Frequently Asked Questions About the ME2011 Robot Project


How do I control motors?

See the notes on how to control a motor.


Is there a shop I can use?

If you have seen the shop videos, you may use the Mechanical Engineering Student Shop, one of the finest student shops in the country. We will try to schedule a shop video viewing in the evening, outside of class time. See the Shop web site for location, hours and rules.


Where can I store my project on campus?

We don't have any storage areas. Sorry.


How do you solder?

See the soldering tutorial located elsewhere on this web site.


How can I make my electronics look neat?

If you have just a few components, mount them on the Stamp board. Bend their leads and push through the holes on the right side of the board until the component lies flush against the board. Wrapping on the back side will hold things in place. Trim the leads if too long.

For more components, try mounting on a piece of corregated cardboard. Just push the leads right through and wrap on the back side. For a more professional look, solder your components on a predrilled breadboard such as Radio Shack 276-150 or Jameco 43140.

Also, see the note on circuit layouts


What if I don't know anything about programming?

This project requires only a minimal level of programming skills. You can learn a great deal about programming by studying the example programs given in the Application Notes in the Stamp manual. Also, study the examples provided in class. See the PBASIC Programming Tutorial elsewhere on this web site. Finally, ask lots of questions of the course instructors and your fellow classmates.


Can I do any computer graphics or have a numeric display?

No, the Stamp has no display and no keyboard. You can build a simple display and keyboard, but for this you need advanced electronics skills.


When should I start my project?

Working to a deadline that is far away is extremely difficult. This is a project where you are bound to fail if you only leave yourself a week in which to do all the work. Recommendation: (1) Start one month before the due date. (2) Finish developing and detailing your concept three weeks before due date. (3) Take two weeks to construct your project. (4) This leaves you one week for test and refinement.


How much can a motor lift? How fast can it spin?

It all depends on everything. A good rule of thumb is that a motor can lift the weight of the battery that drives it; or that a motor can lift its own weight. Remember that motors can either spin slow and be strong (near stall), or can spin fast and be weak (at no load). You can't have both. Motors will spin faster and be stronger the higher the battery voltage. A good test of whether you are driving a motor too hard is to feel it. If it is hot, turn down the voltage or reduce the load. Also, many motors will wear out their bearings if run for more than a few seconds at their no load speed.

Gearmotors have a built in gear train transmission. This means the shaft will spin much more slowly at no load conditions with considerable output torque. Consider gearmotors if you have a vehicle for which you want to attach the wheels directly to the motor shaft.

In all cases, test your motor in a mockup of the intended load conditions and using the intended battery before you get too far along into a machine concept. You could well find out that the motor you have will not perform its intended task. In this case, you have to change your motor, your task or both.

 


What kind of wire should I use?

Use the yellow wire for interconnects on the board and the green/white for interconnects off the board. Never push the green/white wire into the white breadboard; it will break and clog up the hole forever.


What if I don't know anything about electronics?

Read the optional course text book, "Practical Electronics for Inventors". For a more comprehensive approach try "The Art of Electronics" by Horowitz and Hill, available at the bookstore, or by special order. Expensive, but one of the best all-around books on practical electronics.


How can I make my motor go in both directions?

To run your motor in two directions, you need a double-pole, double-throw (DPDT) relay for direction control and another relay or transisitor for on-off control. Look at the notes on how to control a motor for complete details.


Where can I get stuff for my project?

For all kinds of goodies, try Ax-Man Surplus. It has all kinds of motors and lots of "junk" which you might be able to cannibalize, all at very reasonable prices. Bring along a 9 V battery and two pieces of wire so you can try out the motors. Three locations: (1) 1639 Univ. Av., St. Paul (646-8653); (2) 1071 E. Moore Lake Dr., Fridley (572-3730); (3) 8008 Minnetonka Blvd, St. Louis Park (935-2210). See the Ax-Man web site for hours.

For electronics, try AEI Electronics, located at 224 Washington Av. N in downtown Minneapolis (tel: 338-7149, open 7-5:30 M-F, 9-1 Sat). Excellent stock of electronics parts (including many of the items you see in your Jameco catalog) and reasonable prices. Or, try any Radio Shack. See the Yellow Pages for area locations. Or, mail order from Jameco. If you do order from Jameco, be aware they have a $25 minimum and that fast (one or two day) delivery will add an extra charge.

For fasteners and hardware, go to any hardware store. For ideas, wander the aisles of Menards, Target or any decent hardware store. Seven Corners Hardware in St. Paul is particularly recommended.


How big a program will fit into my Stamp?

It depends on which instructions you use. The editor has a % of memory used table, so download a small program and see how much room it takes.


How long will my Stamp run on a fresh 9v battery?

