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Author Topic: Help Me Power My Robot  (Read 615 times)

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Offline uchiha191942Topic starter

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Help Me Power My Robot
« on: March 19, 2013, 05:51:22 AM »
Hey Society of Robots! I have a question relating to how to power my robot. I am using an Arduino Uno R3 (http://www.pololu.com/catalog/product/2191), 4 high torque motors (http://www.pololu.com/catalog/product/1591), and 2 motor controllers (http://www.pololu.com/catalog/product/1110). I am just wondering how much power I would need to power it. Do I just need to power my microcontroller and it passes that energy through the motor controllers to the motors? Also, if I want to stop one motor while leave the other on, could I do that with only 1 motor controller? Finally, do I need to add the power consumption of all the parts to find the correct power amount? I am trying to use solar power and I want to find the proper solar cell to use.

Offline newInRobotics

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Re: Help Me Power My Robot
« Reply #1 on: March 19, 2013, 06:51:12 AM »
4 high torque motors (http://www.pololu.com/catalog/product/1591), and 2 motor controllers (http://www.pololu.com/catalog/product/1110).
Right, under motor specs it says that stall current is 2.2A, where Your chosen motor driver can only provide continuous current of 1A, meaning that if for any reason motor gets stalled for longer time, motor driver will most likely get fried. Also, when motor is starting to move or changes direction, current draw can be double rated stall current, meaning that peak current can be expected to be around 4.4A, where motor driver can only supply 3A.

I am just wondering how much power I would need to power it.
Worst case scenario is that all motors operate near-stall condition, so total curent draw then would be 4 x 2.2A = 8.8A @ 6V = 52.8W. If all 4 motors have to change direction at the same time it is possible that peak current draw can climb to double stall current in each motor, so 4 x 2 x 2.2A = 17.6A @ 6V = 105.6W. You should avoid these cases if possible. Normally You want to drive motors at no more than 75% their capabilities as well as use smooth acceleration and de-acceleration, this way it is more efficient.

Do I just need to power my microcontroller and it passes that energy through the motor controllers to the motors?
No, microcontroller is not capable of such high current output, motor drivers need to be plugged to power supply.

Also, if I want to stop one motor while leave the other on, could I do that with only 1 motor controller?
You should be able to control motors independently.

Finally, do I need to add the power consumption of all the parts to find the correct power amount?
That would give You worst case, which should be avoided if possible. Normally you are aiming for average consumption to determine power source capacity required.

Try this calculator --> http://www.societyofrobots.com/energy_calculator.shtml
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Offline jwatte

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Re: Help Me Power My Robot
« Reply #2 on: March 19, 2013, 01:07:34 PM »
Quote
if I want to stop one motor while leave the other on, could I do that with only 1 motor controller?

Each channel on a motor controller is like one on-off switch. Anything you connect to that channel turns off or on at the same time. If you have four motors and two single-channel controllers, then you will only be able to control motors in groups of 2 (because two channels total.) If you have four motors and two double-channel controllers, then you will be able to control each motor individually.

Regarding "solar" -- the available power from "solar" panels is generally not enough to directly power "high torque" motors. Depending on your particular panel, you may be off by a factor 10, or a factor 100, of needed power. If you're off by a factor 10, you could use the solar to charge a battery, and run at a 10% duty cycle (on 10 seconds, off 90 seconds, say.) If you're off by a factor 100 (very likely) then you're using the wrong tools for the job, and/or are trying to solve the wrong problem.

Offline uchiha191942Topic starter

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Re: Help Me Power My Robot
« Reply #3 on: March 19, 2013, 02:34:47 PM »
Okay Thanks. Just a few more questions. I am using 2 motors for the motion than I have 2 more for a scoop. The robot is meant to roll around and scoop up trash by the way. So the motors I have spin at 12rpm which is much to fast for the robot. It will probably only go 1-2ft/s so I won't be pushing it with all 6v it can take. Also, the scoops will be moving on the 0.25-0.5ft/s range. So I won't be pushing a ton of volts through the motors very often if ever. But, I have an airsoft gun battery that holds 7 Ni-MH Batteries with 2/3A1200mAH 1.2v. So it is running at 8.4v which is a bit more than what I need, but would that be sufficient for what I am using? Also, what does the 2/3A1200mAH. I understand what 1200mAH is, but what is the 2/3A?

Offline uchiha191942Topic starter

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Re: Help Me Power My Robot
« Reply #4 on: March 19, 2013, 06:40:40 PM »
One other note. Would this supply enough power for my robot. I believe it is. http://www.batteriesasap.com/in6v7ahbasl.html

Offline jwatte

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Re: Help Me Power My Robot
« Reply #5 on: March 20, 2013, 09:51:26 AM »
You can use PWM when controlling the motors to give them less power even though you're putting in 8V.

 


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