[TowerTalk] Brake delay adjustment

[Tom Rauch]

Our messages crossed Al.

I was clarifying my own suggestion, but see I missed being clear. 
Understand I'm talking from the standpoint of a long-term 
thousands-have-to-always-work-as-well-as-possible-for-the-cost-of- 
the-components-viewpoint. 

Less "ideal" systems may be just fine. 

> 1) a diode connects to the hot side of the CCW and another to the hot side
> of the CW switch.
> 
> 2) This diode connects (through current limiting resistor ) to a
> parallel circuit
> of a capacitor and relay coil.

There you go. There is the current limiting resistor. As long as it is 
large enough to keep current in the CCW and CW switches at a 
safe value while the capacitor charges, you are all set for switch 
damage.

The only problem I see is the charge time delays the release of the 
brake (unless you open the brake manually first), so you are 
probably applying motor torque and loading the transformer in the 
rotor box with motor load current just before the brake unlocks. 
That could be a problem unless there is some energy storage on 
the brake system ahead of the relay, and as long as the brake 
wedge doesn't "mind" sliding back under load.

A nicer way might be to unlock the brake, and then allow the motor 
to receive voltage after a second or two. Might not hurt to do 
otherwise, but the sequence of:

1.) Disable brake with full voltage available

2.) Apply voltage to motor

3.) Remove voltage from motor

4.) Remove voltage from brake

is a bit better than reversing 1 and 2.

 
> 3) The normally open contacts and the relay arm connect across both
> sides of the
> brake switch.
> 
> Operation is as follows:
> 
> Press the break and a rotation switch.  Let the rotor go where you
> want it to.

What I was thinking of doing was fully automating the brake. All the 
user ever has to do is punch the left or right button. 

> Release all switches.  The break stays activated until the relay drops
> out.  The dropout time is dependent of the RC of the relay coil combo.
> 
> I don't see that this does anything to the break solonoid.  It is
> simply a parallel
> switch on the existing break switch.

Nope, that'll work fine. I didn't understand the system wiring you 
described. As long as the starting function is done in the sequence 
I described, everything is great. I was simply suggesting an goof-
proof one-finger system, and warning about the charge current of a 
capacitor. I get nervous when I see many thousands of microfarads 
being charged without current limiting through a switch or relay 
contact!!!



73, Tom W8JI
w8ji@contesting.com

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