30 replies to this topic

[Bill from NH]

I'm not a drag racer, but could someone with experience explain how the slip-joint rail drag chassis is supposed to work? I've seen several new chassis of this type from the Ohio & Virginia areas being sold on ebay in the past year.

[SlotStox#53]

I've heard about  these "slip joint" cars but don't know how they work either. So good question Bill, shall be intriguing to

hear how they work

[Dan Ebert]

The concept was taken from real dragsters. The chassis provides better traction. They flex under power so there is no need for wheelie bars. Hopefully one of the Drag Gurus will explain further.

[Joe Mig]

They work good . Take a look on club 400 ..

[Don Weaver]

Bracket 500 is also a good good source for info.

Don Weaver

[Tim Neja]

Unless the class is Designed to run without wheelie bars--I don't see building without them!! They WORK!!!  I'm gonna try to build a "Fiat" class car for BPR--- saw them ran last weekend.  20 arms and quick with a "drop and go" rule---no rolling out any glue!! Clean track!! It's a challenge to get the car hooked up!!!  

[Bill from NH]

Bracket 500 is also a good good source for info.

Don Weaver

 

The Bracket 500 site has a rail chassis construction article titled "Slip-joint 101." Thanks Don.   A couple other scratchbuilt drag chassis building articles are also on the site.

[Steve Boggs]

The slip-joint chassis is based on the premise of leverage to increase the traction at the rear wheels. If you put 10 lbs. on the end of a 5 foot rod and try to lift it, it will be difficult , but possible to lift. Put that same 10lbs on a rod 25ft. long, and it's a whole different story. The optimum placement for a motor to provide the most traction is at a 45* angle to the axle. Unfortunately, if you accelerate at a force of more than 1G, it will be a wheelstander. A car that runs 1.000 on the 1/24th dragstrip accelerates at 5G's. So how do you hook this car up?

 

By placing weight farther in front of it with a long wheelbase. Additional flex in the car does 2 things. It lets the motor climb in angle to place more weight on the rear tires for more traction, and it absorbs small bumps without upsetting the car.

 

What I would rather see someone do instead of a slip-joint car, is a dragster made with a Z-rail.

[Gator Bob]

 The optimum placement for a motor to provide the most traction is at a 45* angle to the axle.

 

 It lets the motor climb in angle to place more weight on the rear tires for more traction, ...

 

 

Please explain the 45deg. angle to axle.

Top view or side view?

[Tim Neja]

 

Please explain the 45deg. angle to axle.

Top view or side view?

Has to be top view Bob!!

[racie35]

I have an idea!!

[Gator Bob]

Which one ?

[Steve Boggs]

 

Please explain the 45deg. angle to axle.

Top view or side view?

The 45* angle is in a vertical plane from the axle. I re-read my post and realized I hadn't been very clear on something.

 

The optimal angle places the Center of Gravity of the car itself on an angle to the Center of the Tire Contact with relation to the G forces that the car can accelerate. If the car moves at a rate of 1G, the angle works out to 45*. If you accelerate at 5 G's, then the angle is 11*, 31. For example, if you accelerate at a force of 2 G's, the center of gravity needs to be 1 inch up, and 2 inches forward, 3 G's needs to be 1 inch up, and 3 forward. These measurements create an ANGLE. The ANGLE is what matters, not the 1 inch/2 inch dimensions I used to illustrate. It could be .1 inch forward and .2 inch up and create the same angle.

 

With each increase in power and traction, the capability of the car to accelerate at higher G forces means that to keep the car hooked up, the Center of Gravity needs to be moved forward and lowered slightly.

 

If the Center of gravity is too far back, or too high, the angle will be behind the rear tire contact. In a real drag car, will be a wheelstander. Too much grip early in the run will have the nose clawing at the sky and require a bunch of weight in the nose to keep it driveable and it will still be unstable at speed.

 

If it is too low, or too far forward, the angle will intersect in front of the rear tires, and will be very hard to keep from losing traction. It doesn't have enough built in traction to transfer the weight onto the rear tires. This is a tiresmoking beast in a real drag car.

 

As far as slotcars are concerned, it's easy to see why some cars burn the braid off, or need super-wide rear tires and tons of glue to hook up. The balance can be totally off, and everything needs to be crutched in order to work.

 

In something like Wing cars, you could use C12 and Box12 and draw a comparison. Even if both cars had to weigh the same, and had the exact same amount of power, the C12 would run rings around the Box12 car because of better weight distribution. It would also be able to run narrower tires since it could keep them planted and a lower downforce body which would allow it to run faster. A 16D sized Open wind arm inside a set of 12 segment Neo's would be a powerful beast, just try getting that one around a racetrack, LOL.  Or take the example of the current neo powered AA/FC's in Drag Racing. The Neo cars haven't run any quicker than cobalt motored cars in spite of having more power. The extra power of the Neo motor, and the size of it that makes the CofG higher requires wider tires and more glue to hook up, and a stiffer car to keep it from hopping out of the slot, which in a vicious cycle requires yet even wider tires and more glue. Then add in the Neo cars are about 10 grams heavier.

