Weights of Crawler? Confused.

[soutthpaw]

It seems that the whole weigh thing is confusing (at least to me). on the one hand I see folks trying to make their crawler very light but then they go and add weight to the wheels etc.
There also has to be a point where its too light. the amout of ground pressure is going to decrease with fatter/flatter tires and lighter vehicles to where you don't have enough weight to grip instead of slip.
So please school me on the weight philosophy you all are using.

I do understand the rotational weight is going to get you more traction and help rock you back over. Rotational weight gives a 3 to 1 advantage over static weight.

[Szczerba]

It's a concept of weight in the right places. My comp 2.2 truck is 5.6lbs but at least 1lb of that is in knuckle weights and wheel weights. I run most of the weight in the knuckle weights and then a little on the wheels. I think it's a blend of the two to get what you want.

And it's definitly a test and tune concept concept as well. I switch up weights depending on course setup and layout.

Example.
I see guys go with super light rear axles but then add additional weight back to the axle via static lower cg weights.

[JeremyH]

It's all about the center of gravity. If you can reduce weight that is high above the ground and increase weight lower to the ground, then your truck will be more stable in most conditions...

Originally Posted by soutthpaw

I do understand the rotational weight is going to get you more traction and help rock you back over. Rotational weight gives a 3 to 1 advantage over static weight.

How did you come to the "3 to 1 advantage"?

Yes, angular momentum is directly related to the mass of the rotating object and will help rock the truck when on it's lid.

[Krawler23]

from what i have seen most are anywhere from 4.5-6 pounds. I think the lighter it is then the center of gravity is lower as well. So yes you do not want it to be crazy light but also dont want it too heavy, u kinda have to find what works for you. Most put weights on for added traction. I hope this helped!

[soutthpaw]

Originally Posted by JeremyH

It's all about the center of gravity. If you can reduce weight that is high above the ground and increase weight lower to the ground, then your truck will be more stable in most conditions...


How did you come to the "3 to 1 advantage"?

Yes, angular momentum is directly related to the mass of the rotating object and will help rock the truck when on it's lid.

its all about rotational dynamics and that is just a simplified reference
Moment of inertia - Wikipedia, the free encyclopedia
think of taking a bicycle wheel and holding the axle. now tilt from side to side. easy right? now spin the wheel and try tilting side to side its a lot harder. that is the basic premise. same reason those spinning wrist exersize balls work on. http://www.powerballs.com/

[JeremyH]

Yes, I understand moment of inertia quite well. Adding weight further out will reduce the wheel's resistance to change it's motion. However, I would not say that this is always an advantage nor is it always a disadvantage when it comes to rock crawling.

Both setups have positives and negatives.

[JeremyH]

Originally Posted by Szczerba

Example.
I see guys go with super light rear axles but then add additional weight back to the axle via static lower cg weights.

One major benefit to that is reducing the weight toward the center of the axle and placing it further toward the tire contact patch. This will help keep the truck much more stable in off camber situations.

A good example of this is a tightrope walker. They use those long poles to distribute their weight far away from the wire which helps with their balance.

[Szczerba]

Originally Posted by JeremyH

A good example of this is a tightrope walker. They use those long poles to distribute their weight far away from the wire which helps with their balance.

Exactly what I do, widen the rear out a little when my truck's rear end gets a little tipsy. Don't need to add anymore weight.

[AX10wannabe]

yesterday i was crawling with a guy that had an all aluminum ax10. it had aluminum knuckles, c's, links, wheels, chassis etc and running a 7950mg servo and i got curious to how heavy it was and to my surprise it was ridiculously light, way lighter than i thought it was and it climbed like a goat, he was using 2.2 sedona's with stock foam 5oz in each front wheel and nothing in the rear.. of course this was the one day i forgot to grab the camera.

personally i think its not how much weight you have its more of weight placement. you want your weight down low.

[baconCHDDRchips]

i agree, my rig weighs in at 6lbs even! about 1.1lbs of that is nuckle weight. it really comes down to placement of the weight. if your rig weighs 3lbs but 2lbs of that is on the axles your laughing IMO. but if it is 8lbs and the weight is distributied all over the place your in trouble. just my 0.02

[soutthpaw]

Originally Posted by JeremyH

One major benefit to that is reducing the weight toward the center of the axle and placing it further toward the tire contact patch. This will help keep the truck much more stable in off camber situations.

