wheel and gear configuration VS. efficiency

[jwiger]

I'm in the early planning stages of an experiment. Looking to see relative efficiency of various wheel combinations and configurations. I have the LEGO Energy Meter, and a large mix of wheels, plenty of gears and good collection of PF motors. So I will try three and four wheel combinations, different gear ratios, chain drives, etc to see what gets the farthest on a fixed amount of energy or uses the least energy to go a set distance. Another variable I'm considering is weight, and how it affects power requirements.

It's been a while since I've used any good scientific methods, so I figured I could ask for ideas from you guys. Does anyone have any suggestions for methods or other tips to make it a fair evaluation. What combinations would you really like to see compared? What surfaces? What weights should I target? I have plenty of raw LEGO elements to stack up 5+ Kg of weight or more.

Thanks in advance!

[mattallen37]

Take a look at this article. Philo has done a huge amount of technical research and testing of various aspects of legos (like the motor comparison).

[jwiger]

Good point, Philo is like the Galileo of LEGO Mechanics. I planned on referencing his motor comp, but forgot about his traction article. Although this will be more of a measure or rolling resistance and parasitic loss in driving gears. I plan to avoid traction issues as much as possible, since doing a burnout is a waste of power. Even though it's good for a smile

[spillerrec]

It would be interesting to see how much that internal friction hurts the efficiency, especially with longer gear chains and/or weight. So another test case where some kind of lubrication has been applied to mainly where the rotating axles intersects with the beams.

How many parameters are you going to test? There are a lot of things to meddle with, but it would take far too much time to test them all... Nevertheless, to get the best results you should take as many parameters as possible in account and make sure that everything else than what you are testing for is kept constant so it wouldn't add noise to your readings.

[jwiger]

As far as number of parameters, I'm not sure. Obviously I will try three and four wheel setups of the more common tire sizes. Currently the motors I can use are: PF-M, PF-L, E Motor (PF-E?), and the NXT Servo Motor. The axles are my biggest concern; live or fixed, and end supported (like front wheel of a car) or supported on both ends (like a bicycle).

I do know that DC electric motors are generally more efficient when operated as close to their max RPM as possible, e.g. if not using direct drive, gear reduction is more efficient then slowing the motor. But I suppose I could test that as well. Since I have the necessary components needed to regulate motor speed with PWM, I can see how much that applies to LEGO motors.

[inxt-generation]

There's another thing you might want to test: the efficiency at different speeds using analog voltages and PWM.

[jwiger]

There's another thing you might want to test: the efficiency at different speeds using analog voltages and PWM.

Interesting idea. I would assume there would be a loss with analog voltage control, since I'm guessing you mean a resistor. Which would create heat and thus waste some energy. Not sure if I could accurately record how much energy the motor is using. Any suggestion?

[inxt-generation]

There's another thing you might want to test: the efficiency at different speeds using analog voltages and PWM.

Interesting idea. I would assume there would be a loss with analog voltage control, since I'm guessing you mean a resistor. Which would create heat and thus waste some energy. Not sure if I could accurately record how much energy the motor is using. Any suggestion?

You could use a resistor, but that would be kinda clumsy. It would be better to use a adjustable benchtop power-supply. Or maybe the LEGO 9V train regulator. It provides analog voltages between 0 and 9V. They can be found on BrickLink for as little as $2. I'm not sure how either of them change the voltage.

[h-g-t]

My personal experience is that the fewer gears the better.

The 'square' axles of the Lego system must generate a lot of friction, especially when loaded up.

At the moment, I am only using worm drives because they seem to give about the same performance fora lower number of gears/ axles.

[inxt-generation]

My personal experience is that the fewer gears the better.

At the moment, I am only using worm drives because they seem to give about the same performance fora lower number of gears/ axles.

Yes, the fewer gears the better, but, as any TT enthusiast will tell you, worm drives can be even worse. Under stress, a worm drive is not as good as a gear train, concerning friction. However, the advantage is that it won't backtrack. You see, when a worm gear turns a gear, it has to slide across the teeth. So, the harder a gear is pressing against a worm, the much more force it takes to have the motor turn. So, it really depends on your application. If you need high reduction in a small space, then worms are good. If it's high stress, gear trains could be better.