Restoring a Robotic Arm...newbie needs a hand

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20 Jun 2011 20:50 #10683 by MitchellT
Hello all,

A friend, (I think) , brought home 2 Rhino Robotics XR-3 robotic arms: www.rhinorobotics.com/xr3_flyer.html

Can you experienced EMC folks (I have to admit this is my first foray beyond windows and a stepper 3 axis) recommend a set of (low cost) boards working under EMC2 (gotta have them kinematics) that can replace the original parallel port connected controller that has gone missing?

Here's what the docs say about it::

The Mark III Controller counts three states per revolution on the Encoders for the Small Motors. The Mark III counts six states per revolution on the Encoders for the Large Motors. The Rhino Motor Encoder Disks have the following characteristics. The 2 Small Motor Disks have six segments - three black and three silver. The 6 Large Motor Disks have twelve segments - six black and six silver.

The Optic Boards have two Optics (5 Volt Digital Square Wave) positioned 90 degree out of phase. So I guess this is a typical quadrature encoder?

The Mark III controller is a basic, 8 axis controller with the ability to interact with 8 TTL level input lines and to control 8 TTL level output lines. . All input lines are pulled up to TTL high.. . Output lines provide TTL level signals at 100 milliamps.

I only have and need 6 motors to control

4 Large 12volt motors that are permanent magnet brush servos with a no load draw of .4 amp and a stall about 5amp.

2 small 24 volt motors


I thought that I only needed a break out board and some servo drivers as with Mach 3. Am I correct that EMC needs a breakout board, a separate driver board, as well as the servo amps? Inquiring minds want to know.

Thanks all,

MitchellT:unsure:

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21 Jun 2011 12:05 #10698 by andypugh
MitchellT wrote:

]I only have and need 6 motors to control[/i]
4 Large 12volt motors that are permanent magnet brush servos with a no load draw of .4 amp and a stall about 5amp.
2 small 24 volt motors


Each motor will need pwm and direction and 2 encoder inputs.
I make that 12 outputs and 12 inputs, and so that indicates to me that a single parallel port won't do the job if used as direct IO. You could use two parallel ports, though.

Alternatively the Mesa 7i43 connects to the parallel port and gives you 48 IO lines and onboard PWM generation and encoder counters. At $80 it seems to me a better bet than a second parallel port.

For motor drives you could build your own PWM-controlled H-bridges or scour eBay, or buy new.
cgi.ebay.co.uk/L298N-Dual-H-Bridge-DC-Mo...-Motor-/170646149605
Looks like it would work for your smaller motors (and maybe for the bigger ones if you don't want to supply full stall current). You could drive that from Parallel Port or Mesa card.

If you do go for the Mesa card, then the obvious choice of motor drives would be some combination of:
7i25 2-channel 48V 3A(6A) drive $149
7i30-4 4-channel 36V 3A drive, $89
7i40 2-channel 40V 10A drive, $149

Personally, at $22 per channel I think I would use the 7i30-4 and hope that 3A was enough current, possibly with the eBay controller for the little motors. There is a 7i30-2 which is a fraction cheaper than the -4 and probably leaves you more IO pins free (2 x 7i30-4 would use all the 7i43 headers, but you could declare fewer encoders and PWMs in EMC2, and that would release those lines for general IO, but you would need to make a part-populated link cable to take advantage of them.

More details at www.mesanet.com Look under "Motion Control" for the motor drives.

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21 Jun 2011 19:23 #10728 by MitchellT
Thanks Andy!

I have ordered the 7i43, 7i30-4 and the ebay dual H-bridge as suggested. I think (hope) the connections should be straight forward. Do people recommend a good source for power supplies?

This last question that may be way off this board's topic. But...what's the best way to figure out how to configure EMC to talk not only to this configuration, but to this machine? I know I need real Kinematics. Should I start with one of the PUMA arms in the setup menu, and then start hacking away at the geometry, pins connections, etc.

For me, just like all the threads on Mesa boards, it's pretty hard to sort through all of it and find the appropriate signal from the background noise for this noob.

MitchellT

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21 Jun 2011 19:32 #10731 by andypugh
A good starting point is probably to look at the sample configs, specifically the Puma and Scara robot configs, and the hm2-servo config.

You can probably set up most of it with pncconf.

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