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OneTimeCRX
04-06-2005, 10:32 PM
I've had my Half8 for a couple days now, and here are my initial impressions:

- The build quality and options for tuning are very good out of the box. The manual is very clear as well.

- The car is on the heavy side, so the first thing I did was put it on a diet. I removed the fake heat sink and the tops of the battery holders. On a related note, at the local Kyosho store three weeks ago I saw a very modified version of the Half8, and it had an aluminium fake heat sink instead of the plastic one that comes with the car. Very nice looking, but it's unnecessary weight!

- The suspension is way too soft, but fortunately the kit comes with spring spacers. I inserted one of the thickest spacers for each front damper, and 3/4 of the thickest for each of the rear dampers. The car still bounces a bit since the dampers have no oil in them, but adding the spacers improves this.

- The gears have absolutely no lube on them. I got some uber-expensive grease from work today, and covered all the gears with it. It makes a noticable difference in speed, smoothness, and noise.

- I decreased the toe angle for the rear wheels to 1 degree (part "A"), and now the rear ends slides out more. The car is still very stable.

- Alkalines really suck. I almost didn't buy the car when I tried it out with alkalines at the store. Luckily I read here that rechargeables are much better, so I bought the car anyway. I use 2400 mAh NiMH AA batteries and the performance is ok now.

- The car smells nice. Some kind of chemical smell that's probably addictive and harmful.

- The slipper clutch slips way too much and is difficult to tighten. It's necessary to jam a small flathead screwdriver between the gear's teeth to hold the shaft stationary, while using some pliers to spin the nut. The tool provided by Kyosho is useless; I don't know what they were thinking by making it out of plastic.

- The steering servo is a bit slow but fortunately Kyosho provides adapters for other servos. The controller is cheap but it does the job well enough to begin with.

- The front suspension has good ackerman geometry and the bump steer is designed properly for stability. It's good to see that Kyosho took the time to design the geometry well from the start.

- There is a lot of slop in all moving parts (suspension, drivetrain, etc), but I suspect that future hopups will fix this.

- The lower suspension arms look to be poorly designed from the point of view of max strength with lowest mass. It looks like a considerable amount of mass can be removed, which is especially important since this is unsprung mass. One of these days I'll run the arms through some FEA simulations to see what can be optimized.

- I noticed that the manual mentions nothing of a battery protection unit being required for use with an 8-cell pack. Theoretically this means that the ESC should be able to handle 9.6 volts, otherwise if it breaks they'll have to fix the electronics under warranty.

- I also noticed that 8 NiMH AA batteries sums up to 9.6 volts exactly. Has anyone tried to add 2 more batteries to the AA battery pack? Theoretically this should work as long as you wire up the batteries correctly.

- A final note, I'm very happy with this kit. It was expensive, but the quality and design is worth it.

halfEIGHT
04-07-2005, 12:30 AM
Nice review OTCRX. Great tip RE the slipper clutch, I'm going to try that right now - mine is very loose and I was unable to adjust it before now. :cool:

BitHed
04-07-2005, 01:18 AM
...OneTime...Great review...nice and simple and tells us what we want to know...Good job...

...ditto on the slipper clutch...mine is tight but can be tighter...there are different threads on it on halfeight.com...i am coming VERY close to just closing it up with some CA...Mine is squealing with a 16 tooth pinion...

...same here...un-needed weight s gone...the battery doors, heatsink, the post for the heat sink, everything...still heavy though...

...battery and the BPU still havent been delivered to shops yet...YES in theory the stock esc can take 9.6 volts...I have tried it with 8 cells and it was ok...I didnt thrash it at 9.6 though...

...lubed the diffs but i am thinking the grease was too light...might try something heavier later...its MUCH quiter and smoother...the MAIN problem is the center diff / slipper...

