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Old 07-18-2007, 09:32 PM   #4936
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Originally Posted by steve eaves View Post
Do you mainly use short arm set up for rubber?
I have always run long front arm, and just about always long rear as well, it just helps the car be more consistent and grip better if you ask me....i have run short rear arm on occasion to get it to rotate differently, but it seemed to always be faster with long arm.
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Old 07-19-2007, 08:17 AM   #4937
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Originally Posted by rcracingkid View Post
I have always run long front arm, and just about always long rear as well, it just helps the car be more consistent and grip better if you ask me....i have run short rear arm on occasion to get it to rotate differently, but it seemed to always be faster with long arm.
I concur.
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Old 07-19-2007, 08:18 AM   #4938
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Originally Posted by Besercoe View Post
That is awesome, a slab of steel on a racing car. In the owrld of graphite, titanium and alloy who would think this was a required part
The idea of this part is to bring the weight of the car up to minimum while running a lipo battery.
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Old 07-19-2007, 08:23 AM   #4939
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I had a discussion with a R&D person from another company who acquired a Type R and dissected it and the way I understand it is this. The arms for the type R are too short for asphalt by 1/4 inch either side 1/2inch total this is the length of the arm not including the hub and hex. In fact getting wider hexes doesnt solve the overall situation because there is something to do with the dynamic forces acting upon the distance between the arm perpendicular to the shock tower............ burn out for my brain right there.....Generally speaking the longer the arm the better the traction in med-low grip situations and the narrow the arms the better for high traction situations hence the Losi on carpet is a gem. Making the arms shrter will apparently provide yet more traction on carpet but as with anything there is a point of critical mass whereby too much of anything can be a bad thing.

I am not a designer nor mechanical engineer and I didnt understand, to some extent, all of the physics involved and why this is so, however the person providing the information is and is also a factory driver and therefore I will take his word at face value. If Ron, Todd or Chadwick or anyone else for that matter want to jump in and fill the rest of us in please do so.
Obviously someone from another company is going to have a very biased opinion on our arm length as it is not an industry standard. They also can not argue about our centerline weight either. I can tell you this, we tested short arms on the XXX-S to prior to building the JRXS and it made the car incredibly faster. Our first thoughts were, if the center line does not work with the JRXS we will make a XXX-S with a short arm setup for production.

With the JRXS we were struggling with grip on low to medium surfaces. That is why we developed the Type R, motor in the back of the car. The gyrotational effects of the motor in the rear increased grip amazingly.
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Old 07-19-2007, 08:45 AM   #4940
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As a mechanical design engineer myself, I can tell you that no amount of analysis, or computer simulation will ever duplicate the real-world dynamics that act on anything you design.

It will get you close, but there always conditions that cannot be accounted for. It's why civil engineers design bridges to be a whole lot stronger than what they need to be....a safety factor. It's why these teams do so much testing. Most of what happens in real-life flies in the face of what's expected.

I can tell you here where I work, we have brilliant PhDs that come up with all kids of models and calculations. However, when we do real-world testing, the numbers are ALWAYS different.

So because an engineer can't get an arm design to work on his car layout, doesn't mean it won't work on another. Since the Losi is so radically different than the others, you almost have to throw all previous conventions out the window.

The fact is, the car works...no matter what anyone tells you with regards to the arm length. And it works on the asphalt too....I saw 2 Losi cars make everyone look silly at a big asphalt race last month. To me, that was more important than seeing what the Hired Factory Guns do with it...since they could drive a shoebox with wheels and look good.

Last edited by McSmooth; 07-19-2007 at 08:57 AM.
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Old 07-19-2007, 09:34 AM   #4941
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The fact is, the car works...no matter what anyone tells you with regards to the arm length. And it works on the asphalt too....I saw 2 Losi cars make everyone look silly at a big asphalt race last month. To me, that was more important than seeing what the Hired Factory Guns do with it...since they could drive a shoebox with wheels and look good.
I was there. It's hard to beat the type R. And it's even harder with Fairtrace and Schreff behind the wheel. That race was one of the best field of drivers I've ever competed against. No wonder I ended up where I did. You makin' it up to the Bowl this weekend?
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Old 07-19-2007, 09:36 AM   #4942
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I was there. It's hard to beat the type R. And it's even harder with Fairtrace and Schreff behind the wheel. That race was one of the best field of drivers I've ever competed against. No wonder I ended up where I did. You makin' it up to the Bowl this weekend?
Unfortunately, I won't be able to make it. It's quite a haul from this side of the state, and I've done all my travelling for the summer. It's pretty much Vegas prep and the occasional nitro race for now.
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Old 07-19-2007, 10:05 AM   #4943
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I am running Hodges 06 nat's setup and was curious about a couple of things....he has the front hex at .225 and the rear at stock...if I take the rear out with the .195...wil that make it a little more stable through the turns? Also, with reguard to Caster what affect does increasing the angle have (go from 4 to 6)? and conversly from 6 to 4?
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Old 07-19-2007, 10:15 AM   #4944
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Originally Posted by rcarmchl View Post
I am running Hodges 06 nat's setup and was curious about a couple of things....he has the front hex at .225 and the rear at stock...if I take the rear out with the .195...wil that make it a little more stable through the turns? Also, with reguard to Caster what affect does increasing the angle have (go from 4 to 6)? and conversly from 6 to 4?
The wide wheel base of the front tires is to give your rear more stability throughout the corners. I've always liked a shorter width all the way around (.165 hexes), this allows you to carry more speed all the way around the track.
Caster is relevent to the speed you enter and exit a corner where more caster will bring your steering back to zero quicker less caster will decrease grip and make your car rotate on high bite surfaces.
So ideally if you are running a wide wheel base you could possibly get away with less caster (4 deg.) depending on surface conditions.
Peace,
C
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Old 07-19-2007, 10:16 AM   #4945
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Originally Posted by mojoman View Post
I was there. It's hard to beat the type R. And it's even harder with Fairtrace and Schreff behind the wheel. That race was one of the best field of drivers I've ever competed against. No wonder I ended up where I did. You makin' it up to the Bowl this weekend?
And you'll get to see me and Larry battle it out again this weekend at the Bowl.

