# What's the fastest linear movement you can get from a servo?

I saw two implementations of linear movements form a servo:

Travel-Distance: 290mm
max. Travel-Speed: 200mm/s

with what looks like
Travel-Distance: 120 mm/sec?
max. Travel-Speed: 14 cm?

In both cases it seems they use a 10-20kg-cm servo motor.
I need 80-100% speed and just 0-20% force with maximum travel distance (hopefully 10-20 cm). Is there a get a simple way to get it?

How much current is your motor using? You should be able to increase speed by increasing the current, which means increasing the driving voltage.

Paul

Garfielder:
I need 80-100% speed and just 0-20% force with maximum travel distance (hopefully 10-20 cm).

That doesn't make much sense. 80-100% of what? 0-20% of what? You can't really mean you need zero force.

Can you give the speed and force you need in real units please?

Steve

Garfielder:
I saw two implementations of linear movements form a servo:

https://www.instructables.com/id/DIY-IRONLESS-LINEAR-SERVO-MOTOR/
Travel-Distance: 290mm
max. Travel-Speed: 200mm/s

DIY Linear Servo Actuator, 3D Printed - YouTube
with what looks like
Travel-Distance: 120 mm/sec?
max. Travel-Speed: 14 cm?

In both cases it seems they use a 10-20kg-cm servo motor.

No, the first is a linear motor in a servo loop. Linear motors don't have a torque rating as clearly nothing
rotates.
The second is a motor (not a servo), driving rack-and-pinion.

I need 80-100% speed and just 0-20% force with maximum travel distance (hopefully 10-20 cm). Is there a get a simple way to get it?

You seem to think that speed + force adds up to 100%. That makes no sense - speed and force are not the same "stuff".

I think what you are asking for is how to make a low-force high-speed linear actuator?

I mean of course that I care mainly for speed. I want for example to get from a mg669 a fast (20-40 cm/s) linear motion for ~5cm. Force will be probably minimal (10N would be nice, I hope I'll get at least 1N but I would accept even less).

The below servo mod makes a continuous rotation servo fast (maybe for a boat motor), but might be a little too fast for you.

zoomkat:
The below servo mod makes a continuous rotation servo fast (maybe for a boat motor), but might be a little too fast for you.

How to speed hack a servo - YouTube

I need a linear motion.

Garfielder:
I need a linear motion.

Paul

"I need a linear motion."

Then you need to evaluate various methods/mechanisms that will convert rotational motion to linear motion.

Garfielder:
I mean of course that I care mainly for speed. I want for example to get from a mg669 a fast (20-40 cm/s) linear motion for ~5cm. Force will be probably minimal (10N would be nice, I hope I'll get at least 1N but I would accept even less).

10N at 0.4m/s is 4 watts of mechanical power. MG669 ? Do you mean MG996R ? I'll assume so.

If the speed is 5 rad/s (0.19s per 60 degrees implies this), and you want 40cm/s, then an arm length of 8cm will
do this as 5 x 8 = 40.

The torque is about 1Nm, so at 8cm that's 12.5N in theory.

So a mechanical linkage using an 8cm radius arm might be doable - I've not allowed for the mass of the linkage though, that has to be accelerated, requiring torque.

Just saw this so I thought I would create an account and provide input. I don't know what the fattest is but the world of rc helicopter ( NOT DRONE ) modeling will give you damn good options. Tail rotor servos are designed to give extremely fast reactionin and travel time and deliver incredible amounts of torque and high end ones will have all titanium gears, roller bearings and quality windings. This one traverses 60 degrees in 0.0035 sec @7.4 voltshttps://www.motionrc.com/products/mks-ds-hbl980-tail-servo-for-700-and-800-size-roban-helicopters not extremely high end but not shabby either. Top of the line units will be over \$200 each. All decent ones will have speed and torque ratings.
These toys are extremely powerful and capable of decapitating people.
For fun and to see the stress and reaction times these are put through here's Bobbie Watts Bobby Watts Demo Practice - Gaui X7 - 2013 Orlando Helicopter Blowout - YouTube

himilou:
Tail rotor servos are designed to give extremely fast reactionin and travel time and deliver incredible amounts of torque and high end ones will have all titanium gears, roller bearings and quality windings. This one traverses 60 degrees in 0.0035 sec @7.4 volts https://www.motionrc.com/products/mks-ds-hbl980-tail-servo-for-700-and-800-size-roban-helicopters

Wrong by an order of magnitude, that servo has a slew rate of 60 degrees in 36ms, not in 3.6ms, at 7.4V

And 0.55Nm is nothing special. The speed-torque product says the device has a mechanical max power of 0.55Nm x 29rad/s = 16W

MarkT:
If the speed is 5 rad/s (0.19s per 60 degrees implies this), and you want 40cm/s, then an arm length of 8cm will
do this as 5 x 8 = 40.
The torque is about 1Nm, so at 8cm that's 12.5N in theory.

Great! Thanks a lot.
I saw some nice 3D printed linear actuators for SG90. Does anyone know a similar mechanism for MG669R?