# Servo Question

• 12-10-2013, 04:39 PM
ReglarGuy
Servo Question
How much current does our Spartan servo pull. I couldn't find any spec's on it. Does anyone have an idea...Hog, don't be shy! (lol)
• 12-10-2013, 10:04 PM
I believe it's 125 oz.
• 12-11-2013, 12:29 AM
Spartanator
Do you have the stock Servo (2056) or the 2075?
[url]http://www.servodatabase.com/servo/traxxas/2056[/url]
[url]http://www.servodatabase.com/servo/traxxas/2075[/url]
• 12-11-2013, 03:20 AM
ReglarGuy
I have the 2075. I looked at the above links, but I just don't see anything on how much current a 2075 pulls.
• 12-11-2013, 07:23 AM
Spartanator
The 2075 has 125 for torque, not sure what you mean by "pull". Voltage maybe?
• 12-11-2013, 10:37 AM
Spartanator
• 12-11-2013, 06:18 PM
orca44
Most digital servos that operate on 4.5 to 6 volts and have 125 ounce per inch of torque will draw 500 ma of current under no load, under a load will draw 750 to 1000 ma depending on the load applied..... More load more current draw.

Hope this helps a little.
• 12-12-2013, 06:40 PM
750-1000 ma, i'm not trying to be a you know what by any means, but one servo is not pulling that amount of current. You could use V=IR.
V=Voltage/potential
I=current (Amps)
R=Resistance (ohms)

So it would be 6v/Resistance = Current. But I can't find the resistance anywhere. If anyone knows the resistance feel free to finish the equation.
• 12-13-2013, 10:05 AM
hog
Ok, so I'm not an expert on this by any stretch of the imagination, so I rely upon my Google-Fu for this answer.

It obviously depends on the size, type, quality, and application of the sevo, but for a standard size servo, (I would consider the Spartan servo in this catagory), I found some "rule of thumb" guidelines.

Most of the info available is specific to digital servos, the Traxxas 2056 uses analog modulation, and from what I have read, because of the different technology used in analog servos, the peak draws are buffered a bit compared to digital servos.

The down and dirty rule of thumb is: a standard size servo can draw [B][I]UP TO[/I][/B] 2 Amps (2000 mA) at full load.

Determining the average draw is more complex, and an oscilloscope is the recommended tool for accurate measurement of current draw, including peak draws.

There are three different types of servo current:

[U]IDLE[/U]: The servo is powered, but not working. Current draw is typically very low at 5-20 mA
[U]WORKING[/U]: The servo is in motion moving from one position to another. Typical current draw is 500 - 2000 mA, or more. (Servo size, type, quality, and application dependent)
[U]STALL[/U]: This would be likened to physically holding the servo arm from moving, and activating the sevo. Because the servo motor can't move it acts essentially like a dead short and current draw remains continuously high . Typical current draw would be 500 - 2000 mA, or more.

There is a fourth current type, which is a sort of a combination of the working and stall currents.

[U]START CURRENT[/U]: This is the current draw when the servo has been holding a position, then starts to move. Current typically spikes immediately to Stall Current values, then quickly settles to Working Current values.

So there isn't a simple and direct answer to ReglarDude's question. But Orcas 750 - 1000mA guesstimation is likely within the realm of reasonable for average current draw.

hog

[U][B]2056 SPECS[/B][/U]
Basic Information
Modulation: Analog
Torque: 6.0V: 80.0 oz-in (5.76 kg-cm)
Speed: 6.0V: 0.23 sec/60°
Weight: 1.59 oz (45.0 g)
Dimensions:
Length: 2.17 in (55.1 mm)
Width: 0.79 in (20.1 mm)
Height: 1.69 in (42.9 mm)
Motor Type: Brushed
Gear Type: Plastic
Rotation/Support: Single Bearing

[U][B]2075 SPECS[/B][/U]
Basic Information
Modulation: Digital
Torque: 6.0V: 125.0 oz-in (9.00 kg-cm)
Speed: 6.0V: 0.17 sec/60°
Weight: 1.59 oz (45.0 g)
Dimensions:
Length: 2.17 in (55.1 mm)
Width: 0.79 in (20.1 mm)
Height: 1.50 in (38.1 mm)
Motor Type: Brushed
Gear Type: Plastic
Rotation/Support: Dual Bearings
• 12-13-2013, 08:44 PM
orca44
[QUOTE=96motorhead;5616424]750-1000 ma, i'm not trying to be a you know what by any means, but one servo is not pulling that amount of current. You could use V=IR.
V=Voltage/potential
I=current (Amps)
R=Resistance (ohms)

