Trying to figure out what kind of DC Power Source I will need.

Now that's a lot of motors!  Makes me wonder if the "42" in the name refers to the number of degrees of freedom this thing will have, originally I assumed it was in reference to the Hitchhiker's Guide to the Galaxy!

What you need to do is essentially figure out how much current you could draw under a worst-case scenario. Remember that motors consume a lot more current under load, you need to check out the "stall current" to get this value.

When I look up the NEMA17 motors you specified, I get the current draw at 1 amp each, not 0.1 amp.  You say only four will run at once, already that is 4 amperes. Add in the other motors (and calculate for the different voltages used) and it looks like your "ROBOT 42" will be eating about 7 amps if everything is activated. Of course, it's not likely that all the motors will be on at once, but again there is that "worst case scenario" you need to plan for.

The battery you specified would last about 30 minutes, drawing that current. 

Personally, I would suggest using LiPo batteries, or perhaps build an 18650 battery power bank.  I did a video on using LiPo's that can help you calculate the correct size.

Good luck, and I'd love to see a picture of this multi-motor beast!

😎

Bill

This is Robot 42 and Yes it is a reference to the Hitchhiker's Guide to the Galaxy. I was trying to post this when the forum when down. I hope I was not the cause. - Bill

@greendragon Simplistically, measure how much current your bot uses, then multiply that by the number of hours you want it to run before needing a recharge.

@greendragon No, you were not the cause - I took the forum down to make a few updates.

That's an impressive looking robot, looks like it's built using Actobotics parts?  Perhaps you can explain what all those motors do.

😎

Bill

Posted by: @dronebot-workshop

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That's an impressive looking robot, looks like it's built using Actobotics parts?  Perhaps you can explain what all those motors do.

1. Robot 42 is built out of 1950 to 1960's Erector parts. Before anyone gets any ideas of just buying up old erector parts, and trying to build your own - don't. There are roughly 36 Plus custom hand made parts that do not exist. I love working with metal, and spent over a year building and designing it. I have finally gotten to the electronic stage.

2. What do all those motors do? Each foot has 2 motors connected to a wheel. There is one motor in the head to move it right, or left. 2 Motors in the shoulders to move the arms up or down. Each elbow has a motor. Each wrist has a motor, and each hand has a servo for griping.

I'm old, and I come from a time when robots looked like walking tin cans (lol). So I decided to build a old school robot. If I had money I would have built a full scale model. This version is about 3 feet tall. Imagine if this was full scale where would I store it in my tiny house?

please note: Robot 42 is not a battle bot! It is a real robot (My opinion only). When designing it I set out a few parameters for myself  - No plastic or as little as possible metal only, Take my time and finish the body, buy and install the motors and then work on the electronics. I don't know how many times I started a project when I was young and because of jumping ahead I never finished it. This time I am taking my time, and if it takes a few years so be it (better then watching reruns).

Bill

Hello:

I have done a ton of research on batteries and I think of going with A - 12V DC Rechargeable Lithium-ion Battery Portable Battery Pack 9800mAh w/ Charger Switch.

If I am correct this battery would give me about 90 mins of power. I would like double that, but the cost is the cost...

I know the Admin likes LiPo batteries, but in my opinion they seem like a big pain in the ass. You have to keep them balanced, and charged up or uncharged and check that all the cell's are good.(and it will not last any longer time then the battery I am looking at buying)

Feel free to correct me if I'm wrong on this.

I am looking for something I can plug into a charger and not worry if it's going to explode or have to do a bunch of checks on. I was just going to add a simple led charge indicator on the robot 42's chest.

Bill

@greendragon LiIon are more forgiving, if you can find a size that works for you then go ahead. Keep in mind though that the popular 18650 batteries from places like AliExpress, Amazon, eBay all contain fakes. A battery capacity is a function of the mass of the chemicals. It is a violation of the laws of physics that a same size i.e. 18650 can be both 1800mAh and 5000mAh. The 5000 is a fake. nThey range from 1800 to 3600, but I don;t know how and assume 2000 as a design midpoint.

Hi @greendragon,

   I haven't seen a total current demand estimate, but simplistically, if a 9.8 AHr battery will be completely drained in 1.5 hours, then current demand would need to be over 6 A.