It depends on what the Stamp is doing. In sleep mode, it can run for weeks. If you are turning LED's or transistor switches on for long periods, the battery might run down in an hour or two. If you try to run a motor off the same battery which powers your Stamp, that battery will run down quickly.


How can I power motors or other external components which take more than a few milliamps of current?

Use a separate battery to control motors. Can be 6, 9 or 12 volts; match to your motor. Remember, you must connect the battery ground (the - terminal) of the extra battery to the ground of your Stamp circuit (very important).

Since your Stamp is not able to provide sufficient current to run the device directly, you must use a relay or a transistor controlled by the Stamp to turn high current devices on and off. A relay is basically a magnetically controlled on-off switch. When you apply current to a solenoid in the relay, a small mechanical switch is thrown, and a connection is made. (A relay click is what you hear when you start your car. It is usually masked by the sound of the engine starting. When your battery doesn't have enough power to turn over the car, all you hear is the click of the contacts of the relay touching.)

A transistor is basically an electronic relay. For controlling motors, we recommend you use a TIP120 NPN power transistor. Here is a schematic for controlling a motor:

Note: use a 1K resistor to control the base, rather than the 470 ohm shown above.

When you set pin x high, current flows through the 1 Kohm resistor and into the base of the transistor (labeled b). When current flows from the base to the emitter, the electronic "switch" is closed, current flows from collector to emitter (labelled c and e on the diagram), and the motor runs. Using a TIP120, the motor can draw up to 2 Amps of current from the battery (any more and the transistor gets too hot), but the transistor itself will only draw about 11 milliamps from the Stamp.

In real life, a transistor (TIP 120) looks like this:

When facing the front of the transistor, the pins are (from left to right), the base, collector, and emitter.

For more details, see the notes on how to control a motor.


How much current can the Stamp provide?

The Stamp can provide 20 mamps per I/O pin, but only 40 mamps total for the chip. This means you can have 3-4 LED's on at the same time, or you can turn on 2-3 motors via a power transistor.

 


How many things can I connect to my Stamp?

The Stamp board has 16 I/O pins (numbered 0-15). Any can be an input and any can be an output. Two of the pins are reserved: one for the start button and one for a watchdog LED. That leaves 14 pins to connect to other devices. We recommend that you have as few things connect to the Stamp as you can get away with and still make your concept work. The more things you have connected, the harder it will be to build, test and debug.


How do I tell the Stamp which pins are inputs and which are outputs?

Use the INPUT and OUTPUT instruction. For example, if pin 0 connects to an LED, pin 1 to a switch, pins 2 and 3 to motors and pin 4 to a microswitch, at the top of your code (you only have do do this once, at the top), put these statements:

    OUTPUT 0
    OUTPUT 2
    OUTPUT 3
    INPUT 1
    INPUT 4

On powerup, the Stamp sets all pins to inputs so the above instructions will tell it which pins are outputs. Technically, you don't need these instructions because the HIGH and LOW instructions automatically set the designated pin to an output before changing it's state. See the INPUT and OUTPUT instructions in the Stamp manual for details.

How can I run two motors off one battery and have them act independently?

Easy. Treat the battery as a source of power and just hook up two separate motor circuits, each with its own TIP120 and base resistor to it's own stamp pin.

For more details, see the notes on how to control a motor.

Can my robot control another machine that is not part of the robot?

No. Everything inside the specified footprint is part of your robot. For example, you can't have the robot playing an expensive music synthesizer because the synthesizer would put you over the cost limit.

Will my battery last through the whole show?

Dont know. Depends how much current your robot draws. The 12V NiCd packs have quite a bit of energy in them. Do a test well before the show. Connect the battery to your machine (or motor or solenoid or light or whatever) and cycle until the battery runs down. Then recharge the battery (remember, it takes 12-14 hrs for a full recharge) and try again.

My resistor leads are too long!

So cut them. Also, make sure that nothing is touching and making electrical contact with things it should be touching. For example, you are guaranteed to blow your Stamp board if you run the resistor leads through the board, bend them back towards the area under the Stamp chip, and then put the board down on something. The reason is that the resistor leads will touch contacts on the Stamp chips creating short circuits. Moral: Examine your board carefully and make sure everything is secure and no wires touch.

How do I connect to the pushbutton?

Strip wire 1/4 inch. Pass through the hole on the pushbutton lead (or around the lead if hole is too small) and crimp with fingernails or needle-nose pliers. Then make a secure connection by soldering (but not too much solder)

I'm getting to like building robots. Where can I find out more?

Take a look at http://www.robotbooks.com/ as well as the Parallax web site. Lots of links to robot resources. Also look at the robot links section of the ME2011 web site.

How do I ......

Look around on the Robot Project web site, particularly all the technical notes, do a web search, ask your friends, ask someone who took the course last year, ask/email one of the course staff. And do remember, the job of the couse staff to is make sure you are successful!



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