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Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 8/2/2000 6:43 PM MST


In Reply to: Re: Drill information posted by Brian on 8/1/2000 8:51 PM MST:



The gear is basically a standard gear:

.7 module
12 tooth
Full depth
20 degree pressure angle.

The only source I know of that sells steel .7 module gears out of stock is PIC Design. I have used them, I like them, I recommend them, I don't own stock in them ;-)

As to making your own drill motor gearboxes, I strongly urge teams with the ability to do it. It has been a great improvement to robot performance. Higly recommended!

Tip from DrJoe:

Don't fall into the trap of building your gearbox with only 2 stages (which is just possible with reasonable gears and ratios), use 3 instead.

Why?

The answer comes down to options if your are wrong in your speed-torque calculations.

With 2 gear sets, you have 3 axles to deal with. One is the motor. Another is the Axle of the wheel. The pinion on the motor is fixed. It is very likely that the gear that mounts to the wheel axle is sort of difficult to change too. With both these gears fixed, the only way to change ratio is to change the center distance between one set of gears. Often this is a very difficult option.

Compare this to 3 gear stages. With the first and last gear sets fixed, you can still muck with the overall ratio by changing the middle gear pair but not changing the total number of teeth for the middle gear pair. This means that the center distance for the middle gear stage does not change. Hurrah!

Example:

Stage 1:
12:48

Stage 2:
18:48

Stage 3:
12:72

Overall ratio:
12/48 X 18/48 X 12/72 => 1 : 64

By changing the middle to 16:50 the overall ratio becomes:
12/48 X 16/50 X 12/72 => 1 : 75

By changing the middle to 20:46 the overall ratio becomes:
12/48 X 20/46 X 12/72 => 1 : 55.2

I highly recommend looking in the PIC Design catalog or the Berg catalog or the Stock Drive Products catalog or the McMaster-Carr catalog (or even the Small Parts Inc catalog) and finding off-the-shelf gear pairs that let you build up transmissions with a range of ratios.

If you design your gearbox well, you can switch a couple of relatively easily changed parts and change your ratio up or down to suit your robot's needs.

Good Luck.

Joe J.