24LikesCreating and developing a 2wd buggy
01-20-2018, 06:06 PM
#31
'Kay here's the second idea. The shock tower concept is simple, just like the RC10 it is secured on the suspension bulkheads but mine version only has two shock mounting points. Both provide the shock 90º to the arm when the chassis bottoms out, has two points to tune shock travel when running raised bulkheads from chassis or standard height. The theory behind it is that once we find a suitable spring rate we won't be changing much and the shock travel tuning is paramount to me.
The camber gain holes are a funny thing to me, the normal cars have so much caster they are running camber loss and still getting away with it. There will be at least two holes,one for rounder tire carcass and another for more squarer tire carcass.
The steering axis is pictured in the centre but I will see if negative offset can be run, why? Some thing that I've learned reading about last year top F1 cars
Steering is to be provided by a bearing supported sliding rack, so less slop than the tlr 22 rack. Sliding rack has at least two good things, packaging and geometry. This design will have adjustable Ackerman in the wheel side only, the rack side is bump steer adjustment.
One more, Losi XX style kick up. I want kick up set that way with RC10 style tubes to lock it in place by anchoring them to the servo posts.
01-20-2018, 11:02 PM
#32
Here's my personal take on a few things. I want a shock motion ratio as close to 1:1 as possible. That means putting the shocks as far out on the arms as possible. Think Tekno EB48.4. Yes, you need longer shocks which raises the cg but in my opinion this is a worthwhile tradeoff for the damping control.
More antisquat (generalizations) only gives rear traction when on power. It does nothing to aid rear traction at any other time. It decreases on power steering. Too much antisquat causes lift under braking which can cause wheelhop. A car should always run as little antisquat as possible based on the track. A track with low grip will want more antisquat. A high grip track where sauced slicks works would want less. Less antisquat gives more rear end grip under braking. It increases on power steering.
Front end nose kick. More front end kick gives less on power steering. Less front end kick gives more on power steering.
Caster should be treated independent of kick. On higher grip tracks with firmer tires, less caster is needed. Merely changing to softer tires may require increased caster. On low grip, soft tracks, more caster is needed to get the tire to dig in. The optimal amount of caster is the one that allows for the most tire contact patch for the conditions.
Rear toe. I'd personally only do it at the hubs and not the inner hinge pins. Parallel wheels are faster. Some toe in on a 2wd gives a more stable rear end when on power and a bit more grip. Rear toe decreases on power cornering ability.
Why people setup modern cars on high grip tracks with 30° nose kick and caster with max antisquat and rear toe is a huge mystery to me.
More antisquat (generalizations) only gives rear traction when on power. It does nothing to aid rear traction at any other time. It decreases on power steering. Too much antisquat causes lift under braking which can cause wheelhop. A car should always run as little antisquat as possible based on the track. A track with low grip will want more antisquat. A high grip track where sauced slicks works would want less. Less antisquat gives more rear end grip under braking. It increases on power steering.
Front end nose kick. More front end kick gives less on power steering. Less front end kick gives more on power steering.
Caster should be treated independent of kick. On higher grip tracks with firmer tires, less caster is needed. Merely changing to softer tires may require increased caster. On low grip, soft tracks, more caster is needed to get the tire to dig in. The optimal amount of caster is the one that allows for the most tire contact patch for the conditions.
Rear toe. I'd personally only do it at the hubs and not the inner hinge pins. Parallel wheels are faster. Some toe in on a 2wd gives a more stable rear end when on power and a bit more grip. Rear toe decreases on power cornering ability.
Why people setup modern cars on high grip tracks with 30° nose kick and caster with max antisquat and rear toe is a huge mystery to me.
01-21-2018, 11:35 AM
#33
Here's my personal take on a few things. I want a shock motion ratio as close to 1:1 as possible. That means putting the shocks as far out on the arms as possible. Think Tekno EB48.4. Yes, you need longer shocks which raises the cg but in my opinion this is a worthwhile tradeoff for the damping control.
More antisquat (generalizations) only gives rear traction when on power. It does nothing to aid rear traction at any other time. It decreases on power steering. Too much antisquat causes lift under braking which can cause wheelhop. A car should always run as little antisquat as possible based on the track. A track with low grip will want more antisquat. A high grip track where sauced slicks works would want less. Less antisquat gives more rear end grip under braking. It increases on power steering.
Front end nose kick. More front end kick gives less on power steering. Less front end kick gives more on power steering.
Caster should be treated independent of kick. On higher grip tracks with firmer tires, less caster is needed. Merely changing to softer tires may require increased caster. On low grip, soft tracks, more caster is needed to get the tire to dig in. The optimal amount of caster is the one that allows for the most tire contact patch for the conditions.
