Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

How can robot arms be so strong?

Status
Not open for further replies.
Hi there,

I'm building my own robot arm based on wiper motors because I already have them, and because I know they are strong. However, when doing the math on the torque needed to lift the robot, it seems like the motors one will have to use must be extremely light and powerful. If using one wiper motor with 10 Nm torque, it is only capable of holding a mass of 1 kg in 0.5 m (length of the robot arm + assumed of no mass).

If the robot should at least have one more arm, it must be very light, and the robot will not be able to lift anything bu the robot arms. Is this really the case? I would prefer not to use additional gearing due to the pricing and weight of gears along with the already slow velocity of the wiper motor.
 
It's gearing. Wipers motors might be slow compared to most motors...but how many degrees per second do they travel? They are probably capable at least 2-3x faster than what the fastest robot joint requires, therefore 2-3x weaker than they could be for an arm.

Why would you need more than one arm though?
 
If you use the terminology of base, arm, shoulder and so on, there should only be one arm. What I mean, is that I want a rotary base, two links each with 2-DOF and an end-effector. After gearing down 2-3 times, the additional torque required to lift even small objects seems too much for a realization. Maybe the only thing possible to do is to buy planetary gear heads for the motors.
 
Yeah, it's true. Arms are crazy geared and built really light. That's why we use cranes for buildings and not giant robotic arms.
 
If you look into industrial robot arm design, you'll see that three different power options are typically used (in order of descreasing power): Hydraulic, Pneumatic, and Electric.

There are, though, a few industrial robot designs that use electric, and are quite fast, and very powerful. Typically, these designs use really large motors, as well as coreless motor designs. You'll also see designs where the motor is incorporated into the joint (typically, these motors too will be coreless, and/or they will be pancake style); incorporating the motor as an integral part of the joint (so the joint forms the case and bearing supports) makes for a lighter motor, and thus a lighter arm, but keeps the torque up.

Even so - if you look at what the arm in total weighs, and how much the end-effector can lift, you'll see it is quite low in comparison. I once found an old used Unimate at a local surplus yard (Equipment Exchange here in Phoenix), and was surprised at its size (total length of base and arm together were about the same size as my Ford Ranger I was driving at the time). This was a hydraulic arm, and weighed quite a lot - but the end-effector lift weight wasn't really large.

So - do whatever you can to minimize the total arm weight while maximizing its strength. Keep the motors as close to the base as possible (look at old trainer robots like the Armdroid for ideas; you might also look at the Unimate Puma for some ideas as well). Use lightweight but strong materials for the arm (alluminum space frame?). Use larger and stronger motors for the joints as they approach the base (that is, the shoulder rotation and pitch motors should be -really- hefty, whereas the elbow motor(s) can be lighter, the wrist motors lighter still, and the gripper motor lightest of all). Reduce friction as much as possible (friction wastes torque that could go toward lifting the arm and payload).

There are several books out there on industrial robot arm design (and control); you should try to find some copies of them...
 
Thanks for the reply. I think the Unimate Puma has a very interesting design, which is fairly easy to construct. My first idea was also to use two motors at the base for more torque, and in some way to locate all other motors in the middle of the links to reduce the inertia. But in order to construct robotics capable of lifting a lot, requires materials and motors, which are only affordable for the manufacturers of robot equipment.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top