4EAT Diff-Lock Switch and Handbrake Mod - "Torquemada Lite" - Page 6 - Subaru Impreza GC8 & RS Forum & Community: RS25.com
 
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4EAT Diff-Lock Switch and Handbrake Mod - "Torquemada Lite"
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Old 03-03-2009, 09:29 PM   #51
defcon5
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Quote:
Originally Posted by obsolete View Post
So, you had a scope hooked up, or do you have a DMM that can measure duty cycle?
DMM - I don't even know how to turn a scope on, much less actually use it. I doubt my numbers are super accurate, but it at least allowed me to view the patterns under acceleration.

Quote:
Originally Posted by obsolete View Post
Anyway, a live AWD torque split gauge would be a pretty sweet project too
wink wink, nudge nudge *cough* prototypeonmybenchaswespeak *cough*
Wha?! Who said that??
(seriously, it's freakin' cool)

Quote:
Originally Posted by obsolete View Post
What's the flaw? Does the solenoid disengage too slowly?
Not so much the solenoid, but the TCU is INSANELY slow. Doesn't even budge from 68% duty cycle(~70/30 split) until you're well below walking speed - brakes, no brakes, doesn't matter. And once it decides to ramp up to FWD (95%) it takes about 1.5 seconds.
I was feeling lazy when I installed it, so my current switch just dumps out of the lock and into OEM control momentarily while the handbrake is engaged. Works for my car, but I wouldn't want to advise anyone else to do it. That's a lot of potential torque to be locking up with the handbrake.

No big deal, just a few more wires to pull. Now to figure out if the FWD fuse is putting out full DC voltage, or if it's playing PWM games as well. I see coveralls and a shop manual in my future.
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Old 03-04-2009, 05:28 AM   #52
levis76
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Quote:
Originally Posted by obsolete View Post
I'm not so sure--how does Subaru get away with the 90/10 default split, then? The rear wheels are definitely engaged to some degree, but nowhere near fully, and the car is in this config. most of the time.

That said, I don't really see myself needing anything other than FWD (solenoid fully powered), 4WD (solenoid disconnected), and AWD (let the car handle it).
This is very true, and after reading the results of defcons meter readings while driving, I am even more curious how this is achieved. I'll stay tuned and find out.
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Old 03-04-2009, 11:37 AM   #53
obsolete
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Quote:
Originally Posted by defcon5 View Post
DMM - I don't even know how to turn a scope on, much less actually use it. I doubt my numbers are super accurate, but it at least allowed me to view the patterns under acceleration.
Oh yeah, you have that Fluke--I didn't know the 112 could measure duty cycle.

Quote:
wink wink, nudge nudge *cough* prototypeonmybenchaswespeak *cough*
Wha?! Who said that??
(seriously, it's freakin' cool)
Using discrete components, or a microcontroller? I wanna know!

Quote:
No big deal, just a few more wires to pull. Now to figure out if the FWD fuse is putting out full DC voltage, or if it's playing PWM games as well. I see coveralls and a shop manual in my future.
I bet that the FWD fuse just puts battery voltage (100% PWM) to the solenoid, but I implore you to check rather than taking my word for it If it's that simple, then just have a relay triggered by the handbrake wire...the solenoid should respond plenty quickly enough when you do that!

Last edited by obsolete; 03-04-2009 at 11:44 AM..
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Old 03-06-2009, 07:31 AM   #54
sixth-star
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whoa im assuming this works on legacy's as well? i myself have a 98 LGT wagon and my gf has a 95 LSi. both are equipped with the 4eat trans so im going to follow this thread and see what havoc i can cause to my car before hers lol..
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Old 03-08-2009, 11:01 AM   #55
defcon5
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sixth-star, yes this should work across the entire Subaru lineup from 1987.5 to 2001. It's also applicable to '02+ models without VDC.
I don't have access to anything but a couple of GC Imprezas, but a lot of my initial info came from various Legacy and Forester websites, so I'm pretty confident it should cross over with no real issues.

Completely unrelated - Yahooo! This just got stickied!
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Old 03-09-2009, 01:50 PM   #56
defcon5
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Well, it's been an interesting weekend here at the defon5 Labs....

I woke up Sunday morning to find that my humble little DIY had been moved and stickied by the powers that be (good).

It rained continuously for two days (bad), but that meant that time in the shop was plentiful (good).

My iPod went insane, and is now a white plastic brick, leaving me to listen to horrid corporate radio stations (bad, and bad).

I finished up the prototype of the variable PWM controller, and had a VERY successful bench test (super-good).

Unfortunately, I hit a snag installing in an actual car, and have to redesign some aspects of it (meh).

Anyway - here are some pictures of the controller prototype.





I know it looks like a big confusing jumble of wires, but the general idea behind it is that the knob in front controls voltage to the AWD system, thus allowing the user to "dial in" the appropriate torque split for any given situation.
The tricky part was getting the frequency tuned using discreet components, but this is just a "proof of concept" - the end result will likely be microcontroller based.

To the right is my favorite feature - an LED bargraph that will visually show the amount of torque split.


When the controller is switched off and the car is under OEM control, the bargraph will then display a real-time readout of the torque split as chosen by the TCM - should be pretty cool to watch as it bounces around under acceleration.

Fun stuff!
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Old 03-09-2009, 10:51 PM   #57
obsolete
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That's pretty cool. I just had a brainstorm on the handbrake mod--it's in your PM box.

Sorry to hear about the iPod--should have turned to Pandora radio or something like that, although I hear they now play ads as well. If it's the hard drive that's died, yank it and replace it with solid-state memory
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Old 03-10-2009, 08:58 AM   #58
limited
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Hey! there's nothing wrong with listening to the mainstream crap radio stations are throwing out these days?

And that little gadget looks crazy! can't wait until the final outcome of it.
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Old 03-10-2009, 09:05 AM   #59
nctarheel1089
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If you end up selling the LED Bargraph one. I would definitely be up for buying it!
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Old 03-12-2009, 12:54 PM   #60
mvoulo
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I just installed my switch yesterday (thanks to defcon for assembling it for me) and it works flawlessly. The entire thing took about 30 mins and only cause I was double checking everything.

Now only if it would snow again...
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