Guest Blog - Electricity used when pulling weight

We don't typically post items related to science fairs (I get a lot of them - they're always enjoyable but most aren't related to NXT but just use an NXT robot to facilitate something else), but I thought this was an interesting project worth sharing, especially because it's using an NXT to obtain the results - I've posted Keizo's results in the accompanying image.

BTW - Keizo is in 4th grade.

Thanks for sending this in Keizo! - Jim


How Much Electricity Is Used When A Robot Pulls A Certain Weight

By Keizo M.

I think that the robot will use twice as much electricity when the weight of the car is doubled.

Why I Chose This Project:
Last year I got a LEGO Mindstorms NXT 2.0 for my birthday. I really enjoyed it, but while using it, I noticed that the batteries run out quickly. I decided to measure how much electricity would be used when a robot pulls a weight.

-Lego Mindstorms ® NXT 2.0 -Digital Voltmeter -6 Rechargeable Batteries -Weights


1) Make a robotic car out of Lego Mindstorms NXT 2.0

2) Program the car to go forward and backward for 10
3) Charge the batteries

4) Measure volts in batteries

5) Put batteries in the car

6) Put weight on the car

7) Run the program

8) After 10 minutes stop the car

9) Take out batteries, and collect data

10) Repeat step 3 through 7 with different weights

When weight was increased, more electricity was used but it didn’t double. For example, when I doubled the weight from 1 pound to 2 pounds there was only a 0.066-volt difference.

There wasn’t a huge difference when I increased the weight. Next time, I should make the robot go for 30 minutes instead of 10 minutes or put a heavier weight


Brian Davis said…
Cool. My son & I have done a number of science projects that used the NXT in a variety of ways: data collecting in the school for 24 hours, monitoring the house heating system, instrumenting model geysers, and refining line-following (he won best on show for that one). Really, it's hard to look at most of these as 'NXT based', any more than an electronics science-fair project is 'Multimeter based' - the NXT functions so well as an instrument, it's usually not the focus of the project. Here, in this project, it's more of a focus.

I can think of some fun ways to automate this even more - for instance, the NXT can measure its own battery voltage, so it doesn't even require taking out the batteries to measure them, and the NXT can repeat the measurements again and again and again, storing the data or even calculating results from it, for hours or days at a time. Use rechargeable batteries, and you could not only do this cheaply... but measure how different rechargeable batteries function under different loads.

Cool project.
Unknown said…
It seem that at 2 pounds the NXt uses already the most electricity, the differences btwen 2, 3 and 5 pounds are not significnt, imho. So putting on more weight woudn't make much difference.
Measuring the current used by the NXT during driving would be nice. That aid, it's an inspiring poject that challenges for more uses.
NickNackGus said…
If we plot the data, is the voltage consumed related to the weight moved in a linear or quadratic function?
Unknown said…
@Tim: That's a good question. Looking at the results from 0 to 2, both are possible. Plotted in excel there seems a quadratic function to be. However, maybe it's in the measurement-error, additional measurements between 0 and 2 are requiered. At least for 0,5 and 1,5 pounds.
Linda Zoe said…
Nice project! However, if you do further experimentation, you should use grams, not pounds. Even though the United States is one of only 3 countries in the world that does not use the metric system, all science experiments should use metric measurements.
Unknown said…
Very interesting project, Keizo. One remark - battery voltage is not always the best indicator of the "electricity" used. In case of most common NiCd and NiMH batteries voltage/capacity characteristic is not linear. To examine how batteries discharge under different loads, you need to know the current. Measuring it will be some challenge. Some battery chargers show the charge applied to each battery after the charging is done - if you have one of these you can use it as a measuring device. Keep this project going, results are interesting :)

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