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Comments by Jan
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Electrical characteristics of servos and introduction to the servo control interface
- 14 June 2017Hi, Gustavo.
Your question is not clear. If you are asking about characteristics of servos, as in can you stick 1.2k in series between your RC control signal and the servo (NOT between signal and ground, which would be in parallel with the servo), it's a little more than I'm comfortable with (I would use something like 220 ohms) but should probably be fine. Things like the particular servo you have and the wiring lengths will matter, so you should try to look at the signal on the servo side with an oscilloscope to make sure it looks decent.
If you are asking about the characteristics of receivers or other servo controllers, as in can you put a 1.2k resistor in parallel (NOT series) between signal and ground, that will depend on your receiver, and 1.2k is a little on the small side (I would use about 10k for a pull-down resistor). You can again look at the signal with an oscilloscope to see if the resistor is deforming the signal too much.
- Jan
Understanding battery capacity: Ah is not A
- 31 May 2017Hi, Kerron.
Yes, that's right: 24V could damage a device expecting 18V, and the current part should be okay. (So you should use your device with an 18V voltage regulator, and make sure that it can comfortably take a 24V input and deliver at least the 1.67A you need.)
- Jan
Understanding battery capacity: Ah is not A
- 22 May 2017Hi.
It looks like you either did not read the blog post or did not get the point of it. 20A is about how fast you can get the energy out, not the capacity of the cell. 3.7V and 2.2 Ah give you 8.14 Wh per cell, and that multiplied by 1234 gives you just over the 10 kWh.
- Jan
Understanding battery capacity: Ah is not A
- 16 May 2017Hi.
A 12V adapter connected directly to the battery is unlikely to be an appropriate charger. A 12V battery showing you 9V is definitely not good and charged. I am not sure how you are measuring the 0.2amps, that will be a function of your load, and a good battery should definitely be able to supply much more than that. The voltage will gradually go down as your battery discharges. You can probably find a datasheet for the battery you are using and get more specific information. You will need to regulate to 5V anyway, so your main concern should be not discharging your battery too much. And you should get a switching regulator, which should need less than 500mA to output 1A when going from 12V to 5V.
- Jan
Balboa is here!
- 4 April 2017Thanks, and thanks for sharing your robot! The most difficulty came from wanting the Balboa to be able to pop up on its own. I will write up a blog post about it once I find more old prototypes to take pictures of (this project has been going on for maybe eight years, during which we moved several times).
- Jan
Servo control interface in detail
- 20 January 2017Kenneth,
I don't think I implied what you seem to think I did. Did you see the post before this one?
https://www.pololu.com/blog/16/electrical-characteristics-of-servos-and-introduction-to-the-servo-control-interface
I think it is not helpful to classify the servo control signals as those in 72 MHz systems vs those in 2.4 GHz systems since that is just the frequency that the transmitter uses to communicate with the receiver and says nothing about what kind of signal the receiver is outputting to the servos. There can of course be differences from brand to brand and unit to unit. You should definitely just look at your particular signals with a scope.
- Jan
Understanding battery capacity: Ah is not A
- 3 January 2017Hello.
The math stays the same. An 18 Ah battery should provide 18 A for about an hour, so it should be safe if you only need it to last half an hour.
- Jan
Understanding battery capacity: Ah is not A
- 18 January 2016Your math about how long the batteries would last is fine, but the point is you should avoid putting your battery packs in parallel. You should try to use bigger cells if you really need the 5Ah in one pack, or you could put three fans on each pack and have two parallel systems.
If you really want a single pack of eight AA cells, you could put them all in series to make a 9.6V pack, then put pairs of fans in series and power them from the higher voltage. I don't know about the details of the fans, so this could be tricky in the same way that putting batteries in parallel is tricky: it's difficult to ensure the power will get shared evenly. For instance, if the fan is just a motor and you stall one of the series pair, the voltage across it would go to 0V and the other fan would get the full battery voltage of around 9.6V, which might damage it.
- Jan
On losing my baby
- 31 December 2015It got a lot better, but now it's getting worse as we approach his birthday. There are so many triggers for those sad memories. We haven't made much progress on the core conflicting goals of not being sad and not forgetting him.
Thanks for your thoughts.
- Jan
Understanding battery capacity: Ah is not A
- 15 December 2015Amps multiplied by volts gives you watts. For the same current (amps), higher voltage gets you more power (watts). Factoring in the time (hours) just takes you from an instantaneous rate (watts) to total capacity or energy (watt-hours).
An easy way to see this intuitively is if you think of two 6V, 51Ah batteries. You would need two of them in series to get to 12V and 51Ah. A single battery has 6V times 51Ah = 306Wh of energy in it. If you have two of the batteries, you have twice as much energy stored, which is also what you get when you multiply 12V by 51Ah to get 612Wh.
- Jan