So it would be 6v/Resistance = Current. But I can't find the resistance anywhere. If anyone knows the resistance feel free to finish the equation.[/QUOTE]

You cannot obtain the "Servo's resistance" since the RC servo is a COMPLETE CIRCUIT with a motor and driven from a integrated circuit driver that controls the motor current. The amount of current it draws depends on the servo internal IC workings.

I haven't taught electronics in over 8 years so I had to go to my electronic books to obtain the information you have requested, "[U]Spartan servo current draw[/U]". And believe me, this was quite a challenge for me.

So here is what I have come up with......

The only factors to work with is [U]voltage, 6 volts[/U], [U]torque, 125 oz in. [/U]and [U]time, .17 sec in 60*[/U].

Not to bore everyone with an mini electronics class but I needed to convert [U]torque [/U]and [U]speed [/U]of the servo into watts. Once I had watts I could find current.

The torque needed to be converted to [U]Newton [/U][U]meters [/U](.8827) and the speed to RPM (61.2)

So anyways I came up with 5.6571 watts(P) divided by 6 volts which converts to [U].94285 [/U]amps of current draw.

So with that being done V=6 divided by I= @ .94285 = R @ 6.3636845 ohms

Am I correct? Not positive, but I have given it my best shot.

To be continued???
• 12-14-2013, 11:43 AM
[QUOTE=orca44;5616759]You cannot obtain the "Servo's resistance" since the RC servo is a COMPLETE CIRCUIT with a motor and driven from a integrated circuit driver that controls the motor current. The amount of current it draws depends on the servo internal IC workings.

I haven't taught electronics in over 8 years so I had to go to my electronic books to obtain the information you have requested, "[U]Spartan servo current draw[/U]". And believe me, this was quite a challenge for me.

So here is what I have come up with......

The only factors to work with is [U]voltage, 6 volts[/U], [U]torque, 125 oz in. [/U]and [U]time, .17 sec in 60*[/U].

Not to bore everyone with an mini electronics class but I needed to convert [U]torque [/U]and [U]speed [/U]of the servo into watts. Once I had watts I could find current.

The torque needed to be converted to [U]Newton [/U][U]meters [/U](.8827) and the speed to RPM (61.2)

So anyways I came up with 5.6571 watts(P) divided by 6 volts which converts to [U].94285 [/U]amps of current draw.

So with that being done V=6 divided by I= @ .94285 = R @ 6.3636845 ohms

Am I correct? Not positive, but I have given it my best shot.

To be continued???[/QUOTE]
I am curious what did you do to calculate the watts or power?
• 12-16-2013, 04:44 PM
orca44
To calculate the watts or power, I needed to convert the only known factors I had, which was torque and rpm. P = T x RPM... Power in watts (unknown), = torque in ounce per inch (125) x rpm (Radians per sec) (.17 seconds in 60 degrees). The torque needed to be converted to Newton meters in which a "Newton-Meter" is a unit of torque or turning force.

1 ounce inch is equal to 0.00706155183333 newton meter, x 125 = .88275 Newton meters

I needed one full revolution so .17 @ 60 degrees x 6 gave me 360 degrees or 61.2 revolutions per minute which in Radians = 6.408849

So now I have P = .88275 x 6.408849 = 5.6574 watts....... To convert watts to amps you divide P by voltage P/V = 5.6574 divided by 6 volts and you get .9429 amps.....

I used what information I had and formulas from my electronic books, there may be other ways or better ones.... This is just how I perceived to accomplish the task at hand.

On a foot note this formula is saying that a full 125 oz inch is being used/consumed.

Now I did some actual bench testing this morning on the servo with an amp meter in series with one leg of the servo.

1. With the servo at idle it has a constant current draw of 5.1 ma (.005099 etc amps)

2. When turning the servo the current draw would spike to 200-300 ma. (No load)

3. When applying a load, the current would rise to 500-600 ma.

If I would have had an O scope, the task of measuring the current may have been more accurate.