BitHed
04-07-2005, 01:28 AM
...I tightened the servo saver some and the steering is good now...no complaints...new servo on the way though...also slightly loosened the screws that go from UNDERNEATH the knuckle...this works quote good...also replace front steering rod with adjustable unit...REALLY nice now with some more toe-in...Stock was slightly toe-out and front right was squiffy...Great now though...There was something else i wanted to add to OneTime's comments and I cant remember what it was now :(

BitHed
04-07-2005, 01:35 AM
...ok i remembered now...

...SLOP...GIVE...PLAY...its been all built in on purpose...it means the noobies and the bashers dont break everything first time out...We can shim as we go but there will be some play over the whole thing...Just check the play in your rear lower arms...they are all over the place...lol...I have come to like PLAY because it oftens saves me :o

KURTMEYER69
04-07-2005, 03:12 AM
i sure would like to see some pics guys....ken

OneTimeCRX
04-07-2005, 09:27 AM
A little toe-out in the front is there for stability's sake. Toe-in in the front would result in a car that's unstable - at least this is true for real cars. Toe-in in the rear is also there fore stability. By "stability" I mean that all real cars must be designed to understeer slightly. Providing toe-in in the front will probably give you better initial bite when turning, but will also make the car more nervous and twitchy.

This is the case for real cars, but who knows, maybe the opposite applies for RC's. (Afterall, most of the instability is due to driver reactions to feedback in the steering wheel that doesn't exist in a remotely controlled car.)

Regarding tightening the slipper, I jam a small flathead screwdriver between the teeth of the larger gear, with the screwdriver resting on the plate at the base of the antenna. By placing the screwdriver this way, there is very little risk of damaging the gear. It also becomes much easier to tighten the nut with pliers.

Kurt, sure I'll share lots of pics. Is there anything specific you'd like to see?

chrille
04-07-2005, 01:38 PM
OTCRX, wrong there about toe-in/out, with more toe-in on the front the car would be more stable! :) and with more toe-out it would get some more steering and braking stability... anyway, good review! :)

KURTMEYER69
04-07-2005, 02:28 PM
A little toe-out in the front is there for stability's sake. Toe-in in the front would result in a car that's unstable - at least this is true for real cars. Toe-in in the rear is also there fore stability. By "stability" I mean that all real cars must be designed to understeer slightly. Providing toe-in in the front will probably give you better initial bite when turning, but will also make the car more nervous and twitchy.

This is the case for real cars, but who knows, maybe the opposite applies for RC's. (Afterall, most of the instability is due to driver reactions to feedback in the steering wheel that doesn't exist in a remotely controlled car.)

Regarding tightening the slipper, I jam a small flathead screwdriver between the teeth of the larger gear, with the screwdriver resting on the plate at the base of the antenna. By placing the screwdriver this way, there is very little risk of damaging the gear. It also becomes much easier to tighten the nut with pliers.

Kurt, sure I'll share lots of pics. Is there anything specific you'd like to see?u can post all if possible...thanks ken

OneTimeCRX
04-07-2005, 10:29 PM
I just wanted to share some pics quickly - will reply about the toe-in/out issue in the front suspension later!

H8 pics (http://www.pbase.com/onetimecrx/half8_mini_inferno)

ruknd
04-07-2005, 10:54 PM
I just wanted to share some pics quickly - will reply about the toe-in/out issue in the front suspension later!

H8 pics (http://www.pbase.com/onetimecrx/half8_mini_inferno)
looks like someone got their finger stuck in the pinion :p

KURTMEYER69
04-07-2005, 11:47 PM
thats great!thanks post more...ken

KURTMEYER69
04-07-2005, 11:49 PM
is that the stock motor u are using? ken

chrille
04-08-2005, 10:24 AM
Here is some pics i got! :) The pictures (http://st35.startlogic.com/%7Ersbseaaa/forum/viewtopic.php?t=352&start=25)

And KURTMEYER69, its the stock motor he runs! ;)

OneTimeCRX
04-08-2005, 08:34 PM
Ruknd - The red stuff you see on the gears is some grease I put on the gears. It really helped increase the acceleration and top speed of the otherwise stock car!

