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Comments by Jan
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Understanding battery capacity: Ah is not A
- 27 December 2014Hi, Nate.
If you get two of the same battery, you will have double the energy of one battery, no matter how you arrange them. You do not get to double the voltage AND double the amp-hours, which would be quadrupling the energy stored. If you put the two batteries in series, you will get double the voltage and the same Ah; if you put the batteries in parallel, you will get the same voltage and double the Ah.
By the way, you should be very careful about putting various packs in series or parallel. Particularly in the parallel configuration, you are basically shorting together two batteries that are unlikely to have the exact same voltage. Lithium batteries are especially touchy about being correctly charged and discharged, so I strongly recommend getting a single pack that fits your application rather than trying to assemble your own large pack out of smaller batteries.
- Jan
RC servo speed control
- 2 December 2014Paco,
The hobby servos I wrote about in this article are not well suited for doing what you are asking for since they do not tell you the error. You can do something similar to the speed control I wrote about by picking a virtual set point and then sending your servo appropriate commands based on where you think the servo should be, having it move faster when farther from the point and slower when near that set point. However, this is all just an open-loop motion sequence you would be sending the servo, and depending on the resistance it encounters, the actual resulting movement can be completely different from what you intend.
If you are looking to effectively make your own servo by doing your own closed-loop control system, that is outside the scope of this article, and you should search online for things like "closed-loop motor control with Arduino" as there are many resources available.
- Jan
Understanding battery capacity: Ah is not A
- 18 November 2014Caroline,
You're missing the voltages of the batteries. It's hard to tell much without that. For instance, if your 6 Ah battery is 36 V and your 9 Ah battery is 24 V, they will both have the same capacity. If that were the case, your 9 Ah battery would indeed last longer, but you would be going a lot slower, for no net increase in range. This is is all assuming the bike would even go at 24 V. If both batteries are 36 V, the 9 Ah unit should give you about 50% more time and range. Keep in mind that in that case, the battery should also be about 50% bigger and heavier.
- Jan
Thoughts on journalists checking drafts with sources
- 10 November 2014Dan,
A few quick points:
I am not saying *every* draft needs to be shared with every source. You, meanwhile, are advocating for the extreme of never allowing it.
Given that you are arguing for an extreme, it would be much more convincing if you actually argued for it instead of just saying "imagine if". It looks like you haven't even bothered to read much from those who disagree with you, who are not just imagining sharing drafts with sources but are actually executing the approach with success.
I think there are many issues that a journalist is just never going to understand that well. Plus, who do you think should judge when a journalist has gone "far enough to make sure they understand the concept they are trying to explain"?
- Jan
Understanding battery capacity: Ah is not A
- 3 November 2014Greg,
Assuming the voltage is fairly constant during discharge, you can just divide the mWh number by the voltage to get mAh. So a 1.65V, 2500mWh NiZn cell is probably going to give you about 1500 mAh (and the energy stored would be similar to that of a 1.2V, 2000mAh NiMH cell).
- Jan
Continuous-rotation servos and multi-turn servos
- 27 October 2014Hi, Charbel.
I do not quite understand what you are asking, but I suspect continuous rotation servos, which are not particularly high performance motors, are unlikely to be appropriate for inverted pendulum applications or for retrofitting with encoders.
- Jan
Understanding battery capacity: Ah is not A
- 27 October 2014Zubair,
The 20 mAh low end is probably because the charger cannot get the charge current low enough to charge the battery safely. I am not sure about the 100 mAh upper limit; are you sure that is not a mistake? Maybe that's a typo and it's supposed to be something like 100 Ah, though that sounds a little high (that would take almost 24 hours to charge with the 6A limit, plus 100 Ah is a pretty big battery).
- Jan
New products: Magnetic quadrature encoders for micro metal gearmotors
- 27 October 2014Thank you for continuing to push on this. I've seen that Melexis sensor before, but I think the magnet for the AMS sensor should be pretty simple to make (and we're already working on it), so I suspect that will be the easier route.
As for your performance calculations, I definitely agree that 12 CPR is lacking if you want decent resolution per millisecond. We are targeting 8-bit MCUs with no special quadrature decoding hardware, and I think these 12-24 CPR units are very well matched to that. It's definitely good to hear from customers pushing for more, and we are aware that much better MCUs that can deal with high frequency quadrature are getting more and more available.
- Jan
Understanding battery capacity: Ah is not A
- 9 October 2014Sravan,
Sorry, no "1-amp motor" post yet.
Your math for needing 16 Ah for two hours seems generally right, but you might be neglecting additional power requirements for the rest of your robot.
As for the long-term degradation question, yeah, a battery that gives you two hours of run time new will generally give you less as it gets older. I don't think there's a good general way of predicting that. Even without putting the battery age into consideration, you'll probably get significant variation when you consider various battery types and various loads that average out to 8A (e.g. 8A steady vs. 20A for 25% of the time and 4A for 75% of the time).
- Jan
New products: Magnetic quadrature encoders for micro metal gearmotors
- 9 October 2014$4.21 is quite expensive for us, but I will look into those sensors and keep them in mind. I'll also add a 4 CPR version of the magnetic wheels (half N half S) to our to-do list so that even if we do not have the whole solution right away, we can have magnets for people to make their own systems like that one you linked to on tindie.
We are just starting to work on the additional resolution wheels, so we do not have availability estimates yet or even know how far we can go. It looks like 28 CPR will not be feasible, so we will try 24 CPR even though that will likely require a different sensor arrangement than the 12 CPR version.
- Jan