Thanks to the TechnoKats.

[Elgin Clock]

With the white paper posted on Delphi, at HERE
We at the Sie-H20-Bots, Team 237, have built our motor box(es). A big hearty Thank You goes out to the TechnoKats for thier gracious professionalism in sharing this idea! We modified it quite a bit to accept a pneumatic mechanism, but it's still the same concept! Sorry I can't tell you how many of these wonder boxes are on our robot, but it's more than one!!


See the picture of our modified gearbox here: Our Gear Box(es)

Again Thank you TechnoKats!

The picture quality is not as good as I would have liked it to have been but hey, what are you going to do??

[Andy Baker]

Elgin,

You are very welcome. From looking at the pictures, I see many improvements that you guys have made, and they look great!

Your pneumatic shifter is better than the servo we have used in the past, in my opinion.

Also, the fact that you replaced the gearbox shaft is a smart move.

You have built a nice switcher here, that's for sure, and you will soon realize the multiple benefits to switching gears.

Andy B.

[Elgin Clock]

The idea to replace the servo(s) with a pneumatic cylinder was forced upon us. I think our electrical team already claimed the servo's in the beginning of the overall design process.
Hopefully we will have some good luck with this configuration!

[Jon Lawton]

Just curious... what are the advantages of using pneumatics to switch gears as oppsed to servos? Pneumatics make me nervous because there is a lot of force at the end of that shaft, and that transmission wasn't ment to be pounded...

[Andy Baker]

Here are the advantages I see of using a pneumatic cylinder over a servo:

1. The cylinder gives greater force for the shift, but not too much. This can also be regulated and flow controlled for fine tuning.

2. The cylinder would shift quicker..

3. The cylinder has it's own "spring", and will slip into place easier than the servo. While the servo may need to be indexed back and forth to engage, the cylinder would simply continue to force the arm over while it is trying to find it's mesh.

4. The hardware needed for pneumatic sliding seems simpler than the servo. Although the servo's block slide design has been around for a couple of years, it took us a while to get it to its current elegant design.

Also... there are some negatives to using a pneumatic cylinder for gear switching:

1. It MAKES you use pneumatics on the machine. If you were planning on saving some weight and not using pneumatics, then you're stuck using servos.

2. The servo is a lighter weight mechanism than a cylinder, valve, and fittings involved with pneumatic swithcing.

3. The servo takes up less space.

As for the pneumatic cylinder damaging the gears by slamming the shifter back and forth... I think that the cylinder can be controlled enough so that no damage is done.

Regards,

Andy B.

[Ken Leung]

Just remember that you can only use 5 pneumatic actuator, so you might want to save up two actuator by using a servo instead...

Pneumatics can be really useful at other bigger size components, especially with the 2" bore actuator that can push 180 lbs of force (and a little less pulling). Really good for lifting goals a little bit to transfer weight onto your robot.

Servo is a really weak motor, so don't expect them doing much other than shifting gears for drill transmission, or unlocking devices. When using them, make sure you design it mechanically such that your device doesn't require much force from motor to hold on resulting position...

Take the the technokat's shifter for example. You can design it such that when the drill is in low gear, the servo "plus" attachment is perpendicular to the shifting metal strip. So, if it try to push back, it's pushing against the servo's shaft instead of spinning the "plus" backward... This kind of thing.

But it is a really simple motor to use, if you do it right. Doesn't take as much power as the pneumatics if you are using the electric pump.

[Greg Ross]

Originally posted by Ken Leung
Take the the technokat's shifter for example. You can design it such that when the drill is in low gear, the servo "plus" attachment is perpendicular to the shifting metal strip. So, if it try to push back, it's pushing against the servo's shaft instead of spinning the "plus" backward... This kind of thing.

Sorry Ken, but I'm having a hard time visualizing what you're describing here with the "'plus' ... perpendicular to the ... metal strip". Are you describing the way the Technocats oriented their servo? If I study their drawings, will I be able to figure out what you're talking about?

[Ken Leung]

Originally posted by gwross

Sorry Ken, but I'm having a hard time visualizing what you're describing here with the "'plus' ... perpendicular to the ... metal strip". Are you describing the way the Technocats oriented their servo? If I study their drawings, will I be able to figure out what you're talking about?

Sorry for the weird worded example... It was the only thing I could think of @ 3:30am in the morning.

Anyway, I was refering to the servo shifter technokats have in the white paper section. You see, on the servo, you can put different "heads" onto the servo output shaft, they come with the servo motors inside a little zip-lock bag.

So the "plus" shape is one of the many head you can use for the servo, and put littie screw on it to engage the sliding block that do the actual shifting motion.

When the servo attachment lis locking the drill transmission in one of the positions, my idea is to have the attachment pointing straight at the metal strip, forming a 90 degrees angle between the strip and the servo arm.

This way, when the transmission want to drop out of gear, the metal strip is pushing against the servo arm pointing at it, and there will be little moment generate by this set up to backdrive the servo itself.

My point is, design your mechanisms such that you avoid back driving the little servo as much as possible. Have the servo activate a lock or some sort... Chances are, your lock will hold more force than the servo.

[Greg Ross]

Originally posted by Ken Leung
my idea is to have the attachment pointing straight at the metal strip, forming a 90 degrees angle between the strip and the servo arm.

Thanks. That helped.