Chrille, I'm quite certain that toe-out in the front wheels is more stable. The reason I know this is because I've worked on designing a suspension system for a sports car (a real car, that is) along with the help of the head chassis engineer at the champion rallycross team in Europe, and this topic was discussed between us in detail. We've also done some ADAMS/Car simulations that support this fact.

Here's a looong explanation:

To explain why toe-out is more stable, first we have to agree on some points:

1. That the wheel that contributes the most while in a turn is the wheel with the most weight shifted to it. For example in a turn the outside wheel has the most weight shifted to it, so it contributes the most lateral forces.

2. The a car is considered more stable when it wants to straighten itself out instead of increase its turning rate. In other words, a stable car defaults to understeer.

3. In a toe-out condition, the left wheel points to the left and the right wheel points to the right.

Now for the explanation:

- Assume there's a small disturbance causing the car to shift its weight slightly to the left wheel. This can be caused by a bump in the road, the driver twitching the steering wheel a little, etc.

- Since the weight shifted a little to the left wheel, the left wheel becomes dominant (see point #1). The left wheel is pointing to the left (point #3), so the car turns a little to the left.

- This shifts the weight to the right wheel (because it's the outside wheel in a left turn), which is pointing to the right (point #3). This turns the car to the right, which shifts the weight back to the left. Then the cycle begins again, but to a lesser degree.

- The alternation between turning the car slightly to the left and right and left again has the effect of straightening out the car since it can't turn very much before the weight is shifted to the other side and the car begins to turn in the opposite direction. Therefore with toe-out the car is more stable (see point #2).

Just to make things complete, now lets look at a toe-in condition, with this point:

4. In a toe-in condition, the left wheel points to the right and the right wheel points to the left.

To explain:

- Assume there's a small disturbance that shifts the car's weight slightly to the left wheel.

- Since the left wheel is pointing to the right (see point #4), it makes the car turn to the right.

- This causes more of the car's weight to shift to the left wheel (point #1).

- This in turn causes the car to contribute more to the lateral forces since it's the outside wheel in the turn, which causes the car to turn even more to the right.

- Turning even more to the right causes yet more weight to shift to the left wheel. This cycle continues until the car turns all the way to the right; in other words the car spins out of control. Therefore the toe-in condition makes the car unstable.

Stability (toe-out in the front) of course is important for street-legal cars, since most normal people can't safely drive unstable cars. This isn't necessarily true for race cars though, since a small amount of instability can cause the car to react more quickly (causing more "bite" at the initial turn-in).

So it might be the case that a little toe-in in the front is good for a RC car when the driver wants a more agile and responsive car in turning, but toe-out for stability should still hold true.

chrille
04-08-2005, 09:28 PM
When i read that ill understand exactly how you thinks! But how much you even tell me that its so, i have still been driving 1:10/Mini-Z for about 5 years and there you ALLWAYS uses toe-in ig you want a more stable car! :) Thats because the car plogar(sorry, but i cant find the engligs word for this, but youll understand OneTimeCRX!;)) and therefore the car becames more straightline/high speed turn stable! :)

OneTimeCRX
04-08-2005, 09:51 PM
Plogar = ploughs, yeah I understand. :)

My experience is completely in real cars, not RC cars. It's probably true that some of the principles that apply to real cars don't apply to RC's, so I'd say that your experience is probably more useful than mine! :D

halfEIGHT
04-08-2005, 10:05 PM
I just wanted to share some pics quickly - will reply about the toe-in/out issue in the front suspension later!

