Let's Make Robots!

Best way to Power an 8 servo - Quadbot

Hi. I want to power a Dagu Qadbot without sources, only batteries, but don't know the best way to Do it. It uses 8 micro servo - 8g, 4~6V, and draw a current that I don't know the specific value as I didn't find a Datasheet.

 

So, as I'm almost sure that only Arduino will not be able to power the 8 servos, I'm thinking about 2 solutions:

 

1st - Use 4AA Battery to power - the Arduino i parallel with the servos. This way I'd power the servos directly and just connect the digital pin to the arduino. 

Problems: Reading some posts, I've seen people reporting that arduino resets. A possible solution would be the one described on this topic, which I didn't understand fully : http://letsmakerobots.com/node/7722

 

2nd - Use a 9V battery to power arduino, and 4AA battery to power the servos. This way I think I'd have no problems, but this solution is more expensive and heavier.

 

Please give your opinions,

Regards,

Vítor Augusto

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You may refer to this topic too. People all have their own way to work this out.

http://letsmakerobots.com/node/29875

And this is the UBEC regulator thet talking about that i use on my biped

I will give this a bump ;-)

Important is that it works. I am using just 4 AA Eneloop for my quadruped with 8 servos and it's fine. 

The robot brain is an Arduino Nano. I put the Nano on a selfmade board with all the I/O prots connected to header pins. the pins for the servos are in a triple row...so I can power the servos directly from the batteries and also feeding the Arduino. It's working fine and I did not have any problems with the high current. You can see it here and here

Later (to decrease weight) i will try to power it with 2 LiPo's with each 3.7 V so I am on 7.4 V and hope the servos can handle this or I have to use a voltage regulator.

Hi lumi, thanks for your reply! Misteriously my quadbot is working woth a 6 cell AAA NImh battery, the mistery is that I'm not powering the servos directly, so I can't imagine how its possible that each servo is drawing less than 40mA. I've made a battery yesterday using 2 Hiphone batteires, Lithium 1200mah each, and will be testing soon. 

I guess you will have to use the regulator as you've said.. otherwise they will live less. Very interesting your self made direct input for servos. Keep in touch! Regards

Hi Lumi,

Yes, 7.4V works directly to servos, however, you are in the risk to burn servos without warnning. It just my experience because I thought it was working fine for couple times and one of them stop working and soon one after another stop too. In that day I burned 3 servos within 4 hours.

Also your chopstick Jr is using micro servos and mine was HS-485 regular servo, it might be able to take 7.4V I don't know but physically it looks might gurned easily than regular one.

Anyway, I end up using UBEC 6V regulator and one 7.4V lipo to support Arduino with 18 Servos. They still working fine now. Again, I am not expert and I could be wrong but all I am saying is base on my experience.

@vtsm: NP, I am trying to help what I can.  Yeah it's starnge that your bot is not working with that power source. I am not a specialist and not measuring the current drawn by the servos. I tried, it worked. After a long walk around our hackerspace, the servos was even not warming up very much. 

@hardmouse: As I wrote above, that's always a walk on the blade...my servos did not even get hot when powering with 7.4 V for a test run. But better save than sorry ;-) There is also a difference between Micro servos and standard servos. Keeping the weight down should help so the servos don't have the heavy load to take.

hardmouse, thanks for presenting us this ubec regulator.. when I placed an order on hobby king last month I was looking for something like that and could'n t find... I'll search now for a version that can handle more amps to use with a huge bot I plan to have soon!!

sorry about that.. DSL delayed, and I must've hit the post button twice.

Another example, would be what i've been using in projects I've made.. the drawback, however, is size/weight..

7.2V RC battery

(reference photo shows one available online only, but they do have the same battery in-store)

I recently built a simple wall-avoider robot, using a Duemilinova, 3 servos (2 converted to constant rotation for drive wheels) and a PING))). the power plug was simple enough (same supplier as the battery, 9.6V repair kit to type-N barrel plug) . But, I have the power to the servos, as well as the ping)), being drawn from a separate 7805 regulator on the breadboard. (people have already warned me about drawing the 7.2V through the Vin plug of the Arduino, so it's being drawn from a separate wire from the plug to the breadboard, to the 7805.)

The 7.2V battery, has an output of roughly 3200mAh (the supplier says 3000, but the wrapping of the battery says 3200), consists of 6x Sub-C cells, roughly a good 1-Lb. weight. Easy enough to zip-tie down to the frame.  NiMH, (their old VEX battery was 3000mAh, NiCd)..

I picked this battery, mainly because it was easy to obtain, longer life between charges, quicker to charge (also bought their plug-in-the-wall universal charger. takes roughly an hour from drained.)

Stephen Griswold (gelfling6)

Another example, would be what i've been using in projects I've made.. the drawback, however, is size/weight..

7.2V RC battery

(reference photo shows one available online only, but they do have the same battery in-store)

I recently built a simple wall-avoider robot, using a Duemilinova, 3 servos (2 converted to constant rotation for drive wheels) and a PING))). the power plug was simple enough (same supplier as the battery, 9.6V repair kit to type-N barrel plug) . But, I have the power to the servos, as well as the ping)), being drawn from a separate 7805 regulator on the breadboard. (people have already warned me about drawing the 7.2V through the Vin plug of the Arduino, so it's being drawn from a separate wire from the plug to the breadboard, to the 7805.)

The 7.2V battery, has an output of roughly 3200mAh (the supplier says 3000, but the wrapping of the battery says 3200), consists of 6x Sub-C cells, roughly a good 1-Lb. weight. Easy enough to zip-tie down to the frame.  NiMH, (their old VEX battery was 3000mAh, NiCd)..

I picked this battery, mainly because it was easy to obtain, longer life between charges, quicker to charge (also bought their plug-in-the-wall universal charger. takes roughly an hour from drained.)

Stephen Griswold (gelfling6)

Hi Oddbot !!  Thank you very much for the answer. I could never imagine the 8 servo would draw more than 2 amps... I'll look for a battery like this one, and make the tests.

About the LDO regulator, What one should I use? 6v 3 amps like this one? http://www.ebay.com/itm/UC285-LDO-Regulator-5A-Adjustable-1-2-6V-TO220-/180731435596?pt=LH_DefaultDomain_0&hash=item2a146eda4c  , and How is it connected?  I've never used this component so I don't know how does it propel work, but I intend to use it as I want to power both with  the same battery. 

Best Regards,

Vítor Augusto