A good example of this is a tightrope walker. They use those long poles to distribute their weight far away from the wire which helps with their balance.

That makes sense, good example Jeremy. Thus the benefits of knuckle weights as well as the slug type wheels as you cannot get the weight any further out than that.

[JeremyH]

Originally Posted by soutthpaw

That makes sense, good example Jeremy. Thus the benefits of knuckle weights as well as the slug type wheels as you cannot get the weight any further out than that.

Yep. IMO, it is good to have a mixture of both. On my 2.2 comp truck, I run most of the weight on the knuckles and run heavier wheels in the front (no slugs, but my rear wheels weigh less than the fronts do). This gives the benefits of knuckle weights, but also allows for a bit more angular momentum from the front tires (when compared to the rear).

[soutthpaw]

Now I have a bettier idea of how I want to go about setting up my Berg. Just pulled the wheels and axles apart last night, there are 2 strips of stick on weights in each front wheel. Will leave them setup like that for now till I get it built and do some test runs. have a second set of wheels that will take the slug weights too.

[JeremyH]

Yeah, really it is best to just try different setups and see what you like.

I know it is tempting to try and apply mechanics theories to these little cars, but there are so many variables that come into play that it soon becomes a rather difficult problem.

[junkyardyota]

But you want to keep the wheels lighter makes them easier to spin am I right? Thats the whole concept of knuckle weights, to take some of the weight out of the wheels, but keep it almost in the same place. I am a newb but it makes since to me and if you take rotating mass out of the wheels and tires its easier on parts. I may be looking at it wrong I dunno like I said I'm a newbie

[MudboyNJ]

Originally Posted by junkyardyota

But you want to keep the wheels lighter makes them easier to spin am I right? Thats the whole concept of knuckle weights, to take some of the weight out of the wheels, but keep it almost in the same place. I am a newb but it makes since to me and if you take rotating mass out of the wheels and tires its easier on parts. I may be looking at it wrong I dunno like I said I'm a newbie

I know this plays a roll in the 1:1 world for sure, hence the reason we use carbon fiber wheels, aluminum hubs/driveshafts and titanium lug nuts and studs. There's an old philosophy in the racing world where for every 10 lbs of rotating weight lost equals to about 100 Lbs of static weight. The only way I see this applying to the rc crawler world is strain on the motors.

[troyd]

I'm sure the loss of speed is real with heavier wheels, we just aren't dealing with real high speeds to begin with, and you can always add voltage or more powerful motors to compensate. But, that means you are compensating. It is just a matter of compromising correctly for traction and wheel speed

[junkyardyota]

Yes more volts makes a big difference (and a big smile usually)

[Charlie-III]

Originally Posted by soutthpaw

its all about rotational dynamics and that is just a simplified reference
Moment of inertia - Wikipedia, the free encyclopedia
think of taking a bicycle wheel and holding the axle. now tilt from side to side. easy right? now spin the wheel and try tilting side to side its a lot harder. that is the basic premise. same reason those spinning wrist exercise balls work on. NSD Powerball Gyroscope for sports and fitness, carpal tunnel, tennis elbow, tendonitis, wrist pain and grip strength

Your 2nd example is really more of "gyroscopic stability" which has nothing to do with crawling.

In reality, the heavier wheel helps rock the rig (like when upside down) because when you change drive directions, the moving mass of the wheel resists rotational direction change. Because of this, the applied torque is transferred to the chassis and causes it to rock lengthwise.

OP, as mentioned, it may sound conflicting but the reason do make sense.

A rather light rig that has most of it's weight up high will likely not work as well as a heavier rig with most of it's weight way down low.

Weight is not really the issue, it's WHERE the weight is.
You want it low, rather wide and slightly biased toward the front. Reduced rotating mass is also desired. Partly to reduce drivetrain loads, partly to increase wheel acceleration/deceleration when getting on/off the throttle.

[Trubble]

Originally Posted by Charlie-III

A rather light rig that has most of it's weight up high will likely not work as well as a heavier rig with most of it's weight way down low.

......... as evidenced by how much time my Ax-10 spent on it's lid at the last comps I went to!
And with little or no wheel speed (6 cell NiCad, 55T motor, 14-87 stock gearing), and no weight in the wheels, I couldn't get it to rock for nuthin'. Found a way to get the stick pack off the top and down onto the axle plates, but haven't yet put the effort into making the wheel weights. Figured I'd try the battery relocation first, see if that'll get me where I need to be.