And yes, there is nothing wrong with the car. Everyone can be a skeptic due to the car being completely different than everything else out there. Believe me, I was a skeptic too. I usually base a car on how well it does on asphalt. If you get it to work good on asphalt, where setup is the hardest, it will work on any surface. Larry and I have been working really well together with setups and results show. The Bowl will be no exception. The progress we made last week was awesome considering the uniqueness of the track. I'm definitely looking forward to carpet now too. The stuff we have learned in the past few months is going to help infinitely on carpet.

Anyone that has a Losi car and needs a hand with setup, just stop by and visit us. We're more than happy to help people.
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Old 07-19-2007, 10:43 AM   #4946
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Originally Posted by McSmooth View Post
As a mechanical design engineer myself, I can tell you that no amount of analysis, or computer simulation will ever duplicate the real-world dynamics that act on anything you design.

It will get you close, but there always conditions that cannot be accounted for. It's why civil engineers design bridges to be a whole lot stronger than what they need to be....a safety factor. It's why these teams do so much testing. Most of what happens in real-life flies in the face of what's expected.

I can tell you here where I work, we have brilliant PhDs that come up with all kids of models and calculations. However, when we do real-world testing, the numbers are ALWAYS different.

So because an engineer can't get an arm design to work on his car layout, doesn't mean it won't work on another. Since the Losi is so radically different than the others, you almost have to throw all previous conventions out the window.

The fact is, the car works...no matter what anyone tells you with regards to the arm length. And it works on the asphalt too....I saw 2 Losi cars make everyone look silly at a big asphalt race last month. To me, that was more important than seeing what the Hired Factory Guns do with it...since they could drive a shoebox with wheels and look good.
OK now were getting somewhere, let me rephrase the question to take some of the confusion away.

What effect does legnth of the a-arm have on a car. Ignore shock positioning, and its effect on shock forces as this can be the same. But what really are the effects of the overall length of the a-arm and why is there a difference between a longer arm or shorter arm and hex which equates to the same legnth of the a-arm. Not sure if Im asking the question right. but the question is not who has the best car and what is right or wrong its more of a theoretically speaking why is this the case?

For those of you like myself with small children look at me as the one saying "WHY?" everytime someone says you should do this........ I like to understand the principles behind things not just that it works or doesnt work but WHY does it work? Maybe I should change careers

Last edited by GCracker; 07-19-2007 at 10:54 AM.
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Old 07-19-2007, 10:57 AM   #4947
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In its simplest form, the suspension on our cars act like a 4-bar linkage. 3 rigid bars (arm, hub, camber link) and the fixed bar (chassis).

By changing the length or mounting location of any of the 3 rigid bars, you change the dynamic of how they work in relation to each other.

Even though you might have the same overall "length" of a-arm, there's still a change in geometry since you moved the pivot points as well.

http://en.wikipedia.org/wiki/Four_bar_linkage

There are all kinds of 4-bar linkage simulators out there, where you can change the links around and see the effects on velocity, angular acceleration, etc.
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Old 07-19-2007, 10:58 AM   #4948
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To me, that was more important than seeing what the Hired Factory Guns do with it...since they could drive a shoebox with wheels and look good

True True
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Old 07-19-2007, 11:00 AM   #4949
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Originally Posted by McSmooth View Post
In its simplest form, the suspension on our cars act like a 4-bar linkage. 3 rigid bars (arm, hub, camber link) and the fixed bar (chassis).

By changing the length or mounting location of any of the 3 rigid bars, you change the dynamic of how they work in relation to each other.

Even though you might have the same overall "length" of a-arm, there's still a change in geometry since you moved the pivot points as well.

http://en.wikipedia.org/wiki/Four_bar_linkage

There are all kinds of 4-bar linkage simulators out there, where you can change the links around and see the effects on velocity, angular acceleration, etc.
You the man McSmooth! see I knew someone could answer my question, I just have to ask it in the right way DOH!!!! hmmmm beer

I owe you a beer thanks man see you in the fall.
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Old 07-19-2007, 11:15 AM   #4950
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Originally Posted by McSmooth View Post
In its simplest form, the suspension on our cars act like a 4-bar linkage. 3 rigid bars (arm, hub, camber link) and the fixed bar (chassis).

By changing the length or mounting location of any of the 3 rigid bars, you change the dynamic of how they work in relation to each other.

Even though you might have the same overall "length" of a-arm, there's still a change in geometry since you moved the pivot points as well.

http://en.wikipedia.org/wiki/Four_bar_linkage

There are all kinds of 4-bar linkage simulators out there, where you can change the links around and see the effects on velocity, angular acceleration, etc.
Wow. I didn't think I'd see the day when four bar linkages were mentioned in an rctech post. Awesome. Now we just need a circle from Team Much "Mohr" Racing and we're in business. Sorry, bad ME pun.

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