Luke's Procat rebuild

[kaszal]

Hi Dan, do say hi next time you're at Stotfold... and maybe help me with my setup.

Will you race your RC10?

[kaszal]

These parts are for auction in the usual place...

[DerbyDan]

Hi Dan, do say hi next time you're at Stotfold... and maybe help me with my setup.

Will you race your RC10?

For-sure Luke

I'm afraid the RC10 hasn't been raced since 2010... i've been racing a more modern Losi CR2 since. My Off Road racing is fairly in-frequent/casual - I race my Touring Cars more regularly & with more success. I hope to get out with the buggy more now the weather is getting warmer

[kaszal]

Please can anyone explain how the following set ups will handle differently e.g. roll centres, grip, turning, bump handling?

Thanks

[Jay Dub]

Well, looks like in the pic, the tie rods are in a similar place. What I notice more than anything else is those crazy long outdrives. They should/could bind the suspension a fair amount under acceleration. This is because they will force the sliders to extend and collapse more than usuall. Usually, this "ecourages" the chassis to stay in whatever position it is in when throttle is applied- limiting chassis movement (weight transfer, etc). There are situations where this is beneficial, however it is a finicky "adjustment" and tend to by dynamic -the results will be proportional to the amount of throttle input.

The upper pic does seem to show the tierods lower on the inside however. This will lower your roll center, and make your weight transer more progressive. This means that the chassis will not roll as deeply in the corners compared to a car with parallel upper and lower control arms. Also with a setup like this, the car will have more camber gain. Good for corners, bad for acceleration. As the back of the car squats (under acceleration), the rear tires will camber in thus reducing contact patch with the ground. Less contact patch = less traction. This can result in the back end breaking loose under initial acceleration, and less "punch" for jumps, etc. This is limited however, because of the tire you are running. It has a very round cross section, so most of the adjustments you make will be hard to feel. I know the schumacher tire is the standard over there for most racing. This makes sense from the standpoint that with a carcass like that (very rounded), it will reduce overall traction (making the car less twitchy), and offer a wide possibility for setup, and also help consistency. Very similar to a flexible chassis car.

As far as handling is concerned, it SHOULD run flatter, and be less aggressive. This setup should work well on a track that has lots of medium speed corners, and few areas of hard acceleration. This is the type of setup I would start with on a medium or high bite track. However, much of the current suspension setup theory for high bite tracks revolve around parallel arms with little or no camber gain. Springs, static camber, and tires are what is usuall for fine tuning. In this scenario, the loss of grip due to the tire wheel combo "folding over" is used as a mitigator for high traction situations, and is preferred because the cars accelerate much better (parallel arms, no camber gain).

There is one VERY important point that I am going to touch on next, and this will throw much of what we have discussed here out the window . And that is rim flex, and more importantly the flex in the wheel/axle assembly. The old schumacher, castle drive wheel/axle assembly has and amazing amount of flex in its design, and in high bite situations can lead you to chassing your tail. At low speeds, most of your adjustments will be noticeable, but at high speeds, you might find the changes less noticeable or nonexistant. Or, you might end up having to compensate by running more of a particular adjustment than you think makes sense (static camber for example). I found this was the case with my early schumachers, and ended up switching the rear hub assembly for an AE rc10 hub, with Losi axles, and Losi or AE rear wheels. I also machined rear arms for the car to facilitate this modification.

Ultimatelly, however any modification or adjustment has to be felt on the track to know what it will do. Everything else is just theory. Have fun -Jeff

[Mad Racer]

Hi Dan, do say hi next time you're at Stotfold... and maybe help me with my setup.

Will you race your RC10?

Nice Pro Cat.

Got to get mine up & running soon.

Oh that brings back some memories of Racing in the U.K. Stotfold track running in the BRCA series.. Great track out in the sticks.

[kaszal]

Well, looks like in the pic, the tie rods are in a similar place. What I notice more than anything else is those crazy long outdrives. They should/could bind the suspension a fair amount under acceleration. This is because they will force the sliders to extend and collapse more than usuall. Usually, this "ecourages" the chassis to stay in whatever position it is in when throttle is applied- limiting chassis movement (weight transfer, etc). There are situations where this is beneficial, however it is a finicky "adjustment" and tend to by dynamic -the results will be proportional to the amount of throttle input.

The upper pic does seem to show the tierods lower on the inside however. This will lower your roll center, and make your weight transer more progressive. This means that the chassis will not roll as deeply in the corners compared to a car with parallel upper and lower control arms. Also with a setup like this, the car will have more camber gain. Good for corners, bad for acceleration. As the back of the car squats (under acceleration), the rear tires will camber in thus reducing contact patch with the ground. Less contact patch = less traction. This can result in the back end breaking loose under initial acceleration, and less "punch" for jumps, etc. This is limited however, because of the tire you are running. It has a very round cross section, so most of the adjustments you make will be hard to feel. I know the schumacher tire is the standard over there for most racing. This makes sense from the standpoint that with a carcass like that (very rounded), it will reduce overall traction (making the car less twitchy), and offer a wide possibility for setup, and also help consistency. Very similar to a flexible chassis car.

As far as handling is concerned, it SHOULD run flatter, and be less aggressive. This setup should work well on a track that has lots of medium speed corners, and few areas of hard acceleration. This is the type of setup I would start with on a medium or high bite track. However, much of the current suspension setup theory for high bite tracks revolve around parallel arms with little or no camber gain. Springs, static camber, and tires are what is usuall for fine tuning. In this scenario, the loss of grip due to the tire wheel combo "folding over" is used as a mitigator for high traction situations, and is preferred because the cars accelerate much better (parallel arms, no camber gain).