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Similarly, you haven't specified an actual battery/charger unit, but my first Google hit for the phrase "12V Rechargeable Lithium-ion Battery Portable Battery Pack 9800mAh w/ Charger Switch" went to:

www.amazon.co.uk/9800mAh-Rechargeable-Portable-Li-ion-Battery/dp/B09YHJ8S7G

which in the small print says:

Output voltage: 12.6-10.8V DC
Output current:1-2.4A

which is a long way from 6 A (or more, assuming there may be periods of 'above average' current demand)

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I am only looking at the limited data from your post, so this may be completely misleading, but my first impression is that this needs looking at much more carefully.

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BTW, estimating power demand for stepper motors can be somewhat confusing, as discussed in another thread on the forum. If possible, I recommend you try to do some measurements of current drain before committing significant amounts of money on batteries. It is possible, but by no means certain, that the current demand is less than you might expect. As the chips you are using are 'simple' H-bridges, the current demand will be significantly determined by the software. 3D printers often use slightly 'smarter' devices, which include built-in current regulation, to drive their stepper motors. The software of your system might be able to achieve a similar result, but I am not in a position to judge, so I recommend some measurements.

Also, the well-known marketplaces have offers of cells with claims of higher capacity than they can actually achieve ... I have no idea if that applies to the device I referenced above, or whichever one you found, but I would suggest the principle of 'caveat emptor - let the buyer beware' is a good starting point when choosing batteries of this type. Li-ion technology can be very useful, but it can also turn lethal, especially if misused.

Best wishes, Dave

@davee @greendragon Correct. If his demand is 6A, he is going to need something much beefier. I do know the RC batteries can easily do that, but they are LiPo and require fire bags, stone slabs and expensive chargers.

OR, switch to LiFePO4 battery, they are safe but lower energy density. If he want 6A for 2Hrs, then a 12aH battery can discharge safely at 1/2C or 6A for 2 hours.

@greendragon Have a look at this, it is safe, and will charge at 0.5C so it most likely will also discharge ate 0.5C, but CHECK. It is probably a lot bigger than you expected. If so, then are you sure LiPo is not wanted? I will look for  LiPo candidate and add a link to a follow up post for your consideration. NOTE this is a Canadian Amazon link, change it to your country for local pricing. Wt is 1.83 Kg, and dimensions

https://amz.run/7TXf

Hello: Thanks for all the help. I knew this would be the hard part for me.

After taking in all the suggestions I am thinking of this one:

Kastar 2000 Cycles 12V 6AH rechargeable LiFePo4 Lithium Iron Phosphate Battery

Link: https://www.ebay.com/itm/254832396651

Note: Robot 42 Battery Compartment Size is 5" long x 2 1/2" wide x 3" to 5" Tall

@greendragon That battery is woefully inadequate; just read the specs.

@zander 

Yea just caught that myself! I guess it time to take a rest.

Bill

@greendragon Are you up for some DIY or is cost not a big deal? Otherwise, the battery I posted has the specs to support a 6A draw BUT that is max. I do not know what would happen if you drew max for say 30 minutes or more. Not sure about size, but that can't be changed. Each chemistry has a certain energy density so then it's how to package that volume of chemicals. The more dangerous LiPo has higher energy density so can be packaged very small, the most safe chemistry is LiFePO4 but is a bigger package. Certain Vape batteries will have the discharge rate you want but the market is flooded with fakes so what you get can be a crapshoot plus they are expensive.

That eBay battery seems fake to me, the $ and specs don't add up.

You said you did extensive research so I don;t need to spell out the specs and understand what a cycle life to 70% of 150 cycles means. This battery may handle your 6A peak, but it is right at the limit, maybe go for a slightly bigger pack, maybe 4S and use a buck converter to convert the extra volts to extra amps (with some small losses)

https://amz.run/7TYx

I didn't look around too much for a deal, but this battery should work better for your power hungry robot. https://amz.run/7TZ5

Both those batteries have discharge rates of 50C so that means over 200AMPS, well over your 6A. BUT the cycle life is likely 300 to 500 to reach 80%.

My 12.8V 100AH LiFePO4 are guaranteed for 8yrs with 100% replacement and to 10 yrs with some depreciation. That is 3,000 to 5,000 cycles or 1 complete 0% to 100% to 0% SOC in 24 hrs for over 8 yrs. and then the battery still retains 80% of its peak power. They cost about $1,000USD each when new 4 yrs ago, now about $800.

I would learn to manage the risk of LiPo and go that route with a big RC battery like I posted.