Balancing Weight

[DirkDigler]

I cut and pasted this from another post I did. I thought it was important that everyone reads it, as I believe it to be the most overlooked area in building our trucks. Get it right and you'll build a truck that is unstoppable!!!

I have not done as much trial and error on any truck as with this one. I took my time and tried things over and over and over again. The biggest thing I experimented with was weight placement. I was building my rigs so every ounce of weight was shifted to the forward portion of the truck. This worked.... but what I found was that more balance was even better. You'll notice that the 1:1 comp trucks are putting much of their weight in the center of the truck. The engines are appearing behind the driver, in fact....and almost sitting on the ground. So what I really worked on was getting the perfect balance of weight from front to rear and even side to side. Once I got the motor, tranny and battery placements correct, I worked on other minor areas, such as electronics. I also cut the chasis so it was completely symetrical and then balanced weight from there. Then I played around with weight in the tires and mounting location of the body.....which will be mounted even lower soon! When I was done....I looked at the rig all put together and you can see a big imanginary "V" where all the weight is placed. It took weeks of trial and error to get it perfect but what came of it all is a truck that is very, very tough to get onto it's lid. It climbs as well, if not better than any Clod I have seen. I can hit stuff at speed, on the throttle, off camber...and it will not roll over. The tires, with their new side lugs, bite on everything and rarely lose traction!
In short....I ran my obstical courses many times this weekend, perfecting the truck. As you all know, many of us have run these courses and they are very tough and take many attempts to get past some of them. Some are almost impossible to tackle without stacking up some points by hitting flags, etc. This truck took on every obstical with ease. I rarely had to back up and start again. I never rolled over once! I didn't keep my own score but I went through the whole thing and I don't believe I ever hit a flag, backed up too far or made any other mistake that would have earned a point!!!
I have found that weight placement may be the MOST important ingredient in crawling!!!!!

[SR5Dave]

I totally agree, weight placement is very important.

A lot of it depends on where you wheel. For me, its a LOT of all vertical stuff here, and lots of rocky hill climbs. On my last rig, I had both batteries basically over the front axle, worked excellent for that. In this rig I don't have room for it like that though :? So I've got it on the uppers. Good enough!

[Ace]

I think battery over the axle is a killer... Here's why:



The battery over the front axles seems like the thing to do, when viewed on horizontal ground. When climbing near vertical, it becomes a liability due to the heigh it must be placed at to clear the front axle/sus links.

Tough to do on a shaft truck due to tranny/drive shafts but when I build my next shaft truck the battery will be low and centered...

[DirkDigler]

I thought having all that weight way up front, right on the axles, was the best way to go too. However, I'm quite certain, that it's not! All that weight on the front axle tends to throw things off when climbing steep rocks. Think about it. You get all of it pointing straight up....it's all at the top of the truck. As you give the truck throttle, the weight tends to pitch left and right. It wants to give in to gravity. Picture this: You have a roll of paper towels. You place a bowling ball affixed to the top of the roll of paper towels and try to balance it in the palm of your hand. All that weight wants to shift around. It's unstable at the top because the imbalance of weight. Same thing with the rc crawler. Weight up front is good for climbing but you must compensate by having the appropriate amount of weight in the center and the rear of the truck.

[DirkDigler]

good illustration Andy. That's exactally the point I was trying to make. Low and center!

[badger]

DAAAAMN! I just finished my new battery layout, and now I have to go back to the drawing board! DAMN!

Great info though!

[Ace]

Before you go to a few comps or get togethers everyone thinks their rigs are world beaters, cause even the lamest r/c rigs have awesome abilities compared to 1:1 rigs.

Then you go to a comp and for example if your rig will climb 60 deg angle and someoneelses has a lower CG and will climb 65 deg angle. If the obstacle is 64deg, your screwed. If 6 of the obstacles are 64deg your embarassed! (been there done that!)

