Hello there,
I'm new to the forum and would like to ask for advice on a project that's ambitious for me. I would like to build a gripper arm which should consist of Nema 17 motors and a Nema 23 motor. The arm should be able to reliably lift 500g with a total length of 50cm at a good speed. The arm itself will be 3D printed from PETG. Now to my question. For the main axis, on which the entire gripper arm hangs, I chose this motor with 20Nm torque: https://www.oyostepper.de/goods-306...e-042-Grad-125Nm-28A-26V-Nema23-Getriebe.html
I need advice on whether the engine has enough power and whether the gearbox doesn't make it too slow. I have concerns about the Nema 17 motors (59Ncm), which also have a bit of mass.
I hope you could help me.

 

If I’m understanding the specification correctly the holding torque of the motor without the gearbox is 1.25Nm which could hold about 250 grams at 50cm. The gearbox ratio is 4.25:1 which in theory would allow the output shaft to hold just over 1,000 grams at 50cm - enough to hold your 500g but struggling to move it. I’d certainly select a gearbox with a higher ratio, maybe 12:1 or higher, which will be slower but surely this is of secondary importance. The torque/speed curve of a stepper motor is fairly horrific, torque falls off rapidly when speed increases

I’m confused by the specification line which mentions 20Nm maximum permissible torque? Since the specification details are sloppy anyway, since they mention a gearbox ratio of 4:1 in the title line, and 20Nm seems impossibly high I’d go with the 1.25Nm

If you are using the Nema 23 to lift the arm and the Nema 17 to control the gripper at the end of it, which has a mass of around 250g, plus the mass of the arm and gripper components you are looking at the 23 having to lift a lot more than 500g

 

The torque/speed curve of a stepper motor is fairly horrific, torque falls off rapidly when speed increases

True if a supply with just the the exact plate rating of the motor is adhered to, but can be vastly improved by using a modern drive that maintains the exact plate current as RPM & inductive reactance increases.

 

Max is right about the drives and the power supply. an adequate driver with an adequate power supply using PWM to control the motor current can provide much better performance than used to be available. But not all suppliers are able to provide the more complex drivers.So asking questions will be required.

 

You can improve the design by locating the gripper motor close to the lifting motor, using a mechanical link between the gripper and its drive motor. then the lifting motor will not have to lift the gripper motor as well as the load.
I built mobile one 35 years ago that has 5 axes of movement. The arm is driven by five heavy duty R/C servos located in the body of the machine. The joints are linked to the servos using levers and gears.

 

There is always a tradeoff between complexity and capability and efficiency, and usually cost, as well. That is a basic part of design engineering.