There is one VERY important point that I am going to touch on next, and this will throw much of what we have discussed here out the window . And that is rim flex, and more importantly the flex in the wheel/axle assembly. The old schumacher, castle drive wheel/axle assembly has and amazing amount of flex in its design, and in high bite situations can lead you to chassing your tail. At low speeds, most of your adjustments will be noticeable, but at high speeds, you might find the changes less noticeable or nonexistant. Or, you might end up having to compensate by running more of a particular adjustment than you think makes sense (static camber for example). I found this was the case with my early schumachers, and ended up switching the rear hub assembly for an AE rc10 hub, with Losi axles, and Losi or AE rear wheels. I also machined rear arms for the car to facilitate this modification.

Ultimatelly, however any modification or adjustment has to be felt on the track to know what it will do. Everything else is just theory. Have fun -Jeff

Thanks for the detailed input, Jeff. I know what you mean by the crazy outdrives. They are however very good for locking the diff screw securely and have enough room to house the thrust bearing and 4 disc springs AND allow the dust cap to go on properly. There's going to be a lot of compromise with this old car.

Last time I raced it I was fairly consistent: got 10 laps in every round and kept up with a few modern cars! The back is still too "hoppy" over the little bumps at high speed. Others advise contradicting things e.g. thicker oil / softer oil. I'm also going to get the weight balance closer to 50:50 soon.

[Jay Dub]

Well, the back end being "hoppy" is a little vague. The advice given, could be good depending on what the situation is. It is hard without having a current video to look at. This is where your observational skills (while driving) could be worked on. It took me MANY years to get this down. First however it started with me watching my car being driven by someone else (preferably a better driver). I was lucky enough to live in an area where we had several world class drivers available every club race. It was a real treat to watch them drive my car, give me input, and be able to watch my cars driven the way they should be. Eventually I went from the back end being "hoppy" to well the car is under or over dampened. Then to the static dampening is good, but the pack needs work. There are several layers to pampening -like an onion. First basic static dampening needs to be addressed. Then pack needs to be worked on, shock angle, springs, etc.

It is difficult to describe what to look for, as a video is worth a million words. But the basic observations are "is the chassis moving too much (indicating an under dampened situation)" thus giving you the "hoppy" rear end. Or, are the rear wheels and chassis moving too much (indicating an over dampened situation). Post some video of the car running currently, I am sure we would all love to see it.

One other thing to note however, is that the rear geometry on the car will lend itself to a car that drives how you describe. The upper rear tie rod locations really need to be addressed in order to smooth the car out at speed. I currently have plans to build a procat racer, but the rear will have many mods to address the things you are describing in this thread. -Jeff

[kaszal]

I think it's overdamped or maybe too much "pack". When it hits a small bump at speed the whole rear end "hops" up. Could just be the shock position on the wishbone. I'll move it in and see if it's better.

We'd all look forward to seeing what you come up with for your Procat racer.

Graham of Atomic Carbon in the UK sent me this picture. Was this what you had in mind?

[Jay Dub]

Well, it is a good start. However, the locations on the hub is what really needs to be worked on. I was thinking about fabricating a small tab to move the ball stud mounting out further (see enclosed rc10 pic for example), or maybe a plastic block epoxied in the open void area on the top of the Shotgun style hub carriers. This would then be drilled and tapped to accomidate a vertical ball stud arrangement. Doing this would allow the inner pivot point (on the bracket shown) to be moved out, more in line vertically with the lower wishbone pivot point. All the while keeping the upper link length long to minimize unwanted camber gain. By doing this, the rear will be more consistent with throttle input. FYI, having the inner upper camber link positions close together makes the chassis "square up" and flatten out under power. This can be good, but will make the car less consistent. It will also make the back end of the car feel "choppy" in the rough. I think that this is at least part of what you are feeling or observing.

It sounds like the dampening you are describing could be a pack issue. What weight oil are you using? -J

[kaszal]

Very interesting!

For the rear dampers I'm using Tamiya No.4 pistons, which have 2 x 1.4mm diameter holes, and 27.5wt Losi oil.

On the wishbone, the bottom of the shock is mounted in the second hole from the outside (No.2 in the picture below)

[Jay Dub]

The oil does seem a little on the light side, especially for cold weather. The mounting position on the arm is ok. I personally like to run the lower mount as far out on the arm as possible. This offers the most precision from the components. The only time I will move it in is if the spring is not filling the range of suspension travel that I am currently working with.

The hubs in that pic are actually a little closer to what I am talking about. Unfortunatelly they were to fragile to run for any length of time.

[kaszal]

I could try a heaver oil and drill out 3 holes 1.4mm giving less pack?

[kaszal]

...or keep two holes but make them 1.5mm diameter?

Anyway, what about putting the top link here...

[Jay Dub]

Yes, heavier oil with bigger holes. Technically more holes is more efficient, however at this small size I doubt it would matter much.

Hub carrier: Yes, something more along those lines. The idea was to fill the void on the top of the hub carrier, do some surgery and remove unnecessary portions for clearance, and add vertical holes (mostly because it is all the rage these days ). The only issue you might have with just drilling new holes, is the upper rod angle -it may be too low on the outside for the existing holes on the camber bracket. Give it a try though. I have yet to actualy modify the parts, it may work just splendid . -Jeff