I used to be a shaft truck supporter, But I've learned that it will be very hard to out climb a clod. No matter how low you make a shaft CG, a guy can build the same rig (wb, ground clearance, width etc) in a clod and have a lower CG AND be lighter. Not that I've given up on shafts, you just have to build a shaft better than a clod to be equal. Not an easy task!

Another thing that kills a shaft, at near vertical your front axle experiences driveshaft torque and the axle twists and pushes you away from the rock face. Over backered you go. I know you can controll the torque, but you can't eliminate it w/o putting the motors on the axles (clod). ( I do have a few ideas however...)

[DirkDigler]

Not necessarily! Where is rest of the weight placed?
This whole thing took a lot of time and experimentation but I think I've got it dialed in.
Personally Badger, I would try your mounting point out and if it works for you...stick with it. However, if we get together and see this thing crawl....you are going to start playing around with weight balancing.

[DirkDigler]

You are right Ace!
Everyone thinks they have the greatest crawler on earth....until they see some other creation that is a real force!

I am only basing my comments on the performance over my courses. I have not seen a truck get through them as easily as this truck....even compared to all the clods that have been over here for the comps.

For example...on my first water fall: I can pick any line up the fall and never stuggle. It goes up and over every time, with ease. It really surprised me! the rest of the obsticals are just too easy for it. I will have to redesign the course for the next comp.

[Ace]

That wasn't directed at you dirk, actually supporting your findings!

Just a general comment. Something I had to learn the hard way.

I can't wait to see the new rig.

I think your course favors some strengths of shafys over clods, especialy the "top" sections... Rocky, rough terrain that requires picking lines on top of rock tips, shafts help because the syncroed front and rear (no slip) offers better manuverablily IMHO, less likely to slip the front end into a crack, plus most shaft rigs have better engineered steering than a widened (with wheel spacers) clod due to the excessive scrub radius on the clod.

Having said that, the waterfall is a damn tough climb obstacle that I would think favors clods so if yours walks up that then thats saying something

[fullmodtxt]

Hi guys! Thanx for the post Digler, this ought to turn out to be a healthy discussion! I'm going to keep an eye on this thread!
I have my pack set directly over the front links. The pack is mounted down as low as it can go! The top of the pack is even with the tops of the tires. The links hit the pack when the suspension fully compresses ( I lose about 1/4 inch of downtravel), but I there is no interference with articulation. I also have the tranny/motor mounted as low as they can go. Before I added the GD-600, the motor was below the tops of the tires, now it is slightly above with the reduction. The tranny is turned to put the motor in the front of the truck. Aside from the reciever, there is no wieght in the rear of the truck. I also have slightly over a pound of BBs in the fronts.
I am running slightly over 16 inches of wheelbase with TC tires (just under 7 inches). I have trimmed absolutely ALL of the removeable wight out of my TXT, including cutting the frame down to almost nothing. I have the body mounted so low over the chassis that I had to cut out the bed and put holes in the hood for the cantis and shocks to clear. The wheelwells had to be trimmed bigtime to clear the tires when the suspension flexes. I have 4.5 inches of clearance under the truck. The links are parallel to the ground at ride hieght, with the lower links mounted above the axle housings. My TXT doesn't have a whole bunch of articulation, I get about 7.5 inches under the inside of a tire before it will lift the opposite corner.
I really do think that this is a personal preference/terrain kinda thing. With the wieght in my truck mounted down low and in front, combined with the reasonable articulation, the front tires literally always stay planted. This works out well for me because the front is always planted and ready to point wherever I want it to go. Again, since the fronts are always planted, they are always helping to pull along the rears, even if 1 rear (or both!) lose traction. For whatever reason (gear reduction, suspension geometry, shock tuning, all?), I have totally eliminated the torque roll that TXTs are victim to.
Stability is not an issue with my truck. It will stand on the tire sidewalls, and climb straight up doors, walls, or whatever and stand right up on the rear tires W/O rolling over, with all 4 tires against the wall. All of this is fully loaded, at ready to crawl wieght. I don't have any current pics of this setup, I'll try to borrow a digicam within the next couple days. Vince

[badger]

Originally Posted by WannaBeDigler

Personally Badger, I would try your mounting point out and if it works for you...stick with it. However, if we get together and see this thing crawl....you are going to start playing around with weight balancing.

