AX-12 power
AX-12 power
by Pev
Sun Dec 31, 2006 8:12 pm
Hi All,
Just been playing around with my multimeter and Bioloid or more specifically the AX12s. Have been loking at a way to reduce the weight of the battery pack and am considering changing it. The AX-12 spec states that unit runs on 7v~10v (prefered 9.6v) however when I have the power pack plugged in there is 12 volts being supplied to the AX12s and AX-S1. Seems to be perfectly happy at 12 volts but would appreciate anyones elses thoughts? Am thinking of maybe using an 11.1volt LiPo battery as a replacement????
Cheers
Pev
Just been playing around with my multimeter and Bioloid or more specifically the AX12s. Have been loking at a way to reduce the weight of the battery pack and am considering changing it. The AX-12 spec states that unit runs on 7v~10v (prefered 9.6v) however when I have the power pack plugged in there is 12 volts being supplied to the AX12s and AX-S1. Seems to be perfectly happy at 12 volts but would appreciate anyones elses thoughts? Am thinking of maybe using an 11.1volt LiPo battery as a replacement????
Cheers
Pev
by NullARC
Sun Dec 31, 2006 10:43 pm
If this is true it would be great!!
I have been exploring this too. (for when I get my Bioloid
) The Li-Po or Li-Ion batts will extend the Bioloid's run time and reducing the weight will also lend to longer run times. This could also lead to the ability to build larger robots with more actuators. Very cool! I will keep researching this subject as much as I can. Please keep us updated Pev!
- Marc
I have been exploring this too. (for when I get my Bioloid
) The Li-Po or Li-Ion batts will extend the Bioloid's run time and reducing the weight will also lend to longer run times. This could also lead to the ability to build larger robots with more actuators. Very cool! I will keep researching this subject as much as I can. Please keep us updated Pev!
- Marc
"She'll make point five past lightspeed. She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself."
by JonHylands
Mon Jan 01, 2007 12:11 am
If you want a *real* LiPoly battery 
check this one out:
http://www.all-battery.com/index.asp?Pa ... ProdID=473
- Jon
check this one out:
http://www.all-battery.com/index.asp?Pa ... ProdID=473
- Jon
by NullARC
Mon Jan 01, 2007 1:38 am
JonHylands wrote:If you want a *real* LiPoly battery
http://www.all-battery.com/index.asp?Pa ... ProdID=473
- Jon
For lack of a better term HOLY CRAP!! 6350mah!! I think a Bioloid biped would run about, oh say, 5 days on that! I've never seen a batter with that many mili-amp hours! The funny thing is I've been searching that site too Jon, but I didn't see that one.
I'll need 3 though. Only about $80.00!
169mm that's a little over 6.5 inches. I think our Bioloid's are going to be wearing backpacks!!
"She'll make point five past lightspeed. She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself."
by billyzelsnack
Mon Jan 08, 2007 12:08 am
Seems like a 12V regulator would not have to work very hard to bring down the 12.6V of a lipo. You could also just charge the lipo to 12V max.
I think the bigger concern might be that the lipo could actually deliver the current that the servos want. Even a standard 50oz/in hobby servo can suck up 1amp when it is stalled. A chain of several AX12's might potentially be able to draw 5-10amps?? The wires and connections don't look to be rated for that high of current.
btw. Where's that fuse in the CM-5 used and what's its rating? Maybe that is specifically what it is there for.. To limit the maximum current a chain of servos could draw.
I think the bigger concern might be that the lipo could actually deliver the current that the servos want. Even a standard 50oz/in hobby servo can suck up 1amp when it is stalled. A chain of several AX12's might potentially be able to draw 5-10amps?? The wires and connections don't look to be rated for that high of current.
btw. Where's that fuse in the CM-5 used and what's its rating? Maybe that is specifically what it is there for.. To limit the maximum current a chain of servos could draw.
by Pev
Mon Jan 08, 2007 1:05 am
The fuse seems to sit between the battery and everything else (even the charging curcuit). I had a servo jam in the early days when there were firmware problems and the fuse blew. It definately did its job as there was no other damage to the robot.
I think the fuses are rated a 5 amps
Pev
I think the fuses are rated a 5 amps
Pev
by Juha
Mon Jan 08, 2007 11:33 am
I've been studying this same issue, and also noticed that when I have the charger connected to my bioloid (not charging), I get something like 12.6V etc in the 3-wire bus going to the actuators. And I tested this from the bus, not charger, so this is the voltage actuators get.
