Newbie question ... How to get started

[greg544]

My daughter is in 7th grade and is going to participate in a robotics competition. Today she brough home two motors. The school does not seem to be providing any "how to" guides.

How in the world do you get started building robots???

Thanks.


Greg

greg544@gmail.com

[Billfred]

Welcome to ChiefDelphi--if anybody knows the answers, they're probably around here.

Can you post anything in the way of rules, objectives, or specs on the motors? The best way to get started is to really know what it is you're trying to do.

[greg544]

Thanks for the reply Billfred.

We have received two DCM-104 motors. Does that mean anything?

The robot has to go through a tunnel and then throw some switches. I am not sure what the switch looks like.

The total cost of the project cannot exceed $100.

The full rules are at
http://www.efta-us.org/programs/scit...6%20EDC-JH.pdf
They are long so I don't have any expectation that you would read all of that.

Thanks again for the reply.

Greg

Actually, that's quite short in comparison to the FRC rules, which are for the FIRST competition, that we take part in.

As far as individual ideas for this challenge, It seems you'll need two functions: driving, and a switch flipper. As for steering, I suggest that you put a switch on each lead to the motors, and steer with those switches.

As for basic robotics input, there's only one rule you'll need: KISS! Keep It Stupidly Simple! the less parts, the less complexity, the easier the whole system is to work with.

Good luck!

[kjhobin]

According to the rules, it has to be tethered, so you could just make a switch box, each one leading to a motor. it also says you can use servos. This might be a good idea for the horizontal switch flippers. try these: http://www.intelspy.com/18gmirecose.html

Good Luck!

EDIT: although, i don't think you can control a servo with a basic switch box, it needs a PWM input, too bad, it would be great for presice movement, like fliping a switch!

[greg544]

I am not sure exactly what you mean by put a switch on each motor. This is completely new to us. We will be glad to learn and even a little excited but how do we put wheels on this thing. Do we need to mount the motor on something? What should that be made of?

How are we going to drive this robot? Some kind of wired controler?

Will a guy at Radio Shack know about any of this stuff?

Is there a web site that provideds any kind of instructions?

[kjhobin]

go to home depot a get a electric junction box and a wall plate. At Radio shack, get some3- way toggle switches that return to their starting position by themselves. drill hoes in the wall plate for each switch and mount it to the junction box. run wires from each mounted switch to each motor, it would be a good idea to use tank style steering. have one motor for each side of the robot, each powering 2 or more wheels. then have other switches and motors for flipping the switches in the "tomb"

you have to build a body for this. i don't know if a VEX kit from IFIrobtics.com would be allowed. you could always use legos! like the ones from the RXC or NXT.

[Richard Wallace]

Looks like DCM-104 is a 550 frame Mabuchi motor, similar in case style to the FP and Mabuchi motors we have used in FRC, but with different ratings.

DCM-104: Free speed = 9000 RPM at 6 Volts, Full load current = 1.3 Ampere

See this link for distributor's data, price is $3.50 each.

Based on the rules at the link Greg posted, it appears that vehicle controllers are standardized and include the batteries and motor controllers. Details of their operation are apparently provided only to each team's teacher/sponsor.

So I guess it will be hard to help Greg figure out how to used the DCM-104 in his daughter's competition unless one of the sponsor/teachers posts some more information.

[greg544]

Richard,

I do see in the Power section of the rules that it says that it says Teacher has details about the common power supply. I am not sure what you mean about the vehicle controler being standardized.

I will be sending a note to the teacher tomorrow!

[Billfred]

Originally Posted by greg544

I am not sure exactly what you mean by put a switch on each motor. This is completely new to us. We will be glad to learn and even a little excited but how do we put wheels on this thing. Do we need to mount the motor on something? What should that be made of?

How are we going to drive this robot? Some kind of wired controler?

Will a guy at Radio Shack know about any of this stuff?

Is there a web site that provideds any kind of instructions?

A lot of it is going to depend on the nature of the motors in question (which are new territory to me, at least) and the robot itself.

If you're lucky, you'll be able to mount the wheels directly on the motor, then somehow connect this to your chassis/frame/chunk of material holding everything together and call it a day. (Your motors may have mounting holes built-in; if you can find the matching bolt, use them. If not, since the rules seem to indicate you're dealing with small robots, you should be fine with some other means of securing the motor. Hose clamps, perhaps?)

If your robot doesn't move without a push that way (which, if Richard's right, it probably won't), you'll either need to shrink your wheels (requiring less torque), throw in some sort of reduction, or a combination of the two. The reduction could come in the form of gears, chains and sprockets, or belts. (For the former two, I'd recommend looking at VexLabs; their product may be good for your challenge with a little modification.) This'll raise the amount of precision required in your setup, and probably require some sort of bearing-like mount. You could use ball bearings if you really wanted, but a smooth close-fitting piece of plastic could probably do the job as well. (VexLabs has some bearing blocks for their system; your mileage may vary.)

