I made a remote controlled robot. It runs with treads driven by dual motor and has a small servo on the body. On the controller, I have two thumb joysticks, one of them controls the servo and the other one controls the movement of the robot. I use an Arduino Pro (5V/16MHz) for the robot and a Xbee for wireless part. So the robot has one Arduino Pro(5V/16MHz), one XBee(s1), one servo and two motors.
My problem is, it seems the robot always can not get enough power. I use a 9V battery for the Arduino Pro and the servo(the servo is getting power from the battery, not the Arduino 5V pin), and 4 AA batteries(6V) for the treads. I have to say, it's very heavy. Anyway, in the first one or two minutes, the whole system works like a charm. But after that, everything is getting slower and slower and then stops. It then needs to take a break, like 5 minutes, and then can work for another 1 minute.
This is bloody frustrating. Please give me some suggestions!
Are the batteries getting hot? Sounds to me like you're overheating the batteries. Also, is the server designed for 9 volts? Most servos are only 4.8-6V.
If the batteries are getting hot, I would suggest switching to a rechargable battery pack.
You're missing on telling us part of the puzzle pieces, like what motor controller/driver you are using. Also, how much current do the motors draw under load (if you know).
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The Rugged Circuits Yellowjacket: 802.11 WiFi module with ATmega328P microcontroller, only 1.6" x 1.2", bootloader
I made a remote controlled robot. It runs with treads driven by dual motor and has a small servo on the body. On the controller, I have two thumb joysticks, one of them controls the servo and the other one controls the movement of the robot. I use an Arduino Pro (5V/16MHz) for the robot and a Xbee for wireless part. So the robot has one Arduino Pro(5V/16MHz), one XBee(s1), one servo and two motors.
My problem is, it seems the robot always can not get enough power. I use a 9V battery for the Arduino Pro and the servo(the servo is getting power from the battery, not the Arduino 5V pin), and 4 AA batteries(6V) for the treads. I have to say, it's very heavy. Anyway, in the first one or two minutes, the whole system works like a charm. But after that, everything is getting slower and slower and then stops. It then needs to take a break, like 5 minutes, and then can work for another 1 minute.
This is bloody frustrating. Please give me some suggestions!
Thanks a lot!!
karl
First off, you need to either get specs for the motors and servos (voltages, running and stall currents), or measure them. Likely the gearmotors are rated for 6 volts, since you say it runs well on that. If you can't find the running and/or stall currents for the gear motors, then you need to measure them with a multimeter, at the voltage you are running them at. Use fresh batteries for this test, and you might want to use a larger battery pack (maybe 4 C cells instead) - just for the test. Be sure to test both the free running current need, as well as the loaded (stalled, if you can - if you are able to stall it, only stall it for long enough to read the current on the meter, about a second or two, no more) current needs.
The servo(s) as noted are likely only 6V servos (some can go up to 7.2 volts) - but you shouldn't try to run them at a higher voltage than their rating. You can burn out the motor and/or driver board inside the servo. Find out what the spec is, or assume 6 volts here as well (just to be on the safe side). Once you know the voltage, do a similar free-running and loaded/stall test (ideally, for all motors, you should know what the current needs are for free-running no-load, loaded, and stalled).
Once you have all of these measurements, you then will know what kind of battery system to build (mAh needed), so that it can supply all the current for all of the components, while giving you an adequate run-time. Now for an example - let's say you measure the currents for each - and you find the following (I am assuming one servo here - I don't know what you really have):
Gearmotor No-Load Current (@ 6 VDC): 250 mA
Gearmotor Loaded Current (@ 6 VDC): 400 mA
Gearmotor Stalled Current (@ 6 VDC): 1000 mA (or, 1A)
Servo No-Load Current (@ 6 VDC): 100 mA
Servo Loaded Current (@ 6 VDC): 200 mA
Servo Stalled Current (@ 6 VDC): 500 mA
Arduino (@9 VDC): 250 mA
Once again, all of the above are merely examples - you need to take your own measurements (and/or consult datasheets - note, though, that a datasheet should only be consulted by itself as a guide; you should always try to measure if you can - otherwise, go "worst-case" scenario, and take the upper amount from the datasheet, and maybe add 5 percent).
