HB-25
Bill Chennault
Posts: 1,198
All--
I have asked VERSIONS of this question before. Now, I am ready to buy motor controllers for my skid steer chasis . . . which I just finished. I will use gear motors that have a stall current of 42 amps. Of course, I never expect them to draw anywhere near that much and will protect the motors and controllers (is it necessary to add external protection to·the controllers?) with appropriate fuses.
I am still a little confused by Parallax's HB-25. My (limited) understanding is that it acts like a continuous rotation servo controller. In other words, if you set it at a certain "dead" speed (by sending it a 1.5ms pulse), it stops. If you send it something less than the "dead" speed, it rotates in one direction. If you send it something more than the "dead" speed, it rotates in the other direction. The·difference between the "dead" speed number (750; just for a BS2?)·and the number you send it determines its RPM in either direction. (I believe the range is 500 with half of that on each side of the "dead" speed.")
I know I am confusing pulses with RPM, but I do not know enough to seperate the two. In fact, the Parallax sample code seems to support my "dead" speed explanation, with 750 representing the "dead" speed and anything from 750 down to 500 setting the actual speed in that direction while anything from 750 to 1000 sets the speed in the other direction. (Does 750 translate to 1.5ms when used in the PULSOUT command with a BS2?)
The core of the Parallax sample code for a dual controller HB-25 configuration . . .
· FOR index = 0 TO 250················· ' Ramp Up To Full Speed
··· PULSOUT HB25, 750 + index·········· ' Motor 1 Forward
··· PAUSE 1···························· ' 1 mS Delay For Motor 2 Pulse
··· PULSOUT HB25, 750 - index·········· ' Motor 2 Reverse
··· PAUSE 20··························· ' 20 mS Smoothing Delay
· NEXT
It certainly looks like there are 250 RPM possibilities in each direction. I SUPPOSE (gee! DANGER! [noparse]:)[/noparse] it is actually dependent on maximum possible motor RPM and each different argument used in the PULSOUT commands above represents a fraction of that maximum RPM. (?)
Does the HB-25 perform PWM, as well? If not, I wonder what performance will look like at low speeds?
Will you please correct my misimpressions and fill me in concerning areas I have missed?
Thanks!
--Bill
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You are what you write.
I have asked VERSIONS of this question before. Now, I am ready to buy motor controllers for my skid steer chasis . . . which I just finished. I will use gear motors that have a stall current of 42 amps. Of course, I never expect them to draw anywhere near that much and will protect the motors and controllers (is it necessary to add external protection to·the controllers?) with appropriate fuses.
I am still a little confused by Parallax's HB-25. My (limited) understanding is that it acts like a continuous rotation servo controller. In other words, if you set it at a certain "dead" speed (by sending it a 1.5ms pulse), it stops. If you send it something less than the "dead" speed, it rotates in one direction. If you send it something more than the "dead" speed, it rotates in the other direction. The·difference between the "dead" speed number (750; just for a BS2?)·and the number you send it determines its RPM in either direction. (I believe the range is 500 with half of that on each side of the "dead" speed.")
I know I am confusing pulses with RPM, but I do not know enough to seperate the two. In fact, the Parallax sample code seems to support my "dead" speed explanation, with 750 representing the "dead" speed and anything from 750 down to 500 setting the actual speed in that direction while anything from 750 to 1000 sets the speed in the other direction. (Does 750 translate to 1.5ms when used in the PULSOUT command with a BS2?)
The core of the Parallax sample code for a dual controller HB-25 configuration . . .
· FOR index = 0 TO 250················· ' Ramp Up To Full Speed
··· PULSOUT HB25, 750 + index·········· ' Motor 1 Forward
··· PAUSE 1···························· ' 1 mS Delay For Motor 2 Pulse
··· PULSOUT HB25, 750 - index·········· ' Motor 2 Reverse
··· PAUSE 20··························· ' 20 mS Smoothing Delay
· NEXT
It certainly looks like there are 250 RPM possibilities in each direction. I SUPPOSE (gee! DANGER! [noparse]:)[/noparse] it is actually dependent on maximum possible motor RPM and each different argument used in the PULSOUT commands above represents a fraction of that maximum RPM. (?)
Does the HB-25 perform PWM, as well? If not, I wonder what performance will look like at low speeds?
Will you please correct my misimpressions and fill me in concerning areas I have missed?
Thanks!
--Bill
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
You are what you write.
Comments
The 750 only applies to the BS2 and the number of steps to its resolution of 2us per step. Really this boils down to the pulse width going to the HB-25, regardless of the microcontroller. 1.5ms is the stop position. The valid range is from 1ms to 2ms and in either direction as you move from 1.5ms the speed will ramp up. The motor/load will determine what pulse width is needed at various speeds to maintain that. The HB-25 internally uses PWM to drive the motors. I hope this helps. Take care.
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Chris Savage
Parallax Tech Support
It helped a lot! In fact, it helped both you and me since I now understand the HB-25 a bit better you can expect an order for a couple of them from me.
--Bill
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You are what you write.
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Chris Savage
Parallax Tech Support
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Never give up when things go wrong.
They are going in my new skid steer chassis!
--Bill
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You are what you write.