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Thread: What shifting system do you use?

  1. #11
    After designing the pneumatic shifting system on our car and redesigning it for two years after, I'm still not convinced it is the way to go. For the same on-track performance (show me numbers) simpler is almost always better. I'm on board with UTA/Texas A&M with the mechanical clutch w/ downshift butterfly thing they've got with an electric kill switch on up shift. It just works, it's fast, it's easy to get into neutral, and I prefer that positive feedback; the ca-chunk, that says "you, sir, are in second gear now."

    Also, I like Paradigm Motorsports stuff but we had one of those solenoids that was leaking and I replaced them with the industrial Ingersoll Rand ones from Grainger. Maybe we just got the one bad one, but the IRs worked so I stuck with them. Also, you can look at Grainger/McMaster and find the exact size pneumatic cylinder you need; one that fits your packaging with length and diameter.

    BTW, there's an SAE paper on this worth reading.
    Matt Brown

  2. #12
    BTW, there's an SAE paper on this worth reading.
    Thank you!Any link on this?

  3. #13
    Originally posted by mech5496:
    We have considered building our own system, utilizing components such as purchased solenoids and build our controller, but being a small team (7-8 team members) and having only a little experience, means we cannot afford spending manhours on designing such a system.
    No offense, but I am very unimpressed by this type of decision-making.

    The time to properly decide on a purchased system is the same time, or less, that it takes to design your own. A pneumatic system is a very, very simple design exercise.

    It is my opinion that purchasing a system is actually wasteful in terms of resources, and certainly does not promote any learning.
    -Charlie Ping

    Auburn FSAE Alum 00-04

  4. #14
    We have been using the aforementioned Matt-designed CO2 system for 2 years, with varied success, then switched in '08 to a new system.

    The previous system was a solenoid actuated pneumatic cylinder with CO2. The calculations said "good for 1000 shifts," but in practice, we'd have dead bottles all over. Either they would leak, they'd freeze up the solenoids (even after installing a large expansion chamber) or the bottle would heat up in the sun and blow the safety valve.

    In '08 we switched to a nitrogen (or compressed air) system. It's lighter, theres no phase-change associated pressure spike like with CO2, and better yet, there are fewer connections. We've had the same bottle attached to the car since the California event, and it still shifts the car. Theoretically we have less shifts, but in practice, we actually get to use all of our N2 shifts versus almost none of our CO2 ones.

    The system has been bullet-proof thus far, plus it's easier to hit neutral consistently with better pressure control.
    Wesley
    OU Sooner Racing Team Alum '09

    connecting-rods.blogspot.com

  5. #15
    Thanks for the feedback!
    So, did you use a brand new system, or did you midified your previous one to work with nitrogen? In case of compressed air, did you have any problems with air humidity?

  6. #16
    I think a lot of those pneumatic and electronically controlled systems offer very small gains given the risk they introduce into the system. While a mechanical system isn't exactly easy to design and get right, after they are setup they generally work flawlessly for the life of the car (as long as you avoid lots of misalignment in the joints). It also seems like a big plus to me to not have to worry about refilling tanks and what not.

    Given that you are a small team, I would definitely just go with a good hand shifter so you can dedicate your time to more important issues.

    We use a hand shifter (butterfly style). If you pull the first lever back it up shifts with out clutch. If you push the first lever forward it clutches and then downshifts. You can also pull both levers together to clutch and/or up shift. I like the system a lot because you automatically clutch on downshift and because of the linkage, they are synchronized.

    Up shifting with an ignition cut is a good idea but I don't think it's that simple to implement imo. We have been working on a strain gauged linkage that is used to cut ignition but never really had time to finish it.

    We won acceleration at VIR and West with our current system (with less power and a lot more weight than our competitors (494lb/69peakhp). I think there are a ton more things to look at besides a shifter like, track and wheelbase, weight distribution, gearing, average power, tire selection and pressure, and car setup. Of course, if you don't practice you're not going to be very good either.

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