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View Full Version : Shifting transmissions: servo or pneumatics?

gnirts
13-01-2007, 22:15
A couple quick questions:

What are the advantages of using pneumatics vs. servos to shift the Dewault transmissions?

Do the Dewaults shift optimally without slowing down or cutting power to the motors (however briefly)?

Thanks in advance,
Robinson
gnirts
15-01-2007, 19:23
Anybody?
agndoggieboi
15-01-2007, 19:31
our team suggest using a pneumatic shifter than a servo simply because the servo takes to much time to shift as for the pneumatic its a lot quicker
but most it depends on what your aiming for your robot design
Lil' Lavery
15-01-2007, 19:37
I don't believe you could utilize all 3 speeds on a DeWalt if you use pneumatics (as FIRST pneumatic pistons can only be extended or retracted, not halfway). For that reason, I would suggest using servos.
amos229
15-01-2007, 19:40
From years of rc car racing experience, go with pneumatics, servos strip easy.
robotguru1717
15-01-2007, 20:47
our team suggest using a pneumatic shifter than a servo simply because the servo takes to much time to shift as for the pneumatic its a lot quicker
but most it depends on what your aiming for your robot design

i dont think the time delay is that big of a problem. its like 1/4 of a second of so for pneumatics and maybe 1/2-3/4 second for servos and servos in my oppinion are a lot easier to use.
amos229
15-01-2007, 20:49
But if the servo strips then you are stuck in a gear for the whole game.
gnirts
15-01-2007, 21:46
i dont think the time delay is that big of a problem. its like 1/4 of a second of so for pneumatics and maybe 1/2-3/4 second for servos and servos in my oppinion are a lot easier to use.It would seem to me that pneumatics would be much quicker than a quarter second. It's a tiny piston. Then again, the servos seem to move very quickly as well. But at the same time, they seem weaker and more likely to break.

What about shifting while driving quickly/pushing? Will the Dewaults hold up? Or should I quickly cut power to the motors in software (~1/40th of a second, not really enough to slow the robot) before I shift?

Thanks again,
Robinson
DonRotolo
15-01-2007, 21:52
as FIRST pneumatic pistons can only be extended or retracted, not halfway
Not exactly. Using what I wrote about here (http://www.chiefdelphi.com/forums/showpost.php?p=467706&postcount=12) you CAN position a pneumatic cylinder at some place other than the end points - but note that this can be unreliable (especially when the load is variable, but that's not the case here) and doing so does require some care to make it work properly.

But if I were to implement a shifter, I would use a servo, no question. Far more controllable, lighter (especially if no other pneumatics are used) and more flexible.

Don