Yeah, I will deffinitly run my setup at this weekend's comp since I know I do not have enough time to figure out the balanced setup. The problem I have is if I know there is a possibly better setup I will not be happy until I have tried the setup myself.

I just wish I had more time to work on my crawler!

[MUD4FUN]

I found the best overall compromise was having the weight in the center of the chassis too. This is my first shaft driven crawler I built from scratch and I have tried the battery in several places. In the end because the motor and gearboxes took up all the room in the center I chopped the pack in two and made saddle packs. I also run lead rings in the tyres and lead sheet wrapped around my lower wishbones. CoG is quite low, it has an angle of tip of(sideslope ability) of 52 degrees despite the narrow track and short wheelbase. I'm only running 4.75" IMEX Swamp Dawgs so my CoG is already slightly lower than most anyway.

On the next truck I'm working on I will have these saddle packs located lower down as well. However, this truck performs OK in most situations for a shafty.

I have to agree totally with Ace though, I suffer bad torque twist at extreme angles. The truck reaches a point, normally 50 degree'ish where the torque just twists the truck over backwards or at least lifts the front wheels thereby losing valuable traction.

Although I like the scale appearance of shaft driven I'm also working on a revised design using motorised buggy transaxles. Still want to keep the 'locked' wishbone arrangements as I like the extra under diff clearance they give. With no center motor and transmission I'll be able to drop the pack some 2" lower in the chassis and still keep the 4" clearance.

Here is a pic which just about shows the pack I split into two and mounted either side of chassis members.

[DirkDigler]

the torque twistof a shafty is equivalent to the clod problem of the differentiating motors. They are both annoying and hinder forward progress but much of these problems can be easily over come by the driver learning to cope with them. I have minimized the torque twist by about as much as possible on my truck but it still exists. however, if you are easy on the throttle and control that torque twist by being careful, you can use it to your advantage in certain situations....just like the Clod problem.

[MUD4FUN]

Yes very true, I've also found fitting the lower reduction gearing helps, I can move the vehicle at barely tickover and trickle it over obstacles without having to apply much throttle so the torque twist is either less noticeable or more controllable

[badger]

Well, I finished the new layout last night. I don't think it is as advanced as Dirks setup but the battery is in the center and the motor was moved to the front of the chassis.

I could not test drive it since I forgot to charge the battery.

[DirkDigler]

good luck Badgy!

[Mad Scientist]

I have always favored mounting the pack fairly centered and low. Where I wheel (mainly trials type terrain) you don't see to many vertical climbs, but there is a lot of off camber action, and that is where getting the pack low comes into play. And I agree that with the mass more centralized, you can really tackle obstacles more aggressively. Not only does it keep the truck nice and squarely balanced, it evens out the traction between the front and rear wheels.

[NEMYSIS]

What I want to know is why there is even a comparison between clods and Shafty's, Clods are a totally unrealistic design and shafty's are the real thing. Hell if you really want to go all out make a rig that has a motor for all four wheels and a way to vary the speed on all for motors. Clods are not even a realistic truck so there is no comparison to a shafty.

[Shorty40]

Originally Posted by NEMYSIS

What I want to know is why there is even a comparison between clods and Shafty's, Clods are a totally unrealistic design and shafty's are the real thing. Hell if you really want to go all out make a rig that has a motor for all four wheels and a way to vary the speed on all for motors. Clods are not even a realistic truck so there is no comparison to a shafty.

Sounds like someone has a shafty that cant keep up with the Clods