Crawl Control... is it all it’s cracked up to be???

I don't plan to go wheeling but when I do i venture on my own. When I see a cut in the woods that looks to fit my truck I take it. Sometimes it is smooth and nice other times it's rough and muddy and not enough room to turn around.

 

This is incorrect.

In an open diff, torque across the axle is the same, speed can vary. This allows turning to be easy on dry pavement, but unequal traction causes issues. If one wheel is on pavement and the other on ice, it takes very little torque to spin the wheel on ice. Since torque must stay the same at both wheels, the wheel with traction will get very little power, not enough to move the vehicle forward. Total output is NOT always the same.

Locked diff is the opposite, equal speed, different torque. With one wheel in the ground and one in the air, they will both rotate at the same speed. It takes almost no torque to spin a free wheel, so that side will get very little, and the side on the ground will get almost all the power, moving the vehicle forward.

 

I think we are really splitting hairs here and getting caught up in semantics. In a locked diff both axels are locked together meaning that speed and torque are the same at both wheels always. The only thing that changes is the traction from one wheel to the other. So yes, torque will be applied to the wheel with traction cause it has no where else to go. But the other wheel still carries the potential energy. The power is still there it is just not being transmitted to the ground thru traction.

 

Wut? So I’m not allowed to use the system that is fitted to the vehicle from the factory, and works great, but have to retrofit a winch to go off-road? If crawl control works to get you out, why winch?

Anyways.......here is the Whole Fuckin Truth fellas:

If you’ve never needed crawl control, you just aren’t wheeling hard enough to need crawl control. There is absolutely terrain and situations where it is a godsend, or the best choice to keep moving, if you are brave enough to seek them out. I’d much rather just drive up a janky hill in CC than piss around winching up a hill, or take a run at the hill at full power and snap a CV.

Crawl Control is a technology, 4WD is a technology, shocks are a technology, tires are a technology, a sunglass holder is technology. Unless you are riding a donkey you are using technology.

The problem with discussing Crawl Control on this forum is that it is only on the newer Tacomas, so you are having a discussion with a group of people who own new, expensive, shiney trucks (often fitted with $1000’s of overland gizmos). Save a select few, the majority of people here are simply not willing to risk their truck and their gear in a driving situation dire enough that a system like Crawl Control becomes an important tool.

If anyone wants to go on a run where you will learn the value of crawl control, hit me up with a PM, but you gotta be willing to scratch the shit outta your paint and tear off a bumper cap or two.

 

Well said.

 

Even if it isn't a replacement for driving skill, it's good to have. Why would we yell at Toyota to take away new features that could help inexperienced people? Maybe all of these experienced people are just too full of themselves to try it out. Just my .02. New features are good, especially when they work this well.

I use mine in the winter for hill descent control so that I don't pick up speed and slide out of control on slippery hills. It works as advertised to maintain speed and keep your truck from sliding all over the place. Not as easy to do with brakes and down shifting in an automatic. This system is much better than attempting that, when any mistake can cause you to slide out of control.

 

Read this.
https://en.m.wikipedia.org/wiki/Locking_differential
Speed =\= torque.

 

I was going more towards the why pay for an offroad or pro when you can put that money towards lockers, actual coilovers, and recovery gear while still having money left over...

What will you do if this electronic stuff gives out on you one day or it doesn't work. Then you start posting everywhere asking for someone to come get you out... I haven't been on that side of the stick but I have had a guy post absolutely every where trying to get some one to help him, jeep and Silverado couldn't get him out but the winch pulled him right out.... if you go alone crawl control and lockers won't do shit when you get stuck.

 

I agree.

For twenty-two years, I had a job that required lots of off-road driving. Mostly GMCs, a few Fords, and one Jeep.

Those rigs were bush league compared to what my OR will do. Anyone that claims that they can do the same with lockers and a manual hasn't worked with one of these.

SB

 

Thanks for keeping trying to desiminate the truth... sometimes it can get buried by people who are just absolutely positive in the false.

 

Guess I never learned that rule! Don't much care to follow it either.

Reason I have this very capable rig and recovery equipment is to be able to do JUST that....get the hell out alone and away from everyone. I do like getting out with a few close family or friends, but often nothing beats just being out alone miles from anyone for a week or two at a time. A perfect trip for me is to be at least 50 miles down bad roads, and not see another person for days or a week at a time.

Prepared though? Sure. Winch, shovels, axe, chainsaw, 150' of additional winch line, first aid, SPOT messenger (with check in to family every 24 hours), tools, parts, water, food, etc. Risky? Eh, who knows. I figure my chances of being seriously hurt or dying are considerably greater every time I get on the highway. If I can't get out and back in safely with all of that gear, I've probably got myself into my last pickle, and wheeling with someone else would likely be of little help.

 

Note, i never said it changed input vs output; but you asked for math... So here goes.

Let's say drive shaft is doing 4000rpm and has 25 ft-lb torque. We will ignore all parasitic drag and assume 4:1 rear end.

