Building a gearbox / Attaching a motor?

[CarlosGJ]

Before you can connect a motor to any kind of gearbox, you need a small gear (called a "pinion") on the end of the motor shaft. While CIMs, etc have a small keyway in the shaft, you have to press-fit to smaller motors. On my team, we first heat the pinion to about 300 degrees in a toaster oven (to expand it slightly), then (while it's still hot) press it onto the shaft with an arbor press. When the pinion cools and tightens on the shaft, it is a very strong connection. While I highly recommend the oven and press method, I have heard that it is possible (albeit difficult and risky) to press fit at room temperature with a hammer. Tip: the bearings and bushings in the motor case are nowhere near strong enough to support the loads involved in press fitting. The motor needs to be resting on the bit of shaft protruding from the bottom, so only the shaft is under stress. Other tip: whatever the method you use, the greatest risk is bending the shaft, resulting in a useless motor. Make sure everything is straight before you start. Also, continuous force is less likely to bend the shaft than impulse, thus the arbor press as opposed to hammer.

[coreyjon]

Double post.

[coreyjon]

I've been doing this for a long time (2001) - I remember the drill motors, i've cut gears, and I've designed and built gear boxes from scratch. I can't make a better recommendation than akoscielski3. As a rookie team this late in the game, get yourself some of those CIMple boxes.

If in the future if you want to explore building/designing gearboxes the key is to decide very early on, and then have a back up plan especially the first time you try it just in case things go awry. Things to keep in mind are:

Motors: understanding power output, no load (free) speed, and what speed you can expect under load (my rule of thump 80-81% no load)

Gear Reductions required: Set a target speed (IE 12fps), decide on what size wheels /track set up your using. Then work from both ends IE expected loaded speed of motors on one side to the speed required to move your wheels/tracks to achieve the desired speed. At this point it's just a puzzle to solve the proper reductions.

There are many variables to consider: as you increase the number of reductions (intermediate shafts) you reduce efficiency. How much backlash should you use (.001" is my rule of thumb). don't forget about how you plan on connecting the gear box to the wheels (theres a chance for another reduction, so don't waste it).

Designing drivetrains/chassis (now teaching how to) is primarily where I focus myself. It's very rewarding, but also time consuming. With places like Andymark now offering ready made robust gear boxes it takes a lot of guess work and design work out of it leaving you and your team to spend more time on strategy and other end effectors to play the game.

Good luck to your team, no reason to be embarrassed by a question. This forum is here to be an idea sounding board, sanity check, and learning center.

[Alex.q]

Don't worry about asking "embarrassing" questions. Even if you think something should be obvious, many people don't know it. It is also important to ask and find out the correct way of doing things to prevent destroying components. Nobody expects you to know everything about how to put together a robot if you have never done so before. (Also, for a rookie team, it isn't that late in the season. Some teams come to regionals without a working robot.)

Also, I knew about press-fitting, but I didn't know how to do it, so thank you to the poster and those who answered. I wish I had asked last year when we were trying to make a minibot.