Small Simple Learning Project

Discussion in 'The Projects Forum' started by Santoyo, Aug 1, 2011.

  1. Santoyo

    Thread Starter New Member

    Jul 31, 2011
    Hello everyone. I am new here as I have recently gained quite a bit of interest in electronics. I go to The University of Illinois at Chicago and I'm majoring in ME. I am just now finishing up my summer semester electricity and magnetism class. I guess that is where my new-found interest has come from.

    This is my first thread, and I must say that I feel rather intimidated by the amount of knowledge that lies in these forums. Most things are simply way beyond my current scope. I only know what has been taught in the class, so, please, bear with me.

    Well, anyway, I figure that the only way for me to truly understand electronics is to perform some hands-on projects. So here is where I would like to start...

    Having had a certain interest in engineering since I was a kid I have accumulated vast amounts of the building toy k'nex over that time period. I am sure most of you have come across them at some point. These seem to be the perfect place to start experimenting. The overall basic thing I want to do is propel one of the roller coaster trains along the track via wheels that operate at increasing speeds.

    One of these sets came with "boosters". These boosters are made up of 2 DC motors (one per shown black wheel) powered by 3 C batteries. I would like to take these apart, reposition the wheels and motors underneath the track, make them run off of a single power supply, and make each wheel run at a different speed without using gear ratios.

    So, here is my thinking. I would wire all the motors in parallel and connect different resistors to each motor to control the current flowing through it. Is it unreasonable to think that the motors would run slower if I used higher resistors then are currently being used? If so, I would use high resistors for the slower wheels and gradually step down the resistance until I get to the last (fastest) wheel. To tell you the truth, I could use as much explaining on this subject as possible.

    Also, I really have no idea how I would power this thing. Preferably I would use an adapter connected to mains to run it, but I don't know if this is practical.

    Upon taking apart the boosters I also found that a capacitor is placed across each motors terminal. After researching this I found that this is done to reduce electronic noise. Is this true, and, if so, can I get some explanation as to what exactly this does and why it is needed?

    I apologize for not having specific values on the motors, resistors, and capacitors. I am back at school for my last week of summer semester. By the weekend I will be able to assign values for these components. Although I would not be surprised if you guys could give a good guess as to what they are.

    Sorry for the long, poorly structured, post, but, as I said, I am new to all of this. Any help is much appreciated. Hell, taking the time to read this all is too :)

    I look forward to your responses.

  2. Wendy


    Mar 24, 2008
    Welcome to AAC. I'm not even remotely a gear head, but I suspect we'll interact at some point on another project.

    A quick note, though it doesn't apply to your post in the slightest. I use the term gearhead, the owners of this site have decided automotive applications are out. Something to be aware of.

    I have had some experience with combat robotics, which may or not apply for your current project. A common phrase with these is somewhere along the lines of "overvolt it, the motor can take it". I doubt this applies for your application though.
  3. Santoyo

    Thread Starter New Member

    Jul 31, 2011
    Thank you for your reply, and although it basically had nothing to do with my questions I thoroughly enjoyed reading it.

    Although my major may lead you to believe differently I myself am not a gear head. Car modifications do not interest me in the slightest.
  4. zero_coke

    Active Member

    Apr 22, 2009
    In most voltage regulators they use capacitors to get rid of the "ripple voltage". You will see this later on in your classes. There are a few steps to getting AC Mains 120V/60Hz down to a steady 12V (for example):

    Step down transformer --> Bridge rectifier (or any other rectifier design) to get current in one direction only and unipolar voltage --> Capacitor in parallel to load used as a filter to leave ripple voltage --> voltage regulator to flatten the ripples

    Although I myself am a student in 2nd year, the information above may not be accurate.
  5. russpatterson

    Senior Member

    Feb 1, 2010
    So your 3 C batteries are in series and produces ~4.5V to the motor? You should verify with a meter (if you don't have one get a multimeter that will do voltage, current, and has an audible beep for continuity check). Then check how much current the motor draws from the batteries. Once you are sure of the voltage and current you can go get a power supply to suit your needs.

    I think that putting resistors in series with the motors will slow them down and burn off the extra power as heat. Use Ohms law to figure out how much current each resistor will let through to the motor. Keep in mind how much current your motor would like to pull from you test with the meter. You'll also need to figure out how much power will be dissipated by your resistor and then get resistors that are rated for that amount of power.

    However, a more efficient and controllable way is to make or buy a motor controller. These use PWM to turn current on and off to the motor very rapidly, effectively making it run at a lower voltage and go slower.

    If you look at the upper right of this schematic you can see what a basic motor controller looks like. I use a PIC microcontroller to generate the PWM signal, a MOSFET transistor and a diode.

    It's switching the motor's ground connection on/off ~2Khz.
  6. elec_mech

    Senior Member

    Nov 12, 2008
    Hi Santoyo,

    Welcome to the forum and electronics! Many moons ago, I got my ME degree but was fascinated by electronics and even built a simple remote-controlled robot while in college. I too had no interest in cars and was probably the only one in the department who knew next to nothing about cars. However, I was the first person other students saw whenever they had an electronics question for a class or fixing something with electrical power. I've gone onto design and program circuits both for fun and professionally and still love it! You can learn a lot here. And you're right, nothing replaces hands-on experience.

