Precision

I am building a custom arm of about 4-5 axis

the weight at the end is maxed 1 kg

but I need high precision and control

which of the following is best for highest precision & consistency?

  1. using stepper motor
  2. using a stepper motor with gearbox gear ratio 10:1
  3. using servo motor

consider all above can provide enough torque for my application

accuracy require = 0.4-0.5 mm

MjYxMTEwOQ.png

A diagram of your proposed machine would be a good idea so we can visualise what you are doing.

You need to calculate the torque at each joint in the arm and choose a motor that can comfortably provide it (exceed it by a factor of at least 2, I suggest).

A large part of the precision in your machine will depend on it being built very solidly with good bearings.

A gearbox increases torque but will probably introduce backlash - which may not matter.

You need to put numbers on the level of precision you require. The word "high" is meaningless.

...R
Simple Image Posting Guide

Robin2:
A diagram of your proposed machine would be a good idea so we can visualise what you are doing.

You need to calculate the torque at each joint in the arm and choose a motor that can comfortably provide it (exceed it by a factor of at least 2, I suggest).

A large part of the precision in your machine will depend on it being built very solidly with good bearings.

A gearbox increases torque but will probably introduce backlash - which may not matter.

You need to put numbers on the level of precision you require. The word "high" is meaningless.

...R
Simple Image Posting Guide

very very similar to this, in this video, they used a stepper motor
check the precision in this video(at 6:01)

if I use servo motor will the precision be higher or lower

I need this be running almost 24*7

Interesting video. Considering that the video tells us that the its creator has made ALL of his robot design publicly available I don't really understand why you are asking a question here.

It will not be possible to build an equivalent robot with inferior equipment.

If you want a cheaper robot then you need to decide what functionality you are prepared to sacrifice.

...R

Use Servo Motors and Harmonic Drives. This will do all your requirements, but pricey! Hahaha. Im using Stepper motors for my application in combination of Harmonic Drives! These cost around 2000 euros each and second hand about 300 euro's.

Greets,

Nena

NenaGirl:
These cost around 2000 euros each

The guy in the video said the total cost of the more expensive robot was about $2000 (I may have the currency wrong) so he certainly was not using €2000 motors

...R

Robin2:
Interesting video. Considering that the video tells us that the its creator has made ALL of his robot design publicly available I don't really understand why you are asking a question here.

It will not be possible to build an equivalent robot with inferior equipment.

If you want a cheaper robot then you need to decide what functionality you are prepared to sacrifice.

...R

I am not saying i want to build the same one with inferior or superior motor or equipment

my question was simple
which among of this thing will get me highest precision

  1. using stepper motor
  2. using a stepper motor with gearbox gear ratio 10:1
  3. using servo motor

sunny163:
I am not saying i want to build the same one with inferior or superior motor or equipment

my question was simple
which among of this thing will get me highest precision

  1. using stepper motor
  2. using a stepper motor with gearbox gear ratio 10:1
  3. using servo motor

Do you mean a hobby servo or the sort of expensive servo that is mentioned in Reply #4? Hobby servos are not precise, but they can very convenient.

The output shaft of a stepper (before any gearbox) will give you a precise 200 steps per revolution. But whether that is adequate depends on the project you want to implement - hence my question in Reply #1 - which you appeared to answer by referring to the YouTube video. Now you seem to be saying the YouTube video is irrelevant. Are you just trying to waste our time?

...R

Cheap (Hobby) Servo’s aint precise. And it depends also on your application. I needed steppers because i need a full stand still with a high torque. The precision of my combination is 80.000 steps per revolution. No backlash! So if you want to get some precision you need to buy some good motors. Steppers or Servo’s are both a good solution. The thing is what do you want to do with it and how much do you want to spend on your project.

Cheap = Not Precise
Hobby = Not Precise
Gears < 100 Euro = Not precise.
Steppers = Precise (Depends on Brange) Cheap!
Servos = Precise = Expensive
Harmonic Drive = Very precise, Expensive!