There was some discussion about using >10V, and I think it should be ok, since also the charger is giving higher voltage for the bus. Could be, that the actuator don't last as long with 12V then 9V or something.
My plan is to run my bioloid with 3-cell LiPo. As said earlier, when fully charged this gives you 12.6V. Also, you _must_ cut the power when the voltage drops to 9V.
So, this way I'll have range from 9-12.6V, which seems quite nice from both battery and bioloid point of view. Only piece of electronics I need is a circuit to cut the current when voltage drops to 9V (and maybe a fuse). No regulators, no capacitors.
There is absolutely no point in using _regulated_ voltage for the bioloid 3-wire bus. That's just waste of energy. Especially, since my understanding is that ax-12s adjust to the voltage they get. So, if you tell them to move at certain speed / set torque etc, it will be the same if the voltage is 10V or 8V.
Also remember that the voltage on LiPo drops almost linearly. So, you must make use of as wide range as possible, or else you'll only get current for very limited time.
I bough a dc/dc converter which gives me 9-18V -> 5V regulated for the electronics (something like >80% efficiency). I also have a 3.3V linear-regulator which is needed for few components, like my cameras.
Some one asked if the LiPo can provide enough current. Oh yes, they're a lot better then nimh etc batteries. Many of them can provide something like 20A of constant current, with peaks up to 30A or 40A. So with this solution you would not even need the capacitors etc which cm-5 has to make sure there's enough current for the actuators.
Mine will Not for the battery, but electronics. Most of the LiPos are really long in one dimension. My plan is to build a bit higher torso for the robot, where I could fit 2 of these (rather in the center of the torso, not back, to keep the gravity center in the middle)
http://www.verticalhobby.com/kauppa/pro ... ucts_id=59 (click English flag in the lower right corner).
But this is when you're running it with battery, right?
Pev, thanks for the info on the fuse. I was meaning to ask about it or try to figure it you myself. If the fuse is rated 5A, and it sits between battery and everything else, I have 2 questions:
1) I guess the current in the bus can be higher then, 'cause of the capasitors?
2) So is there no fuse protecting the system, when you run the bioloid with the charger?
Cheers, and good luck for my fellow roboteers for the 2007
-- Juha
There was some discussion about using >10V, and I think it should be ok, since also the charger is giving higher voltage for the bus. Could be, that the actuator don't last as long with 12V then 9V or something.
My plan is to run my bioloid with 3-cell LiPo. As said earlier, when fully charged this gives you 12.6V. Also, you _must_ cut the power when the voltage drops to 9V.
So, this way I'll have range from 9-12.6V, which seems quite nice from both battery and bioloid point of view. Only piece of electronics I need is a circuit to cut the current when voltage drops to 9V (and maybe a fuse). No regulators, no capacitors.
There is absolutely no point in using _regulated_ voltage for the bioloid 3-wire bus. That's just waste of energy. Especially, since my understanding is that ax-12s adjust to the voltage they get. So, if you tell them to move at certain speed / set torque etc, it will be the same if the voltage is 10V or 8V.
Also remember that the voltage on LiPo drops almost linearly. So, you must make use of as wide range as possible, or else you'll only get current for very limited time.
I bough a dc/dc converter which gives me 9-18V -> 5V regulated for the electronics (something like >80% efficiency). I also have a 3.3V linear-regulator which is needed for few components, like my cameras.
Some one asked if the LiPo can provide enough current. Oh yes, they're a lot better then nimh etc batteries. Many of them can provide something like 20A of constant current, with peaks up to 30A or 40A. So with this solution you would not even need the capacitors etc which cm-5 has to make sure there's enough current for the actuators.
NullARC wrote:I think our Bioloid's are going to be wearing backpacks!!
Mine will
Not for the battery, but electronics. Most of the LiPos are really long in one dimension. My plan is to build a bit higher torso for the robot, where I could fit 2 of these (rather in the center of the torso, not back, to keep the gravity center in the middle)http://www.verticalhobby.com/kauppa/pro ... ucts_id=59 (click English flag in the lower right corner).
inaki wrote:According to my own tests the power supplied to AX12s by CM5 is 9.6-9.8Volts. I get the same results with two instruments.
