MathProf
So, here’s the deal. My project will place, say, 25 robo heads in a (college, university, or high school) computer lab with 25 PCs, one head at each PC work station. In that environment, it will not be feasible to schedule battery recharge on a daily basis. So I am looking for a direct connect scheme from the EZ-B to the PC or to a 110 AC outlet, that will replace the LiPo battery pack.
The first idea would be to consider a USB connection between the PC and the EZ-B, with a DC-DC boost converter, boosting the USB supplied 5V to 7.5V. However, while the EZ-B required voltage of 7.5 volts can be met, the real question is whether the USB/converter combination can supply required amperage. In another thread, Steve G described the variation in USB ports available on typical PCs, USB 1.0, 2.0 and 3.0, and how each supplies different current ranging from 5V at 500mah to 5V at 900mah. In another thread (now I can’t find it) one of our community members reminds us that we are working with a moving target: as we design products based on currently available technology, we need to understand that such technology will likely change between now and the completion of the development project. So it looks like I would need to investigate the amperage generated by typical DC-DC boost converters, as a function of supplied amperage by the USB port, to see if required amperage (500mA?) is available. Do I have this right?
The second idea is to require an additional 110 AC outlet at each workstation for the robo head and its EZ-B. Then a straightforward AC/DC conversion (with the required amperage) would solve the problem. However, it’s not clear that, with all that’s going on at a typical PC workstation in a lab, that another AC outlet would be available there. But if such an outlet is available, isn’t this a straightforward solution?
Thanks for any light you can shed on this design issue.
Hey Ron.
So what sort of gizmos will a typical "Head" you would be using have (servos, sensors, camera ect), just so we can get an idea of what power requirements they will need?
It always comes down to the amps, not the volts. The EZ-B will actually run on 5v, you just need to disable the low battery warning. But 1/2 amp is barely enough to keep the EZ-B itself running. Certainly won't be able to use the camera or LED array. Can probably use the speaker.
Alan
Good questions Steve and Alan,
For prototype head, I see just the gizmos that come with the JD head. At this time, I don't have an inkling what head or heads will be used in production, and what amp needs they will have. So for now, I guess I should be able to answer the question for the vanilla JD.
Ron
So does the 2 LiPo battery pack provide 7.5 V at 500mA? Should that be the target of a direct connect?
Ron
Actually the 7.4v LiPo battery pack sold in the store could potentially provide about 30 amps, but that would only be for a few minutes. As Alan has mentioned, is really not a lot of power at all. Most sensors need very little amperage, a camera will need a little more as with LED arrays, and sevos will need the most amperage to deal with the initial in-rush current to make them move.
To run an EZ-B with a JD head with the included LED array and camera (not forgetting the head comes with two micro servos), you should get a good couple of hous run time with a 7.4v 1300mah battery. Or you could use a power adapter which can knock out a few amps, and should run the v4, camera and LED array okay (if you intend to use servos as well, you will need to look at double figures for amps, around 15 to 20 depending on how many servos you would use).
Yeah, Steve, the neck servos will be important.
Wouldn't the best bet be to try to reproduce the "power" provided by the typical LiPo battery pack? That profile would be able to handle most anything a prototype would need.
Ron
Yeah, if you can reproduce the power (voltage and amp output) that a LiPo or Nimh battery can offer, than that will be fine.
To handle the servo inrush current you'll need at leasr a 10 amp supply at 7.5 volts. 20 would be better but with just the 2 head servos 10 should do. Most of the time the draw will be much less, but whenever the servos start to move they pull a lot of amps for a very short time (inrush). Search the forum for inrush current or in-rush current and there are dozens of posts about EZ-B 's resetting and every one of them was using an insufficient plug in power supply or alkaline batteries.
Alan