Gearboxes

[DrewMatic]

Hey everyone. I'm from 240 T.E.M.P.E.S.T and I'm trying to do some research. Last year we used tough box minis with mecanum wheels which worked pretty well. This year we used 2 speed supershifter gearboxes which were slow in low gear and jerked coming into low gear from high gear as well as into high gear.

I know there has to be a variety of different gearboxes to choose from. Is there any ones that your teams have used which worked pretty well in past years?

Thanks, Drew

[Peyton Yeung]

461 has used toughbox minis in the drivetrain for 2014 and 2015. This year we used sonic shifters. We liked the toughbox minis since they were so simple to integrate into our sheet metal drivetrain (direct drive using the frame as the output plate). The sonic shifter worked well for us all season until we sheared the pin in the dog gear. We had been using the internals of a super shifter from '08 so the dog gear/roll pin was the older revision than the current model. I'd also recommend not running the shifter on 60 psi (we feel comfortable with 35 psi).

In regards to the "jerk" when shifting, you might experiment with ramping your motors and auto shifting for a smoother more efficient drive.

[Knufire]

...which were slow in low gear

Most COTS gearboxes actually have multiple ratio options that you can try. Did you try swapping the gears in your SuperShifter for a faster low gear? Ratio selection is a bit of a seperate topic from "What gearbox should I buy?".

jerked coming into low gear from high gear as well as into high gear.

Were you shifting with servos or pneumatics?

[DrewMatic]

461 has used toughbox minis in the drivetrain for 2014 and 2015. This year we used sonic shifters. We liked the toughbox minis since they were so simple to integrate into our sheet metal drivetrain (direct drive using the frame as the output plate). The sonic shifter worked well for us all season until we sheared the pin in the dog gear. We had been using the internals of a super shifter from '08 so the dog gear/roll pin was the older revision than the current model. I'd also recommend not running the shifter on 60 psi (we feel comfortable with 35 psi).

In regards to the "jerk" when shifting, you might experiment with ramping your motors and auto shifting for a smoother more efficient drive.

We were talking about programming them to auto shift to low gear before stopping completely for less jerk. Thanks!

[DrewMatic]

Most COTS gearboxes actually have multiple ratio options that you can try. Did you try swapping the gears in your SuperShifter for a faster low gear? Ratio selection is a bit of a seperate topic from "What gearbox should I buy?".



Were you shifting with servos or pneumatics?

Didn't think about changing gears for faster lower speed. I will use that in the future. And we used pneumatics for shifting gears.

[InFlight]

There's been quite a few gearbox threads that you could look at. We used vex ball shifters, custom AM super shifters, and various AM single speeds (Nanobox, Toughbox, etc); all with good success.

Lubrication and attention to detail when assembling gearboxes is critical.

We generally choose our gearboxes based on the drive type, and wheel size, and desired speeds.

For a CIM
Wheel Speed = (4455rpm/60 sec) * ( 1/gear ratio) * (wheel size/12")*3.14

For a shifter size your high speed gear ratio to ~15 ft/sec and the low speed will just fall out of the high/low ratio. For a single speed aim closer to 12 ft/sec.

[Basel A]

I really doubt your problem is that you bought the wrong gearbox. My first guess would be that you're shifting at the wrong speed. There is an optimal speed for up-shifting and down-shifting. You want to look at the acceleration vs. speed curve for your drivetrain with that gearbox and shift where the curves for the high and low gears cross. This means you won't experience sudden changes in acceleration because they're matched (fun fact: "jerk" is actually the technical term for rate of change of acceleration). This can be done theoretically, but you can also play with it and try different speeds (if you'd like help let me know). Setting these speeds and auto-shifting is highly highly recommended. Also note that (1) the optimal speeds are different for up and down shifting because gearbox efficiency acts differently each way (hurts when accelerating, helps when decelerating) and (2) if you have one shifting speed and you're driving near that speed, it may shift back and forth repeatedly which is not good.

Rahul's question about servo vs. pneumatic shifting gets at another possible reason for that jerk. I don't think pneumatic shifter would have trouble, though.

[dk5sm5luigi]

If you want to see what gearboxes are out there you can compare them at http://findrobotparts.com/gearboxes