Victor logistics.

[B.Johnston]

Originally Posted by Hazmatt

thanks 1680Bruce, but I understand how victors control a motor with varying pulses. I also understand that the control signal going into a victor is different than what comes out. What goes on in between these two signals is a mystery.

let's say I used some general microcontroller. Pretend that the "servo-type" signal goes into this microcontroller. Now i'm guessing that this microcontroller needs to measure the time of the input pulse. The time of the input pulse could then be applied to some formula or something to transform it to "motor-type" control signal.
How would one go about measuring the length of the "servo-type" pulse
No, as stated in my first post, I am attempting to design my own controller.

Are you making this control in a pure hardware design via logic gates or in a software application running on a microprocessor?

In either case to convert from the lower signal level to the higher drive level would require a measurement of both input and desired output against a continuous and stable reference. In hardware and in software this would be derived from a clock oscillator like a 555 chip.

Signal conditioning and output sequencing are extra to the basic functioning of measuring against a reference so these would be dependant mostly on and specific to whatever components you choose for implementing your design.

[yongkimleng]

No, as stated in my first post, I am attempting to design my own controller.

Are you using the Arduino? The uC on it should have a hardware based PWM generator suitable for driving H-Bridges.. try reading the datasheet

Do share with us what MOSFET you are trying out and how easy/hard it is to interface them.

[Hazmatt]

yes, as soon as I figure everything out/purchase parts I'll make a project page.

[Generalx5]

Actually, H-Bridges can be made with all low side Metal Oxide Semiconductor FETs. This being that N channel fets can handle much more current than the high side fets.

Also, there are more than a few ways to make an H-Bridge work. The pair of low side and high side MOSFETS are just one of them, this being that only 1 signal comming in will only activate FETS that are diagonal to one another. Reffering to the classic H formation on an H Bridge. This method is easy to make, and prevents shoot thru...

Method 2 uses only N channel fets, but requires an inverted MOSFET driver to drive each Side, so driver 1 controls the upper left and lower left, while driver 2 controls upper right and lower right. This also prevents shoot thru of current.

Many more ways to make an H bridge.

Signals of 1 - 2ms enters on one end, with 1.5ms being neutral. The other end where the motor is connected to, has a duty cycle that varies. going from low frequencies such as 20hz to 40Khz. varies greatly, most applications, a frequency of 6khz is about just in the middle. I read that from somewhere, but can't source it.

As for the polarity changes, you can make the microcontroller do that for you. Make an H bridge with a pair of MOSFET Drivers connected to the Gates on the mosfets. then have your digital output pull up or pull down the inputs on the MOSFET Drivers. The mosfet drivers are used because of the low gate resistance on the MOSFETs them selves. Having low resistance when a high current prescence at the channel makes the gate hard to open. So by using a driver, you can dump high currents at the gate at high frequencies to allow the channel to flow. If you need high duty cycles, you will have to load your routine in the user_routine_fast.c file. And go from there.

You can start experimenting with a bread board, and single mosfets first. after you know the fundementals, you can beef up and parallel your MOSFETS to handle currents as high as 80 amps steady loads or more.

As far as I know, the Victors use FETS that are about 65Amps on each MOSFET on a steady load, but be careful, because the power dissapation can be around 40 -80W each, and the pakage is only about a cm^2 area if you attach a heat sink.

Those victors use 12 fets, 3 per quadrant of the H bridge. So it would be able to handle high current loads for longer periods of time. They were able to make the duty cycle efficient enought that the fets dont requre added heat sinks.


International Rectifier makes MOSFETS with various pakage types, the ones used on the Victors are pakage: TO-220

Microchip.com makes the MOSFET drivers, other do too....Anyways, look for a pdf document on the website: "Mosfet Driver guide" or something along the line, it helps you select the right MOSFET drivers for the right type of MOSFETs....
GL with your experiments!

[yongkimleng]

Well said!

Any recommended mosfet & drivers?

[Gdeaver]

If you want to build a motor driver and are going to use 12 volt or more then there are some single chip solutions that can offer more ability. The victor everybody is familiar with is an open loop design. It provides no feed back or protections. If you going to use a micro controller to command the H-bridge then with a little more work you can have Current feed back, thermal protection and over current protection. With current feed back and knowing the motors current function then you can have sensorless speed control with fair accuracy. For low current motors look at the Freescale MC33887. For more current ability the ST Micro Electronics VNH2SP30 chip offers many features.
Infineon also offers the BTS 7960 and BTS7930. These are half bridge chips.
Pololu.com offers the first 2 chips on carriers and would simplify working with them. They are surface mount and not for bread boarding. Robotpower.com offers the simple H with the BTS7960. The nice thing about the VNH2SP30 is that it only needs the fixed frequency - variable duty cycle PWM on 1 pin. The other chips need 2 PWM outputs from the microcontroler. The next step to this is to control the speed controller over a serial buss. Note that the Lego NXT offers I2c and RS485 for this purpose. May be First and IFI will add some intelligence to the next generation speed controllers.

[yongkimleng]

VNH2SP30 - 30A, surface mount only
BTS7960B - 60A half bridge

Personally would prefer the BTS7960 as two of them make a full bridge and I can directly drive them using the 2-phase PWM output of the PIC or ATmel controller, and you can also add a heatsink to it. Now my only issue is having a bunch of them shipped to my location...

[Generalx5]

Originally Posted by Gdeaver

If you want to build a motor driver and are going to use 12 volt or more then there are some single chip solutions that can offer more ability. The victor everybody is familiar with is an open loop design. It provides no feed back or protections. If you going to use a micro controller to command the H-bridge then with a little more work you can have Current feed back, thermal protection and over current protection. With current feed back and knowing the motors current function then you can have sensorless speed control with fair accuracy. For low current motors look at the Freescale MC33887. For more current ability the ST Micro Electronics VNH2SP30 chip offers many features.
Infineon also offers the BTS 7960 and BTS7930. These are half bridge chips.
Pololu.com offers the first 2 chips on carriers and would simplify working with them. They are surface mount and not for bread boarding. Robotpower.com offers the simple H with the BTS7960. The nice thing about the VNH2SP30 is that it only needs the fixed frequency - variable duty cycle PWM on 1 pin. The other chips need 2 PWM outputs from the microcontroler. The next step to this is to control the speed controller over a serial buss. Note that the Lego NXT offers I2c and RS485 for this purpose. May be First and IFI will add some intelligence to the next generation speed controllers.

The chips referred use duty cycle pwm up to 20Khz as input, this would not work with the RC pwm used on the microcontroller...... At least, I think thats right.

As for mosfet types:

http://www.irf.com/product-info/data...a/irf3704z.pdf
The IRF3704Z is a pretty powerful fet. And Current output to power dissapation ratio is fairly good.

Go here if you want to pick your own mosfet specs.
https://ec.irf.com/v6/en/US/adirect/...N=0+4294841672

You can read this guide for pairing up FETS with drivers. Provided by Microchip.com

http://ww1.microchip.com/downloads/e...tes/00799b.pdf