Hi Rob
That sounds like it should work since the two motors will not bind against a rigid frame. You're right about those motors jumping whichever direction they please when you apply power. As long as you don't have to worry about loosing steps, both motors could be driven from the same set of step and direction pulses -- except when trying to find home. I'm thinking of a real kludge here but since you can home anytime, you could build a little switch that disconnects one drive from the step and direction signals at a time while the other one homes. Once both are homed, send the motion pulses to both and you should have a well behaved system.
Rayh
--- [EMAIL PROTECTED] wrote:
From: Rob Jansen <[EMAIL PROTECTED]>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Subject: Re: [Emc-users] Homing using 2 motors per axis
Date: Thu, 13 Mar 2008 07:51:11 +0100
Rayh,
the whole gauntry acts as a swivel :-}
It's all made of aluminium sheet 15 mm thick, 30 cm wide and 70 cm height with two 80x80 beams of 122 cm long. If I remove one of the ball screws I can move that side a few centimeters without applying too much force.
I thought of adding a timing belt like Dennis mentioned but was afraid there is too much elasticity in such a long belt (when using two motors).
When switching on the power supply to the motors both stepper motors will switch to a full step so one motor may move clockwise while the other goes ccw, one full step means 5 mm (pitch of ball screw) / 200 (steps/rev) = 0.025 mm difference. This does not seem too much so maybe I should not worry too much about this and just measure the difference between both sides from time to time.
There never is a problem during operation of the machine - at least not after setting up the stepper timing correctly.
Meanwhile I decided to leave it as it is, there are enough tother things I have to do before the machine is 'finished' - unless of course someone has a complete canned solution that I could use.
My next machine will most likely use just one motor with a belt drive to two ball screws but I have to look at the specs for the timing belts first to see if this will give me the accuracy wanted.
Regards,
Rob[EMAIL PROTECTED] wrote:
Hi Rob
I've been curious about these dual drive axes for quite a while now. There are several possible mechanical lashups with something like this. It seems to me that in order to allow separate homing of each drive, there would have to be a swivel on one side or the other of the mechanical slide. Is that the case with your machine?
Rayh
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