# can 360 g-cm servo lift 90 pounds?

#### dl09

##### Full Member level 4 can a servo rated at 360 gram-centimeters of torque lift 90 pounds, if the servo has rod that is 35 cm long and the 90 pound weight is attached to the other end?

#### KlausST

##### Super Moderator
Staff member Hi,

Show a simple but complete drawing.

Klaus

#### FvM

##### Super Moderator
Staff member g-cm is no torque unit. I guess you mean 360 p-cm, as you can easily calculate, the required torque to lift the weight is factor 4000 higher, at least on earth.

#### dl09

##### Full Member level 4 #### KlausST

##### Super Moderator
Staff member Hi,

It can be simple done by your own.

Then read about how to calculate pounds to kg with the help of gravity.
What direction do you want to move your 90 ponds object? Purely vertical?
The math is simple "multiply".

Klaus

#### dl09

##### Full Member level 4 Hi,

It can be simple done by your own.

Then read about how to calculate pounds to kg with the help of gravity.
What direction do you want to move your 90 ponds object? Purely vertical?
The math is simple "multiply".

Klaus
i know gravity is a force. therefore pound and kilogram are used to measure force. i kilogram equals 2.2045 pounds. torque is equal to force times lever arm. lever arm equals distance from fulcrum to point of application of force times sine angle between axis of rotation and lever arm. i have already read about torque. so to move 90 pound object vertically multiply 90 pounds by 36 centimeter? well that would be 1469 kg.cm. is this calculation right?

#### KlausST

##### Super Moderator
Staff member Hi,

i know gravity is a force.
No. Gravity is acceleration. With the unit "m/s^2"

therefore pound and kilogram are used to measure force.
No. Kilograms is a mass with the unit "kg"
And there is
* pound-force (which is a force) with unit "N"
and there is
* pound-mass (which is a mass and can directly calculated as kg)

well that would be 1469 kg.cm. is this calculation right?
Seems to be correct.

Klaus

#### FvM

##### Super Moderator
Staff member so to move 90 pound object vertically multiply 90 pounds by 36 centimeter? well that would be 1469 kg.cm. is this calculation right?
Numerically correct. I notice that servo vendors still use outdated g-cm or oz-in torque units. Seems to be an unbreakable habit.

#### wwfeldman can a servo rated at 360 gram-centimeters of torque lift 90 pounds, if the servo has rod that is 35 cm long and the 90 pound weight is attached to the other end?
no
360 gm-cm will not lift 1469 kg-cm (1469000 gm-cm)

#### dl09

##### Full Member level 4 torque produces angular acceleration, if i use a 180 kg.cm servo,connected to a rod and with the 90 pound mass on the other end, will the 90 pound mass move, but at a smaller angular acceleration than if i use a 1469 kg.cm servo.

#### wwfeldman 180 kg-cm is 180,000 gm-cm
you need more than 1,469,000 gm-cm

this servo simply does not provide enough torque to move your mass

did you (or a friend) ever put a wrench on a nut and not be able to turn it?
or not be able to open a jar of something?
that's because you could not provide enough torque.

there will be no acceleration
your 90 pound mass will not move

#### KlausST

##### Super Moderator
Staff member Hi,

Yes it will move, downwards.
With a little less acceleration than earth gravity.

Klaus

#### c_mitra Yes, you need gears.

Use gears such that 360 gm.cm gets converted into 35x90 lb.cm (slightly more).

You can also use pulleys.

There are other ways too.

#### wwfeldman the OP needs 1,469,000 gm-cm of torque to balance the torque presented by the load (90 lbs or about 41 kg at 35 cm)

clearly more is needed to cause some angular acceleration to get started, then 1,469,000 gm-cm
is needed to maintain whatever angular velocity was achieved.

with the 180 kg cm servo motor described, there is 180,000 gm cm of torque
if you put in a gear ration of 10 to 1, you will boost the torques to a little less than 1,800,000 gm cm
(less because of the need to also rotate the gears and overcome axle friction etc, and for the twist in the drive shaft)

lets say that motor and gear set is enough. because of the 10 to 1 gear ratio, the angular acceleration will be 1/10th what
it might have been, had there been no need for gears.

since the motor and gears are only marginally able to exert enough torque, the lift rate will be painfully slow.

pulleys and ropes introduce the same sort of extra losses - rotating the pulleys, axle friction,
rope stretch (different materials will have different stretch, but there's losses in any case)

so, OP, what other things are going on in this project that have a bearing on the question?