Rear toe. I'd personally only do it at the hubs and not the inner hinge pins. Parallel wheels are faster. Some toe in on a 2wd gives a more stable rear end when on power and a bit more grip. Rear toe decreases on power cornering ability.
Why people setup modern cars on high grip tracks with 30° nose kick and caster with max antisquat and rear toe is a huge mystery to me.
More antisquat (generalizations) only gives rear traction when on power. It does nothing to aid rear traction at any other time. It decreases on power steering. Too much antisquat causes lift under braking which can cause wheelhop. A car should always run as little antisquat as possible based on the track. A track with low grip will want more antisquat. A high grip track where sauced slicks works would want less. Less antisquat gives more rear end grip under braking. It increases on power steering.
Front end nose kick. More front end kick gives less on power steering. Less front end kick gives more on power steering.
Caster should be treated independent of kick. On higher grip tracks with firmer tires, less caster is needed. Merely changing to softer tires may require increased caster. On low grip, soft tracks, more caster is needed to get the tire to dig in. The optimal amount of caster is the one that allows for the most tire contact patch for the conditions.
Rear toe. I'd personally only do it at the hubs and not the inner hinge pins. Parallel wheels are faster. Some toe in on a 2wd gives a more stable rear end when on power and a bit more grip. Rear toe decreases on power cornering ability.
Why people setup modern cars on high grip tracks with 30° nose kick and caster with max antisquat and rear toe is a huge mystery to me.
If you don't mind revealing the why behind your choices I am interested to know why 1 MR? If going that way, then cantilever suspension could be done so you don't get monstrous shocks? What's the bad of having less than 1 MR?
I don't think anti squat causes lift under braking, during braking weight transfer goes to the front so that means you have less load on the rear tires and more on the front but the same spring rate therefore your choice of spring rates are now out of the window. The rear raises and the front dips as a direct relation of load carried. My findings and my google searches present that anti angles react to a force with the set amount intended and each end is calculated separately. If you show me differently of what I know I'm all ears.
Caster is good here, as the front tires are only used to steer I don't have to worry about grip under braking so I can choose between caster or camber gain, think I'm going with caster because the way the tires are cambered when cornering.
I though about using outboard toe only... Think I'm going with that and straighten the axle to wheel angle with the arm swept forward.
I don't know too but I can guess. Driving full chat 100% of the time, if you increase everything the car generates too much grip so you can drive like a maniac and get away with it, trouble is when you run out of talent and then the car is just slow and burns tires faster than I burn fat. There's more to it than corner speed, car placement on track and effortlessly cars to drive are usually the most important things most drivers need.
01-21-2018, 12:57 PM
#34
Shock location on the arm is easy from a spring standpoint. If you've got a spring mounted at the wheel, its half the rate that a spring would be at the mid point of the arm to achieve the same wheel rate. That's easy. The trouble is with damping. Damping is a factor of oil weight and the rate at which oil can pass through the piston. If you have a shock mounted at the wheel vs one mounted at the midpoint of the arm, using the same piston and oil combination you do not have the same damping. Not even close. The arm farther out has far more damping as it is trying to move twice as much oil through the piston holes per the same amount of wheel travel. A tiny change in hole piston size on the outer shock will give you half the amount of change as on the shock at the midpoint. It is far easier to control damping over a longer stroke. Our shock technology is already limited compared to full size cars. Don't mount them in close to handicap them further.
More antisquat doesn't necessarily result in less rear grip during braking. At high amounts it can though. On a 2wd car, we only have rear end braking. You can only shift so much weight forward under braking before the rear wheels slide.
More antisquat doesn't necessarily result in less rear grip during braking. At high amounts it can though. On a 2wd car, we only have rear end braking. You can only shift so much weight forward under braking before the rear wheels slide.
01-21-2018, 01:35 PM
#35
Shock location on the arm is easy from a spring standpoint. If you've got a spring mounted at the wheel, its half the rate that a spring would be at the mid point of the arm to achieve the same wheel rate. That's easy. The trouble is with damping. Damping is a factor of oil weight and the rate at which oil can pass through the piston. If you have a shock mounted at the wheel vs one mounted at the midpoint of the arm, using the same piston and oil combination you do not have the same damping. Not even close. The arm farther out has far more damping as it is trying to move twice as much oil through the piston holes per the same amount of wheel travel. A tiny change in hole piston size on the outer shock will give you half the amount of change as on the shock at the midpoint. It is far easier to control damping over a longer stroke. Our shock technology is already limited compared to full size cars. Don't mount them in close to handicap them further.
