Z axis servo help needed...

[Toysrfun]

I’m new to servos so I’m not pretending here to know what I’m talking about entirely. I’ve done a fair amount of research to know what I want and possibly be dangerous, lol. Can one of you masterminds of great knowledge help me out here? I’m told that the servos I have chosen if used on the z axis would cause the z axis to drop to the table when the power was off. I don’t want this. When I ask about a brake they want to sell me a regenerative brake addon like we use on our vfd’s. So this now becomes a two part question.

A.) do I want regenerative brakes on all or some of my axis?? If so.., what’s the benefit it’s only $75 so not a big deal to get that added on.
B.) what kind of brake am I looking for or do I need to ask for about my Z axis? When I mention a power off brake I get the deer in the headlights response so it’s making my lack of knowledge drop my confidence a few tiers.

Am I missing something here? Another gentleman I talked to online who did a build similar to mine told me specifically to get a power off brake or I’d be blocking up my mill head with wood. My servo supplier confirmed that I’d be blocking it up but had no solution for me. I have all the servos I need in the shopping cart right now that are compatible with the Oak board except I did not add the Z axis because I want the right one and would like to get this figured out so I can purchase that tonight if possible and then move on to the oak controller next and be done. I want to thank you ahead of time for the help. It’s the little idiosyncrasies that get missed in much discussion I think either some people don’t care, already know, or figure out after the fact and live with it so the subject seems to get overlooked under many topics. Perhaps it’s assumed we should know? I appreciate all the knowledge I can absorb and someday share again.

[Toysrfun]

I should add I am aware of counter balancing the head and I intend to do something although I am not certain how elaborate that venture will be. I doubt I will use gas shocks. Likely it will be a twin chain drive and some type of single pneumatic cylinder in the rear. Keeping in mind that’s still a mechanical component that can fail. So anywhere I can implement more safety features such as a internal brake in the servo to energize the poles when it’s off or however they work to keep it from allowing the weight to roll down the ball screws would be a satisfactory solution.

[Dave_C]

If you happen to study the Tormach PCNC 1100 parts diagram, you will see they have an external brake on the Z axis stepper. This brake will hold with no power applied so even in a power failure the Z will not fall.

This is a mechanical brake, not a regeneratrive brake like you would use on a VFD to quickly stop the motor! This mechanical braker requires power applied to release the brake.

If you study the acorn wireing diagram you will see an output that can be used to "release" the brake.

The external brake is way easier to install than trying to counter balance the head in my opinion.

Dave C.

[diycncscott]

Brakes are "nice" to have to prevent the Z axis from falling. A properly balanced axis is a far better solution than a brake however.

FWIW Some machines just use a spring for counter balance (though obviously the spring suffers from fatigue over a period of time)