But this is when you're running it with battery, right?
Pev, thanks for the info on the fuse. I was meaning to ask about it or try to figure it you myself. If the fuse is rated 5A, and it sits between battery and everything else, I have 2 questions:
1) I guess the current in the bus can be higher then, 'cause of the capasitors?
2) So is there no fuse protecting the system, when you run the bioloid with the charger?
Cheers, and good luck for my fellow roboteers for the 2007
-- Juha
by JonHylands
Mon Jan 08, 2007 2:05 pm
Juha wrote:There is absolutely no point in using _regulated_ voltage for the bioloid 3-wire bus. That's just waste of energy. Especially, since my understanding is that ax-12s adjust to the voltage they get. So, if you tell them to move at certain speed / set torque etc, it will be the same if the voltage is 10V or 8V.
I do not believe this is the case. The AX-12s have a voltage regulator in them to run the electronics, but the motor speed/torque is not adjusted.
If you look at the specifications chart on page 3 of the AX-12 manual, it clearly states different values for max holding torque and rotation speed between 7 and 10 volts.
With respect to not letting the battery get below 9 volts: Run the battery voltage through a resistor divider, with the appropriate shift so that 12.6 volts on the input side ends up being less than 5 volts, and then run the output side into one of the A/D converters on whatever micro-controller you're using.
Find the A/D value that corresponds to 9 volts on the input side, set a sefety margin, and check for that in your main loop somewhere. Have it sound a buzzer or flash a special LED or something unusual, or maybe run the ground line going to the bus through an N-channel mosfet, and switch it off when the battery power gets to that point.
- Jon
by billyzelsnack
Mon Jan 08, 2007 3:37 pm
Some more random lipo infos.
Lipos have an extra stat that most battery don't bother mentioning. That is discharge rate ( C ). I'll just give some examples to show how it works..
A 10C 1000mah pack has a discharge rate of 10amps
A 20C 1000mah pack has a discharge rate of 20amps
A 20C 2000mah pack has a discharge rate of 40amps
Often a manufacturer will mention both the maximum continuous discharge rate and the maximum burst discharge rate.
8C and 10C packs can be had for pretty cheap now. 15C started showing up at reasonable prices in the end of last year. 20C packs are starting to become reasonable now.
Lipo packs can be placed in both series and parallel.
3s ( 3 cells in series )
3s1p ( 3 cells in series, 1 in parallel)
Most lipos are recommended to be charged at no more than 1C and ALWAYS use a lipo specific charger.
Lipos do not have a memory, so you can recharge whenever and without cycling.
There is some debate to what is a good minimum voltage level is. The current recommended is No less than 3.2V per cell. Note. I said per cell. So while that means 9.6V for a 3s pack, what really matters is that no cell falls below 3.2V.
As for sizes, there are many different options. Especially if you are willing to build your own packs and keep the cells separate.
Something else to keep in mind.. Lipos are potentially a LOT more dangerous than NIMH. ( http://www.liposack.com )
Lipos have an extra stat that most battery don't bother mentioning. That is discharge rate ( C ). I'll just give some examples to show how it works..
A 10C 1000mah pack has a discharge rate of 10amps
A 20C 1000mah pack has a discharge rate of 20amps
A 20C 2000mah pack has a discharge rate of 40amps
Often a manufacturer will mention both the maximum continuous discharge rate and the maximum burst discharge rate.
8C and 10C packs can be had for pretty cheap now. 15C started showing up at reasonable prices in the end of last year. 20C packs are starting to become reasonable now.
Lipo packs can be placed in both series and parallel.
3s ( 3 cells in series )
3s1p ( 3 cells in series, 1 in parallel)
Most lipos are recommended to be charged at no more than 1C and ALWAYS use a lipo specific charger.
Lipos do not have a memory, so you can recharge whenever and without cycling.
There is some debate to what is a good minimum voltage level is. The current recommended is No less than 3.2V per cell. Note. I said per cell. So while that means 9.6V for a 3s pack, what really matters is that no cell falls below 3.2V.
As for sizes, there are many different options. Especially if you are willing to build your own packs and keep the cells separate.
Something else to keep in mind.. Lipos are potentially a LOT more dangerous than NIMH. ( http://www.liposack.com )