H8 pics (http://www.pbase.com/onetimecrx/half8_mini_inferno)

Just wanted to let everyone know that you can upload pics to your own Member Album here:

http://halfeight.com/gallery/index.php

Once you've created your Album, add a link to your Signature so that people know where to find it (like I've done below)! :)

chrille
04-08-2005, 10:18 PM
Plogar = ploughs, yeah I understand. :)

My experience is completely in real cars, not RC cars. It's probably true that some of the principles that apply to real cars don't apply to RC's, so I'd say that your experience is probably more useful than mine! :D

Thanks! Yep, but its a little strange that it can be so totaly different betwen 1:1 and 1:10! :)

Thomas-no
04-09-2005, 11:31 PM
My experience with mini-z is the same as crille, mini-z is more stable with toe-in.
But my experience with 1:1 racing is the same as OneTimeCRX, 1:1 cars is more stable with toe-out. :confused:

12 year racing go-cart.
4 year racing 1:10 Track and 1:12 Track
3 year racing 1:1 Formula 3.
4 year racing 1:27 mini-z

Thomas-no
Ballerud MiniRacing
www.miniracing.no

BitHed
04-10-2005, 02:51 PM
...i dont know ANYTHING about 1:1...You put gas in, turn the key, it breaks and you take it to the garage guy...

...I too 'grew up' on the Mini Z platform and i would spend hours trying to get my toe-in right...

...BTW sometimes when i accelerate the front wheels will splay outwards anyeay so i need to counter that a bit...I feel that with so many different parts to adjust the Mini Inferno is a LITTE tricky to get right and will give noobies LOTS of homework but the benefits once its dialed in are excellent..

OneTimeCRX
04-10-2005, 03:57 PM
I agree, all the options for tuning the suspension alone will make it difficult to optimize. With all the variables available, I wish that Kyosho would have included coordinates of all the hardpoints so that I could run some suspension simulations. It's much easier to tune a suspension when you can see graphs of all the movments IMO.

chrille
04-10-2005, 07:16 PM
But if you are a newbie, you dont have to adjust every single wheelangel! ;) But i love that you can adjust everything! :D

halfEIGHT
04-10-2005, 07:20 PM
Yep, it's set up really nicely out of the box! :cool:

BitHed
04-10-2005, 09:04 PM
...very true....which is what they wanted to do you know...Great for noobs but with enough interest to keep the maniac crowd happy...I think its achieved that for sure...

chrille
04-10-2005, 09:38 PM
BH, if thats what they wanted the car to, then they have succeded!! :D I just love it! Cant wait til wednesday when im gonna drive it on the 1:10 carpet cource again, just to hope that Fire will be there to...

m18racer2003
05-05-2005, 06:40 AM
OneTimeCRX, I don't mean to prove you wrong but i've always believed that toe-in increased stability. One this to get clear, the car will go in the direction the front of the wheels are pointing... you are turning right, wheels are pointing right, step on the gas, car goes right and vice versa.

You are absolutly correct when you say rear toe-in increases stability because the right and left wheel are pointed towards the center of the car, right wheel pointing towards center, left wheel pointing towards center, so rear will "center" itself when it breaks loose, being stable..

Regarding toe-out in the front, the front of the wheels are pointed away from each other. right wheel pointing right, left wheel pointing left. That causes the wheels to pull in different directions, causing it to be unstable or twitchy.

where as opposed to toe-in, the front of the right and left wheels are pointing toward the center or the car, so there for better straight line stability and more corner grip for RWD cars (I say for RWD car bc rwd cars tend to oversteer and toe-in creates oversteer which balances out the car and a balances car is a good handling car.