Servos = Difficult to get it running!
Steppers = Easy to get it running!

Servos < 6000 rpm (full torque)
Steppers < 3000 rpm (torque depends on speed & voltage/amperage)

Your choice!

Nena

We’re talking about 1kg load on a 4 or 5 axis arm, hobby servos aren’t remotely in the picture, unless
there’s a gripper…

You ask about precision, but refuse to disclose any values, so lets see if you can work out what you need.

Precision of a robotic arm is how close can you reposition the arm to the same 3D location after moving away from that point.

So, is 1 inch close enough? Is 1/4 inch close enough? Is .01 inch close enough? Is .001 inch close enough? Or is the number smaller, still?

Paul

Paul_KD7HB:
You ask about precision, but refuse to disclose any values, so lets see if you can work out what you need.

Precision of a robotic arm is how close can you reposition the arm to the same 3D location after moving away from that point.

So, is 1 inch close enough? Is 1/4 inch close enough? Is .01 inch close enough? Is .001 inch close enough? Or is the number smaller, still?

Paul

I didn't refuse to disclose any value
its pick and place robot arm I even added a youtube video link to which I want a similar one
but I need accuracy, I think about 0.4-0.5 mm is close enough
I added earlier that the end weight will be maximum 1 kg, will be running it 24*7
I don't know what else info you need, please ask me
I am unable to decide
stepper, stepper with encoder, stepper with gearbox, servo, anything other

sunny163:
I didn’t refuse to disclose any value
its pick and place robot arm I even added a youtube video link to which I want a similar one
but I need accuracy, I think about 0.4-0.5 mm is close enough
I added earlier that the end weight will be maximum 1 kg, will be running it 24*7
I don’t know what else info you need, please ask me
I am unable to decide
stepper, stepper with encoder, stepper with gearbox, servo, anything other

Thank you, let’s say 0.5mm is what we want. Now, how long is the arm from the final position to it’s first joint? If the end of the arm must be in position w/in 0.5mm, what is the maximum error in movement that the first joint can make?

Once you can compute that, then do the same for the next joint, using the total distance from it’s joint to the final landing spot for the placement. And continue for the remaining joints.

Paul

arm from final position to first joint is approx around 3.5-4 Feet(1066.8-1219.2 mm)

sunny163:
arm from final position to first joint is approx around 3.5-4 Feet(1066.8-1219.2 mm)

Perhaps you can make a simple pencil diagram with the approximate dimensions marked on it for each segment of the arm.

If you mean that the arm will have to lift 1 kg (plus it's own weight) at a radius of 1.2m then the torque at the first joint will be well over 1.2 kgm (12 Nm) - maybe more than 25Nm. That's going to require a hefty motor if it is to be able to move precisely in increments of 0.5mm.

Are you sure this project is within your present capability?

...R

With an arm that long, you are going to need significant dampening when movement is stopped.

You also did not compute the joint movement that will give you the 0.5mm at the end of the arm. The 0.5mm is actually +- 0.25mm.

I, too would like to see your design and the materials used.

Paul

Not mentioned: resolvers

Robin2:
Perhaps you can make a simple pencil diagram with the approximate dimensions marked on it for each segment of the arm.

If you mean that the arm will have to lift 1 kg (plus it’s own weight) at a radius of 1.2m then the torque at the first joint will be well over 1.2 kgm (12 Nm) - maybe more than 25Nm. That’s going to require a hefty motor if it is to be able to move precisely in increments of 0.5mm.

Are you sure this project is within your present capability?

…R

MjYxMTEwOQ.png

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@sunny163, thank you for the diagram.

However you are looking for advice about a very complex project so perhaps you could take the trouble to communicate with us about it - for example to respond to comments you have been given. Better still, do your best to put us in the position of knowing as much about your project as you know. At the moment the dialogue is all one-way, from our side.

On your diagram, where are the motors for the joints going to be located. If motors are mounted at the head and at the middle joint they will greatly add to torque on the bottom joint. Stepper motors are very heavy.

...R