How much weight?

[pixelstick]

Hi, new to the crawler game and just got the newest version Capra 4WS RTR. So far I'm loving this thing but would like it to be able to climb steeper inclines a bit better without flipping. Wondering how much weight is really necessary in the front and was thinking of getting brass knuckles and portal covers. A few questions:

1) Is "the more weight the better" the general rule or is it more nuanced than that?
2) Extra weight front and back, or just front?
3) What hardware do you guys suggest (knuckles/portal cover)?

Also, the Capra has no overdrive so thought I'd handle that while I had the knuckles open. What percent overdrive do you guys suggest and why?

Thanks

 

[ferp420]

there are 2 schools of though 1 light as a feather
2 heavy as a pig

ether way your tires will need alot of tuning for your specific weight to light and theres not enuff pressure on the tire to much weight and you cant climb up
theres also temperature when jts hot out your tires get softer when its cold out they get hard you can change tires to differnt compounds and see what works best
when climbing you have to pull every ounce up the obstacle

the most important thing is weight distribution put the weight low and forward
usually the trick is to start with moving stuff around then run it add little bits of weight at a time

on a scaller things are a bit different top heavy hard bodys need added weight to keep it from flopping over at every turn how much depends on how top heavy it is

what ever way you decide to go you need to remeber that there is no 1 best tire and the more extreme you get the more tuning you need to do on the tires

the most important thing to upgrade is the driver that takes lots and lots of runtime you can have a wold class crawler but if ya dont know how to drive it than whats the point

personally if it were me i would go with some potmetal axles and heavy aluminum 2.2 wheels but thats just me it works for my terrain

 

[Col_Sanders]

As ferp said, people have different preferences on weight. Some like really heavy rigs with brass all over, others only want minimum brass up front only or none at all. A 60/40 front to rear bias is what people mostly shoot for. Maybe start with knuckles or portal covers up front and add more if needed.

Overdrive is also subjective. For a trail style truck I like ~20%, but for more serious rock crawling, I like 30-40%. The closer to 40 the better...I've got ~38% in my comp trucks. I ran ~44% briefly but it just felt like too much to me.

 

[pixelstick]

Thanks guys! That definitely gives me room for thought and places to start!

 

[pixelstick]

So a bit of progress since I was last on here. Several upgrades:
* Replaced the Mickey Thompsons with JConcepts Ruptures (using the stock 2-stage foams)
* Put brass knuckles/portal covers on the front (increased front weight by around 7 ounces)
* Put 25% overdrive gearing up front (14/21)

I can take lines that I couldn't take before, especially steeper climbs. I'd still like to be able to climb steeper. Any suggestions? I've read about the following:
* More droop... maybe deez bands at least on the front? Or different shorter travel shocks?
* Firmer foams in the rear

The stock foams are 2-stage but the outer stage is awfully soft and I think with the softer/thinner ruptures maybe a firmer foam would work better in the rear for steeper ascents?

 

[HenryCrawllins]

Ferp and Sanders covered everything pretty well. I wouldn't disagree with anything they suggested, so I'll just try to add to it.

Get scales, and learn how to use an online calculator to figure out your actual center of gravity. Cheap digital kitchen scales will work just fine.

As you are adding weight to the axles, see if you can remove weight from the chassis.

I've never owned a Capra, but I have a custom rig with Capra axles. There are options for moving the servo behind the axle instead of on top. You can also mount the battery to the axle, if you're okay with running a smaller pack, like a Tattu 650mah.

I'm not sure what the stock shock length is, but if it's taller than 80mm, consider switching to 80mm shocks. Portal axle rigs usually perform very well with that length. You may consider getting a flat skid if you do this, however, so you don't lose out on breakover clearance.

If you're just looking to hit those hard lines and steep climbs, try removing the springs from the outside of your shocks, and instead, run negative springs inside the shocks. Not good for trail running, but phenomenal for slow crawling.

I don't have a large sample size for this one, but I have been doing some weight testing on a few rigs, two of which have Ruptures. I've found a good operating window between 2100g and 2800g. Where you'll land in that window will shift with the type of insert you're running. I still have to go through all of my 3D printed inserts and dual stage foams before I can make a more specific recommendation here. The best thing to do in your situation is to get some stick-on weights. Add them incrementally to your axles, and find where your sweet spot is. Try shifting your weight bias while you're doing this. A good window here is 68/32-58/42.

Hope that helps. You're already on the right track. Soft front, medium rear inserts are a good idea. Just make sure they are soft/medium relative to your rigs actual weight.

 

[pixelstick]

Thanks for the info! Good information from you guys and confirms my thought process. It's funny you mentioned sticking weights on the axles for testing. Before I added the brass I tested with 1g and 2g lead fishing weights zip tied to the front axle, which largely contributed to my adding weight to the front.

 

[HumboldtEF]

Most folks agree that the 100mm Capra shocks are a bit too long. Swapping those out for 90mm shocks really improves stability by lowering the CG.

I finally swapped in 90mm shocks on the Capra I've had for years, it made a big improvement. I should have done that ages ago.

 

[pixelstick]

Ok, thinking more about ride height and breakover clearance. If I go with a shorter shock then that will lower the ride height and thus lower CG but also at the cost of breakover clearance. I've seen videos of some crawlers with lower linkage that is bent at an up angle effectively raising the skid plate, but wouldn't that offset the shorter shocks leaving you with potentially the same ride height? I guess I'm wondering what's special about those awesome rides where they can both make steep climbs AND have enough breakover clearance. Maybe that's not something that is easily done with the Capra. Any thoughts?

 

[ferp420]

i think your over thinking it

it is what it is sure you can make it slightly better but it is what it is
you can spend a bunch of money and end up with a bunch of spare parts and not get much more performance out of it

my opinion is
buy a set of axles and start freash enjoy your capra for the awsome machine it is and turn your sights on too a custom build then kill lines !

 

[pixelstick]

Cool thanks for the confirmation ferp. Again, appreciate the wisdom.

 

[HumboldtEF]

Ok, thinking more about ride height and breakover clearance. If I go with a shorter shock then that will lower the ride height and thus lower CG but also at the cost of breakover clearance. I've seen videos of some crawlers with lower linkage that is bent at an up angle effectively raising the skid plate, but wouldn't that offset the shorter shocks leaving you with potentially the same ride height? I guess I'm wondering what's special about those awesome rides where they can both make steep climbs AND have enough breakover clearance. Maybe that's not something that is easily done with the Capra. Any thoughts?

Yeah it is a trade off. 90mm shocks get you the lower CG but that also reduces the breakover clearance/angle. Bent links give you more clearance at the links themselves but do not alter the actual ride height or the skid height. You will be able to climb steeper angles but breakover will be reduced.

IMO bent links are great on straight axle rigs but with a portal rig the links are already sitting 10-12mm higher (than a straight axle) and dont beneifit as much.

 

[hnoroian]

On a budget and run what you have? As for the shocks you can put a limiter on the inside of the shock body to make the 100mm to 90mm (or any length) some sort of tubing, plastic spacers, reusable straws work fine.

 

[Col_Sanders]

Shorter shocks would help with COG. The high clearance links on the rear help reduce hangups.

If you're looking to do extreme stuff, Capra axles are pretty popular for builds. There are quite a few "Chopra" builds out there that use the axles and a bit of the cage bolted onto an aftermarket carbon fiber chassis. I do not know if there are any that use the Capra transmission. The original Capra transmission was not very popular since the gearing was crap, but the new one is supposed to be better. Maybe some chassis will work with it.