Speeding up a Non-Stepper motor

Discussion in 'General Electronics Chat' started by MurToTheRay, Jun 10, 2014.

1. MurToTheRay Thread Starter New Member

Jun 10, 2014
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The school i currently attend has a "young engineers" extracurricular club that i currently work within. We enter an electric car race called F24 which is run by GreenPower that sets guidelines as to limit the parts you may use. The motor that is currently used is as shown here and here.

As the current club's leader is currently quite old-fashioned in that he is not willing to try new circuits or mechanically based ideas which could improve the car's speed and efficiency i feel as if i have to do a lot of things in my own time and prove their worth to him quite frequently or else he is not willing to change a thing on our cars. Because of this i am forced to come up with solutions which are quick to test and implement although this current idea isn't as easily done.

The idea: To double the voltage across the motor but applying it for half the time, this could be done with an oscillator of some type (although i have not worked too much with motors so im not sure which type would be best) as to boost the motor's speed without risking the destruction of it.

Note: Up to two 12v, car-type, lead electrode batteries may be used at any one time and neither the batteries' or motor's internals may be tampered with. Only 4 batteries of the previous specification may be used on the day and the race day consists of two 90 minute races from which a winning team is decided based on the highest number of laps.

Last edited: Jun 10, 2014

Jul 18, 2013
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That appears to be a DC brushed motor?
Supplying a motor voltage that is higher than the plate voltage is common when the method of control is PWM, The critical part is ensuring that the the continuous rated torque (mean current level) is not exceeded, at least for any significant length of time.
If the control is simple on/off to the motor, then nothing will be gained by increasing the voltage and damage to the motor may occur if done without consideration of max rpm and load current.
Max.

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3. MurToTheRay Thread Starter New Member

Jun 10, 2014
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yes, it is a DC brushed motor. Thank you for answering my question and if i may then i would like to follow it up with another question; is there any way to maintain the lifetime of two batteries whilst only using one and doubling the voltage?

4. #12 Expert

Nov 30, 2010
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Many considerations call for caution in this method.
Increasing the voltage can over-current the brushes and damage them.
Higher current for half the time will cause more losses as heat in the motor winding wires because of their inherent resistance. This is an efficiency killer, but efficiency might not be a serious goal in this case.

If you want to PWM this (pulse width modulate), you will be able to find what levels of voltage start causing damage to the motor by merely observing the effects. The basic method is a variable duty cycle oscillator (which can be done with a 555 timer chip) and a high current transistor like a Mosfet. These transistors have improved immensely in the last 20 years.

Do you want a schematic of a likely circuit to control the motor?
Know that details about wire sizes and layout can make or break this design, and the schematic rarely shows the available errors.

Edit: your question in post #3 is not clear.

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5. MurToTheRay Thread Starter New Member

Jun 10, 2014
11
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I have taken into consideration that the best chip for the job would most likely be the 555 unless more specialist types of oscillation were needed (i.e. sabretooth, etc.). I forgot to mention in the question (which will now be edited in) that the race day consists of two races (both with the target of completing the highest number of laps in that time) both with a duration of 90 mins. Therefore it is not favourable to sacrifice efficiency for speed unless the gain is greater than that being sacrificed. Also, only four batteries may be used for the race (that are changed in pit stops).

6. #12 Expert

Nov 30, 2010
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Your question still is not clear, but I can remind you that every energy conversion is an efficiency loss. Much better for efficiency to use 2 batteries in series than to let one rest while using a voltage doubler on the other.

Now is the time to confess the amp-hour ratings of the batteries so we can see if you're trying to violate the laws of energy.

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7. MurToTheRay Thread Starter New Member

Jun 10, 2014
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Thanks for the replies, i guess i will have to try and focus on the mechanical aspects of the car as the circuit can't get much simpler.

Thanks again,

-MurToTheRay

8. inwo Well-Known Member

Nov 7, 2013
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It seems that doubling the voltage is the biggest challenge.

A dc doubler at well over 10 amps is not trivial.

Do you have any ideas on how to do it?

If you can double the gear ratio (speed) the motor may have ample torque. And if it doesn't, it may not survive the over voltage either.

9. MurToTheRay Thread Starter New Member

Jun 10, 2014
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That is something that i need to really have a look at (thanks for reminding me), i was trying to have a look-see today but all manner of writing has been rubbed off the top side of the batteries so ive asked the leader of the club for their source but i'm yet to get an answer so i guess ill have to get back to this one.

Oct 4, 2013
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I may off base here but I used to build a pretty simple circuit that is commonly called a joule thief. We used to use it to light LEDs from dead aa batteries. I built one that had a rather large torroid and measured 5v from a dead 1.5v battery. Could you use this type of circuit to better regulate and maintain the overall storage capabilities of your batteries? I know your using 12v batteries but it works with all voltages. just a thought. I could be totally wrong..lol

11. Markd77 Senior Member

Sep 7, 2009
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If I found the right rules, you are not allowed to do it anyway.
It may be possible to apply the power only at the most efficient points on each rotation (assuming running at less than 100% power) similar to how a brushless motor controller works, but this is certainly not trivial and would require quite a bit of coding using a microcontroller.

12. MurToTheRay Thread Starter New Member

Jun 10, 2014
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Thats a very good idea (that is, if it works) i'm not completely sure about how a "joule thief" works so perhaps an explanation would be helpful

Last edited: Jun 10, 2014
13. MurToTheRay Thread Starter New Member

Jun 10, 2014
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This sounds like an idea that could be possible in the future (altough i have no experience in using micro controllers - but a little in programming) and thank you for the reference to the rules - they have been updated very recently because there was an incident where a team was modifying battery acid and modifying other parts of their car making it dangerous but fast (i.e. around 70 mph). for my school's team we have been working under these regulations but that must have been a part that i skimmed over when trying to think of ideas that could enhance our cars.

14. alfacliff Well-Known Member

Dec 13, 2013
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changeing the timing of the power fed to the bruses would require a way to measure the shaft rotation on the motor. I am not too sure if that would have the effect you want of speeding up the motor. how about finding some supercharged brushes? like the ones used in the electric rc cars? they have silver in the mix for the brushes to increase conductivity.

Jul 18, 2013
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16. MurToTheRay Thread Starter New Member

Jun 10, 2014
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As previously mentioned; the internals of batteries and motors cannot be altered; thanks for the input though!

17. alfacliff Well-Known Member

Dec 13, 2013
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then it looks lioke the aerodynamics of the car are all that is left to improve.

18. ronv AAC Fanatic!

Nov 12, 2008
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How do you currently control the speed of the car?

19. MurToTheRay Thread Starter New Member

Jun 10, 2014
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It seems so, of course there is also weight, gear ratio and finally driver skill but all these things lie outwith the subjects detailed within these forums so i guess this concludes this thread (unless anyone would like to say anything else) - thank you to those who commented and if anyone could give me an explanation of how a joule thief works then it would be greatly appreciated!

Last edited: Jun 10, 2014
20. MurToTheRay Thread Starter New Member

Jun 10, 2014
11
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a single push-to-make SPDT switch which is mounted on the steering wheel of the car which completes the circuit and therefore provides current to the motor. So basicly the parameters of control are "on" or "off".