First off, I want to say I am so excited I found this place... I'm almost bouncing off the walls waiting for my first beginner pack to come in. While I'm waiting, I'm trying to absorb everything I can. I think I've watched almost every youtube video that has been mentioned throughout this site, and a few folks that frequent here, I've lived on their youtube channels for days!!
With that said, one thing I keep hearing over and over again is how you need to run the Arduino(what I'm getting, but really any "brain") on a different power source than any motor. I think I understand the reasoning behind that, but the thing that everyone keeps saying "or you'll fry it"... is scaring me a bit :P
I have time to learn before my kit comes in, so I want to try to understand this a bit more. Anyone have a good starting place to learn what I'll need to know to reduce the chances of damaging the equipment I've purchased? Or, do you have some basic things I should be thinking about whenever I'm plugging stuff together? Most of the videos I've found gloss over this area.
A good place to start is drawing a schematic or wiring diagram of your configuration. Accurately label power sources such as batteries with their voltage and current capabilities, logic (cpu) boards with their voltage and current use and supply parameters, and your motors and actutators with their voltage and current consumption requirements.
Power, measured in Watts, is the voltage multiplied by the current. If you have a 6V motor at 500 ma you will be consuming 3 Watts. That means that your batteries, motor driver circuits, and wires need to able to handle that much power. You also have the power consumption of the digital electronics and, leds, etc. To be safe, you might want to spec you batteries at being able to deliver 5W.
As you advance you will get a feel for what is ok/typical/max. I posted a “spider” robot today on LMR where I failed to read the specs on the cpu board power regulator. Turns out it can only supply 150ma while I needed 300ma.
Use colors for wires. Typically in the US Red & Orange are power while black is ground. Other countries use blue for positive rails. I typically use orange to designate raw battery wires, andred for outputs from voltage regulators such as 3.3V or 5V. I also like to use line thickness to denote current capacity. Wider for heavy loads, narrow for I don’t care. There are quite a few free schematic drawingt tools available.
In general, a CPU can tolerate a few mill amps at ~5V on an I/O pin while a motor requires a few hundred ma at perhaps 9V. When you encounter such mismatches you must provide a “driver” circuit capable of performing the translation. It is also possible that you might have a 5V cpu and a 3.3V peripheral chip. Again you must account for the difference.
Everyone on this site started sonetime. Almost everyone has allowed the smoke to escape from some pretty expensive chips. pPrhaps the hardest thing to using LMR is asking the proper question. Simple direct questions with supporting details get the best response. Vague what is “best” or “do it for me” can get some very curt replies.
a microcontroller on a different supply from the motors is that you may cause the controller to reset if the motors get power hungry and cause a voltage drop on the power supplied to the controller.
As ggallant pointed out, trying to drive a motor directly from a controller pin could very well damage it, because, many motors require more current than your typical I/O poon can supply. The other issue is back EMF that can/will occur when you cease sending power to the motor. That is why you usually see does connected backwards across coils of relays and motors. When the field collapses a voltage spike occurs. Feeding it back through the coil protects the rest of the circuit.
I may be a bit off on what happens with the voltage, but, the reason is right.
Also make sure that you have Also make sure that you have the proper charger for your batteries. Each battery chemistry has a specific way of charging it. If you use multiple types of batteries, there are chargers that will charge multiple types but you have to set them up before charging so the charger knows how to charge the battery.
I just wanted to thank everyone for their responses. I actually took all your info and went off to the races. It wasn’t till George responding that I even remember where I got it from
Now that I remember, I must say thank you and George your response is quite timely, I’ve learned enough now to start really getting into the thick of it(multiple motors/servos, switches, various voltage requirements, multiple power sources etc…) and your message has given me the confidence that I am really starting to know what the heck I’m doing(validated a few “I think this is right” moments).
If anyone is interested, I’ve actually built my first prototype of the project I was setting out to build. I’m now in the refining stages… taking the “whatever I had laying around the house” or “this is cheap and I may be able to mod it to do what I want” out of it now… which is proving to be interesting, and expensive
I’m just now starting to use my multimeter, as up to this point it’s all been 5V and the only thing I needed to test was connections
Here’s hoping I don’t produce any smoke in my next adventure!!
I’ve done it both ways: I’ve done it both ways: single battery or seperate. For the bot’s I’m building now I use a single battery unless there is a really good reason not to.
I am designing a high powered balancing bot (24v, 100 amp-hr battery) and using that as my single battery. Other voltages will be obtained via switching regulators of the appropriate power.
I was thinking about using two batteries, but the cost got me.
