board of education and hb-25 motor controller

hualala

Hi all,

I am planning to buy the board of education and HB-25 for my project. My project is to build·a model plane·that·takes information flight simulator and·make use of 3 dc motors to turn it.·Since it is a huge sum of money, i would like to ask some questions.

Is·the board of education able to drive the motors without the help of HB-25 motor controller?
How many motors can 1 HB-25 motor controller drive?

Help is greatly appreciated. thankyou.


Post Edited (hualala) : 8/5/2009 12:55:13 PM GMT

dandreae

The Board of Education is not able to drive the DC motors by itself.· The HB-25 can drive 1 to 2 motors in the same direction.



Dave

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Dave Andreae

Parallax Tech Support·

dev/null

You could build your own DC motor controller... Here is a schematic for one, which uses 3 stamp pins for each motor.
(you can avoid this by using dual-channel potentiometer). This is a highly effective controller, comparable to HB-25.


The parts for this controller will add to around $6 if you buy them at Tayda Electronics.

I have the PCB layout file if you're interested.

Voltage:
The maximum operating voltage of the LM324 is 32V, so this is also the max voltage available to run the motor.
Current:
The IRFZ44 MOSFET can handle 49A; the IRF4905 can handle 74A. Depending on your PCB design, you might have to run wires between the high current tracks. Normally, the PCB tracks can handle around 5A.

Parts list

Semiconductors
IC2 - MCP41100 100k Single Channel Digital Potentiometer
IC1 - LM324 Quad OpAmp
D3 - 1N4004 Rectifier
D1,2 - 1N4148 Zener
Q1,2 - BC547 Transistor
Q3,5 - IRF4905 P-Channel MOSFET
Q4,6 - IRFZ44 N-Channel MOSFET

Resistors
R15 100 ohm
R9,14 - 4K7
R2,7,10,11,12,13 - 10K
R8 - 12K
R6 - 33K
R3 - 47K
R1 - 100K
R4 - 220K
R5 - 470K

Capacitors
C1 - 10nF 63V box poly
C3 - 100nF mono
C2 - 100uF 63V electrolytic

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$WMc%

dev/null

Nice little circuit.

I added a drawing that has all the info on it, Just for clarity.


____________$WMc%__________

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The Truth is out there············································ BoogerWoods, FL. USA

Post Edited ($WMc%) : 8/6/2009 1:00:17 AM GMT

dev/null

Thanks.

Attached are PCB files. I have the Express PCB file, but I can't attach it (get an error message). If someone wants it, email me.
The layout needs a double-sided PCB, or you can run wires for the crossover sections.

I haven't tested this controller with the Stamp actually, but I am going to soon.
Need to find the right SHIFTOUT/IN commands for the MCP41100 potentiometer.

The MCP41100 fits this circuit perfectly. When the potentiometer starts up, the wiper will be in mid-position, so the motors whill stand still at startup.
And since it's 8-bit, you get 128 different speed levels in each direction.

If you need lots of ampere, adding a fan (like on the HB-25) would be recommended. Also, good heatsinks between the MOSFETs is a must.

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Don't worry. Be happy

dev/null

Here's how it works:

The circuit has four main parts:
1. Motor control – IC1:A
2. Triangle wave generator – IC1:B
3. Voltage comparators – IC1:C and D
4. Motor drive – Q3-6

Only two MOSFETs are on at any one time. When Q3 and Q6 are ON then current flows through the motor and it spins in one direction. When Q4 and Q5 are ON the current flow is reversed and the motor spins in the opposite direction. IC1:C and IC1[noparse]:D[/noparse] control which MOSFETs are turned on.

Opamp IC1:B is set set up as a triangle wave generator and provides the trigger signal for the voltage comparators. The frequency is approximately the inverse of the time constant of R5 and C1 – 270Hz for the values used. Reducing R5 or C1 wil increase the frequency; increasing will decrease frequency.

The peak-to-peak output level of the triangle wave is less than the difference between the two voltage references. Therefore it is impossible for both comparators to be triggered simultaneously. Otherwise all four MOSFETs would conduct, causing a short circuit and destroy them.

The triangle waveform is centered around a DC offset voltage. Raising or lowering offset voltage changes the DC position of the triangle wave accordingly. Shifting the triangle wave up causes the comparator IC1[noparse]:D[/noparse] to trigger; lowering it causes IC1:C to trigger. When the voltage level of the triangle wave is between the two voltage references then neither comparator is triggered.

The DC offset voltage is controlled by the potentiometer IC2 via IC1:A, which is configured as a voltage follower. This provdes a low output ompedance voltage source, making the DC offset voltage less susceptible to the loading effect of IC1:B. As the 'pot' is turned the DC offset voltage changes, either up or down depending on the direction the wiper terminal is moved.

Diode D3 provides reverse polarity protection for the controller. Resistor R15 and capacitor C2 are a simple low pass filter. This is designed to filter out and voltage sikes caused by MOSFETs as the switch to supply power to the motor.

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Don't worry. Be happy

dev/null

Here is the PCB file: http://forums.parallaxinc.com/files.itslearning.com/data/his/39381/Elec/DC%20Motor.pcb
Here is an Openoffice doc. with descriptions:
http://forums.parallaxinc.com/files.itslearning.com/data/his/39381/Elec/DC%20Motor.odt

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dev/null

FYI; the MOSFETs are lined up so you can put a heatsink between each pair.

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hualala

Wow. Thank for all your help. I will give some thought over it.=)

dev/null

Someone (WMc) wanted to omit the digital pot and send instructions to the LM324 directly, I hope he posts it here if he does.

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Android

Hello Guys. I dont understand schematics very much. Does anyone know where i could get instructions for this
- android