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Making a vehicle with regenerative breaking

  1. Jan 6, 2016 #1
    So I'm a mechanical engineering student, we are asked to make an autonomous vehicle with regenerative breaking.

    Info. about the project:
    dimensions of vehicle to be about 25 cm long, 16 cm wide and 8 cm high

    should be low weight
    should be low cost
    should be fast
    should carry weight

    -In the competition day the vehicle will start on top of a ramp, the vehicle must only use gravitational potential energy to move.
    -The vehicle must store energy from breaking for at least 1 second at full stop, then release the energy stored to move as far as possible.
    - there will be 4 stages and we are allowed to tweak the vehicle between stages

    I haven't done a lot of research on everything, but i have some basic ideas of how to tackle this project. But I need some advice on somethings.

    since we're not allowed to use batteries to propel the vehicle, I guess the only choices are using a Flywheel or Spring to store energy. From experience which do you think will store more energy or which one is more applicable in this case?

    I think micro-controller will be extremely helpful because we will need to control the speed the vehicle at all times.
    I dont have a lot of experience with micro-controllers, what micro-controller do you recommend for a beginner or what micro-controller is more applicable to use in this case?

    Laser Beam sensor:
    In the track there will be multiple laser beams in which the vehicle must slow down or propel from rest. This is the most difficult part for us, we are told the laser beam will be at a height of 1.5 - 5 cm. What type of sensor do you think will work in this case? or how will our vehicle know that it passed through the laser beam?

    I appreciate your help.
  2. jcsd
  3. Jan 6, 2016 #2


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    Why do you need to control the speed artificially? Surely it will be self-governing. The flywheel or spring, which is connected to the axle, will slow the vehicle down as it is storing up energy.
  4. Jan 6, 2016 #3
    The breaks should be applied only when applicable. We will be doing 4 rounds and on some rounds we want the vehicle to stop when it defects the laser beam and then propel. Other rounds will be to go to a complete stop at a short distance and stay at rest, so I think a micro controller is ideal for breaking
  5. Jan 6, 2016 #4


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    Oh. You mean mean speed as in: go now, stop now. Not as in: control the speed during the descent down the ramp.

    Perhaps a simple 555 timer might be a good place to start. You can simply program it to send or cease a signal after a certain duration, which would elsewhere be determined by the sensor input. There'd be more to it, obviously.

    I wonder if that is over-engineering though. Rotating cams might be a more mechanical way to go. They could be made out of any material such as cardboard or plastic, and can be easily programmed - including on-the-fly tweaks, with a deft flick of an exacto knife - to start and stop things, flip switches, release latches, etc.

    When I was a young lad, I got a toy car that could be programmed to do all sorts of tricks by inserting one of a series of carefully-configured cams that controlled steering (you could even make your own).

    Last edited: Jan 7, 2016
  6. Jan 7, 2016 #5
    You could also raise a weight on the vehicle, such as a heavy ball bearing on the end of a lever. If you need more weight to raise, add more ball bearings on levers to be raised in succession.

    You know, or should know the height of the ramp, so thus know the potential energy of the car at top of the ramp.
    You know how springs, flywheels, raised weights store energy.
    Your job is to figure out the most economical, ie the one that can store the most and recover from breaking with the least amount of loss in the transmission drivetrain and how to do it. You don't want a whole lot of complicated machinery with parasitic loses.

    I agree with dave that a μP is overkill here. The cam thing might work quite well.
    A simple timer could be just as simple as an RC circuit with a time constant that triggers on the up or down charging curve.
    Then you need a small generator to supply power to that and the electric eye circuit to detect the laser. A silicon version might be the way to go. A lot of line followers use this type of circuit to detect the difference in light intensity between the line - either white or black - from the background surface. Investigate on internet search.
    To restart, either block the eye or time the duration needed electronically.
    You could also release a small tiny ball down a winding path that takes x-amount of time to get from top to bottom where it hits a lever to restart the spring, flywheel dropping masses turning the wheels again - that might be entertaining for the spectators.

    lots of ways to accomplish the task.
  7. Jan 7, 2016 #6
    thank you for the information.
    can you please explain what a 555 timer is and i didnt understand how i would use it in my case.
  8. Jan 7, 2016 #7


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    It's a general purpose integrated circuit chip that is very commonly used in electronic projects requiring any kind of timed events.
    You'd definitely have to have someone comfortable with making electronic devices with custom circuit boards.
  9. Jan 8, 2016 #8


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    Are batteries or super capacitors specifically excluded because..

    ..does not necessarily mean..

  10. Jan 8, 2016 #9


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    Perhaps you could also store the energy as gravitational PE (eg raise a weight on the cart).

    Edit: Oops I see 256bits already posted that.
  11. Jan 8, 2016 #10


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    I think it would be essential to have more details of what the organisers are expecting the cart to do. Am I right in thinking that the organiser wants the cart to roll down a slope, keep going until it crosses one beam and then stop for 1 second before setting off again? eg it must not cross the second beam until after 1 second is up? or is the second beam used to tell the cart when it can set off again?

    If that sort of detail isn't known before the event then I think trying to do it mechanically would be hard. Easier to reprogram a micro?
  12. Jan 8, 2016 #11


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    You can't really select a sensor without more info on the laser. Beam width? Visible? Is this the first year the event is being held? If not find out what worked last year. Test your solution in the actual room because there might be issues with the room lighting (eg 50/60 Hz flicker or just too bright).
  13. Jan 9, 2016 #12
    We will have 4 rounds:

    Round 1: the vehicle will go down a slope and keep going until it crosses a beam and must brake before it passes the second beam( the distance between the two beams is known)
    Round 2: the vehicle will go down a slope and somewhere near the bottom of the slope a beam will measure the speed of the vehicle, the vehicle will reach a second beam at a flat surface and must stop for 1 second before it passes through the third beam, the fourth beam will measure the speed of the vehicle and that speed must be greater than the speed measured from the first beam.
    Round 3: the vehicle will go down a slope and must make a full stop in the stop zone which will be in a flat surface.
    Round 4: same as round 3 but the vehicle will be carrying some weight.

    So basically, only round 2 requires regenerative braking.

    Yes, the professor clarified that up, there will be a diffuse beam, C18E-0N-1A, and one is a laser, FALH-X0-0A. The laser is not visible.
    All the required dimensions of the track will be given to us on the day of the competition, and we will have time to adjust our vehicle, but will not be able to do test runs.
  14. Jan 9, 2016 #13
    That's true, as long as we only use the energy the has been stored from braking to propel the vehicle, we can use any method we want.
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