So input power = 4000×25/5252 =19 hp

Normal open diff driving straight
Axle speed is reduced 4:1, so output rpm on axle is 4000/4 = 1000 rpm
Each axle takes 50% on flat level straight ground, with 4:1, each axle is 25*4/2= 50 ft-lb
Each axle takes 1000x50/5252 = 9.5 hp
So open diff, flat surface, Input = 19 hp, LH=9.5 hp, RH=9.5 hp

Normal open diff turning a sharp corner, with same input conditions
Axle speed average = 1000 rpm, but turning corner so LH axle = 750 rpm, RH axle = 1250 rpm
Each axle has same as previous 50 ft-lb
LH = 750x50/5252 = 7.1 hp, RH=1250x50/5252 = 11.9 hp
So open diff turning, Input = 19 hp, LH=7.1 hp, RH=11.9 hp

Normal open diff with one wheel on ground not moving, and the other wheel slipping and spinning, with the same input condition
Axle average speed = 1000 rpm, LH axle=0 rpm, RH axle=2000 rpm
Each axle still has 50 ft-lb
LH = 0x50/5252 = 0 hp, RH=2000x50/5252 = 19.0 hp
So open diff stuck with one wheel spinning, one wheel stuck, Input = 19 hp, LH (on ground)=0 hp, RH (in air) =19.0 hp
So tire on ground takes 0% of the input power, free wheeling one in the air 100% of the input power.

Normal open diff with LH on ground, and RH in air with ATrac or MTS applying brakes.
Each wheel has matched wheel speed, because of computer controlled braking on tire in air.
Each axle still has 50 ft-lb
Axle speed = 1000 rpm
LH = 1000x50/5252 = 9.5 hp, RH=1000x50/5252 = 9.5 hp
So the tire on the ground takes 50% of the input power, the tire in the air being braked, has 50% of the input power.

Locked diff, same 4:1 axle ratio.
Input 4000 rpm, 4:1 ratio, Output rpm = 1000 rpm
Total rear axle is 25*4 = 100 ft-lb
This is distributed to the LH and RH axle in an unknown distribution in general.
Assume 50% for first case.
LH axle = 50 ft-lb, RH axle = 50 ft-lb
LH power = 1000x50/5252 = 9.5 hp, RH = 1000x50/5252 = 9.5 hp

Now assume locked axle with LH tire on the ground, RH in the air
Input 4000 rpm, 4:1 ratio, Output rpm = 1000 rpm
Total rear axle = 100 ft-lb
LH is on the ground, it takes 100% of torque.
LH axle (on ground) = 1000x100/5252 = 19 hp, RH axle (in air) = 1000x0/5252 = 0 hp
So the tire on the ground takes 100% of the input power, the tire in the air has 0% input power.


So to review (ignoring friction losses)
Open diff, wheel speed not constant across the axle LH to RH. Axle torque same LH and RH. The wheel that spins faster takes more power. This goes to the extreme, where a wheel in the air takes 100% of the power.

Open diff, add A-trac or MTS. Braking the free wheel takes 50% of the power, remaining grounded wheel gets 50%

Locked diff, grounded wheel gets 100% of the power.

Crap, I should have just started a new thread.
Sorry.

 

My mistake. Torque will be different from side to side as traction/resistance from side to side can vary yet speed does not. I see your point.

 

I see my confusion with what you where saying now.

I was thinking in terms of the amount of energy required to turn the wheel in a locked setup . Energy at the wheel only

You went further and were describing in terms of torque felt by a surface in contact with the tire .

I'm sorry you think I'm wrong but I don't believe what I said was incorrect I terms of output at the axle .

I was absolutely incorrect in terms of what you described as the point of measurement at the surface where traction is occurring .

The MTS math though I believe is more complicated than presented. In my experience the wheel speed doesn't match across the axle. The wheel in the air is spinning much slower or even completely stalled. When stalled I believe the torque output is minimal to the axle in the air .

 

I did at the end use the winch to recover. While using the crawl control the truck kept creeping forward a little at a time (displacing the sand under the skid as I later found out) Pretty much like the video shows. I was waiting for it to popup and be on it's marry way. It just never did and we got bored with it.

 

Interesting observation. If it can do that, it becomes more and more equivalent to 100% locked diff. (I think any arguments of wearing out brakes are just misguided.)
Its a little harder to get opportunity in florida to get articulation to experiment.
I more ASSUMED that they would brake the floating tire to be slightly faster than the grounded tire. Then the computer would be able to detect when the floating tire was making contact again, because it would 'slow down' to match the unbraked tire. But that was really just an assumption.

Never really experimented or really played with it extensively, besides the work contained and then continued in later posts in this thread (https://www.tacomaworld.com/threads...s-non-trd-offroad.437814/page-7#post-16935442)

Should probably do a techstream log of tire speeds next time I think i might have an opportunity to get enough articulation, and maybe get some actual data on what the computer is doing to adjust wheel speeds.

 

I think that would be interesting if you could do that .

You can see it on some random YouTube vids as well .

There are instances where you see the wheel in the air stop completely. Especially when using crawl control.

This was a most enlightening exchange of information . I think it'd be great if you could add to it with that information

 

Even on the non OR’s, a lifted wheel will get locked by the TRAC system and transfer all the power to the opposite wheel. There’s a vid floating around. I posted the vid plenty of times, LOL. Awesome to see the wheel lift, get locked, then the truck’s right front tire doing most of the work, pull it up and over while dragging the rear end. Toyota seems to be going in the right direction with traction control.

 

Awesome.

I knew I'd seen videos of what I'd observed .

I couldn't speak to ATRAC though since I've only wheeled with Jeeps with lockers and other vehicles with MTS and crawl like 4runners.

The Toyota electronics work great though in comparison to any others

 

If you haven't read about it, techstream program and the OBD2 reader is pretty cool. Can collect data on the order of 10 hz, with quite a list of parameters. Not too expensive for an ebay copy (or use your OVtune dongle if you are tuned) https://www.tacomaworld.com/threads/how-to-log-data-using-techstream.543307/

(Just to give an idea, here is a 2 minute data capture I took when looking at the rear diff lock currents and status).