logic. Today people think that more is better simply because there is more of it. Adding a little weight made me faster. I don't know why exactly but it did therefore it's better. Next time I'll add more weight and will do better yet.

It's obvious that there is a sweet spot for weight. The question is where is it? That sweet spot is also going to vary with design as you won't have the same perfect weight with any design tried. Clearly if the car were weightless there'd be nothing to hold the tires to the ground to generate grip. However at some point there is too much weight to be useful. Lighter weight built within the same strength parameters is always more reliable that the same car that is heavier.

My driving isn't perfect, that I'll admit to. However I see lots of people break cars so apparently it's not limited to just me. The track here (the nicest one) is very hard packed, near blue groove clay. It may as well be concrete with jumps. If you land wrong, you're going to break something. Pick the best driver out there. Name one of them. Anyone. They wreck and they break from time to time. To say that I broke simply because I'm lousy is a bit of arrogant presumption in itself. I'm definitely not perfect but everyone breaks at some point. Even the best guys. That excuse is a wash. Old tracks were slower. They were also far softer and didn't have these stupid double and triple jumps that allow you to fly through the air for a half an hour before landing again. I shouldn't be able to land on my wheels and have parts break. Yes I have had some break from wrecks too but just having things break on a good landing is a bit unacceptable.

I get it now. Thanks for setting me straight. More weight is always better. It always handles better, because it makes the car less responsive (and that's desirable apparently?) and I shouldn't ever question it since the pros (who are constantly changing things) do it right now. I apparently need to add lots of it and need to be the worlds most infallible driver since only an absolutely pitiful driver with zero driving talent would ever break anything at the track ever. Then I should wait for someone else to think of a better way to do it so I can copy them. In fact I should just copy someone else's setup and forget about the future. We've peaked in performance and I should accept that. That's how I'll be as good as they are. It's guaranteed. Got it! What was I thinking? A good car is a heavy one that is less responsive but that uses ultra hyper fast servos for increased responsiveness. So to be perfect I need to be heavy and then I need to run the fastest, most responsive components possible. It all makes sense now. The perfect balance. Who needs it when heavy and overpowered is the correct way to do it. Duh!

If that last paragraph sounds a bit stupid just remember, it's basically just the logic of many people today. When you step back and look at it from the outside, it really does seem a bit silly which is why I question it. Yes I'm arrogant. I always have been. It's also done very well for me in life since it has allowed me to look at things in a different way and find solutions that others didn't. I'm never content with the status quo. I'm not here proclaiming that I'm going to design and build a better rc car than anyone else ever has and hence revolutionize the industry. I'm not. I'm not planning to build or prove anything to the world. I'm still going to question it though and I'm going to encourage others to do so as well. I will be a bit harsh against many of the excuses out there simply because they are comments that signify no desire to improve. Some don't want to. I want to hear the thoughts of those that do. I don't like the excuse "because that's the way they do it".

[jwscab]

So did you get a chance to run the lighter car yet, or are you still working towards your goals?

at the end of the day, the guy getting the checkered flag is what counts, unfortunately. he might have been the only guy left with a running car, or the fastest in the pack, or *dare I say it* was just lucky....

I applaud the effort you are putting forth, but you appear to be ignoring some basic principles which have been shown to be proven time and time again on the track. To say you did something different just to be different is noteworthy, but if it's not consistently winning, then it's all a moot point.

classic examples are tesla vs edison, vhs vs betamax, apple vs android. doesn't matter if you have a better mousetrap if it's not catching mice....

[minichamps11]

I'm not sure where you get the idea that I'm confused on mid motor cars. I have one! I said that rear motor cars already have so much rear traction that they can often lift the front wheels off the ground and hence can lose some of that grip and not suffer for it.

No you didn't...your sentence was about mid-motored cars

An interesting thing is that people complain about mid motor setups in off road due to less forward traction during acceleration. If you've got so much forward traction that you are pulling the front wheels off the ground, you can stand to lose some forward traction!

If you meant to write it about rear engined cars then yes, what you're saying about the slipper makes more sense, but in the context of saving weight (which is what this whole thread is obviously about) there is a flaw in your logic. My original Kyosho RB5 was one of the best handling 2WD's I've ever owned running when NiMhs. 18 months later with Lipos, the car's weight distribution has moved rearwards far more than it was originally designed for, with the result that the front wheels pointed skywards pretty much every time I touched the throttle. If I backed off the slipper then a) it overheated b) I got left for dust by everyone who's fitted lead weight to their 2WD's and can actually accelerate and keep the front wheels on the ground. Bit of a pattern here......see it now?

BTW my comment about breaking your car due to bad driving was tongue-in-cheek, hence the smiley face. I'm guessing from your paragraph long response you missed it.....