 

The slip joint car does 2 things to enhance traction. It accentuates the weight in the nose making it act like the weight was increased while still being light, and it lets the motor climb higher increasing weight transfer to the rear. it also has the effect of absorbing irregularities in the track surface without losing traction.

 

Hope this was a better explanation.

[Tim Neja]

WOW--you mean the motor can climb to a "vertical" plane above the axle and tires under acceleration!!??  Can you draw me some pics?  That seems to be extreme?  

[Steve Boggs]

It's only a very slight amount and it depends on just how flexible the chassis is.

[MSwiss]

Are these slip-joint chassis in the witness protection that there aren't any pictures? LOL

[Steve Boggs]

http://bracket500.com/links/sj/sj.html

 

Try this......

[Tim Neja]

Ok---after seeing the pictures--I'm still not understanding this "45" degrees thing?? Can you illustrate somehow?  

[Steve Boggs]

The "45 degree" thing was only meant as an illustration for the center of gravity height for 1G of acceleration, not the last word on the subject. And no, I don't have a picture.

[Gator Bob]

Tim, think of it like this.

 

1:1 ... your Yenco-

If the transmission mount was a hinge and the motor mounts are 90/10 shocks... under acceleration the motor would rise thus moving more weight to the back and the front wouldn't start feeling light till the shocks 'top-out'. 

 

slot drag guys are doing what the T/F 1:1 guys are doing with the slip joint. Motor raises ... C/G rises ... weight moves to the back and the front (although lighter) stay on the ground.

 

1:24 ... With In-line or SW/AW the motor 'wants to' climb up the crown or spur. The slip joint rail 'lets' the motor and bracket effectively 'climb' the crown with out pulling the guide (all the way) out of the slot.

 

If the rule stated that *no motors are to be mounted behind the rear axle* (with wheelie bars) then this in-line slip joint movement is effective.  

Think of a Cox 2E with the movable wing .. the motor is free to (float) move under load (torque). Mount full sidewinder and make a bracket that allows rise/float and it will do the same thing. With a simple bell-crank the 'force' of the rise can be transfered to the guide flag to add (bite?) mechanical down-force and move the CG back and provide more Bite (traction)  There is more then one way to skin this cat. Think True ISO....

 

 

 

The 45* angle is in a vertical plane from the axle. I re-read my post and realized I hadn't been very clear on something.

 

The optimal angle places the Center of Gravity of the car itself on an angle to the Center of the Tire Contact with relation to the G forces that the car can accelerate. If the car moves at a rate of 1G, the angle works out to 45*. If you accelerate at 5 G's, then the angle is 11*, 31. For example, if you accelerate at a force of 2 G's, the center of gravity needs to be 1 inch up, and 2 inches forward, 3 G's needs to be 1 inch up, and 3 forward. These measurements create an ANGLE. The ANGLE is what matters, not the 1 inch/2 inch dimensions I used to illustrate. It could be .1 inch forward and .2 inch up and create the same angle.

 

Where did this xG's to xDeg. therory come from?

 

With each increase in power and traction, the capability of the car to accelerate at higher G forces means that to keep the car hooked up, the Center of Gravity needs to be moved forward and lowered slightly.

 

Hooked up as in 'to the the DC power source' ?  The term 'hooked up' normally pertains to 'traction'.

 

If the Center of gravity is too far back, or too high, the angle will be behind the rear tire contact. In a real drag car, will be a wheelstander. Too much grip early in the run will have the nose clawing at the sky and require a bunch of weight in the nose to keep it driveable and it will still be unstable at speed.

 

If it is too low, or too far forward, the angle will intersect in front of the rear tires, and will be very hard to keep from losing traction. It doesn't have enough built in traction to transfer the weight onto the rear tires. This is a tiresmoking beast in a real drag car.

 

As far as slotcars are concerned, it's easy to see why some cars burn the braid off, or need super-wide rear tires and tons of glue to hook up. The balance can be totally off, and everything needs to be crutched in order to work.

 

In something like Wing cars, you could use C12 and Box12 and draw a comparison. Even if both cars had to weigh the same, and had the exact same amount of power, the C12 would run rings around the Box12 car because of better weight distribution. It would also be able to run narrower tires since it could keep them planted and a lower down-force body which would allow it to run faster. A 16D sized Open wind arm inside a set of 12 segment Neo's would be a powerful beast, just try getting that one around a racetrack, LOL.  Or take the example of the current neo powered AA/FC's in Drag Racing. The Neo cars haven't run any quicker than cobalt motored cars in spite of having more power. The extra power of the Neo motor, and the size of it that makes the CofG higher requires wider tires and more glue to hook up, and a stiffer car to keep it from hopping out of the slot, which in a vicious cycle requires yet even wider tires and more glue. Then add in the Neo cars are about 10 grams heavier.

