I’ve been hunting for power supplies/ transformers/ wall adapters, but I’m not sure exactly what I’ll be needing.
I do know that the voltage should be 6V’s, since the botboard and ssc-32 can take in 4.8 to 7.4.
But, I’m not sure how many amps that I’ll need (I know you can destroy the lynxmotion pcb’s with too much voltage, but is there a such thing as too much amperage?).
I’ll be powering ~20 5645’s, and a WiPort.
Andy said before that the WiPort can draw up to 430mA (5V).
I’m not sure how much amps 20 servos will draw, but Jim once said that his hex would draw up to 6A.
So, do you think that a 6V 10A power supply sounds ok?
You will not damage any of these devices by supplying them with too much amperage. If your bot is drawing more current than your supply can handle, the voltage will drop causing micros to reset and various other undesireable things to happen.
For this reason, most people will recommend that you separate the supply for the logic boards (servo controller, wiport, etc…) from the supply for the servos. So a lot of people are running with two batteries.
I use a high voltage battery (11.1V) and regulate down to 5V for logic and 6V for servos. Aside from the phyiscal space required for the high amperage regulators in this setup, I’d recommend it if you don’t mind burning your fingers on a soldering iron.
It’s not the easiest thing to find, and I don’t recall where I found my data, but the HS475HB’s stall current at 6V is 1.1 amps. So if each and every one of my servos is stalled, I’m drawing nearly 20A just from the servos. This is a scenario that needs to be considered. In my setup, the regulators are 3A each and I’ve got 3 assigned to the servo rails. 9A is significantly less than 20A. The regulators I’m using will not catch fire as some will when overdrawn. The other way to deal with it is fuses.
The gague of the wires that you’re using nearby the supply deserves some attention too. Too thin of a wire combined with too high amperage will heat up and catch fire too. Do the reading on wire gague vs. current ratings. Pay attention also to the ratings of connectors.
Batteries have maximum discharge rates to which heed should be paid as well.
All of that is the very conservative view of things. I can just about assure you that at one point in developing the bot, you’ll end up with all your sevos stalled, but you’ll be on top of it and cut the power before things really heat up. It’s not going to be a regular occurrence, and beyond that you won’t know how much current the thing is drawing until you measure it. It’s going to be profoundly different based upon what the bot is doing too! The servos will draw more current when they are strained then when they are idle.
Last note: Get a fire extinguisher. I haven’t needed mine yet, but I’ll be glad I have it when I do need it.
At 0-30V and 0-20A, I should only have a problem when every single servo stalls on me.
And, it has it’s own set of techno-garble mumbo-jumbo back-ups.
Supposedly, it’ll brown out if it it detects a short, or if it’s overdrawn.
That’ll mean that I will have to be ready to catch my biped, if it stalls, but that’s nothing new.
I’d rather have few breaks than a fire, anyway.
I’ll use that supply to charge the NiMh’s as well as to power the biped while I’m programming it.
When I’m actually close to being ready for competition, I’ll start worrying about on-board power supplies and regulators.
my solution is very cheap get a pc power supply use the 5v output and add a series arregement of 4 1.2v batteries in parrallell so you would get 6.2v you can work with this for about 2 hours in the same biped you got.
i have the same stuff that you do for the logic connector just use a 9v recahrgable battery i mean for the ssc32 it will last 10 hours or more so you can recharge them at night
That supply should work perfectly. You may want to add a 10A quick blow fuse if you are concerned. All of this talk about fires and such… I have never burned anything up making a servo based robot. Yeah an 18 servo hexapod can draw around 6 amps, but it’s not constant. You should never have to worry about locking 18 or more servos all at the same time. The only way this could happen is if you goofed up your program to send all servos to a min or max position, that the servo is not capable of reaching. This can easily be avoided in software by setting up a min and max filter command for all servo channels used. Now if your making your own servo controller this can be more difficult to deal with, but if your just sending commands to the SSC-32, it’s really easy to prevent.
A biped will not draw near the current that an 18 servo hexapod will. The biped will be putting into load bearing position only a few servos at a time, and for a limited time. An 18 servo hexapod (3DOF) will have 6 servos in load bearing position at all times. This is why we humans walk so effeciently. Pete Miles demonstrated our humanoid biped design numerous times on a single charge of a single 1600mAh NiMH 6 volt pack.
Because there is no method to prevent one battery from doing more work than the other. With LiPo batteries some aspect of the chemistry allows this, but I don’t think it is allowed with NiMH or the others. I may be wrong, but I’m pretty sure it’s not allowed.
Ooooh, thanks!
I didn’t know that I’d need a 10A fuse.
As to 18 servos never locking up…
Well, Murphy’s Law.
I’ll be using a Basic Stamp 2px with the Botboard to control the SSC-32, so I shouldn’t run into those kinds of problems.
Then again – as I said… Murphy’s Law.
It’s nice to hear that the 1600mAh pack works so well, though, since I’ll be using that until I can afford the power supply and the LiPo’s that I want.
Putting batteries in parallel causes no harm to the packs as long as they are the same size.
Example is if you have a 3000 7.2v pack you can put it parallel with the another 3000 7.2v pack and in the end you get a 6000 7.2v pack. Putting the packs in parallel will double the capacity. I would make a connector that would connect the two packs together but when i want to charge them I would charge them seperatly. If you put the packs in series you double the voltage and capacity stays the same.
I would not hook a battery pack to a power supply in parallel with this setup you could have potential fires and ruin the pack quicker.
You can only put nimh with nimh, lipo and lipo, nicad and nicad. No mixing and same capacity and putting them in parallel will work just fine.
