Quote:
Originally Posted by adityaag
For either chain system or the pulley system, what do team typically do to keep the load off the motor while not actively lifting? I'm assuming you don't want to have the CIM be constantly supplying force to the lift mechanism in order to keep it going. Anything remotely COTS that someone can link to or previous designs? I'm a relatively new mentor and our team has never built a lifting mechanism like this in the past.
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There are multiple ways to prevent the lifted weight from drifting back down or at least controlling the speed at which it drifts.
Using a high reduction gear box and the motor controller set to brake will cause it to come down slower than it goes up. Note the brake setting is a dynamic brake, the braking force is directly proportional to the speed of the motor. Once the motor speed approaches zero so does the braking force. With this method you can get away without the need to stall the drive motor, just lift say x inches higher than you want it let it fall x inches before applying more power to raise it back up again. With the right ratios and some practice you will be able to get away without burning up the motor particularly when using a CIM or mini CIM. We did this with a RS-775 for Team [REDACTED]'s Ri3D machine. The RS-775 is a fan cooled motor and it didn't heat up that much even with 5 minute "matches".
A worm drive transmission will not back drive, or at the very least it is very hard to back drive. The Window motor is a worm gear, my team used this in Overdrive with success. The Window motors are not that strong but there are now some COTS worm gear boxes available.
You can attach a bicycle rotor to your drive and use brake caliper that is operated by a pneumatic cylinder as Mike mentioned. We have done this in the past. We used this for the climber in Ultimate Ascent and the lift for Logo Motion.
Depending on the design of your lift you can use a "pin" that is engaged by a pneumatic cylinder to lock the position. You may have to power the lift back up slightly to get it to disengage. You could also use a pneumatic cylinder to force a high friction brake "shoe" attached to the cart against your mast. You would want to attach the brake so that the act of falling tends to wedge it in place rather than push it out of place.
If you wish to hold it at the top of its travel you could use a gate latch to lock it in place and then a pneumatic cylinder to release it. Depending on the latch geometry you may need to power it up slightly to be able to release it.