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What Is The Amps Per Hour Draw On The Heavy Duty Servos?

Hello again all. I have a question regarding the heavy duty servos sold in the ez-b shop. I have looked through the specs on the servo in the shop, and read the tutorials that I thought would be applicable, but I can't find the Amps per Hour draw on the servos. I am working on a large project that requires 16 servos, and I am aware that the batteries and battery holders sold in the shop can't provide that much power through the EZ-B and the servos will brown out. I can't select the battery to provide the servos with direct power unless I know the amperage though. Also, an additional question. Does anybody have a suggestion for a rechargeable 7.4 volt battery (or batteries) with appropriate amperage? I planned on using the LiPo batteries from the shop, until I realized that I wouldn't have the low battery warning from the EZ-B, and I really don't feel like replacing that many AA batteries when they die, lol.

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Synthiam
#1  
Not sure on the Amp/Hours for these servos.

What i do for large projects is add an additional battery for each servo or servo cluster to prevent brownout in a y-connector. Not tried that with the EZ-B as yet, but it works well with an R/C RX servo hookup.

For hobby grade (albeit strong hobby grade) servos like these they don't draw all that many amps unless you are running them at a full stall.

Tom

Edit:

Hitec HS-311.
Hitec specs that this servo will drain 7.7mA iddle / 160mA no load (normal working?) at 4.8v and 7.7 mA iddle / 180 mA no load (normal working?) at 6.0v.

The EZrobot servos are likely somewhere around double this, as this is your basic hobby servo, and the heavy duty servos are a bit more beastly. If i get a closer match somewhere online i'll update:)
PRO
Synthiam
#2  
The most HDD Servo we've run from our LiPo Robot Battery 7.4v 1300mAh is 24 at once. That's every port on the EZ-B v4/2 Wi-Fi Robot Controller. You can run 2 LiPo batteries in parallel - just do not charge them in parallel.

What do you mean by you won't have the low battery warning with LiPo's? The low battery warning was specifically designed for LiPo batteries.

If you're wanting to run a robust system and unsure of the current draw - maybe power the servos from the battery directly rather than running them through the ez-b for power. I only mention this not because the EZ-B v4 can't handle it, but because with that many amps, the risk of shorting something out accidentally can get expensive!:D

I do not know on average how many amps the LiPo Robot Battery 7.4v 1300mAh draws at idle or under load. Jeremie might chime in when he's back from vacation.
United Kingdom
#4  
Nomad, you linked to a post which was speculative not measured. HD servos can draw up to 3A in my experience however this was based on TowerPro MG995s not EZ-Robot's servos - I've never checked the current draw of the EZ-Robot servos.

That 3 Amps is not running current, it is peek demand, this would be for an extremely short period, literally milliseconds. This could possibly have been more than 3 amps if there was more load, the fact is there was little load on the servos and they still drew enough to brownout my V3 EZ-B (which through an educated guess that the V3 could only handle 5 amps, at least one of the servos was pulling at least 2.5 amps).

Without measuring over a period of time through standard operation you can only guess at average consumption. If you are guessing, guess high.

In short, Nomad's 3 amp answer and link are not relevant to this particular topic and should be disregarded. Wait for Jeremie to respond or measure the current draw of the servos.
PRO
Belgium
#5  
rich

thank you for the correct information.
#6  
Hey DJ, when I said there would be no low battery warning I meant if I used one or more to supply direct power to the servos. I should have been more specific.

That's irrelevant if i can run 16 heavy duty servos from the ezb directly. This was posted under the assumption that the amp draw from the servos would be too great for that and they would brownout. That being said I also had no idea what the MApH draw on the servos was.

If I were to power 16 servos from the ezb directly, how long would the LiPo battery hold a charge? Also, would it be safe to run 2 LiPo's in parallel directly to the ezb?

Special thanks to first responder Tom, thanks for giving me an idea of what I was looking at.
#7  
First, yes, you can run 2 in batteries without any issue and no it wont damage anything as long as you configured them for more Amps and not more Volts.

The answer as to how long the charge will last is dependant on what you do with the robot and what the mah rating is on the batteries you are using. For example...

If you had a battery that was 1300 mah or a total of 1.3 amp hours, you could run 16 of the hd servos continuously for maybe 5 minues. That is not how robots are setup to work and how you setup yours to work will be different than how someone else sets theirs up to work. Lets just assume that the 5 minute estimate is correct. If you ran these 16 servos 1/20th of the time while using your robot you could get 100 minutes out of these batteries (5 minutes x 20 times less use = 100 minutes). Now there are other things running like sensors which draw very little current and the EZ-B which too draws very little current. How much load each of these servos is under also plays a factor.

Unfortunately, the question is impossible to answer until you know what you will be doing exactly with the robot. The good news is that batteries can be added in many different configurations to overcome the issues you have.
#8  
@Nomad, Your quick to the draw but have a lot of grace when your proven incorrect. I admire that kind of social respect in a person. I wish more people on the internet had more of that skill (including myself). ;)

Like Rich, I've never been able to draw current through an EZB for large HD servos on a large robot without browning it out. I've had to draw their power directly from the power supply. Others seem to have accomplished this so I may be wrong. Either way I don't like drawing this amount of current through the EZB partly for what DJ states. It seem just as easy to channel power around the EZB.
#9  
Thanks @d.cochran. I figured extra amperage wouldn't be a problem for the ezb, I just wanted to make sure. Also, I agree with @Dave schulpius, more people, (myself included from time to time) could benefit from being humble when proven wrong.

I've had similar brownout problems with arduino based projects, like @dave schulpius described. I'm going to try powering them from the ezb for now though, and if it proves too problematic I'll power them directly from the battery.

Thank you all!:D
#10  
For a 'low battery warning' with external power supplying the servos, you could make a resistor voltage divider between the supply and ground, then use one of the 8 ADC inputs to monitor the divided voltage.
#11  
Nice suggestion Oldbotbuilder. Another way (and the way i'm doing it) is to place a voltage regulator (properly sized for amp draw) before the EZB to supply voltage within the range EZB is looking for, power your less current demanding servos and sensors requiring that voltage through the EZB and channel the other HD current hungry servos around the EZB.
United Kingdom
#12  
There is a voltage divider battery monitor tutorial I wrote kicking around the place somewhere, including script to monitor it (however it's probably from before some EZ-Script syntax changes so may need adjustment).

Here it is