12-17-2011 08:29 AM

Ninja_Bait

Re: paper: 2337's One Way Friction Brake

Can you elaborate on the implementation? I don't really understand how the brake was used to limit the elevator's backdriving.

12-17-2011 11:37 AM

thefro526

Re: paper: 2337's One Way Friction Brake

Seems like it's a neat way to get around disengaging the ratchet and paw.

The arms weight isn't enough to over come the friction brake on the ratchet and paw, but when you apply enough power from the motors, the brake it over powered and the arm drives down while the ratchet and paw are still engaged.

Or I'm totally wrong.

12-17-2011 02:15 PM

GDG 2337

Re: paper: 2337's One Way Friction Brake

Need to start by explaining how we raised and lowered our arm for those of you who are unfamiliar. In the picture on slide 1, lever arm (right side) with the nylon block attached pushed/pulled the arm up and down (thanks Adam) like HOT in 07. We used a chain driven trolley to move the lever arm, essentially a vertical conveyor. Now to answer your question, friction brake is attached to the 3/8 “hex upper shaft of conveyor system. The two hockey puck brake pads attached to shaft are tensioned against gear by compression springs. In the screen prints, going up would be in the clockwise direction, with the gear trapped between the tensioned brake pads, teeth contact curved side of pawl and force it to walk up and over the teeth producing the familiar click, click, click ratcheting noise. When arm stops, torsion spring helps push pawl down in between the gear teeth locking it in position. With lifted arm stopped, gravity takes over (blame Newton), as you know tries to back drive lift system down, turning brake pads against stationary gear. Key is finding the right balance between having brake pads stick to gear holding arm in position and still be able to have them slip to drive arm back down. Compression springs allow fine tuning tension (think of a slipper clutch) instead of just cranking down on the lock nuts and act as a self adjuster mechanism to compensate for pad wear. This where the superior problem solving and design skills came into play, it was priceless watching son (who isn’t an engineering graduate) outshine his talented father. Hope is answers the question.

12-17-2011 06:58 PM

Mr. B

Re: paper: 2337's One Way Friction Brake

I can see the gear rotating counter-clockwise, but how can it rotate clockwise? Doesn't the pawl stop cw rotation? What is a TB gear?
Thanks

12-17-2011 07:02 PM

Madison

Re: paper: 2337's One Way Friction Brake

TB is Tough Box.

The gear never rotates clockwise. When the arm is driven downward, the motors have to exert enough force to make the friction pad slip on the gear.

12-19-2011 10:44 AM

IKE

Re: paper: 2337's One Way Friction Brake

This is a pretty neat design. I am a big fan of Bungee, but I can think of a few other areas I would love to use a unit like this.