Power Supply for AX-12

[Starlight]

Hi, currently i'm doing a quadruped robot with 3DOF by using 12 number of AX-12. i'm noticed that the AX-12 require 9V for operating (16.5kg.cm).
In order to supply 9V (LiPo 11.1V battery) to AX-12, I'm using the voltage regulator LM7809. And my question is : how many voltage regulator needed in order to supplied 9V for each AX-12?

if one voltage regulator can only drive 3 AX-12, then I need 4 voltage regulator to drive 12 AX-12? Thanks.

[Nathan Monson]

i'm noticed that the AX-12 require 9V for operating (16.5kg.cm).
In order to supply 9V (LiPo 11.1V battery) to AX-12, I'm using the voltage regulator LM7809.

You can directly power the AX-12s off the 11.1v source. I've built two robots this way. If you plan to put your motors under a lot of load, they'll get hotter faster at 11.1v, and may shut down due to thermal limits.

Of course, you could void your warranty or cause damage that way... But I've never damaged an AX-12 this way. (Knock on wood.)

And my question is : how many voltage regulator needed in order to supplied 9V for each AX-12? if one voltage regulator can only drive 3 AX-12, then I need 4 voltage regulator to drive 12 AX-12?

The answer is: It depends on how hard you push them, and the rating of your regulator. Let's assume your LM7809 is rated for 1.5A. Each AX-12 can draw up to .9A at max load, so you would need more than 4 regulators.

But, usually you don't run your motors anywhere near that hard, so 3 per regulator makes sense. You can also find a regulator rated for higher amperage and use just one. In your example, a 6A regulator could be enough for the whole robot.

- Nathan

[StuartL]

You can directly power the AX-12s off the 11.1v source. I've built two robots this way. If you plan to put your motors under a lot of load, they'll get hotter faster at 11.1v, and may shut down due to thermal limits.

Of course, you could void your warranty or cause damage that way... But I've never damaged an AX-12 this way. (Knock on wood.)

The brick PSU runs the servos at about 12.2v. 11.1v shouldn't void any warranty

The answer is: It depends on how hard you push them, and the rating of your regulator. Let's assume your LM7809 is rated for 1.5A. Each AX-12 can draw up to .9A at max load, so you would need more than 4 regulators.

We've far exceeded 1A per AX-12 when stalling an entire robot. We scale our power supply to 1.5A per servo and it seems to work for us.

With LiPos, of course, you do need to be careful about drawing too much current from the pack, so scale the pack for the stall current of the entire robot.

[Starlight]

I'm noticed that for AX-12, the maximum voltage is 9.6V, how come we can directly power the AX-12s off the 11.1V source? it'll not damaged the servo?

what is brick PSU ?

for the LM7809, the output current is 5mA to 1A, so for 12 number of AX-12s, it does need 12 voltage regulator? the weight of robot is about 1.5kg to 2kg.

besides using voltage regulator, is there any method to drive the AX-12s at 9.6V?

thanks.

[srobot]

If you are using the CM-5 as your controller, you will be fine running the robot at 11.1V.

You should also be able to run the robot directly off of the LiPo (no protection circuits) like you would with the NiCad, be sure to check voltage while running the robot, and charge with protection.

Source:

http://robosavvy.com/forum/viewtopic.php?t=2919

[Starlight]

I'm not using the CM5, instead, I'm using PIC18F452 as the controller. I'll connect 12 numbers of AX-12 with the same power supply (LiPo).

May I know inside the AX-12, is there a voltage regulator in them to run the electronics? So even I connect directly the LiPo (11.1V) to the AX-12s, the motor still can drive at 9.6V? my concern is even I'm fully charge the LiPo, but actually I'm pumping more than 12V through, not 11.1V. I'm worried that it'll damaged my AX-12s.

[Nathan Monson]

May I know inside the AX-12, is there a voltage regulator in them to run the electronics? So even I connect directly the LiPo (11.1V) to the AX-12s, the motor still can drive at 9.6V? my concern is even I'm fully charge the LiPo, but actually I'm pumping more than 12V through, not 11.1V. I'm worried that it'll damaged my AX-12s.

Yes, the AX-12 has a 5V regulator for the electronics. So only the motor portion will be overvolted, not the CPU.

I can tell you from experience that my fully charged (12.6V) LiPo has never damaged an AX-12. If anything, they perform much better at this voltage. But, they do get hot. The overload and overheat protection should prevent them from damaging themselves. Just leave that turned on.

Here's another thread where people discuss the overvolting -- lots of folks are doing it:
http://robosavvy.com/forum/viewtopic.php?p=5655

- Nathan

[Starlight]

Thanks for the reply. I'll connect directly my LiPo (11.1V,2200mAh) to 12 number of AX-12s, hope it can perform well as what I expected for.

[srobot]

We've far exceeded 1A per AX-12 when stalling an entire robot. We scale our power supply to 1.5A per servo and it seems to work for us.

With LiPos, of course, you do need to be careful about drawing too much current from the pack, so scale the pack for the stall current of the entire robot.

Stuart - Do you use any regulators for discharging?

1.5A = 1500mA
1500mA * NumberOfServos = Minimum mAh for 1 hour of use

So to run 18 AX-12+ servos for 10 minutes you would need a 4500 mAh battery.

LiPo batteries are rated in C, Amps, and Volts.

C * mAh = actual mAh

If your pack is 750mA rated at 15C, it can be discharged at 11250mAh (11.25 Ah). Your robot would safely run 25 minutes with 18 servos.

Please correct me if this is wrong.

[i-Bot]

In my understanding the battery has a capacity C which is expressed in mAh. You can probably expect to get 80% or more of the capacity from the battery.

Thus a 750mAh battery can actually delivery around 600mA for one hour.

Your servos have max current of around 1A, but will usually take much less unless they are moving fast, or are under great load. Maybe your total load is only average 2 or 3 A. So you battery should last 15 minutes or so.

When a battery is quoted as 15C, then this defines the maximum current that can be drawn = 15 * .75 = 11.25 Amps.

It unlikely all servos need max. current at the same time. A Capacitor may help for when all the servos start at the same time.

So a 750mAH 15C is probably the smallest to use.

[StuartL]

It unlikely all servos need max. current at the same time. A Capacitor may help for when all the servos start at the same time.

So a 750mAH 15C is probably the smallest to use.

We have huge capacitors on our PSU to stop interference and try to smooth out the current draw, but it's still not perfect

We use 750mAh 15C and just cycle the packs when they discharge. Typically they last 10-30 minutes and charge in about an hour from completely flat. Easily workable if you have multiple packs ...

[Starlight]

Hi all. For the 11.1V LiPo connected to 12 number of AX-12s, I need a current booster to provide exactly 9.6V to the AX-12s. So my question is, have u guy ever experience with the current booster ? any suggestion circuit be like ?

thanks.