Gear Types

[Joe_Widen]

Well, I was just looking at 968's robot. I was trying hard to keep my jaw off the floor and then I saw their gearboxes. Those are beautiful. I did notice that the gear on their CIM and the gear on the first reduction were different then what I'm used to. They gears were on like a 30* Ang to the gear. It was weird. Heres the link to the picture,

http://www.chiefdelphi.com/forums/sh...hlight=pic+968

Look at the third picture to see what I mean.

Now is there an advantage to doing that, or do they just do it because it looks cool?

[Conor Ryan]

It's unlikely that its cut at 14.5*, 30* would more likely than not HAVE to be custom made, and a 20* pressure angle, commonly refered to as a Metric gear, is the only other reasonable alternative.

From what I've heard from people, though Metric gears are better for some purposes, I'm not sure if they are a step up in effiency though, and they aren't desirable because usually of a higher price, and a lesser availability, but at the size 968 looks to be using them, the price difference would be minimal I believe. However that depends on where you live (see Tristian's Response)

[Joe_Widen]

Well I figured it out. Its a helical gear and the reason they use them is because there is more surface area in contact allowing to transfer more torque. The down side is they are a very little less efficient.

[Cory]

Originally Posted by Joe_Widen

Well I figured it out. Its a helical gear and the reason they use them is because there is more surface area in contact allowing to transfer more torque. The down side is they are a very little less efficient.

I'm not entirely sure what you're talking about. neither 254 nor 968 used anything other than plain old spur gears in our drivetrain.

There are two possibilities to what you're seeing.

1) It's an optical illusion

2) (the more likely reason) SDP sent us gearstock with messed up teeth. They were slanted in multiple directions. The shop that made the gears for us did everything concentric to the teeth of the gear, and as such, they wobble slightly. You're probably looking at the gear when it's in the part of it's rotation that throws it off center the most.

[Tristan Lall]

I've got to admit that I can't see what he's talking about in that picture...they look like spur gears to me. But, just to clarify this:

Originally Posted by Conor Ryan

It's unlikely that its cut at 14.5*, 30* would more likely than not HAVE to be custom made, and a 20* pressure angle, commonly refered to as a Metric gear, is the only other reasonable alternative.

The pressure angle of 20° isn't limited to gears governed by Metric standards. Years ago, AGMA instituted Imperial standards dealing with 20° pressure angles, which were originally intended to replace the older 14.5° standards. But for various reasons (some performance-related, some logistics-related), the 14.5° gears never really died. So, to summarize: Metric gears are usually (but not always) 20° pressure angle, while Imperial gears are usually 14.5° or 20° pressure angle; note, though that the terms "Imperial" or "Metric" refer to the measurement system, and not to the actual dimensions, and that custom gears in either measurement system can have any pressure angle that satisfies the involute curve equations (though this is limited by practical considerations).

Originally Posted by Conor Ryan

From what I've heard from people, though Metric gears are better for some purposes, I'm not sure if they are a step up in effiency though, and they aren't desirable because usually of a higher price, and a lesser availability, but at the size 968 looks to be using them, the price difference would be minimal I believe.

As noted above, this statement is not correct. In the U.S., Metric stock gears tend to be more expensive than Imperial stock gears, because there is relatively little demand. The reverse is true in Europe.

Also, note that helix angle (i.e. in a helical gear, it's non-zero) and pressure angle are distinct quantities.

[Joe_Widen]

I swear its a helical gear. It cant be anything else. I'll post a picture on CD media, because my computer wont let the attachment thing come up.

http://www.chiefdelphi.com/media/photos/25071

[Madison]

It's not a helical gear. You can see the same gearboxes in the photo above the one yours is taken from and it's obvious from that photo that they're using plain old spur gears, just like the rest of us. There's no special sauce or anything.

[Joe_Widen]

Then why is the gear on the motor and the gear it meshes with have slanted teeth like that? I do agree that from the other angle it looks different. It just seems wierd.

[Richard Wallace]

Originally Posted by Joe_Widen

I swear its a helical gear. It cant be anything else. I'll post a picture on CD media, because my computer wont let the attachment thing come up.

http://www.chiefdelphi.com/media/photos/25071

Maybe the gear was moving when the picture was taken?

Digital cameras can do strange things when the target is moving.

[Ben Piecuch]

I think the resolution of the picture is what is making the gears look odd. Once the gear tooth size is on the same order of magnitude as the image's pixel size, the image gets a bit distorted.

Now, helical gears obviously exist, and there are probably more than a few FIRST teams that have used them. However, team 968 is not one of them...

BEN

[Travis Covington]

This should help...

Spur gear it is.

[Lil' Lavery]

Any chance the rest of us can see the designs on those transmissions?


And yup, definately a spur gear.

[JoelP]

I read that you guys used 32 pitch gears. Why did you choose to use those over more common (as far as I know) 20 pitch gears? Advantages/Disadvantages?

[Joe_Widen]

How do you guys get those gears to stay put with out keys or set screws? I know you used hex stock on the final stage. I'm mainly asking about the gear on the Fischer Price.

[Travis Covington]

Originally Posted by Joe_Widen

How do you guys get those gears to stay put with out keys or set screws? I know you used hex stock on the final stage. I'm mainly asking about the gear on the Fischer Price.

Are you refering to the pinion or the driven gear? The pinion is mounted onto the CIM and AM planetary shafts using the supplied 2mm keyway with an internal spline retaining ring.

The driven gear is also a hex. The only other place we used a keyway within the gearbox was on the output shaft to retain the sprockets that go to the front and back wheels. There is no easy way to put a hex there, as much as I would have liked to.

As for 32 pitch vs 20 pitch, the 32 pitch at 3/8" face was far strong enough for the initial reduction off the motors and allowed for a more compact gearbox overall. The large 32 pitch gear is a 96 tooth, and the large 20 pitch dogged gear has 72 teeth. Both are relatively large, but allowed us to have only one intermediate shaft with no chain reduction.