Home/Limit switches

Questions about using encoders with the Roboclaw product line
dudlee
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Joined: Wed May 24, 2017 3:37 am

Re: Home/Limit switches

Post by dudlee » Wed Sep 20, 2017 4:05 am

Hello,

if I understand well this topic, I can not build a "home made linear actuator"
with 2 limit switches on each end of the slider without avoiding somehow the forward limit startup case? So basically I would need a linear actuator with limit switches at each end to prevent overrun .
I use potentiometers to control the position of the motors which is connected to another board. And if that board would fail or the potentiometer would fail I want these switches to prevent damage the hardware.Or do you know any solutions to build this with RC?

Thanks a lot.

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Basicmicro Support
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Re: Home/Limit switches

Post by Basicmicro Support » Wed Sep 20, 2017 9:39 am

For a full proof hard limit you need physical limit switches with diodes on each end(this is how most comercial linear actuators are wired up). Any other method will leave the potential for a failure that will cause the motor to move, eg bad pot, bad controller, bad digital inputs on limit switches or leaving the forward limit switch triggered when powering off.

The diodes still have a small chance of a failure into a short(usually a diode will fail into an open circuit). In that case they would bypass the switch allowing the motor to still run past the switch so even that option is not 100%.

gimsonrobotics
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Joined: Wed Feb 28, 2018 9:00 am

Re: Home/Limit switches

Post by gimsonrobotics » Wed Feb 28, 2018 9:07 am

Hello, we have an application where overcoming the "forward limit startup" case is a real pain, short of introducing an additional microcontroller to manage two independent limit switches and then driving the RoboClaw from that we don't have any other way of having motor braking at both limits reliably (since a conventional limit switch circuit with diodes wouldn't provide any braking). Is there a firmware update to support two independent limit switches for operating a single motor on the horizon? Or, failing that, memory of the last limit state as mentioned further up this thread?

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Basicmicro Support
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Re: Home/Limit switches

Post by Basicmicro Support » Wed Feb 28, 2018 10:16 am

Both options are on our wish list but I cant give a definitive timeline of when one or the other will be implemented.

Can you tell me what your application is and how it is being controlled? RC, Analog or packet serial? if it is packet serial there are options to work around this.

gimsonrobotics
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Re: Home/Limit switches

Post by gimsonrobotics » Fri Mar 02, 2018 3:06 am

We're using a simple analog input, trying to avoid adding another tier of complexity to this build by adding external processing & using serial. It's a prototype sliding gate system, with limits at either end, effectively a large linear actuator, where it's a regular possibility that power may be turned off and on again while in either end position.

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Basicmicro Support
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Re: Home/Limit switches

Post by Basicmicro Support » Sat Mar 03, 2018 5:16 pm

I made some changes to the firmware to allow both signal pins to be used as limits for one motor. This will only work when Bridged Channel mode is selected. You dont have to actually wire both motor channels together, but the mode must be selected. When it is the new firmware will let you use both limit signal pins with one motor. One can be setup for forward limit and the other for reverse limit or home.

I expect to release this firmware at the end of next week assuming we can finish all the testing by then.

gimsonrobotics
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Joined: Wed Feb 28, 2018 9:00 am

Re: Home/Limit switches

Post by gimsonrobotics » Tue Mar 06, 2018 8:28 am

Sounds great will keep an eye out for it! Thank you

gnordin
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Joined: Fri Apr 05, 2019 6:15 pm

Re: Home/Limit switches

Post by gnordin » Fri Apr 12, 2019 12:44 pm

Basicmicro Support wrote:I made some changes to the firmware to allow both signal pins to be used as limits for one motor. This will only work when Bridged Channel mode is selected. You dont have to actually wire both motor channels together, but the mode must be selected. When it is the new firmware will let you use both limit signal pins with one motor. One can be setup for forward limit and the other for reverse limit or home.

I expect to release this firmware at the end of next week assuming we can finish all the testing by then.
I don't recall seeing this capability described in the documentation and assume it is there now. Can you point me in the right direction? Thanks.

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Basicmicro Support
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Re: Home/Limit switches

Post by Basicmicro Support » Mon Apr 15, 2019 10:03 am

You have to be in bridged mode. You dont have to actually have bridged the two motor channels but in bridged mode you can only control one motor. It is a check box option in Motion Studio. Once in bridged mode you set S4 and S5 as limit switched. One for home/rev and one for forward. The Roboclaw automatically knows to use bopth switchs on the single motor since it is in bridged mode.

gnordin
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Re: Home/Limit switches

Post by gnordin » Mon Apr 15, 2019 11:57 pm

Basicmicro Support wrote:You have to be in bridged mode. You dont have to actually have bridged the two motor channels but in bridged mode you can only control one motor. It is a check box option in Motion Studio. Once in bridged mode you set S4 and S5 as limit switched. One for home/rev and one for forward. The Roboclaw automatically knows to use bopth switchs on the single motor since it is in bridged mode.
Thank you--this is very helpful. Is there a way to set bridged mode with packet serial operation so that Motion Studio isn't needed? We are developing custom python code to control a motor for our specialized application.

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