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Old 09-09-2003, 09:57 PM   #1
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Default Chassis Dynamics and Rollcenter Discussion!

Ok, I have a question...i'm not the most versed with chassis dynamics for RC, as I come from an full size automotive background.

I am working on developing a chassis and have another chassis that a friend developed out for testing with various reviewers.

A question that has come up is this.

The chassis kit is based on a TC3 from AE. Now, most aftermarket kits out there(warpspeed V1, IRS) are a 3.0mm deck with .5mm milled out where the bulkheads sit. This is supposedly to retain stock center of gravity and rollcenter. Now, the V2 Warpspeed is comming out with a 2.5mm main deck, and from what I can infer from my own research, is so that no milling is necessary to keep the stock COG and rollcenter...I may be wrong, not actually having that chassis in my hand.

Now, my question is, on a graphite plate, granted that on the stock TC3 chassis, the bulkheads both sit on the same plane, what is the advantage of milling out .5mm of a 3mm deck to get the 2.5mm, or using a 2.5mm deck? Couldnt we retain the same effect as using a 3mm unmlled deck?

If we used a 3mm unmilled deck, granted that the bulkheads stay at the same plane, angles for all the arms and suspension stay the same angles and geometry, wouldnt the NET effect of the setup be that the bottom of the chassis be .5mm closer to the ground, and the electronics would sit .5mm lower then a milled 3.0mm deck, lowering the COG and the rollcenter??

I am confused, as a tester asked me this question, and I cannot seem to find an answer for it.

If you need further clarification of my question, let me know...as this is one heck of a confusing topic.
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Old 09-09-2003, 10:13 PM   #2
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I think it is a combination of Stiffness of the chassis, and Low Center of Gravity.

With a 3mm Chassis milled out .5mm, you have the best of both worlds.
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Old 09-09-2003, 10:25 PM   #3
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Old 09-09-2003, 10:27 PM   #4
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Default Hmm

I'm not too sure if I get what you mean. Why is a milled 3mm deck the best of both worlds in comparison to an unmilled 3mm deck? The way I look at it, an unmilled 3mm deck sits closer to the ground and the electronics are .5mm closer to the ground also. A milled 3mm deck that is milled by .5mm would effectively have the electronics .5mm higher then an unmilled deck...

Let me know
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Old 09-09-2003, 10:46 PM   #5
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I think I get what you're saying but you have to look at minimum ride heights. Take the stock 2.5mm chassis setup to run at 5mm (often the minimum by regulation) to get everything sitting at the same height on a 3mm chassis you either mill it out 0.5mm like they do, so the bottom of the chassis is at the same height and so is everything sitting on it. Or you have everything sitting at the right height but the bottom of the chassis is at 4.5mm, which would be illegal in a lot of places, so you have to raise the whole car 0.5mm, raising the CG and adjusting the geometry of the suspension.
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Old 09-09-2003, 10:55 PM   #6
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Why don't you just mill out the area the electronics and motor sits in so they will be at the same height as the 2.5mm chassis and retain the same COG while still having the center and sides of the chassis 3mm which will result in a car almost as rigid as if it weren't milled? The battery slots will still be bevelled to where the battery sits almost flush to the bottom by the racers- which keeps the battery COG the same.
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Old 09-09-2003, 10:57 PM   #7
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Quote:
Originally posted by BigDogRacing
Why don't you just mill out the area the electronics and motor sits in so they will be at the same height as the 2.5mm chassis and retain the same COG while still having the center and sides of the chassis 3mm which will result in a car almost as rigid as if it weren't milled? The battery slots will still be bevelled to where the battery sits almost flush to the bottom by the racers- which keeps the battery COG the same.
thats what they mostly do do, and he's asking why
I think.....
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Old 09-09-2003, 11:06 PM   #8
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Default Ahhhh

Ok, Herminator,

That makes alot of sense. Without keeping the minimum ride heights in mind, the unmilled 3mm deck makes sense in that it is a lower COG overall. Because the bulkhead ride height is independant of where the actual chassis sits, that makes it one less variable. Regardless if the chassis is 2mm or 10mm, if the bulkheads sit on the same plane, the height from the bottom of the bulkhead to the ground will remain the same.

With the minimum ride height regulation in mind, however, I do see the point in a unmiled 2.5mm deck or a milled 3mm deck.

However, looking at it all, debating about .5mm is pretty laughable in itself... .5mm is pretty small in that tires can lose .5mm in a race day.

Ypu got a very good point that I did not think about.

The reason for tryin to avoid the milling is that it is another step involved in the process of making a chassis, and thus another step where mistakes can arise. ....plus, honestly, the reason why most racers get carbon fiber converion kits is for the coolness factor...if we mill away the nice shiny surface in these areas, 1) would they really notice a diffrence in handling, and 2)would it interrupt the coolness factor of smooth CF with rough milled CF?
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Old 09-09-2003, 11:07 PM   #9
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Actually I think he's asking why they mill out the pads where the bulkheads sit to get the same roll centers as a 2.5mm car but still have the electronics etc .5mm higher thus raising the COG.

I think his point was; 6 of one, half dozen of the other. What's the point of gaining a small amount of rigidity when you substantially raise the COG?
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Old 09-09-2003, 11:16 PM   #10
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Well the majority of the heavy stuff is still at it's original height, ie. cells and motor. Only the servo, speedo and reciever are 05mm or whatever higher, which isn't a huge amount, thinner double sided tape could help there
keeping the heavy cells and motor at the original height will be one of the biggest reasons for milling the chassis at all, and if you lower the motor in a lot of cases you have to lower the whole drivetrain.
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Old 09-09-2003, 11:19 PM   #11
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I think the motor is also .5mm higher. How would it be lower if the chassis isn't relieved so it can sit lower?
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Old 09-09-2003, 11:23 PM   #12
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if the chassis is milled for all the bulkheads then the motor will sit lower since it mounts to a bulkhead
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Old 09-09-2003, 11:26 PM   #13
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On a 3mm milled(bulkheads only) chassis, then all the electronic goodies would be .5mm higher, on a 2.5 and 3mm unmilled chassis, everything would be oem height, without keeping in mind the minimum ride heights...correct?
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Old 09-09-2003, 11:32 PM   #14
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Quote:
Originally posted by dynamic_e
On a 3mm milled(bulkheads only) chassis, then all the electronic goodies would be .5mm higher, on a 2.5 and 3mm unmilled chassis, everything would be oem height, without keeping in mind the minimum ride heights...correct?
kind of but you could put the 3mm milled chassis at the same height as the unmilled one so that the electronics are at the same height but the bulkheads would be 0.5mm lower than the other two chassis. Best to always think of the height of things relative to the bottom of the chassis as it's height will be the same in each case, 5mm+ depending on setup.
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Old 09-10-2003, 12:08 AM   #15
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They milled out the 3mm to get the same rollcentre as the stock car at the same ride hight.

Rollcentre is affected by ride hight.

The motor will always be level with the bottom of the chassi as it sits in a cut out.
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