Kullthulu
EZB-V4 Battery / A/C Adapter Usage
Hello everyone,
Have a power question and any advice with this is appreciated. I’ve searched the forums but haven’t quite found a thread that answers my questions.
I’m building a service bot that stands 5’8 running 2 servos for the Head, 5-6 for each arm and gripper, 2 -4 Led’s For eyes, an el-wire ring in the chest around the speaker, and two 12v (max) motors for the base wheels running through a motor controller connected to the ezb.
I’ve been using the battery pack provided with the developer kit with rechargeable AA’s in the provided battery pack but it’s already insufficient and I haven’t even added the arms yet. Dies within 20 minutes at best. I’ve seen LiPo recommendations but this is what I’m looking for:
what batteries are are you running?
How much are you operating off of them (device wise) and how much longevity do you get?
are there any ac adapters on the market that you’ve been able to use for larger projects that can allow you to bypass batteries all together during prototyping? Anyone have experience using automotive SLA’s regulated down to work with the EZB? Overall I’m looking for the best way to keep my bot powered for the longest amount of time weather it involve a teathered electrical connection or rechargeable and wireless. It’s a front I’m fuzzy on and could use advice with so I don’t accidentally burn out hundreds of dollars in equipment and components.
The answer to your question regarding how long batteries last is related to the current draw - so it’s impossible for me to answer but you can identify it yourself. If you are serious about your project, a bench adjustable power supply on eBay is a good choice and only costs approximately $100 usd. That will give you the current draw which will help calculate your power consumption.
Because the motors will be holding weight that is specific to your configuration, it’s not as simple as assuming a servo draws X amps. You will have accurate assumptions by monitoring the current while the robot is in use.
Because of the hardware you’ve described, I would configure the adjustable bench supply for 7.4 volts
If your robot is drawing 1 amp continuously, and you want it to run for 4 hours, you’d need a 4 amp battery. The batteries you will find have an amp hour rating. That’s how many amps of current it provides in an hour.
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.ca%2Fulk%2Fitm%2F323817738170
10 amps are ideal
However I'll have to wait up to 28 days for it to arrive. I guess this what they mean when they say "Slow Boat From China". LOL
Thanks for the heads up DJ!
.... or, they light on fire and burst into flames when we turn it on
Alan
The powersupply can fit on board. Any thoughts on potential issues with putting the powersupply on board the bot and using extension cords as a feather to power to give it some range?
Also, I know 7.4v is the right calibration but what’s the max current we can push through the EZB? Obviously going to check my current draw as mentioned once I have the arms working but don’t want to accidentally burn the brain
Has voltage limits etc. The biggest concern is the power for the servos and sensors, etc.. They're powered off the power supply so they can't have any more than 7.4 volts
There isn't a concern of having the power supply on the robot if it fits. Although, it won't hurt to consider getting smaller switching power supply once you identify the amps that's needed
I don't know your knowledge level with electricty so I'll assume beginner level. Please forgive if you know what follows.
Disclaimer: Electricity could hurt or even kill you. You could even burn down your house. If you do any of this after reading my article below I am not responsible. If you have any doubts about handling electricity please ask a professional to help you.
With electricity a lot of people get amps (current) and voltage mixed up or think it's the same thing. Very simply put, amps are the electrons in electricity that actually make things happen. Voltage is the pressure behind the amps that push them along. Resistance is another component in an electric circuit that you need to be very aware of. Resistance is made up of the type and size of the material that the voltage is pushing the amps through to get to the device you're trying to make work. Some material is easier for the electrons to flow through. For example copper has less resistance than aluminum. With that in mind you would need to use a larger aluminum wire for the same amount of amperage to flow then you would if you used copper wire.
An ampere is the unit used to measure electric current. Current is a count of the number of electrons flowing through a circuit. Here's the fine print: "One amp is the amount of current produced by a force of one volt acting through the resistance of one ohm". Here's another way to say it: Your device will pull Amps from a power source like the power company through a wall outlet (AC power), a battery (DC power) or a switching power supply that will convert AC power to DC power. Your device sucks (pulls) the amps it needs. It doesn't care what is between itself and the power source. Something will heat up If your power supply and/or the wires or connectors in the circuit are not rated to provide the amount of load (amps) being demanded. This heat is the result of the electrons being sucked through a undersized part of your circuit. This is true all the way back through your house and out to the power generation plant that feed power to your neighborhood and your house. Depending on how much load you pull through an underrated part of your power grid you could just get a little warmth or complete failure with smoke an/or fire.
You could also burn out a device you are trying to power by starving it because of one of the issues mentioned above. Another way to burn out your device is to supply too much or too little voltage. An exception to this are DC motors. You can run your voltage down to zero and a DC motor will only just slow down and stop. However it's still true that with DC devices you need to have a big enough pipeline (wiring, connections, power supply) to feed them the amps they demand. DC motors will also tolerate slightly higher voltage but be careful here.
So, you're thinking about using an extension cord to supply power to your robot? I read all the time on things I buy NOT to use an extension cord. I think it's just fine to use one as long as you keep in mind the things we discussed earlier in my ramblings above. Just make sure it's not too long and it's big enough to carry the load your robot will demand. Don't share the cord with other robots or power hungry devices like a microwave oven. Also you will find that your voltage will drop over very long runs of wire like an extension cord. A larger gauge wire in your extension cord will help here.
There is one other thing to be aware of. This is start up demand. When motors and other devices on your circuit first start up they usually draw more current then when they are just sitting or under normal use. This startup will make the voltage sag (lower) for a short time and starve the devices that are trying to draw the current they need. Always design your circuit (including your power converters) at least 25% larger than your total load (motors and devices).
How do you know what your total amp (load) needs are for your circuit? Simply study each device on your circuit and add up how many amps each one will draw. Pay close attention to motors. They should have a rating for normal load and peak load. Design your circuit around the total amps all your devices will draw under peak and startup load.
One other thing. It's a very very good idea to add fusing to your circuit. This will protect your motors and devices from shorts, failures and pulling too much current. Size your fusing using the things we discussed above.
I hope this was of some help to you or others that may be wondering about feeding power to their robots. Please be safe with electricity and have fun.
https://synthiam.com/Community/Robots/Artemis-The-household-service-bot-17757
I’ll be updating it soon. Since then It’s been given a silver paint job, hooking up the arms over the next few days and then probably swapping out the head (I snagged an Elvis alive bust off eBay last night that will likely replace the omnibot head on it now)
Just curious, how did the above power supply turn out?