Toe-Out in the front is used in FWD cars, which tends to understeer, Toe-out increases turn in response, (which will cause a RWD to be twitchy and oversteer, therefore considered "unstable") and exit corner grip, so more front grip to a car that tends to oversteer (FWD) balances out the car, and again a balanced car is a good car.

here's a link, renforcing my theory. thank you

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=4

BitHed
05-05-2005, 10:52 AM
...great post m18racer...to the point, basic and easy to understand while being full of good indormation...If Martha Stewart was explaining toe-in she would have said the same things :o Good job and welcome to the boards...Now I just have to sit down with my buckle wrench and see what happens :D

OneTimeCRX
05-07-2005, 12:29 AM
Thanks for the reply M18racer2003, but I still stand by my statements. Although the tirerack link looks like it's factual, actually it's quite wrong with some of the details. I don't want to make it sound like I'm bragging or anything, but to qualify my statements it might help to know some credentials about myself - I have a masters degree in automotive engineering, and I'm currently teaching university courses in the subject. I've also done extensive suspension design in collaboration with a top suspension engineer in the industry, as well as conducted simulations to prove the fact.

Although simplifying the scenarios is helpful with understanding the basic concepts, the fact is that vehicle behaviour is extremely more complex than can be explained in a forum post. If you look at concepts like weight transfer, roll center, bump steer, slip angles, tyre deformation, etc, and especially look at the equations that describe these components, you'll see that it's not as simple as thinking about which direction the tyres are pointing. Actually if you look closely it becomes amazing at how easy it is to design suspensions to be unstable.

I think I mentioned this before, but "stable" is when a car understeers at least a little in all situations. Any kind of oversteer is considered unstable, even if it's favourable for quicker turns. In other words, "stable" does not equal "good handling". "Stable" equals "safe from mistakes".

I can find some literature to back up my statements, but not right now since all my books are in the office. However if you know any suspension engineers for a big car company you can ask about toe-out in the front and the answer will 99% be the same.

It's good to hear your opinions in any case; I find these discussions interesting. :)

m18racer2003
05-07-2005, 03:28 PM
Intresting reply, OneTimeRCX. I totally agree with what you're saying, stable is more of "safe from mistakes" rather then "good handling" I am not an expert in this field. I'm a 20 year old business major in California, but I'm a really big car fanatic.

I guess it was just really weird hearing you say something opposite to my belief when i've tested toe angles and stuff on my 1/10 nitro and when my car is oversteering exiting a corner, add some front toe-in.

I assume, you were referring to more street car type situation and i was referring more to racecar type situations. I never really thought about stable as being "safe from mistakes" but now i understand where you're getting at.

Thank you for broadening my perspectives alittle more into the automotive world.

OneTimeCRX
05-08-2005, 11:31 AM
My experience lies in full-size vehicles, mainly for road use (passenger cars, sports cars, etc). It seems that the rules that stand for full-size cars don't always apply for RC cars. There could be many reasons for this, for example in RC the steering is an open-loop system, plus at smaller scales the forces and coefficients do not scale down proportionally (this would require all equations to be linear, which they are not).

In the automotive industry, there is a legal requirement to design cars that understeer in all normal conditions. This is a primary goal to meet in suspension design. Once this is met, then the engineers can try to minimize the understeer if the type of car asks for it (such as in a sports car). Understeer can be minimized, but oversteer is never reached. If oversteer is reached, then the car will not be road legal.

Technically oversteer is defined as the situation when the slip angles for the rear wheels exceed the slip angles for the front wheels. When you're driving and you feel something that you might consider as slight oversteer, in reality you're probably still understeering a little. It only feels like it's oversteer because you feel the rear wheels sliding. In reality the front wheels are sliding a little more than the rear but you don't notice it since the front wheels are also pointed in towards a turn. If you do reach oversteer, you'll notice it because all of a sudden you're fighting to regain control of the car and basically ruined your lap time.

To make things more complicated, you also have to take into account ackerman geometry. Positive ackerman (where the inner wheel points more towards the center of the turn) is good for lower speeds, but when you reach higher speeds negative ackerman is preferred. This is because at a certain speed the slip angle for the outer wheel becomes much larger than for the inner wheel, and keeping in mind that the outer wheel applies the majority of the forces (since there is a weight transfer to this wheel), negative ackerman compensates for this increased slip angle. Adjusting toe-in can somewhat compensate for the wrong ackerman geometry, so this might be what's happening in your case.