More antisquat doesn't necessarily result in less rear grip during braking. At high amounts it can though. On a 2wd car, we only have rear end braking. You can only shift so much weight forward under braking before the rear wheels slide.
More antisquat doesn't necessarily result in less rear grip during braking. At high amounts it can though. On a 2wd car, we only have rear end braking. You can only shift so much weight forward under braking before the rear wheels slide.
Learnt in these last two weeks the same amount I learnt the entire last year. Appreciate all the help guys.
01-21-2018, 01:58 PM
#36
Antisquat affecting rear end grip under braking would really be more of a concern on a 4wd where all wheels brake. Incidentally, how many people do you see run max antisquat on 4wd vehicles but then run a lighter center diff oil? To a point, less antisquat could help keep the front wheels down during hard acceleration vs a slightly lighter center oil but the car with a heavier center oil and less antisquat will have slightly more braking power. You aren't designing a 4wd so this is irrelevant to you anyways.
01-21-2018, 02:58 PM
#38
More antisquat (generalizations) only gives rear traction when on power. It does nothing to aid rear traction at any other time. It decreases on power steering. Too much antisquat causes lift under braking which can cause wheelhop. A car should always run as little antisquat as possible based on the track. A track with low grip will want more antisquat. A high grip track where sauced slicks works would want less. Less antisquat gives more rear end grip under braking. It increases on power steering.
EDIT: I believe what you're saying is the same thing as the AS in the rear. Correct?
I don't think anti squat causes lift under braking, during braking weight transfer goes to the front so that means you have less load on the rear tires and more on the front but the same spring rate therefore your choice of spring rates are now out of the window. The rear raises and the front dips as a direct relation of load carried. My findings and my google searches present that anti angles react to a force with the set amount intended and each end is calculated separately. If you show me differently of what I know I'm all ears.
. With more antisquat the weight doesn't bleed through the suspension, i.e. the shocks, it goes through the car. Like when you accelerate with more AS the rear doesn't squat as much because the load gets to the tires faster. With less AS the suspension has time to absorb all of the weight transfer. The same thing happens under braking. With too much AS the rear suspension won't be able to droop fast enough to keep the tires on the ground, if they're not on the ground you don't have any traction in the rear.Shock location on the arm is easy from a spring standpoint. If you've got a spring mounted at the wheel, its half the rate that a spring would be at the mid point of the arm to achieve the same wheel rate. That's easy. The trouble is with damping. Damping is a factor of oil weight and the rate at which oil can pass through the piston. If you have a shock mounted at the wheel vs one mounted at the midpoint of the arm, using the same piston and oil combination you do not have the same damping. Not even close. The arm farther out has far more damping as it is trying to move twice as much oil through the piston holes per the same amount of wheel travel. A tiny change in hole piston size on the outer shock will give you half the amount of change as on the shock at the midpoint. It is far easier to control damping over a longer stroke. Our shock technology is already limited compared to full size cars. Don't mount them in close to handicap them further.
01-21-2018, 04:04 PM
#39
My oval car, the Invencer, is different than others. I do use equal length arms all around, which is a compromise, but it's the same arm all around. The front end kick is the same as the caster, which is also a compromise. The front kick is adjustable from 10° to 25° and independent left and right. The rear end has no toe or antisquat. Lots of tuning is done with battery placement. Saddles for low grip or a left side shorty for high grip. It uses a direct drive with the motor offset to the left. The car is narrower than others.
01-21-2018, 04:20 PM
#40
At this point the direction is trying the theory stuff on the tlr 22 with different uprights front and rear and work from there.
Now about anti angles, they work exactly like roll centres, in fact for me they are pitch centres. Same deal as roll centre height, the closer to the CG the less force goes through the springs and more through the arms, like you said the rate at the force travels from the linkages and arms is far greater than through the springs. In 2wd cars the front doesn't play much but 4wd is like having different roll centres left and right as the front tire definitely lifts the rear under braking, what I'm unsure is 2wd cars.
And what roll centres and anti angles do is influence car position in yaw, roll and pitch. For lower weight transfer you want the car to be as low as possible so I'm going with the less anti angles and more balanced jacking forces from the beginning, because I feel the current designs are wrong in that the rear roll centre is lower than the front and both underground.
Liked your FB page. Nice cars!
Now about anti angles, they work exactly like roll centres, in fact for me they are pitch centres. Same deal as roll centre height, the closer to the CG the less force goes through the springs and more through the arms, like you said the rate at the force travels from the linkages and arms is far greater than through the springs. In 2wd cars the front doesn't play much but 4wd is like having different roll centres left and right as the front tire definitely lifts the rear under braking, what I'm unsure is 2wd cars.
