Luke's Procat rebuild

[kaszal]

Hi Paul, it does have a 5.5 but only a 6.6v Li-Fe so the power's less, plus I was holding back a little. At the time the damping was too soft so that was not helping the jumps either.

I'm pretty sure the diffs and belts are set OK but I think the front end could be a little light. I swapped out the front one ways for standard driveshafts and there's some extra weight at the back e.g. alloy bearing housings, alloy trans housing, alloy z bracket, Bosscat pro-diff and the chunky 5.5 brushless. I've added 15g back on the front (under the servo) and might fit an alloy bumper.

Probably another big factor is that I'm not the best driver so I might be applying the throttle at the wrong point.

Anyway, appreciate your comments

[uzzi]

Alloy bumpers are illegal for racing mate

[Jay Dub]

Did the car have the one ways in in the video? If so, that is one of the areas where the nose high attitude is from. As mentioned before, the back end seems a little light. Go to 35wt and give it a go. -Jeff

[kaszal]

Thanks Jeff, it didn't have the one ways in. Are you saying that running these increases the nose high attitude? They weigh about 15-20g more than standard driveshafts so I though the extra weight would help keep the nose down.

[Jay Dub]

Yes, the gyroscopic forces of the spinning wheels will help keep the front end high. Without the one ways, the front wheels will be more controlable via throttle, and with brakes should be able to keep the front end down more easily in the air . -Jeff

[kaszal]

Thanks Paul, Jeff and Chris

I measured various components and found the following...

At the rear: alloy inner transmission housing, alloy eccentric bearing housings and alloy z-bracket weigh 22.5g more than the plastic parts. Plus the brushless motor and Bosscat pro-diff (has alloy carriers and extra bearings) add more weight at the back.

In the middle: Li-Fe cells are about 140g lighter than the old Ni-mh.

At the front: swapping the XLS bumper for a Procat one, front one-ways for regular driveshafts and Bosscat hub carriers loses 24g.

I've put 45g under the cells, mainly to balance the BL motor on the other side. I've also put 55g nearer the front under the servo and steering. It was going nose up so hopefully this should help. Lots of modified bits and pieces in there. I'll measure the distribution when I've put the shocks and wheels back on.

[kaszal]

I've just realised I left out a piece all along - the spacers for the steering joints. I think this is why the toe in went wrong at full droop. According to the manual, these should be on both the Procat and Bosscat hubs.

[Jay Dub]

One word of caution redarding adding weight to the chassis. Usually one would not add weight to get the car to handle in the air, this is usually reserved for on surface tuning. I usually will only add or move weight when the car handles inconsistenly as the track surface changes. When tuning a new car, I will run the car with the SAME compound tire front and rear, and see what happens to the car through the day (as the track surface and bite changes). As the track changes, if the car begins to push then I would add weight to the front. If the car begins to oversteer as the track begins to change, then I will add weight to the rear. I do this until the car handles consistently through out the day. This type of tuning is usually a back and forth battle for a while, because other chassis and suspension changes will need to be made to counteract the weight shift. But eventually you will narrow in on a very consistent setup that will feel comfortable through out the day and from track to track. I usually will add weight in 1/2 oz. increments as it helps to narrow in more quickly. -Jeff

[kaszal]

Thanks for the detailed reply, Jeff.

I'm adding weight for, as you said, on-surface tuning. There's at least an extra 30g of components at the rear, 25g less up front and 140g less in cells so I reckon restoring the weight distribution can only help. On the track it does feel light and the front lifts up too much under power. It's also too "pushy" in the corners and understeers. I realise access to the weights under the servo isn't easy if I want to do trackside adjustments At least it helps keep the c.o.g. low.

Better get the spacers back on. I've also wondered is a servo saver neccessary with the Cat crash-back system? With "give" in both does it making the steering sloppy or do the servo and bands work independently? I've got a fairly stiff Kimbrough saver which I'm thinking I should put on.

[Jay Dub]

I haven't run a servo saver in years. With the quality of todays metal gear servos, I just havent had any issues. The old cats however have a fragile steering system and would recommend one for the steering system more than the servo . However, your steering looks to have been upgraded to a newer more robust type, and should hold up well (good job btw).

One thing I forgot to mention is that once you get a good car (believe me you will know , then you want to record a weight balance (e.g. front to rear). This will be a perfect starting point for your future 4wd cars. Often I will weigh a fast, consistent competitors car to get a starting point. This saves time and money (tires, rims, etc.). Just be sure you watch his car throughout the day, to see if it picks up any odd handling issues. This will give you a direction to move in if you use his weight distribution.

Usually I accomplish this weight distribution thing by weighing the front of my car, and then the rear of the car (make sure that the car is level when doing so). This will give you a ratio with which you can use for future cars. -Jeff

[QuackingPlums]

Just a question about weight distribution: if the ratio of front to back is important, wouldn't it be easier just to find the point at which the car balances level and just measure the distance from that point to each axle?
I don't remember ever messing about with weight BITD (I don't race off-road much these days as I don't have as much time for cleaning up afterwards!) as I always assumed that if a car wasn't handling well then it was due to my driving!

[kaszal]

Hi Eric, don't forget this car has lighter cells than the original Ni-Cd, heavier parts at the rear and some lighter parts at the front so the weight distribution will be different. Anyway, this is RC model cars... we LOVE messing about

[Jay Dub]

I used to do what you are describing (finding the CG by balance and then measure), But I soon found it usefull to have actual weight in ounces (or grams if you happen to be of that persuasion). This would not only give me an actual weight of my car, but of my competitors cars as well. This proves usefull in deciding weather to add weight to one end of the car, or remove weight from the other. It is just a little more info, which is always good. -Jeff

[kaszal]

The ball joint spacers are essential. After I fitted them no more toe in at full droop.

Also weighed the car... total 1730g and rear : front = 57 : 43

How does this compare to other 4wd?

[isobarik]

Just look at the cat 2000 series the first one is the one with battery placement further back and then came the ec where the battery style was moved an bit forward and then the cat 98 where you ran the battery along the side.

Compared with the sx and sx2 they are running battery lenght wise motor is almost in the same position just in front of the rear axle.

Try just to move the battery forward at first and se what differance it makes....

before the zx5 came the zxs cars had an chassi with battery slots on one side lenght wise. would love to get my hands of one of those chassi.

Just for the fun of it double tape the battery lenght wise under the top deck and have the servo moved to one side in the back ie predator styling long steéring rod.

mvh Isobarik
mvh Isobarik