Current based motor control circuit

Hope someone can help me.

I have a servo that operates a series of interconnected levers through a range of motion. I need a control device that will stop the motor when any of the levers encounters resistance. This only needs to be done in one direction- the other direction will return it to its home position. My thoughts are that is could be done by sensing a spike in amperage.

My wish list would include an adjustment for sensitivity and an operating range of 4.8 to 9 volts (or so).

Is something like this available or possible?

Thanks for any help,

Hello, Rick,

Just to clarify, are you using an RC servo? What you want to do should be possible, but our servo controllers do not have any current sensing capability built in, so you would have to use an external current sensor in conjunction with the controller.

If you are considering one of our Maestro servo controllers, it might be possible for you to use its built-in scripting capability to read the current sensor and detect when the servo is straining, although it would probably be easier to do this with an external microcontroller.

The simplest solution might be to use a limit switch (kill switch) instead; would that be an option in your setup?

- Kevin

Hi Kevin
Thanks for the reply.
This is for a prototype I’m developing for market. I need the cost to be as minimal as possible (never heard that before, right?)
The drive mechanism I’ll be using is a worm drive which can be used with or without a linear pot depending on the controller. I need the current sensing feature to only work in one directon- the other direction is a return to home and can be controlled with a micro switch. I’ve considered using a micro switch for both directions but it would be problematic to implement in the design.
Maybe I posted this in the wrong location- it doesn’t have to be one of your servo controllers. Sounds like an external microcontroller would be the way to go but I haven’t been able to locate any schematics for something like this.
Thanks again,

From what you are describing, it sounds like you might not be using an RC hobby servo, but rather a standard motor with some kind of feedback (like the linear pot you mentioned). If it is a brushed DC motor, our Jrk motor controllers are more suitable controllers, and they have built-in current sensing capability. However, they cannot be configured to use a current threshold as a “kill switch” autonomously, so you would still need an external microcontroller to query the current reading and run/stop the motor accordingly.

- Kevin

What I’m actually using are the Pololu micro metal gearmotors driving a threaded rod. I cannibalized a standard size servo to operate it and got some 5 or 10k (don’t remember which right now) linear pots. So I can go either way- current sensing or micro switches. Preference would be current sensing. What micro controller would I need to use with the jrk controller? Is this something that would basically be pnp?

How do you ultimately want to control the motor? (Will it be controlled by a PC, manual buttons/switches, autonomously, or some other way?)

You could use any microcontroller that has a TTL serial interface with the jrk. You would have to program the microcontroller yourself to obtain the current reading from the jrk and process it, then send appropriate commands to the jrk to make it behave as desired.

- Kevin

I need to control it by manual switches. It’s looking like it’s beyond my abilities. I was looking for something “off the shelf” that could be modified to my needs.

Unfortunately, we do not know of anything suitable that would work for you “off the shelf”, so it’s likely you would have to use a microcontroller and do some programming to achieve what you want to do.

- Kevin