Electronics > Electronics

Getting a motor to run as fast as possible..?

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Botanic:
Well. We have to use a dc/dc converter to step up the voltage. It's a part of the mission. The robot would be too slow with only 6V.
We also have to use 8 AA batteries. 4 for the electronics and 4 for the motors.
Any suggestions are welcome.

Botanic:
The robot has to travel to all those four points within 150 seconds. There is a prize for the fastest robot.
The robot would not make it under 150 seconds if the engines would be running with 6 V.
To power the two motors we have 4 AA batteries, 1,2 V Ni-MH. Which gives 4,8 V.

I did some tests on the motors today. I got a little surprised of how little heat there was. I ran the motor with 20 V without problems.
With 20 Volts, running for 5 minutes:
The motor was not too hot to hold with my fingers. According to my multimeter the temperature was 55 Celsius. Running with a tire without putting any pressure on the tire, it was 0,7 A. When I slowed down the speed as much as I could with some pliers directly on the motor, it was about 0,5 A.

With 6-8 Volts I was able to brake the motor to stand still, the current went up to 0,79 A in that case.

How does the servo affect the motor? I didn't notice before I did my tests that the motors had servo. Does the servo make the motor create as much heat as it would without it?

What should the maximum output of the dc/dc convertor be? The motors are quite strong, so there is no chance that the robot would ever need more current than 0,5 A. 0,25 A would probably be enough.

Upto how many volts would it make sense to drive these motors with, with these four AA's? How may Watts should the DC/DC converter be able to cope with atleast?

Sorry for all these questions, but it turned out to be more complicated that I had planned with  :(

Admin:
If you are only allowed to use 4 1.2V batteries, how would you get more than 4.8V?!? The best you can do is keep your batteries fully charged, as a fully charged battery has a somewhat higher voltage. Perhaps 1.4V/battery, depending.

Is it a typo when you say .7A when the motor is spinning freely but .5A when under load? Do you mean the reverse? The maximum current you found before overheating should be your maximum allowed current spike in normal operation. Current spikes are usually twice that of stall current (when going from full forward to full reverse), so you would now want to use a voltage that is half of what you found. So if 15 volts gave you an overheating stall current, use 7.5V on your motors.

What servo? Are you running basic DC motors or servos (little black boxes)?

If your motor has a lot of torque but not enough speed, use big wheels with large diameters. Larger diameters mean more speed, assuming torque isnt an issue.

Botanic:
We are allowed to use only four AA batteries. According to what I read on the page that you ponted at before, Ni-MH are good to use if I am not mistaken. 4 * 1,2V = 4,8V. I am supposed to have a DC/DC converter to convert that 4,8V to something bigger. My big problem right now is to find a suitable DC/DC converter that will have the correct output without costing way too much.

Sorry, it was a typo. When the motor runs freely at 6V the current is 0,12 A. When the motor runs freely at 19V the current is 0,17 A.

I fed the motor with 20 V without overheating it. I could have gone even further, probably 25 V without damaging the motor it seemed.

The motor is two parts put together. One basic motor, just like the ones I am used to from my battery driven cars I had when I was little. Directly attached to that motor there is another box, that looks like the motor. From that box the axle comes out where the tire is mounted. My guess is that it is some kind of gearbox. I had the impression that it is called a servo, but I guess I was wrong. Sorry for that  ::)

We are going to fit bigger wheels to the robot. But just changing the tires is not enough for the speed.

I hope that what I write makes sense  ;)

Admin:
If you want high current, use NiCad not NiMH. NiMH can can hold more amp hours, but it cant pump out current as fast as NiCad.

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