It always handles better, because it makes the car less responsive (and that's desirable apparently?)

Yes! I can't drive many top driver's setups because I don't have the talent to handle a car with the responses they prefer. My off-road buggies could be tuned to change direction far quicker than they do, but I'd probably gain fractions of a second per lap versus an average loss of 5 - 10 seconds every time I need to be marshalled. When you have 1.6kg of plastic travelling at 30mph 30 metres away and your only feedback is visual, stability counts for a lot.

[fredswain]

I think the confusion over what I said comes from not realizing that I was talking about 2 different motor positions. I may not have been too clear on that although I thought I was. Yes I was referring to the slipper on a rear motor car btw. I mentioned a scenario that you said did in fact happen with your RB5. I stated that it is hard to remove weight from a buggy (rear motor) in a proportionate manner. In other words it is easy to remove weight from the middle of the car by using a lighter battery or other parts but very hard to lower weight at the motor and gearbox. This would mean that a lighter buggy (rear motor) will have a higher percentage of it's weight at the back if made lighter. A greater percentage of it's total weight is now at the rear than before. It is less balanced front to rear. It is for this reason that I then went on to suggest that for a lighter car, it would become more important to find a way to distribute it's weight more evenly front to rear which means making a lighter car that is mid motor. Once in mid motor mode, and due to the lightness of the vehicle, it will have a harder time getting forward traction. This is where motor and gear rotation direction in relation to the wheels comes into play. They will have a more pronounced effect on a lighter car than a heavier one and will definitely have to be taken into account.

The conclusion that I had come to based on these discussions is that in order for a very light car (2wd) to be made that worked decently well, it wouldn't look like the traditional rear motor buggies that we have today. It most certainly wouldn't be rear motor. It isn't as easy as just removing all the weight we can from our existing cars. Current designs have been getting heavier but have still remained the same basic designs. They are perfecting/improving existing car design and while there have been innovations they have still been primarily on the same basic package. With the traditional designs and tire compounds it would seem that there are some definite benefits in the handling department to adding weight. There is a point of quickly diminishing returns though so a heavier car just isn't always better. Clearly the longer more forgiving suspensions and added weight are designed to be more controllable at the much higher speeds that people run at today. 15 years ago the fastest cars at the IFMAR finals (modified btw) were hitting 27 mph on the long straight. That's slow today. It would be interesting if we can use good design to make a light car corner well yet through some aero treatments and a bit slower servo speeds make one that isn't hard to control at high straight line speeds. The best design change would be to find a way to limit servo speed as vehicle speed increases.

What I've been trying to figure out isn't how to make my existing cars as light as possible but rather what would it take to design a very good performing light vehicle. The reason I had weighed my own RC10 was not because I am trying to make it as light as possible. Not at all. I'm just building that car the way I've always wanted an RC10. It will probably end up within the ROAR weight limits. I'm mostly building it for reliability since I want that car to be one that I love when I'm done. The point in weighing it was to see what the car weighs and then to determine parts that could be done differently in order to shave weight. I also wanted to know how much weight the electronics contribute. Basically if a car wanted to be designed and built from scratch, what realistic weight would be attainable. Even if we can design and build a light balanced, very good handling car, the next problem is going to be the tires. Modern tires have evolved with the cars and are less suited to lighter cars than the older tires were. It's all about figuring what it would take.

[Charlie don't surf]

What was the purpose of setting up you car without oil in the shocks again? A weight thing?

[fredswain]

In order to determine spring rate balance between front and rear. It's not the static spring rate that counts but rather the effective spring rate. The front weighs less than the rear so the front gets a lower effective spring rate. The static rate may be higher but the front shocks are also mounted farther inboard and has less leverage on the arms. By figuring out what springs front and rear work in conjunction with shock mounting points to obtain springs that balance we can be assured that the springs are setup evenly. When you push down on the center of gravity on the car, both ends should go down at the same time. When you let go each end should rise at the same rate. If you drop the car from a few inches you want the front and rear suspensions to go up and down at the same rate. The rear being heavier may move farther but the point is that if the rear is moving downwards the front should be too and vice versa. The effective spring rate is balanced and it is possible to balance springs no matter the car setup. After you get this figured out you then add oil and work from there. Spring rates are just the starting point in tuning. Once you achieve balance, if you change a spring at the front you must do so at the rear. You don't increase spring rate at one end and not the other if it means messing up the balance.

There is a very methodical way to go about tuning that pretty much eliminates the guess work. It is still trial and error but it is done in a way that is according to a set order which makes things predictable and easy to anticipate. This technique makes it clear that shocks and springs are used to dampen bumps only. They are not cornering tools. Camber links are used to determine corner behavior and so forth and so on in a big list of other things. Everything has a certain job to do and you work them out one at a time.