And what roll centres and anti angles do is influence car position in yaw, roll and pitch. For lower weight transfer you want the car to be as low as possible so I'm going with the less anti angles and more balanced jacking forces from the beginning, because I feel the current designs are wrong in that the rear roll centre is lower than the front and both underground.
My oval car, the Invencer, is different than others. I do use equal length arms all around, which is a compromise, but it's the same arm all around. The front end kick is the same as the caster, which is also a compromise. The front kick is adjustable from 10° to 25° and independent left and right. The rear end has no toe or antisquat. Lots of tuning is done with battery placement. Saddles for low grip or a left side shorty for high grip. It uses a direct drive with the motor offset to the left. The car is narrower than others.
Last edited by 30Tooth; 01-21-2018 at 04:52 PM.
01-21-2018, 04:29 PM
#41
There's no reason that a roll center can't be below ground level. It depends on the track. The key is balance between the front and rear.
01-21-2018, 05:13 PM
#42
With underground roll centres the forces at play are too big, no need to have anti-jacking forces sucking the car down making it roll too much placing the tires on the positive camber side. You can then decrease the moment while keeping roll stiffness the same, keeping the tire cambered in the right way and having a less inclined roll axis. This all plays together, shock package and chassis attitude, using one to affect the other only causes headaches (same shock pistons front and rear).
01-21-2018, 05:40 PM
#43
I'm about to say something that is going to be controversial. The faster the car, the lower the roll center needs to be. A car tuned for a 6.5T motor will want a lower roll center than the same car in 17.5T blinky on the exact same track. This makes the assumption that the track is large enough that lap times would be noticeably quicker among the classes. On a small, tight track it wouldn't matter.
01-21-2018, 10:34 PM
#44
Shock location on the arm is easy from a spring standpoint. If you've got a spring mounted at the wheel, its half the rate that a spring would be at the mid point of the arm to achieve the same wheel rate. That's easy. The trouble is with damping. Damping is a factor of oil weight and the rate at which oil can pass through the piston. If you have a shock mounted at the wheel vs one mounted at the midpoint of the arm, using the same piston and oil combination you do not have the same damping. Not even close. The arm farther out has far more damping as it is trying to move twice as much oil through the piston holes per the same amount of wheel travel. A tiny change in hole piston size on the outer shock will give you half the amount of change as on the shock at the midpoint. It is far easier to control damping over a longer stroke. Our shock technology is already limited compared to full size cars. Don't mount them in close to handicap them further.
Spring rate is Force over Distance. (spring rate of 1N/mm) When the shock is in the middle of the arm (MR=0.5), the spring will have a deflection of say, 1mm, and a force of 1N. So, with that setup, the wheel will experience a deflection of 2mm, and experience a force of 0.5N. Thus, spring rate at the wheel is 0.5N/2mm, or 0.25N/mm. Using the above equation: 1N/mm*0.5^2 = 0.25N/mm. If you moved your shock to the outside of the arm, MR = 1, your wheel spring rate now becomes 1N/mm.
Damping rate (coefficient) is Force over Velocity. (damping rate of 0.1N/mm/s) When the shock is in the middle of the arm (MR=0.5), the shock will have a velocity of say, 100mm/s, and a force of 10N. So, with that setup, the wheel will experience a velocity of 200mm/s, and experience a force of 5N. Thus, damping rate at the wheel is 5N/200mm/s, or 0.025N/mm/s. Using the above equation: 0.1N/mm/s*0.5^2 = 0.025N/mm. If you moved your shock to the outside of the arm, MR = 1, your wheel spring rate now becomes 0.1N/mm/s.
While I did say the spring rate and the damping rate change the same, they interact with a different relationship called the Damping Ratio. The damping ratio is defined as: DR = C/(2*sqrt(m*K)) Where C= Damping coefficient, m = mass of moving parts, K = Spring rate. So, DR is directly related with the Damping coefficient (that changes by MR^2), and DR is inversely related to the square root of the Spring Rate (that changes by MR^2). Since the spring rate is in the denominator, and is a square root, it will exponentially spike the effective damping ratio as you move the shock outward, giving you an over damped system, thus the need to reduce your oil, or increase your piston hole size.
Looking at the above math equations, it seems to me you have lower resolution using spring changes than you would have with damping (piston/oil) changes.
01-22-2018, 12:56 AM
#45
Tech Adept
I'm about to say something that is going to be controversial. The faster the car, the lower the roll center needs to be. A car tuned for a 6.5T motor will want a lower roll center than the same car in 17.5T blinky on the exact same track. This makes the assumption that the track is large enough that lap times would be noticeably quicker among the classes. On a small, tight track it wouldn't matter.