I have decided on a Basic Stamp 2px also! The Atom looks so much better but I need resources to go with the microcontroller. I have been to Basic Micro’s website and it has not been touched in over 3 years, and there are virtually no example code either. Parallax has reams of documentation and example code to give anyone that needs the extra help, like my self, a chance at making their idea a reality.
I also don’t think I would use all the power and features in the Atom or the Stamp2px for that matter. What I do need, however, is the execution speed but at 19,000 instructions per second, it should do what I need. With the SSC-32 doing a lot of the work, I can have the stamp focus on the sensor data.
I didn’t want to turn this into a proper battery use thread. I simply said it was not a good idea. I can see scenarios where this can be really bad. I have worked in the electronics industry for 25 years, and have never seen a battery connected in parallel in any piece of equipment or on any schematic. I have heard of LiPos 's being used this way for RC aircraft, but I’ve never seen it in print. This is all a moot point in the context of the original thread, because the SSC-32 has two VS inputs for this exact reason. To allow two packs to power the robot, without concern of problems. The SSC-32 can handle around 15 amps on the connectors, terminals, and traces. So by using the two VS terminals the thing can actually sustain up to 30 amps of throughput. This is not possible by connecting two batteries in parallel and connecting it to one of the VS inputs.
maybe you didnt understand what i did
i took a normal pc power supply and to the 5v output connected in series pack of batteries in paralell so the totat output of the power supply would be 6.2 v
i didnt use only one battery for raising the voltage output i connected 4 ni-cd batteries in parrallel giving me 1.2 volt 8000 mah so the servos would work at 6v with a simple power supply from a pc
just saying is a cheap cheap solution
The larger RC helis use a mixture of series and parallel wiring to get the right combination of voltage and run time… On this page you’ll see some batteries with designations like “3S2P” for “3 series 2 parallel”: helihobby.com/html/batteries.html
That kind of thing was unheard of when NiCd batteries were state of the artm but it’s fairly common with LiPo (in fact it’s the norm for bigger helis). I’m not sure if that’s because nobody tried it with NiCd or because NiCd batteries blow up when you wire them that way. Back in the day I was told that parallel wiring would result in some batteries charging more than others, possibly cooking the batteries that charge first (during charging) or causing the less-charged batteries to overheat (during use).
It might be because many LiPo cells have protection circuitry in them to govern the charging phase and to keep them from blowing up when they overheat… but that’s just a guess.
Whoa there, cowboy!
There is a significant risk if you put any high-current battery in parallel with another in a way that is not permanent. If one is charged, and the other is not, then you’ll get very high currents when they are connected together. This can lead to Bad Things.
However, lots of commercial packs do have cells in parallel, but they are permanently connected that way, to ensure that they charge/discharge together. An example is in many LithiumIon laptop PC packs.
I did a quick (really quick) google search for (lithium battery parallel) and the first link I checked out said the following.
“Unlike Ni-Cd and Ni-MH cells that self-discharge when wired in parallel, LiPo cells can be hooked up, charged and discharged in parallel with no detrimental effect. Wiring two LiPo cells in parallel doubles the capacity (more run time), plus an important advantage of wiring in parallel is that each cell only sees half the total current.”
So it apears that I was right. The reason it is only used for Lithium batteries is due to the fact that the chemistry or characteristics of Lithium technology allows it, but NiCad and NiMH does not. Writing it down on the calander… Jim was right…
Hi Jim,
To be clear to everyone, I want to re-state a couple of points on this (because it’s a safety issue). My “real job” at HP involves writing PIC code to manage the charging/discharging/testing of Lithium-Ion and lead-acid batteries that are used as cache backup in our large storage subsystems. To meet Federal regs, we have to put multiple safety features in the electronics that controls the batteries. I’m still learning, but:
As you pointed out, it is true that putting Lithiums in parallel will “behave as you would expect” - the A-hr capacity increases. The same would be true with lead-acid cells.
Because of the chemistry involved in some other types, putting them in parallel will cause both of them to self-discharge faster than if they were separated.
HOWEVER - connecting any high-current battery that is charged to another battery that is discharged will result in high currents between the 2 batteries. This is dangerous and not recommended.
Item 3 is why hobbyists should not design their gear to use two packs in parallel unless they are permanently wired together. Otherwise, it’s too easy to charge one guy, and forget to charge the other, and then plug them together…
The Bad Things that happen can include:
If the wiring between the batts is on the small side, the wires will get very hot and could start a fire (i.e. burn your house down).
The cells will overheat, possibly leading to explosions and such.
The “best case” scenario is that you would be exceeding the rated charge current on one cell, and the discharge current on the other cell, thus damaging the batts. It would be an expensive mistake.
A brief side-note: Lithium-Ion and Lithium Polymer batts are similar, but not the same. My limited understanding of LiPo’s is that they are lower performance, but also safer.
Lipos are not safer then Li-ion. They both actually have very similar safety issues along with chemistries. The main difference is that one is a dry cell and the other is wet.
One thing that was not mentioned but is important is matching. In order to have a well performing long lasting pack the cells need to be matched. Anyone who has raced RC cars before knows all about this. I know with NiMH and NiCD you can cycle the batteries so there numbers will be similar to eachother assuming they are the same grade cell. I dont know if this works with Lithium type cells or not, I have never seen a lithium pack as “matched” so I guess it doesnt matter to much.
Coming from someone who has built built many battery packs in most chemistries I suggest that if you do run seperate packs in parallel then charge and discharge them as one single pack. Your cells will last longer as well as perform better, especially with NiMH.
