X axis problem

[sowjoe]

I'm looking for the simplest way to build a gantry that travels back and forth on the X axis only without it being hooked up to a computer. It will be belt driven and controlled by an 18v dc drill motor.

I was thinking about using an "on-off-on" switch at each end of the gantry slide to reverse the direction of the gantry, but I think the motor won't last long if I do that. I need something to slow the motor at each end before it reverses direction.

I've thought about Hall sensor's, 555 timers, limit switches etc., but they seem complicated being that I don't know much about them. Just want something simple.

Any idea's?

 

[Harald Kapp]

You could use two switches at each end.
switch 1 is positioned a short distance before the end of the axis. When the sled or gantry reaches that switch, the motor is slowed down e.g. by switching a resistor in series with the motor.
When the gantry reaches the end of the axis, a second switch reverses the direction. Onnce the gantry has moved far enough from the end, the 1st switch is de-activated, the series resistor is short circuited and the motor runs at full speed.

The same setup for the other end.

 

[Electrobrains]

I think Harald has a good solution.
Practically, if only for one project, I would use a mini-PLC (you can buy them quite cheap second-hand, for instance a Siemens LOGO, Moeller EASY etc.), a couple of relays and a power resistor as Harald suggests.
See circuit diagram below.

.

Instead, for the brake function you could switch a resistor in an adjustable power supply, reducing the motor voltage (for instance down to 6V).
That would probably give less power loss and you could do without the mechanical relay (REL2).

For an even smoother but still simple solution, you could add a short stop cycle at the end positions. For that you would need another on/off relay though.

 

[sirch]

At its simplest I believe a double pole double throw switch and a leaver mechanism will do it. Put buffers at either end of the travel with rods to trip the switch one way and then the other. The DPDT switch changes over the +ve and –ve to the motor.

<<edit>>
Or I suppose you could mount the switch on the carriage and trip it at either end with some sort of leaver that trips it one way but allows it to pass freely the other.

Either way I guess you might want some sort of soft start on the motor.

 

[sowjoe]

I think what I'm going to do is build a test model using one on-off-on switch. The 2nd on will reverse the polarity of the dc motor thereby reversing the direction of the carriage. Simple and easy. If I have a problem with reverse-direction smoothness (which I don't think I will because of the friction of the belt, motor and other things) then I'll try something else.

Here is the belt drive design I want to use....

http://bell-everman.com/products/lin...elt-linear-sbl

Video.... http://bell-everman.com/products/lin...elt-linear-sbl

Maybe use some type of soft-start motor controller too ....
http://www.skpang.co.uk/catalog/pololu-highpower-motor-driver-18v25-cs-p-662.html