Serial PWM motor controller

[smartkid]

I went ahead and whipped up a small 3D model showing what I have in mind for the bot design. This model is very incomplete but it does show the computer components to scale. The red part is the frame and wheels I hope to build for the project later on. The whole thing is about 24in x 24in x 16in. I believe that I've allowed plenty of room for custom made electronic components and a car battery.

The design allows the motors to be in their own little area in the omni-directional wheel pattern. I'm going to have to figure out a way to make my own omni wheels but at least I know what I'm doing there.

Any comments?

[dtengineering]

Yes but what I said is that the battery cannot be drained lower then 20% charge. So if I'm right then that gives me 80% usable charge with is 32 Amp hours.

The figure of 20% is somewhat arbitrary, and refers to the amount of charge that you can use from a car battery without eventually causing damage to the plates. So you CAN extract 100% of the charge and drain a car battery to zero... but the deeper you drain it the more rapidly damage accumulates. Looking at what you have in mind, a car battery will be more than sufficient. I suggest that the power source is not going to be the "bottleneck" that holds you back.

While I'm here, whats the difference between a stepper motor and a regular DC motor? I remember finding a small stepper motor in a hard drive and doing a bit of research on it but besides that their foreign to me.

Did your "bit of research" include checking wikipedia? Simply googling "stepper motors" brought that up as one of the first links. Remember to read to the bottom of the wiki entry for the links if you don't get it just from the article. One of the reasons you are getting good answers to your questions is that you have done some research and are asking intelligent questions. Please don't stop now. You might have luck for some of this at howstuffworks as well, or by googling "stepper vs. servo".

Also, where would be a good place to look for cheap DC motors? I need something in between Vex motor size and FRC motor size. We'll call Vex small and FRC extra large, I want a medium.

Did you look for motors at the robot shops such as www.robotshop.ca as mentioned earlier in this thread? You may also wish to try out banebots. You will probably be wanting a gear motor of some kind unless you are planning to build your own gearbox... which is probably more expensive than just buying the gearmotor. I can't promise that you will find any gear motors that fit your definitition of "cheap", however.

Perhaps you need to contemplate what is important about your project. Is it the size of the project, or the skills you are learning? Scaling back the size of your robot to use vex sized components (there's your omni wheels for you...) could be done without losing any of the educational or technical value and may put the project within your financial reach.

You may also wish to consider checking books such as "Robot Builder's Bonanza" from your library and reading them before carrying on further.

Jason

[Kevin Sevcik]

If you're looking for motors and any of this other stuff, find out if you have an electronics surplus or hobby store in your area. They're somewhat more rare than they used to be, but they're often a good resource for parts and motors if they exist. There's one in houston that has a decent selection of all sorts of surplus motors for pretty ridiculously cheap prices. Amazingly there's apparently one in your town. Check out AstroToo

[smartkid]

Thanks again. I did do a Wikipedia search on stepper motors, at the time I really didn't understand much of that article but now I should be much better off.

As far as the Vex parts go, well I don't personally own any of those either. I do have some of my schools vex parts but those are just to work on our FTC bot for this year. I would consider using the vex parts but I'd still want to use the motherboard instead of the vex microcontroller. Which could still be done however it would make a rather large vex bot.

But in this case small might be good. The question is will the vex motors be able to handle moving the computer components and a battery to power the whole thing... I don't think so.

I think it's time for me to stop asking questions and start finding answers on my own. You guys have been so helpful, thanks!

-Smartkid