Let's Make Robots!

Big Motor Driver (Inspired by Chris the Carpenter)

High-Current Motor Driver

I'm not sure how I stumbled upon this site but find myself visiting it on a daily basis now.  I spent the better part of a week reading through a numerous amount of posts and became inspired by some of the designs.

One design that caught my interest was the motor controller made by Chris the Carpenter (with contributions from others).  So, instead of mooching information off of the site I decided I should contribute something.

I have posted a motor controller design that is supposed to be simple, robust, cost effective, and able to handle high currents.  Above is a schematic of the first part of the design.  I will post an updated version to include a PIC to accept commands from a PC, Microcontroller, etc. and provide the direction/PWM signals to the H-bridge.  I am still working on the PCB but here is what I have done so far for review/critism.  What is not shown in the schematic are the in-line fuses for protection.

For the PIC, I use MBasic and PicBasic Pro to write the code.  This should convert easly to the BS2 and PicAxe.

More to come and thanks for whatever welcome I may receive (hopefully a warm one).


** Updated 04 January 2009 **

Here is an updated version based on advice provided below.  Again, if you find any errors let me know.

Thanks to all who provide help/advice and to those who show interest.  I know there are easier ways to do this but this is sorta an addiction now.

Updated controller


** Updated 10 Jan 2009 **

 I updated the schematic again.  As suggested I changed the MOSFET driver to a TLP250 and dropped the 1K resistor across the Gate to source.

Update the schematic to show that the logic grounds are isolated from the dirty motor grounds.



** Updated 10 Jan 2009 **

Updated the schematic for those that want to save an I/O pin.  There is a Hex Inverter/Buffer circuit (U1) that feeds the inputs of the Optoisolator (U2).  If you look at the wiring for the Hex Inverter you will notice that the output of the second inverter feeds the input of the first inverter.  So, when a logic 1 is placed across pin-3 it is inverted into a logic 0 which turns off the Reverse Relay.  A logic 0 is also placed at the input of the first inverter which gets converted to a logic 1 on its output and turns on the Forward Relay.

By using the inverter circuit you will no longer have the capability for dynamic breaking.  In other words, one of the relays will be active as longs as powered is applied to the circuit.  Disabling the PWM signal will keep the motor from turning.



** Updated 11 Jan 2009 **

Finished the PCB design.  Once boards are complete will test and post schematic and board files once any kinks are worked out.



** Updated 22 January 2009 **

I got the prototype boards back from the manufacture two days after I sent them off.  As you'll see below, the quality is excellent.  Tonight I populated the board and checked out functionality with a multimeter prior to testing with a motor.  I managed to get everything put together right so on to the smoke check.  I hooked up a good size motor with a lot of torque and applied power.  The motor moved in both directions and the MOSFET did not even get warm.  This test was applying full power to the motor and not PWM.  Next, I'll write some code and test functionality with PWM hooked to my Oscope so I can check the signals and see how high I can take the frequency.  I'll get around to posting some video but, in the mean time, here are some pictures of one of the finished boards.


PCB Bottom








** Bill Of Materials **

Component Description Part Number Vendor Cost
C1 220 uF P10325-ND Digikey $0.72
C2 0.1uF BC1114CT-ND Digikey $0.20
D1 1N4001 Rectifier 50V 1A 1N4001DICT-ND Digikey $0.30
D2 1N4001 Rectifier 50V 1A 1N4001DICT-ND Digikey $0.30
D3 Schottky Diode 45V 15A STPS1545D Mouser $0.80
D4 Schottky Diode 45V 15A STPS1545D Mouser $0.80
D5 Schottky Diode 45V 15A STPS1545D Mouser $0.80
D6 Schottky Diode 45V 15A STPS1545D Mouser $0.80
J1 4-Pin Header, Male 2077095 Jameco $0.19
J2 Screw Terminal, 2-Pin 160785 Jameco $0.65
J3 Screw Terminal, 2-Pin 160785 Jameco $0.65
J4 Screw Terminal, 2-Pin 160785 Jameco $0.65
LED1 3mm Red, T1 253278 Jameco $0.26
LED2 3mm Red, T1 253278 Jameco $0.26
LED3 3mm Red, T1 253278 Jameco $0.26
Q1 2N2222 NPN Bipolar Transistor 600mA 75V P2N2222AG Mouser $0.21
Q2 2N2222 NPN Bipolar Transistor 600mA 75V P2N2222AG Mouser $0.21
Q3 IRFZ44N Single-Gate MOSFET Transistor N-Channel 60V 50A IRFZ44NPBF Mouser $1.30
R1 270 Carbon Film 1/4W P270BACT-ND Digikey $0.08
R2 270 Carbon Film 1/4W P270BACT-ND Digikey $0.08
R3 270 Carbon Film 1/4W P270BACT-ND Digikey $0.08
R4 1K Carbon Film 1/4W P1.0KBACT-ND Digikey $0.08
R5 1K Carbon Film 1/4W P1.0KBACT-ND Digikey $0.08
R6 10K Carbon Film 1/4W P10KBACT-ND Digikey $0.08
R7 10K Carbon Film 1/4W P10KBACT-ND Digikey $0.08
R8 39 Metal Film 1/4W 39.2XBK-ND Digikey $0.11
RLY1 SPDT 12V @ 20A ACT112 Mouser $2.17
RLY2 SPDT 12V @ 20A ACT112 Mouser $2.17
U1 PS2501-2 Dual NPN Phototransistor PS2501-2-A Mouser $0.87
U2 TLP250 Photocoupler IGBT MOSFET Driver TLP250F-ND Digikey $1.88
PCB Printed Circuit Board N/A
ExpressPCB $20.28

** 24 January 2009 **

I added a few of pictures of the test application and the temporary PWM controller used for testing.

Test Application

Temporary PWM Controller and Motor Controller


** 02 February 2009 **

Added a crappy video of the motor controller being tested.

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Your finished product looks like a work of art!  Can't wait to see the robot it will go in!

Hi Curtis,

It's great to see you fight the good fight of motor controller design. 

I have a couple of suggestions you might consider.

1. electrical isolation is a very good thing, especially for larger current motors - I have uhh I mean, I know people who have smoked  a large amount of work in a micro-second because it was more expedient to make the controller without isolation.  It looks like you've done this in your last revision.

2. if you aren't going to do high-side braking or low-side braking - then why not save a BIT (they are precious you know?) and combine FWD & REV into a single bit - where high is FWD and low is REV.  This could be done with a small NPN & PNP with combined base and output to your current FWD-A & REV-A



That is an ingenious idea.  Naturally, I never considered doing it that way.  I like that idea and will work that into the design.

 Thanks a lot



Grog is a very competent person!

(Just for the record)

I agree with you.  That is why I took his advice and added the alternate circuit.  Thanks to all who is/has helped with this circuit.  I have received all of the components and will be testing the circuit and designing a PCB shortly.
The schematic does not show it but I added a bypass capacitor between VDD and GND as the TC4427A Mosfet driver datasheet recommends it.
The change was good but isolation was lost. The TLP250 suggested can be found at Digikey for $1.88 and would get you back the isolation, which is a very good feature of this design. Oh, the 10k resistor between the gate and source of the FET is not needed with an active driver like the TC4427 or TLP250. The small 39 ohm gate resistor is still a help though. Good thinking on adding the capacitor.


I did order some TLP250 chips.  I'll update the schematic and give those a try.  I was worried about losing the isolation with using the TC4427.

Oh yeah,

If you heard Frits speak Danish (or whatever) it sound like he is singing... It's just the English where he sounds like a jerk...

You should see me dance!