How do I control the EPM with Arduino? With logic of servo servo.write() functions dont do much Help

Hard · February 28, 2019, 12:32pm

Hey
So I am creating a certain application where I control OpenGrab EPM with arduino, but with simple PWM and utilizing arduino code for servo.write() doesnt work
0 degree maps to 1ms
180 degree maps to 2ms
as per my knowledge but doesnt really discharge instantaneously
I am really struggling with discharging my EPM instantaneously like within 500ms delay

Answers are really appreciated

pavel-kirienko · February 28, 2019, 12:50pm

Perhaps your library implements some kind of slope control? I can’t really comment much on Arduino-related stuff. Consider using a signal generator to ensure that the RPM responds properly, then investigate Arduino separately.

Hard · March 1, 2019, 9:03am

So, I have one more question
1ms pwm will release the gripper
1.5 will go into the neutral zone
2ms will activate the gripper
am i correct?

pavel-kirienko · March 1, 2019, 10:54am

Yes.

Hard · March 1, 2019, 11:17am

So, there seems to be some problem, if i give a continuous trail of 2ms it does holds then after a delayed time it releases it, even if there is only 2ms.
Thank You

pavel-kirienko · March 1, 2019, 11:31am

Please make sure that your hardware emits a correct signal. You could connect an oscilloscope or a logic analyzer to the signal line to search for abnormalities. Also consider connecting a UART adapter to the diagnostic UART output on the EPM to see if there are any useful diagnostic messages being emitted.

Hard · March 1, 2019, 12:55pm

While debugging it showed some rate limiting which triggers the epm in the opposite state
Could you tell me more about this rate limiting please?
And another question that 2ms pulse should be one single pulse or continuous till the time I want the epm to be in on-state
Thanks

Hard · March 4, 2019, 2:11pm

Last question, I am getting a discharge time of more than 3 seconds how can I change that? It is shown that discharge is in 1.2sec. Is there any way I can change that ? any change in firmware or anything?
Require Assistance, Thanks

pavel-kirienko · March 5, 2019, 4:07pm

One or several pulses are enough to trigger the magnet; it is not necessary (and is, in fact, not recommended) to keep the signal at the high level continuously because that would cause the magnet to remagnetize repeatedly.

Concerning your other questions, I believe it’s best to consult with the firmware:

github.com

Zubax/opengrab_epm_v3/blob/master/firmware/src/main.cpp

/*
 * OpenGrab EPM - Electropermanent Magnet
 * Copyright (C) 2015  Zubax Robotics <info@zubax.com>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Author: Pavel Kirienko <pavel.kirienko@zubax.com>
 *         Andreas Jochum <andreas@nicadrone.com>
 */

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Hard · March 6, 2019, 6:27am

Thanks for the information but I am getting a discharge time of more than 3 seconds how can I change that? It is shown in the datasheet that discharge is in 1.2sec. Is there any way I can change that ? any change in firmware or anything?
Require Assistance, Thanks

pavel-kirienko · March 6, 2019, 7:55pm

I am inviting @NicaDrone to join this thread please.

Hard · March 13, 2019, 7:10am

@NicaDrone @pavel-kirienko I request you to please reply to this thread

NicaDrone · March 18, 2019, 9:25pm

Hello Hardik, yes, use low impedance power source at 6.5V for fastest switching times