I'm working on a project that uses 18 actuators, it may sound crazy, anyways the designs have been developed in CATIA and the present design uses cables and pulley systems in a closed loop for bidirectional motion. The actuators would be stacked in separate unit. The major flaw in this design is the effect of one cable extension on the other and also the length between the actuators and the joint.
I really wanted to know whether there is any motor that could be placed directly at the joint location. The max dimensions are 20mm length and 15mm diameter (the smaller the better). But at the same time it should have considerable torque that is at least 5-6 kgcm. Also it should have position control with at least 1 degree accuracy. The angle variation for each actuator would be 0 degree to 130 degree. The motor speed should be not lesser than 0.15s/60 degrees. Once the motors have reached the required angle it should lock onto this position.
As I did mention there are 18 actuators, is there any single driver to control all the motors individually or does it need separate drivers.
Can you put the feedback position sensors on the joint and then just drive the cables to put the joint where you want it?
It seems to me that your specifications are close to what RC servos can do. I'd just pick a servo. Of course they look ugly, so if this is intended to look good you have a lot more work to do.
We are involved in the research on a prosthetic arm. The prosthesis uses 18 actuators. At present the design uses cables and pulley systems in a closed loop for bidirectional motion. The actuators would be stacked in a separate unit.
Each finger consists of three joints in which the last 2 joints near to the finger tips are cross-linked.
For the feedback, yes we need to place the encoders/sensing element at the joints itself. But the main problem in using cables is the effect of opening and closing of one joint on the next joint ie the cables of the next joint will also need to move accordingly. Also we have to set pathways for the 36 cables without
touching one another.
I really wanted to know whether there is any motor that could be placed directly at the finger cavity. The max internal dimensions of the finger cavity is 20mm length and 15mm diameter and the motor( along with the gearhead if required has to fit within this cavity) the smaller the better.
But at the same time it should have considerable torque that is at least 5-6 kgcm. Also it should have position control with at least 1 degree accuracy. The angle variation for each actuator would be 0 degree to 130 degree. The motor speed should be not lesser than 0.15s/60 degrees.
We need to interface with Arduino/Raspberry Pi. The input to the motor will be the angle the servo needs to rotate. Once the motors have reached the required angle it should lock onto this position. This would be easier or if there is any other alternative please do suggest.
As I did mention there are 18 actuators, is there any single driver to control all the motors individually or does it need separate drivers.
What's your budget? Bespoke high performance miniature motors are not going to be cheap.
Thinking about it something like a harmonic reduction gear might be the only way to get
enough reduction into a small space, and there are sometimes miniature motors on ebay with
harmonic gears.
They look like the same type, the "planetary" gears are actually a type of harmonic drive
which is effectively a plantary gear with two anullui that differ by 3 gear teeth, giving a large
harmonic step down in a small volume.
These motors are not rugged, but are compact and worth a look perhaps.