 

The slip joint car does 2 things to enhance traction. It accentuates the weight in the nose making it act like the weight was increased while still being light, and it lets the motor climb higher increasing weight transfer to the rear. it also has the effect of absorbing irregularities in the track surface without losing traction.

 

Hope this was a better explanation.

[Steve Boggs]

Where did this xG's to xDeg. therory come from?

 

Don Long, Chuck Haase, Al Swindhal, and Murf MicKinney. Basically the best TF and FC chassis builders of the last 40 years, and after that much time in the field on real working cars, it's not a theory anymore. It's really used by everyone who designs any type of racecar, they just don't reveal the whole answer most of the time. What you usually hear is "get the weight as low as possible".  The design parameters they have to work in wont allow it most of the time. A square car with the driver in the center sitting on the motor isn't very practical.

 

At best, any car is a combination of compromises. Nothing ever accelerates, decelerates, and turns at the same constant G force all the time. It is a moving target that you always have to work around.

 

Hooked up as in 'to the the DC power source' ?  The term 'hooked up' normally pertains to 'traction'.

 

As in traction.

[Gator Bob]

Dude ... you are switching back and forth between 1:1 and slot cars and I just can't keep up. 

 

question - Did you ever see a sidewinder funny car? 

request - Please explain this square car with the driver sitting on the motor.

 

Slip joint started as a theory and is a theory in practice now.

So you are saying 4 guys came up with the 'theory' all at the same time about 40 years ago?

 

'Nothing ever accelerates, decelerates, and turns at the same constant G force all the time. It is a moving target that you always have to work around.'

 

If so then there are no absolutes ... wouldn't theory and modeling apply?

 

With each increase in power and traction, the capability of the car to accelerate at higher G forces means that to keep the car hooked up, the Center of Gravity needs to be moved forward and lowered slightly.

 

question - when does a drag car have maximum traction? 

 

 

[Steve Boggs]

I keep going back to the 1:1 examples just because the scale makes it easier to understand.

 

Not a sidewinder Funny Car, but there was 1 Top Fuel car that did it. Don Garlits tried it in the mid 70's. It worked ok, but the driveline was a nightmare with all of the right angle gearboxes.

 

No. 4 guys didn't all come up with the same theory all at once. It's actually just a standard engineering practice, that's been applied to racecars. I'm sure you have heard of a car or anything else for that matter, that had a "too high center of gravity". They not only had to figure out that it was too high, but also a way to quantify where it really needed to be. That's where these calculations came from.

 

If so then there are no absolutes ... wouldn't theory and modeling apply?

Certainly. All you would have to do is figure out what G's your car accelerates, and then find the center of gravity of your car. That entails measuring each half of the car separately, then elevated to a certain difference, then weighed again.

 

question - when does a drag car have maximum traction?

A real Top Fuel car? or a slotcar? With the real ones, it's just about 1.4-1.6 into the run. That's when the G's usually peak around 5. Then it drops to 3 at mid-track, and finally 2 near the finish line.

 

[Gator Bob]

First off Steve.. I do appreciate your enthusiasm.

 

I keep going back to the 1:1 examples just because the scale makes it easier to understand.

I wasn't working for me.

 

Not a sidewinder Funny Car,

Chain drive - John Force

 

but there was 1 Top Fuel car that did it. Don Garlits tried it in the mid 70's. It worked ok, but the driveline was a nightmare with all of the right angle gearboxes.

21% parasitic loss

 

No. 4 guys didn't all come up with the same theory all at once. It's actually just a standard engineering practice, that's been applied to racecars. I'm sure you have heard of a car or anything else for that matter, that had a "too high center of gravity". They not only had to figure out that it was too high, but also a way to quantify where it really needed to be. That's where these calculations came from.

You are confusing me again ... a slip joint 'raises' the CG 'higher' as the mass moves up under torque load.  

 

If so then there are no absolutes ... wouldn't theory and modeling apply?

Certainly. All you would have to do is figure out what G's your car accelerates, and then find the center of gravity of your car. That entails measuring each half of the car separately, then elevated to a certain difference, then weighed again.

 

Moving target .. even with a G meter in the car .. then on a static set of scales. Active measuring of ALL 4 corners during a run is the only way to get a 'non-theory' plot

 

question - when does a drag car have maximum traction?

A real Top Fuel car? or a slotcar? With the real ones, it's just about 1.4-1.6 into the run.

Clutch setting dependent

That's when the G's usually peak around 5. Then it drops to 3 at mid-track, and finally 2 near the finish line.

That's more then I know if it is in fact... fact. 

 

 

Answer - When 100 percent of the weight is on the back tires.

[Steve Boggs]

Bob, I worked on these cars for 15 years and did the clutch for 13 of them. I know exactly what works in the real ones. A chain drive funny Car? C'mon man.  I would LOVE to see how they routed the headers on that thing. Which window was the injector sticking out of?