So - from the above, two gearmotors would need to be supplied with 2 amps (2000 mA) of current in the worst case scenario (both motors stalled); for the servo, worst case is 500 mA, so we are at a total of 2500 mA (2.5 Amps). Now - the Arduino should be considered separate, and run off its own battery - because unless you are able to use a low-dropout regulator or a switching regulator, the standard on-board regulator needs at least 7 volts to work properly. What you might find, if you want to use a single battery for everything, is to get a large capacity 6 cell NiMH (7.2 volts) R/C rechargeable pack. Otherwise, you'll want a separate 9 volt (or better, a pair in parallel for double the current available) for the Arduino by itself.
So 2500 mA at 6 VDC for the motors (worst case) - if you wanted that to run for 1 hour, you would need (at minimum) a 2500 mAH battery; actually, you want something larger, because you don't want to discharge the battery completely (its bad for the battery's life), so I would go for a 3000 mAH battery pack (or larger). If you were using standard alkaline AA cells - see the following:
...you would probably want at least 8 or 12 of these (2-3 x 4 cells per pack, 6 VDC per pack - in parallel), to allow for an hour's worth of run-time (it depends on what the battery can supply under heavy load - typically, the ratings you see for the battery are for "lightly loaded", and the current capacity goes down with increased load). Now (looking at the same chart) if you went with C cells, you would only likely need 4 cells in the pack to run everything.
The single 9V DC alkaline for the Arduino will likely allow it to run for an hour at least, based on the above numbers. To verify all of this, though - make sure you look up each battery cell's datasheet - it will tell you everything (including the de-rating based on load and temperature).
Now - if you went with a 6 cell NiMH (7.2 volts) R/C rechargeable pack, most are made with sub-C batteries (according the wikipedia list above, @ 5000 mAH), they also tend to be able to supply this current pretty steadily under load. One pack for the entire system will likely get you a good run time (maybe close to an hour, maybe more). It will also be lighter weight. Once again, check the spec sheet for the pack and/or the individual cells used.
Hi magnethead794, The battery is not getting hot. But I agree that I shouldn't use 9V for the servo any more.
Hi RuggedCircuits,
The motor stuffs are working well, I think. I just took the robot apart and wired Arduino Pro, XBee, servo and the 9V battery.
It could work for about just one minute, and then the power LED on Arduino board faded out, the system down. I tried to use Arduino's 5V pin for the servo, but the system didn't work at all. Then I took the XBee away and run Arduino's example servo code "Sweep", everything was working alright.
Hi cr0sh,
I really appreciate your help and information! I'll definitely take time to read your post for many times and follow your suggestion. I hope anyone who has the same problem can see your post as it is really cool for beginners!
Kickstarter: "A typical Application consists of using a 9V Battery to Power a Robotics Board that may have logic section needing 3.3V. The Motor may be operating 5V, while an Audio Amplifier could be operating at 8V."
And for how long? 9V battery is good for 300-400mA capacity tops.
So assuming 100% efficiency in the converter, that gives about 3.6W output.
Motor running at 500mA x 5V = 2.5W
Logic section at 100mA x 3.3V = 0.33W
Audio Amp running at 200mA x 8V = 1.6W
Total: 4.4A.
So you won't get an hour out of that 9V battery.
I like the idea of the card, the example used could have been better.
"All or nothing. This project will only be funded if it reaches its goal by Tue, August 25 2020 12:36 PM EDT."
Only need $2 to get there, hope you make it.
vipin8821:
I saw this project on kickstarter it's looking better, but I have few questions
How can I get variable output?
Can I use this in drone?
Is this a linear voltage regulator?
Two of the three power supplies are Fixed. Third one is variable. It can be adjusted using potentiometer. Other two can also be changed by changing the resistor
