Calculating

[Flippt]

How do I calculate the speed/torque of a servo with a new voltage?
In my case from 3kg @ 4.8V up to 8.4V
Speed is

Maybe some other things good to knwo could be put up here

[Raizor]

Something is inversly proportional when something increases the other decreases.

So S1*V1=S2*V2

S1= Quoted Speed
V1= Origional Voltage (4.8)
S2= New Speed
V2= New Voltage.

However you have not given the origional speed of teh servo so I cannot calculate but I will assume a speed of 0.13 for arguments sake.

S1= 0.13sec/60degrees
V1= 4.8v
S2= to be calculated
V1= 8.4v

S1*V1=S2*V2
0.13*4.8= S2*8.4
0.624=s2*8.4
S2= 0.624/8.4
S2=0.074sec/60degrees

As for torque Torque is proportional to Amps but lets assume that when the VOltage increases that the amps increase proportionaly aswell.

T1/V1=T2/V2

T1= Origional Torque
V1= Origional Voltage
T2= New TOrque
V2= New Voltage

SO for yours we have
T1= 3kg/cm
V1= 4.8v
T2= To be calculated
V2= 8.4v

T1/V1=T2/V2
3/4.8=T2/8.4
0.625=T2/8.4
T2=0.625*8.4
T2=5.25Kg/cm

I hope that helps you.
Although in practice you will probably not see these exact figures.

[Flippt]

However you have not given the origional speed of teh servo so I cannot calculate but I will assume a speed of 0.13 for arguments sake.

Yeah, sorry about that, I thought I had typed it, but my memory is good, but short

Original Speed; (Sec/60`) - 0.07 8)

[BeligerAnt]

Ian's figures appear correct, but some of the terminology is a bit misleading.

DC motors have a constant relationship between speed and voltage:

speed / voltage = K (rpm/volt)

So speed = K * voltage

If you know the speed at a given voltage you can calculate K and then calculate the speed at any voltage.

Note this is speed, what most servo manufacturers specify is time per 60 degrees. (That is the misleading bit)

Now 0.1s / 60 deg is the same as 0.6s / 360 degrees

So the speed is 1 revolution per 0.6s, or 100rpm

Assuming 4.8V we get K = 100 / 4.8 = 20.83 rpm/volt

Thus at 8.4V we get 8.4 * 20.83 = 175rpm

For a servo specified as T secs / 60 deg @ 4.8V, run at V volts, we end up with a short-cut formula of:

S (rpm) = ( 2.083 * V ) / T


One thing to remember is that power is proportional to voltage squared, so if you double the voltage you quadruple the power. A fraction of this power is dissipated in the motor, so the motor is now trying to dissipate 4 times as much power (as heat) as it was designed to do. Beware of overheating motors as they lead to burnt-out windings and scrapped motors!