[Charlie don't surf]

Why do both ends have to have the same rate of bound and rebound in relation to each other?
How do springs and oil not effect cornering?
What do you do about the jumps?

[Jirka]

Why do both ends have to have the same rate of bound and rebound in relation to each other?
How do springs and oil not effect cornering?
What do you do about the jumps?

No, the springs does not have to move car up and down as same time. This is only some academic stuff and that works nicely only when You grope Your car in kitchen table. But like You are guessing, You could use suitable front and rear springs and equal good driver with different driving style could use different spring rates on same track, no matter which level You are racing. Same kind of academic stuff is ackermann steering theory, works in parking lot but not when tires are sliding.

But l will get to the original subject, how to make a light 2wd offroad car that might even be competitive.

- Use so little weight on suspension arms, wheels and tires as possible. Make narrower rear tires and wheels, this is a must. I even once used on high bite soft sand track back in the days 4wd front tires, some Yokomo TR320, in rear on my Jrx Pro SE on national in qualifying and A-main. The reason was to make car more lighter, since the track did have long straights. I did even won Jukka Steenari with that. OK, Jukka was not a WC level driver on that day, but fast he was. That should tell that thing like narrowing rear tires works when environment (car, track, driving style) is right. Also use or make narrower front tires.

You could also use A&L style trailing arms in rear. With them You might get better acceleration and rear bite. Has anyone tried them on mid motor cars nowadays? I would like to hear some guru's opinion on this.

Use aluminium and titanium screws, pins, balls, drive shafts, outdrives etc. everywhere. All stuff that goes up and down should be light.

Smaller shocks might also work, like red Kyosho shocks from Optima. Since the car is lighter, shocks can be smaller too. Of course You have to found suitable springs and modify the pistons.

- On chassis as narrow as possible. Nothing outside inner suspension arm hinge pins, expect rear trailing arm mounts if they are used. Since the car is light, mass outside hinge pins makes chassis tilt more than it should. See Durango, Losi 22 and this: http://www.oople.com/rc/photos/midlosi/imagepages/midlosi03.html . Do a body from big Coke bottle so is is narrow too.

- If You have stability problems in high speed play with wings, rear and front. Some years ago front wing was commonly used, but now it is replaced with cab forward bodies (The uglyness spreads....).

- Mid or rear motor? I don't know. My guess is rear motor is better, lets say with 75% probability. Why? See some videos at latest races, like 2WD ROAR Nats or worlds from this year. You could not make them significantly better than they are now, 2wd offroad cars reached their highest level more than 10 years ago to me. Better then average story about this mid or rear motor car is here: http://www.youtube.com/watch?v=nDjGPfyqOi0.

Jirka

[fredswain]

Balance tuning is tbe best way to do it. There was a thread on rctech that got pretty in depth about the technique and it took many many pages. It's not simple to explain in only a couple of paragraphs. It's based on tuning methods of real cars. Physics is physics and doesn't care about scale. The people that argue agaist that are usually the people that don't know what they are doing. Do you need to have everything balance? No. Then again you don't need to have a good driving car either. Everything on a suspension has a specific job to do and the key is to understand what is supposed to do what. Your shocks can't be optimized for bumps and also optimize cornering. They can only do one thing well and if you try to make any component do multiple jobs at best you have a compromise which will typically cause you to make another compromise somewhere else to fix the problem that you created.

I would argue that if you want a good handling car, IT ABSOLUTELY POSITIVELY HAS TO BE TUNED FOR BALANCE! That may as well be rc car law. Anything less is a compromise and a compromise is when nothing does anything well.

[minichamps11]

The best design change would be to find a way to limit servo speed as vehicle speed increases.

Every car has one of those, it's called your thumb....(or hand, if you use a wheel Tx)

[mikedealer]

ive seen alot of these units used in offroad buggies, if i have trouble steerring this is the way to go

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMVE1&P=ML

[Bongo Fury]

Springs aren’t involved in cornering? What about roll stiffness?

[minichamps11]

Springs aren’t involved in cornering? What about roll stiffness?

Agree- Fredswain's statement mostly made sense until he wrote that....

Damping afects the way the car begins to roll. For example, a car with no damping will still run in a straight line and go over small bumps reasonably, if a bit uncontrolled, but will want to collapse every time the smallest steering input is given. Damping controls the way a car enters a corner by dictating the initial rate of roll … increasing damping will give a more direct feeling to the front end and a looser felling to the rear … decreasing damping will do the opposite.
Springs control (along with the roll centre) the overall amount of roll the car has before all the forces balance and the car stops rolling further. Obviously you have to factor ARBs into the springing if they were fitted....