    Onto your project - capacitors on motors help absorb the noise generated by the motor. When motors spin, especially inexpensive toy motors, they generate all kinds of spikes (noise) on the power lines and this noise can interfere or damage other electrical items on the same lines. You can do a search on this forum or in Google on capacitors and motors for a better explanation.

    It is also a good idea to put a diode across each motor's leads to prevent back EMF (look this up also - I can't explain it clearly without doing some research myself).

    You can reduce a motor's speed by using a resistor, but as others have mentioned, the resistor will need have a high wattage rating to handle the power and heat and this really isn't very efficient. Motor speed is controlled by voltage - the higher the voltage, the faster the motor. Of course, each motor will only handle up to a certain voltage, so you don't want to go too high.

    That said, instead of using resistors, a motor controller would certainly be ideal (look up pulse width modulation or PWM and motor control), but you either need to buy one (can be pricey) or make one (fun, but not an ideal first time electronics project).

    Instead, most DC motors will accept a small range of voltages which will allow you to vary the speed. Since these motors are designed for 4.5VDC, it's a safe bet you can power them with 1.5V, 3V, and 6V safely. Therefore, as an experiment, try hooking one up to a single C battery, then two, then three, then four and see if the speed changes to your liking. If so, I can help you figure out a single supply circuit.

    If you really want to learn more about motors and driving them, check out the following book: This is all about motor types, controlling them, how they work, etc.

    Give the batteries a shot and let me know what you find and if that reduces the speed enough for you.
  7. Santoyo

    Thread Starter New Member

    Jul 31, 2011
    Thanks for the comments guys.

    I will be sure to get the required equipment needed such as a multimeter Russ.

    elec_mech: Thank you for your great descriptions. It's nice to find a fellow ME major who is not into cars :D

    That is what I figured the capacitors were for. What you said about back EMF seems to make sense except for one thing: which terminal is considered the lead on the motors?

    As for voltage controlling motor speed, I remember reading that somewhere now. If I am not mistaken, voltage controls speed and current controls torque, correct? If that is the case, putting a resistor in series with the motors would really only lower the power output of the motors and reduce torque (assuming some power is lost to the resistor). Please, correct me if I a wrong about anything within this post.

    I am certainly willing to put money into the project especially if the parts I gather are reusable. If you believe that buying a motor controller is the ideal way, I will look into it. Going back to the topic of toys, I do have an old lego train controller. I am assuming this controlled the voltage that was supplied to the tracks and thus to the motors. Could something like this be used for now? I believe it runs on a 9 volt adapter.

    As for that simple battery experiment, I will make sure to do it. As I said I am at school for this last week so hopefully I can get some results by this weekend. With my basement being destroyed by a flood, however, I may not be able to work on this until I start fall semester in a couple of weeks and can bring all my materials to school. Either way, it is nice to know these things in advance.

    I will also look into getting that book. It's too bad my grandfather is no longer alive, he loved experimenting with hands-on projects. He also didn't mind funding them ;)

    I appreciate your timely responses. Keep 'em coming!
  8. russpatterson

    Senior Member

    Feb 1, 2010
    The back EMF diode is shown in the schematic I posted above.
  9. Santoyo

    Thread Starter New Member

    Jul 31, 2011
    Thanks Russ!
  10. elec_mech

    Senior Member

    Nov 12, 2008
    And I thought I was the only one . . .

    By leads I mean terminals, so there is no one lead. Note that you can change the direction a DC motor spins by reversing the polarity going to the terminals. Not so with single-phase AC motors, but that is another ball of wax altogether.

    Yes. You are correct that by using a resistor, you are reducing the current to the motor which will affect torque. Resistors convert current into heat. Following Ohm's law, since the resistor is consuming current (and has resistance), there will also be a voltage drop which is why you could use a resistor to reduce motor speed. However, you're not only reducing voltage (speed) and limiting current (torque), you're also wasting energy as heat. This is why you'd need a high wattage resistor to do this. It just isn't efficient or ideal.

    The Lego controller sounds perfect. I would only be careful when turning it on to full speed, because I do not know how much voltage your K'Nex motors can handle. If the motor starts to really whine/scream or get hot, reduce the speed immediately. You can use a multimeter to check the voltage output of the controller at different settings and mark or note them before you attach the motor. If this doesn't work or you want to be extra cautious, try powering your motor with one, then two, then three, and maybe then four batteries in series and see if you get the desired speeds you want. You can purchase single cell AAA, AA, C, or D battery holders from RadioShack locally or cheaper online at say (but you need to factory shipping costs, so unless you're buying several things, I'd just go to RadioShack). Note AAA, AA, C, and D batteries all have the same voltage, 1.5V. The bigger the battery, the longer it will supply power to the same load. For experimenting, I'd recommend AA batteries and holders as they'll be cheaper. If you really want to try a controller, let me know and I'll do some looking for something simple and cheap, err, inexpensive.

    I will be mocked for this, but if you don't already have one, you can pick up a simple, cheap digital meter which will work fine for your experiments at There is one near Chicago here:
    7602 S. LA CROSSE AVE
    BURBANK, IL 60459

    These are not high quality, but they'll measure voltage and resistance just fine. If you want to go really cheap, they usually have coupon for 20% any one item in the coupons section of the Sunday paper. Once in while, there is also a coupon for a free digital meter - I might still have one I can mail you too if you'd like.

    Hope this helps.