Is there any way to build a linear actuator or is there a cost effective and legal actuator that we could use.
In general, linear actuators aren’t cheap because nice leadscrews are expensive. Although-
Select Automotive Motors (Window, Door, Windshield wiper, Seat, Throttle)
are legal. Find an automotive linear actuator that is provably marketed as one of these, and you should be good.
We have also done “lead screws” using threaded rod and coupling nuts, and may do so again this year.
Conveniently, 5/16" coupling nuts are 1/2" on the hex outside making them easy to couple to a number of common FRC components. If you drive this rod with a CIM with no reduction at 75% of free speed and keep the nut from rotating, the nut will move ~3.7" per second. A 775 pro or red line is about 13 ips at 75% of free speed.
We had good results using these devices retrofitted with BAG motors in 2016:
I would not recommend LIN-101 due to the sheer amount of tuning required to make it work. I was working on a new one in the pre-season but never got it finished. The DART can be ok but it has mechanical issues that make me shy away from using them. If you can, try and make your own or find something else.
If you could maybe provide some of the requirements, such as travel length, and how much force it needs to exert…???
Would you mind describing the Retrofit process ? I would like to know if custom machining was required and how you interfaced with the existing gearing of the Actuator.
FRC 6012 Lead Mentor
Swapping the motors was not too difficult. The motor on the actuator I linked to has the same case diameter and shaft diameter as the BAG motor.
The motor feeds into a gear set that provides reduction and interfaces to the lead screw. Unbolting thr cover from the gearbox section allows you to get at the screws that hold the motor in place. You then need to do the following mods:
Remove the internal electrical wiring (the actuator has internal limit switches that stop over travel but you cannot use them as wired since they would alter the pathway between the controller and motor).
Remove the pinion gear from the original motor shaft.
File a flat on the BAG motor shaft to fit the pinion gear onto it.
Drill new mounting holes in the gearbox case to line up with the BAG motor (unfortunately the originals don’t line up). As I recall we also had to remove a bit of material with a file or dremel to make a flat area for one of the holes.
Re-assemble the gearbox section with the BAG motor attached.
Be careful to implement some sort of limit switch for over travel since the actuator can tear itself apart if driven hard into its end limits (yes - we did do this - oops).
The BAG motor is much more powerful and much faster than the original so you actually enhance the capability of the actuator this way.
Hopefully you find this useful and can find a source for these (or something similar) near you. The store I linked to (and we purchased from) is in Canada.
Thank you for the details.