Luke's Procat rebuild

[Jay Dub]

No, but they do drive with the radios inverted, antenna between their legs that sort of thing . -Jeff

[isobarik]

No, but they do drive with the radios inverted, antenna between their legs that sort of thing . -Jeff

I thought that it was the auzzies that did that.

mvh Isobarik

[Jay Dub]

Not trying to hijack the thread, but here are pics of the new rear tower I promised. So far they look pretty good, but I may revise the holes a little. The wing mounting holes are made for the ZX5/Ultima RB wing mounts btw. -Jeff

[kaszal]

Those look sweet, how did you cut them?

Does anyone have some rear Bosscat wheels new or in good condition?

U1147X AERODISC REAR WHEEL

Cheers

[Jay Dub]

CNC.

I have an OK set for a runner (front and rear) they are not new, and have small scratches and cracks from running. I don't plan on using them on my procat as I will be sourcing a different option (they are not my definition of "shelfer"). You can have them if you pay shipping. -Jeff

[kaszal]

I understand the concept of Ackerman steering angles but does the Cat/Procat/Bosscat have any? Looking at the hub carriers it seems not i.e. the wheels stay when steering. Just curious to learn more so any feedback welcome

[Jay Dub]

Yes, the cat series of cars do have ackerman. However, this is a loaded question (and answer). It is not "if", but "when and where". -There needs to be clarification.

The term ackerman as we use it defines the difference in angles between the inside and outside tires as the car is turning. Generally the more you turn, the more the ackerman effect increases. Generally, with a rack type steering system, you get less ackerman than with a bell crank type of system.

A rack system has two ball joints set at a fixed distance appart, and maintain an equal distance between those two points throughout the steerings' range of motion. As the steering system moves left to right, there is little shortening of the entire steering linkage. This is especially true when you first start to turn the steering system left or right. This means that off center, you will have very little ackerman and the car will tend to initiate its turning more quickly (then with a bellcrank system).

A bellcrank system on the other hand has two points that are fixed (via the center link), and two points (the outer link balls) that vary the distance between them according to their position in the steering range (usually shortening off of center). This means that there there is an immediate deviation in length as soon as the steering begins to move off center. The more the steering moves tward its end point, the shorter that distance becomes. This translates to more ackerman (usually).

One other thing to consider is that the length of the steering arm itself will effect how the system works. As the steering system moves left and right, the links on a rack will move rearward, causing the steering linkage to effectivelly change length. This will also effect ackerman .

This is a simplified explanation however, as the angle of the tierods running out to the steering system knuckles also greatly effects how much, and when your ackerman really comes into play. This is especially important on the Schumacher cars because of their extreme/crazy steering link angles. On the Cat series of cars the links are angled really far forward. This means that when the steering rack starts too move left or right the tierods angle even more greatly and begin to pull in the outside wheel in creating ackerman. However, this doesn't come into play untill the end of the range of movement. So with the cat series of cars this means that there is little ackerman in the beginning of the steering range, and alot at the ends of the range. It works kind of "exponentialy" if you will.

So how do you use this info? Well, typiclally a rack system is better on loose surfaces because it gives better steering response off center, and the loss of ackerman isn't felt because of the slip angle of the tires on the loose surface. However, on a high bite surface you will often have the front tires binding (scrubbing) and loose corner speed. The opposite is true with bellcrank systems. Slower response off center, and better corner speed on high bite surfaces because there is less scrubbing (think RC10. Bellcranks+highbite surface = dialed). This makes the CAT steering systems a little difficut to use. On high bite surfaces, you would want to drive the car at its steering limits (because that is where your ackerman comes into play), but you rarely need this much throw. On low bite surfaces, it is good until you get to the ends of the steering throw and you have put too much steering input for the surface.

I have simplified this quite a bit, but covered the main points . The only other thing that really effects the items discussed is tow in/out on the front. Allot of mitigating can be done with this on various systems (think 1/8th scale buggies with 3-4 degrees of toe out on the front rack type steering system). Ultimately, there are infinate variations in steering systems, and without tons of testing it is hard to settle on a perfect one for a particular car. The schumacher CAT and Cougar systems are at opposite ends of the spectrum with good in the middle and bad at both ends. Hope that answered your question. It might help to post pics .-Jeff

[kaszal]

Looking at the wobbly axles I realised there were never any crush tubes which means the tighter you do up the wheel the more the bearings bind. I found this more noticeable in the Works rear hubs.



I plan to fix this with a few bits...

8x14x4mm bearings (2 pieces) from RCbearings.co.uk (remove the inner race and use as a crush spacer in the rear Works hubs. This might push the bearings clear of the hub a little but a 12mm shim thickness 0.1mm or 0.2mm should fix that)

I'll make a crush spacer for the front with 1.2mm worth of 8mm shims (e.g. 2 x 0.5 + 0.2)

I'll check the fit by disconnecting the driveshafts and spinning the wheels with the bolts done up tight.

Now all I need are some nice alloy roller driveshafts

[kaszal]

[kaszal]

Rear crush tubes work great. Did the screw up tight and the bearings run very free. A little less axle wobble too.

The parts needed for the Works hubs are the inner races of two 8x14x4mm bearings (70p each from RCbearings.co.uk) and two 12x15x0.1mm shims (Kyosho ones are available from JE Spares)

[Bormac]

Luke you seriously put soo much thought into what you are doing with this car. I bet the Schumacher Team never went to soo much trouble with this car. I simply love what you do and really appreciate the ideas you share with us vintage schumacher tragics.
Keep up the outstanding work good sir.

[kaszal]

Thanks Jason!

I seem to keep spotting these details Like with all good ideas, it's a wonder how it was missed before e.g. no crush sleeves or disc springs (which you have experience of)

Glad it's of interest to you! Got to do the front as soon as the 8mm shims arrive.

[kaszal]

The Wasp ballraced steering didn't have crush tubes either. I found these quite fiddly to get right: too tight and the bearings bind, too loose and there's more play. I got busy with the calipers and found that the inner race of a 3x7x3 bearing should fit. Need 4 at 70p each from RCbearings.co.uk

These are the original instructions (with red annotations by me)

[kaszal]

Please join in my Procat paint scheme survey...

http://www.oople.com/forums/showthread.php?t=75460&referrerid=7282

[kaszal]

Can anyone help me out with two of these in new or good condition?