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Comments by Jan
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Understanding battery capacity: Ah is not A
- 7 October 2014Jerry,
Did you read the post and comments and try to do the calculation yourself? There is one wrinkle in the specs you've provided: 12V at 400mA is 4.8W, not 5.6W. If we go with the 400mA figure, your 4800mAh battery should be good for around 12 hours. If we go with the 5.6W figure, your 12V * 4.8Ah = 57.6Wh battery should be good for about ten hours. Either way, you should easily get four hours even if there are some inefficiencies or optimistic specs on your battery.
- Jan
New products: Magnetic quadrature encoders for micro metal gearmotors
- 7 October 2014dragonet80,
Thanks for your feedback. I'm very excited about 12 CPR because I think it's close to ideal for robots like our 3pi and Zumo. With a 30:1 gear ratio, we get 360 CPR on the gearbox output, and with a 32 mm wheel, that comes out to about 0.25mm linear resolution. You can see what kind of performance you can get with that combination on Paul's dead reckoning robot:
http://www.pololu.com/blog/312/lvbots-march-2014-dead-reckoning-competition
These motors can go up to about 30,000 RPM, or 500 revolutions per second, so with 12 CPR and two channels, that gives us about 12 events per ms for our controller to deal with, which starts getting close to the limit of what is practical on a microcontroller without needing special hardware counters. I realize not everyone needs 30k RPM, and we are working on slightly higher resolutions versions of our magnetic wheels (to give us 20 or 28 CPR).
Those absolute position sensors are very nice, but they are also very expensive, and my general sense is that they are overkill for these motors. Can you share more about your applications and why you need such high resolution?
- Jan
New Product: 5V, 5A Step-Down Voltage Regulator D24V50F5
- 7 October 2014Hi, James.
Thanks for pointing that out. While the 3A header ratings are probably fairly conservative, you should solder wires to the regulator if you want to push it to its limits. Current limits or ratings in general are quite complicated for products like this since there are so many factors to consider, including ambient temperature, airflow or lack thereof, how many other contacts or heat-generating components are nearby, and what kind of duty cycle is necessary.
We expect to be updating these regulator pages and perhaps to be adding other resources to help specify and clarify what kind of performance you can expect at various operating points.
- Jan
New products: Magnetic quadrature encoders for micro metal gearmotors
- 3 October 2014Yeah, they fit in there! It will still take some work to design the right corresponding PCBs and to come up with a good assembly procedure, so we're still at least a few months out from having a complete encoderized Zumo.
- Jan
New products: Magnetic quadrature encoders for micro metal gearmotors
- 3 October 2014That sounds great; thanks.
- Jan
New products: Magnetic quadrature encoders for micro metal gearmotors
- 3 October 2014We have evaluated many gearbox suppliers, and the ones we use are the best we know of. We would definitely like to hear more about your tests; can you provide us with more information about your setup? You could email us if the comments here on the blog are not convenient for getting into details.
- Jan
Thoughts on Open-Source Hardware
- 1 October 2014If you want to have a meaningful discussion, please be more specific about what you are complaining about.
If you are talking about our Maestro servo controllers, it seems like you might not be aware of the Pololu USB SDK, which has example code that shows how to use the Maestros' USB interface. Although the code is written in C#, you can use it as a reference for developing your own code that talks to a Maestro in the language of your choice. Many of our customers have done this, and you can see several examples in the "Related Resources" section of the Maestro User's Guide.
- Jan
Thoughts on journalists checking drafts with sources
- 8 September 2014In the most extreme cases, the wrong information, whether intentional or not, could lead to things like war. Even in more mundane situations, impressions journalists give the public can have significant repercussions for things like allocations of permits or public funding, which can impact a community with things like creation of jobs or improvement of safety or eradication of a nuisance.
To bring it back to Richard's example of not caring about the impact his writing might have on a manufacturer ("I'm not interested in their profit margins"), I say we should care if our mistakes bring economic damage to others. And while Richard might think that it's not his or his readers' problem if some product doesn't sell or some company goes out of business, what he is leaving out is the cost of his being wrong. In this case, it would mean that a good product stops being available or a company making good products stops existing, which is bad for more than just Richard's readers. I doubt that writers like Richard actually want to be responsible for this kind of outcome, but my suspicion is that they are blinded by reckless arrogance.
- Jan
Thoughts on journalists checking drafts with sources
- 8 September 2014Hello, Richard.
I appreciate your posting since it gives us a specific instance of this journalistic haughtiness I think is very damaging. Manufacturers of products you review are a little different than the kind of information "source" I was talking about, but what I think are the flaws in your mentality are the same. I don't know you or your writing (though for all we know, I might have read some of it), so I am going just off of the comment you posted here.
The only reason you gave for defending your position is "it can stifle the right to freely comment". I do not believe this, and the comment from Aeroengineer1 indicates it is possible to maintain the independence of your commentary while having facts checked. Journalists should exercise their integrity by considering feedback from interested parties, not by sticking their heads in the sand. Regarding your SparkFun example, you seem quite content not to care about my response after publication, so why would you care so much about upsetting me prior to publication? If I give you some factual feedback because I am upset, does that invalidate those facts? Are you not able to evaluate my claims of fact just because I have a bias?
The rest of your comment is full of the arrogance I was originally commenting on in this post. You think that there is some virtue in your consequences be damned attitude just because you claim to be serving your readers. Journalists, like everyone, should care about the adverse consequences their mistakes could have on the broader community, not just some subset they decide is all that matters. I am not at all saying you should be some corporate shill, but part of taking responsibility for your work is caring about its consequences. Furthermore, it does not serve even your readers for you to artificially limit the validity of your writing just because you think your own analysis is good enough.
To be clear: I am not at all arguing against your right to have an opinion or to publish an opinion. What I am saying is that your claim that "I come to my conclusions after careful and considered deliberation" is quite disingenuous if you do not avail yourself of easily available feedback (even if it's from biased sources).
I am quite curious about what problems you are talking about when you say "On the occasions it has happened (without my consent), it has caused nothing but problems." If all those problems were like what you continued to present for most of your comment, I really don't see the validity at all: it sounds like some people were ticked off, which they probably would have been after your publication, too.
I am not the one arguing for some extreme, such as that every article should be pre-approved by sources or that you have to make your sources happy. I think most reasonable people can immediately imagine scenarios where other considerations outweigh the benefits. What I continue to believe is that arguing that such draft checking is almost never appropriate significantly undermines the credibility of journalists.
- Jan
Simple hardware approach to controlling a servo
- 3 September 2014David,
I am not sure what is typical. I suspect sequential pulses are more common for cheaper and lower channel-count units, but eventually, the pulses have to overlap if there are enough of them. When we develop products such as the TReX, we make sure that they can read all the channels no matter what their relative timing might be.
- Jan