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Issue controling multiple servos

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#1

Hello,

I just purchase the MiniMaestro 18 channels and I am working with these type of servos:

ES08MAII
Voltage : 4.8-6v
Operating current 200mA/60deg
Dead band 1.2 usec

I am using 18 units to move a humanoid, but I am getting a bit frustrated with this issue.

Something weird happens when I am working with the maestro control center.

When I try to move only 2 servos, they move just fine but when I try to move more than 2 as soon as the first motor moves of the frame, that action makes rotate all them in a way that is chaotic wat that I need to turn the power off to avoid damage.

Any clue what might be happening?

I am using a battery power of 4 AA 1.5volts to power my maestro.

I can also post a video for better explanation.

Thanks for your feedback and I would be glad to share more details if someone can give me a hand

#2

From your description, it sounds like a power issue. What kind of batteries are you using? When the issue happens, are all of the servo channels enabled or only the ones you are trying to move? Could you monitor the supply voltage when this happens (preferably with an o-scope)? A video of the issue might help if it’s easy for you to get, as well as pictures of your setup that show all of your connections.

If you post a copy of your Maestro settings file, I would be happy to double check that nothing seems odd about the way it’s configured. You can save your settings file from the “File” drop-down menu in the Maestro Control Center.

Brandon

#3

Hello Brandon,

Thank you for your help.

I am using alkaline batteries 1.5V I have a battery pack for 4 batteries which in theory gives me 6v and in series which I read that provides 1150 mah

When it happens all the channels are activated, I have 5 servos activated. I am attaching a short video for better explanation.

I don’t have an o-scope, I will try to do with a multimeter.

Below you will find my settings

maestro_settings.txt (3.5 KB)

#4

Thank you for the video. When you load frame 0 at the end, it looks like the Maestro is doing what it is expected to do (i.e. all of the sliders return to the neutral position, indicating that it is sending 1500us pulse widths to each servo). So, I still suspect it is a power issue. Alkaline batteries are usually not great for handling higher current loads, and in general we recommend rechargable NiMH batteries instead; however, please note that since NiMH batteries have a slightly lower nominal voltage (1.2V), you would probably want to use 5 instead of 4.

I would still be interested in what you can measure with your multimeter while they are all trying to move at once.

Do you have a different supply you could try? If not, in the meantime you might try setting the speed and acceleration of all of the servo channels to something low like 10 in the “Channel Settings” tab to see if that makes any difference (maybe try with just 3 servos then if that works adding more one at a time). You should also be careful that none of the servos are being driven to a position that is physically limited by the setup and cause them to stall.

Brandon

#5

Thank you for your help Brandon.

I feel the same way about the power issue, I will try to get a different power source, but I am also very curious to understand this issue.

I also noticed a phenomena when I did the experiment using only 2 servos, moving servo 1 at high speed will cause a random shake in servo 2 and a current raise, will this be caused by the peak of current when I tried to move my servo 1 affecting the servo 2?, is this a normal phenomena? a more powerful battery will be able to handle this issue?.

Moving servo 1 slowly will not cause an impact so badly in servo 2, like you indicated it will cause a small shake but no chaotical rotation at least.

Like you said, I worked it around using 2 servos at the time and deactivating the others so they will not interfere to each other, but I would still need to move 4 servos at the time so for now the solution is limited to understand the issue, slow speed seems to help to avoid this “random” peak in current…

Thanks again for your support Brandon.

#6

Typically, power issues like this are caused by the battery voltage dipping because it cannot handle the current draw. If the current draw is large enough, the voltage could dip low enough that the servo’s electronics can do some unpredictable things.

Using a more powerful battery is the most reliable way to fix the problem (especially in a case like yours where you can only move 2 of your 5 servos). Additionally, there are a couple ways you could help reduce the impact of the current spike. A quick movement (for example, moving full speed from a stopped position or switching directions at high speed) will have a larger current spike, so if your application allows for it, you could use acceleration limiting and keep the movements smooth and slow (like you mentioned). If you were just seeing some small jitters, adding a capacitor to your servo power could help smooth it out by allowing the servos to pull a little extra current before the voltage dips.

Brandon

#7

Thank you Brandon!,

Given the specifications above for my servos I was given a battery pack of 4.8V 3000mAh, Ni-MH however according to the maestro specs this board works at 5V minimum, would this represent a problem when working with my battery pack? or should I consider buying only 6V with less mAh capacity?

Thank you again for your great assistance!

#8

When fully charged, a 4.8V NiMH pack is upwards of 6V, so it might be okay, but you will have to recharge it sooner than you would normally (since the nominal voltage is too low for the Maestro). It is hard to say if you would be better off with a 6V pack with a lower capacity, since it would depend on a lot of the specifics. However, if you want to stick with your 4.8V pack, you might consider using a step-up regulator to provide the logic power to the Maestro. Something like our U3V12F9 would work for that.

Brandon

#9

Thank you Brandon,

Amazing support of you guys.