I'm not sure I agree with Richard's interpretation of the control system rules--if they're providing the controls for these motors in addition to the power, then skip this paragraph. For controlling it, you'd be looking at some sort of three-position switch--on/off/on, preferably a momentary switch to make the actual driving easier. (Momentary switches return to their normal state--off, in this case--when released, unlike, say, a light switch.) One direction would drive the motor one way, while the other direction would drive it backwards. Do this on each side, and you're driving like a tank or a bulldozer. (As the voice of quasi-experience, this is how you want to roll.)

Now throw in some sort of switch-thrower, and you're in business. (Just remember, the less well-lined-up you have to be to make it work, the more likely you are to get it to work. For some reason, robots never quite drive the way you expect them to when you reach the field.)

[Richard Wallace]

Originally Posted by greg544

Richard,

I do see in the Power section of the rules that it says that it says Teacher has details about the common power supply. I am not sure what you mean about the vehicle controler being standardized.

I will be sending a note to the teacher tomorrow!

Greg,

By 'standardized' I only meant (and I'm guessing here) that all teams use identical vehicle controllers and that internal modifications to the controller are not permitted. I'm also guessing that each DCM-104 motor's terminals get connected directly to a pair of terminals on the vehicle controller that are dedicated to that purpose.

Let us know what you find out from the teacher, and I'm sure some of us here on the ChiefDelphi forum will try to help.

Good luck,

[fimmel]

also dont forget that the motors are 6 volts and the power suppy is 12 volts so you need to add eithe a voltage regulator, or resitors to make it so the motors wont burn out.

[sanddrag]

Originally Posted by greg544

Will a guy at Radio Shack know about any of this stuff?

I don't mean to generalize but, no. Last time I bought a transistor at Radio Shack, the cashier said "we sell this?" which wasn't really as bad as when I bought a potentiometer and I got the "what the heck does this do?" look. I always love it when they ask me "can I help you find anything" and I reply "no thanks, I've got it" and then you know they're thinking "whew. I only know about the cell phones." If your Radio Shacks are anything like my Radio Shacks, you're better off here with us, unless perhaps you're looking for a new cell phone or toy-grade RC car.

For just getting started in robot building, a really great book is Robot Builder's Bonanza. See if you can find it at a local bookstore (Barnes and Noble for example) or perhaps order it online.

[greg544]

I started this question about a month ago. People here were very helpful on steps to getting started.

I have finally gotten a response from the teacher about the power source.

Here it is....

The power source is a car battery charger. We bought ours at either O'Reilly
auto parts or Auto Zone auto parts. I think they are about $25.00 . There are
different brands. Ours is SE Series Schumacher (SE-82-6). It says 6 amp
medium charge / 2 amp slow charge on it. We cut the clamps off and connect the
female plug to it using electrical tape. The plug on the power source is like
a car cigarrette lighter plug (they may have these at the auto store but I know
they have them at Radio Shack ) and the end attached to the tethered vehicle is
the male part (like the end of a cell phone charger) that plugs into the power
source.
We have told the kids that they can come in any time to use our power source
and/or practice track. We will have another workshop after the holidays but do
not have a date set yet. I will announce it at least a week ahead of time and
it will be on my board, as well. There is a late bus that leaves at 5:00 that
Allison could ride home if she needs to.
Hope this information helps. Have a safe and happy holiday.

Is this enough information to get going with?

Thanks for your help.
greg544

[Richard Wallace]

Seeing the teacher's response, I now think Billfred is right. And the advice that he and kjhobin gave above is the best -- keep the concept simple.

Since greg544 confirmed via PM that the DCM-104 motor his daughter received looks the same as the one linked in my earlier post, it appears that one challenge may be getting the right wheel speed. The machine will be small and light relative to FRC robots, and so won't need huge pushing power; however, for controllability it will require some reduction of the motor RPM to get a usable wheel RPM.

Feeding the DCM-104 directly (through a switch) from the battery charger supply will result in about 20,000 RPM free speed. Since the track boundaries are 1.5" PVC pipe and the game objects (scoring switches) are 2" off the floor, wheel diameter will be small -- let's assume 2 inches, but 1.5" would also work. A 2 inch wheel mounted directly on the motor shaft would translate at about 175 ft/sec or 120 MPH -- clearly too fast to control.

One way to gear down to a controllable speed would be to fit each DCM-104 motor with a gearbox similar to this one from BaneBots; however, at $38.95 each these would consume most of the $100 project budget.

The competition rules don't allow pre-engineered kits, or specially modified gearboxes, or inappropriate outside assistance. Still there should be some realistic way to get the wheel speed right. Maybe some VEX components would be allowed, if they are considered "parts" rather than a "pre-engineered kit"?