Has anyone ever considered using an AC adaptor to power the robot, rather than the gigantic batteries. Does an adaptor even exist for our power needs? (not that we could actually use it at competition) We’re working on a test electronics board we can use whenever we need to test a motor or a sensor, and having to drag around a battery kinda ruins the portability, although it doesn’t really matter.
The controller itself doesn’t need a real big battery (the backup battery is about right for the job), but running the robot drive motors does.
Well, the idea is that the board will be an entire electronics system, with an RC and the whole power distribution system, and victors and spikes, etc. and theoretically capable of running an entire robot by just plugging things in, so we can test-drive the first-week chassis, and other things, without having to mess with the new electronics equipment until we have a better idea of all the parts we need. This year’s electronics mounting was beautiful, but we built it a bit too soon and had to later add a victor and two spikes randomly to the frame, and had to run extra wires accordingly.
So, yeah, we need the same kind of power you get from the big battery.
You could run the whole system with a small 12v battery, but don’t expect to be able to run any motors that are under much physical load. Look at the motor specs in the Tips and Good Practices manual, they give the no-load current draw. Figure out how much current it will take to power those motors, and read up on how battery specifications work. You should be able to figure out about how long you can run some motors with different size batteries (assuming the motors are not mechanically connected to anything, they just spin freely). Perhaps a 12v nicad battery pack would do what you want, with less weight/inconvenience. Just make sure to use the appropriate charger for it.
Meh. Convenience isn’t really an issue. I’d use the normal batteries before I’d go buy another battery. I just kinda thought being able to plug into a wall would be ain interesting feature.
Here’s a link to a video of our “little black box” which enables us to drive any chassis with just the motors and gearboxes installed. http://www.youtube.com/watch?v=Bw7-EVB-XZU In the video we’re using it to test drive a rookie team’s chassis two weeks before they were able to get all the electronics installed. This box has become one of our most important development tools.
I just realized I did not answer the question you asked…which is whether or not you could use an AC adapter to power the robot.
You might want to ask IFI about this, as there may be some specifications for the power supply that would limit what you would want to do. Typical “wall wart” power supplies are rated to put out a specific voltage at some specific current load. If you have less load, they put out more voltage, which could possibly damage the controller. That is why think that using a battery might be wise.
A lab type regulated DC power supply would probably be fine, but it will be even more cumbersome to use than the regular robot battery!
Well, I knew there had to be a reason no one’s tried it before. I just kinda wanted to know what it was.
And that black box is very nice. Could that battery fit any more perfectly?
We had something similar to that as our actual electronics system two years ago. It was actually a large tupperware box that had the Breaker panel and all the Victors bolted in it, with the RC, Radio, and backup battery suspended from the lid. With the held of quick connectors, it could be completely removed from the robot in under a minute. Won us an award too. But then we tried it the following year with a Craftsman toolbox and that was just plain horrible. I’d have to cut metal off of the robot just to get the box out anymore.
Once I get the new Autodesk downloaded to my computer (2.16GB download on Dial-up!) I’ll cad up our ideas and put up a picture.
Jake,
Because the motors are in stall when they are not moving, the initial start current on a typical robot may be in the 200-300 amp range. An AC supply of that size would be enormous. I know that my 25 amp ham radio power supplies get bogged down just trying to start one motor. The supply is a linear supply and weighs over 20 pounds.
If you’re just after a bench setup to test electronics, why not use a power supply and get small motors. I’ve noticed our programmers dragging around a big board with a battery on it to test sensors. A lot of the time, they could have gotten away with a smaller setup to run their experiments. I have yet to convince them of this though…
I won’t say it can’t be done, but I can tell you that you’re talking about a HUGE AC/DC converter, and it’s going to be very expensive.
For instance, if you want a DC power source of 10 amps, you’ll pay ~$60 at radio shack. 20 amps is ~$100.
If you’re running two motors for an arm at 15 amps each, 4 sim motors at 20 amps each, a compressor at (I don’t know how many)…
You’re talking hundreds of amps.
Not really, for testing out the electronics you would not run all these motors at once, and you would not be running the drivetrain under load, etc. 10 amps or less should be sufficient. The only thing that I can see causing problems could be the compressor, if you try to start it when there is pressure in the system it will draw a big load on startup.
That’s about what I thought. Again, it’s not a big deal.
Why not just use a car battery charger? The higher quality electronic will put out around 100 amps at almost a perfect 13 volts, which should be within tolerance of the whole system.
-Mike
You might check out the battery chargers themselves. I can’t remember correctly, but I believe they’re rated to 6 or 8 amps. The thing you may have to worry about is voltage - I think they’re 12v output, but they might be higher. Time to break out the DMM.
Yeah… This whole thing doesn’t sound to promising…
Sure, the battery might be rated at supplying so many amps, but when a motor turns on, it spikes way more than this. That’s why the ‘motorcycle’ batteries that we use are so convenient; They can handle the high current spikes. I just don’t think a AC-DC converter can handle this… Now maybe a system where its an AC-DC converter with a battery to handle the high current spikes… Kinda like the IFI 7.2v charging circuit, where the input voltage and the battery are used (but perhaps a better designed circuit… If we could only put in the one diode to prevent the battery from backcharging the robot… [/OffTopicRant]…)
Just some off-the-top-of-the-head thoughts… I could be completely off-base.
Jacob
We have two wall-wart adapters which we use for testing the electronics. One provides 9v at 1/2 amp for the backup battery, and the other provides 12v at 1.5 amps for the RC. This works fine for testing the electronics, camera, sensors, etc, but will NOT run any motors.
Think about this – the battery on the robot goes through a 120 amp breaker. That’s a good indicator that to run it (with full motors) off of wall current, you’d need a power supply capable of providing 120 amps!
Al’s reply got me curious…so I connected a lab power supply to an RS540 mabuchi motor (the BaneBots motor) and switched it on and turned up the voltage. With the current limiting set to 2.0 amps, the ammeter indicated a spike to about 1.5 amps, and running currrent of about 1.0 amps with the voltage adjusted to anywhere from a couple volts to 10 or so.
I think my estimate of 10 amps needed to test the system, having the motors without mechanical load on them, is probably reasonable, asuming you don’t try to run more than two motors at once.
Might be able to use an old computer switching power supply, they have decent regulation, and should handle 5-10 amps on the 12v circuit.
Guys,
Battery chargers rarely put out a pure DC voltage. Never use them for power supplies. Often they put out a pulsed DC that averages about 13 volts but peaks much higher. Popular 50 amp chargers just connect a few diodes to a big transformer and add a few lights and an ammeter and call it a day. Remember that a wet or gelled cell battery will charge (current flows) if the input voltage exceeds the battery voltage. That is why 50 amp chargers are not allowed for our batteries as the high current is capable of destroying the battery. (read that catastrophically) The charger supplied in the kit is a smart charger and won’t even turn on unless a valid battery is connected and in need of charging. The internal electronics test the device connected before supplying full output current.
As for the compressor, start current is about 25 amps while run current is about 10 amps. Again, start current on the Chalupas or the Fisher Price is over 95 amps. With many of the modern power supplies, the start current (of even one motor) will force the supply into current foldback or just simply trip the breaker. The supplies that go into current foldback will not go back to normal output until the load is removed or the power is reset.
And you don’t want to turn on a power supply at a low voltage and run it up with the electronics. For starts the RC is disabled until the input voltage is above 8 volts.
Although the breaker is rated at 120 amps, if you look at the curve you will see that it can handle a 600% overload for a few seconds and can handle almost 200% for 40 seconds.
120acb.pdf (237 KB)
120acb.pdf (237 KB)