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Old 01-14-2016, 11:24 AM   #1
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An interesting POV on technology

Ever wonder why those of us with computerized buses need authorization from manufacturers before we can tinker with the computer's programming (particularly locked double overdrive on MD3060 trannies from Allison)? Because of copyright laws, something that needs to be fixed, as explained in this blog on Slate
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Old 01-14-2016, 04:39 PM   #2
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Yep! As they say in the Maker Movement, "If you can't open it, you don't own it."
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Old 01-14-2016, 05:33 PM   #3
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Quote:
Originally Posted by dan-fox View Post
Yep! As they say in the Maker Movement, "If you can't open it, you don't own it."
If is not under warranty, you ca do whatever you want.

all those companies that sell those chips for "performance improvements" will be out of business if that was the case.
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Old 01-15-2016, 12:05 AM   #4
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That's not quite accurate. Why do the performance chips people not get shut down? I don't know exactly, but I imagine it has something to do with their symbiotic relationship with automakers. You don't see performance chips for minivans. You see them for pickup trucks and sports cars -- the vehicles that traditionally provide the largest profit margins for automakers. It isn't hard to imagine that automakers recognize that the ability to performance-tune those vehicles helps drive sales of new vehicles to the die-hard fans, and that said fans are likely to order all the profit margins, er I mean optional equipment, on their cars. It also isn't hard to imagine there's a tolerance, likely written agreements, and possibly even mutual support between the automakers and performance vendors. Where there's permission given there's no violation of DMCA.

The chilling effect of DMCA is very real. Myself, I've been tempted to build hardware to download the calibration out of Allison transmissions to see whether I could work out how to binary-edit mine and unlock my second overdrive. One of the reasons I don't is that if I override some security feature in the process, even unknowingly, and even though I "own" the equipment outright and there's no warranty or other claim to be made to Allison, it could still be illegal under DMCA.

It shouldn't be that way.
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Old 01-15-2016, 08:18 PM   #5
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what does the second overdrive do? why would you want to tinker with it? can we make our buses get super mileage and fly uphills? no really, i completely dumb to the programming end of things inside my buses brain so i do mean it what would you do if it was legal and why?
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Old 01-15-2016, 08:56 PM   #6
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Long ago (I presume -- it's before my time!), the top gear in transmissions had a gear ratio of 1.0. Transmission gear ratio is the input speed in RPM (which is also the engine speed) divided by the output speed in RPM. So in the top gear, the engine is spinning 1.0 times the speed of the prop shaft going out to the differential. Engines grew stronger and vehicles traveled faster and eventually somebody asked "could we make the prop shaft spin FASTER than the engine?"

And so "overdrive" was born. In the medium-duty Allisons I'm aware of (MD3060 and B400) the first overdrive ratio is 0.75. In that gear the engine is spinning 0.75 times the prop shaft speed: if the prop shaft is doing 2000 RPM then the engine is doing 1500 RPM. The engine consumes less fuel and makes less noise as compared to running in the direct 1.0 ratio/gear.

Those medium-duty Allison transmissions are 6-speed boxes. The 4th gear is the 1.0 ratio, the 5th gear is the 0.75 ratio (first overdrive) and the 6th gear is 0.65 ratio (second overdrive). It's the same principle as the first overdrive: the engine can turn even slower for a given road speed. For the same 2000 RPM prop shaft speed the engine would do 1300 RPM in 6th/second overdrive.

I'm comfortable cruising my bus at 70 MPH. With the transmission in 5th gear the engine has to turn nearly 2400 RPM, which is fast for an 8.3L diesel. The rev limiter is right there, so it's the "full throttle cruise control" method.. I'd really like to have 6th gear available so on flat land I could still do 70, but drop the engine speed to a more reasonable 2100-ish RPM and hopefully boost the fuel economy.

Probably one reason why the bus was built with 6th gear disabled is that if a person wound the engine out to 2400 RPM in 6th, it'd be a road speed around 80-ish MPH. I suppose Blue Bird wasn't comfortable with the idea of their buses running that fast and decided to prevent it rather than rely on the good sense of school bus drivers everywhere.
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Old 01-15-2016, 11:56 PM   #7
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Actually, Allison's statement regarding the limiting of sixth gear relates to the speed limit of school bus tires more than anything else. Go figger'.
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Old 01-16-2016, 07:45 AM   #8
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strong work explaining. thanks. guess i will need some racing slicks and a good hacker! lol
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Old 01-18-2016, 12:29 PM   #9
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The speed limit thing is a good point. But that doesn't answer the question of why no 6th. If they were worried about speed, they could simply select the speed limiting feature in the control module, then they you would input the tire size(revolutions/mile) and the engine wouldn't be allowed to turn over X amount of rpm in Y gear.

It just doesn't make sense to me why you would go about limiting the speed by eliminating a gear.
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Old 01-18-2016, 01:37 PM   #10
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I've wondered why they might limit speed via the transmission too. I've seen (and modified) the speed limit control in the Cummins ECM on my bus; that was very accessible/easy to do with Cummins tools anybody can get. The change to add 6th gear is a much higher bar. Perhaps that's why it was done? Maybe the policy dates back to the time when these transmissions came on the scene but engines were not yet computer controlled?

It could be that the concern is something other than road speed (whether for chassis dynamics, tire rating, or other reason). Drive shaft speed maybe but it's intimately tied to road speed and easily controlled by the same means. I haven't been able to concoct any valid reason why 6th should be disabled, and thus my desire to ignore "those who know better," enable it, and enroll in the school of hard knocks to learn for myself!
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