Let's Make Robots!

Big Motor Driver Done

Run 2 Motors, Fwd and Rev with PWM Control


Well, it seems I might have smoked something. I am in the process of testing the motor driver, with a load, and using 2 motors. While my "B" channel seems to be working fine, the "A" channel seems to be stuck on. Not to mention, the FET driver sorta burned my finger when it was touched. All this and I have yet to blow my 20 AMP safety fuse! I'm letting it cool off a little and am going to try again. ---I am not looking forward to asking for "purchase authorization" from the wife for more parts!



What started as a simple question about running big motors has turned into 2 threads and over 110 posts.

First Post

Follow-up Post

What has come of this is wonderful submissions from BOA, GroG, Robologist, Krumlink with Rik and others filling in a bunch of gaps and disputing what everyone else has said. I have gleaned what I could from this firehose of posts and decided to go with the BaseOverApex/ Robologist plan. As an overview this is a high power motor driver with logic level inputs for PWM and "reverse", a FET driver chip and FET's for main power switching and 2 high power relays for reverse. Here is the original schematic from the second follow-up post "H Bridge Matrix":

BOA's Brilliant Hybrid H Bridge - Robologist Mod

BOA's Brilliant Hybrid H Bridge - Robologist Mod
Description BaseOverApex's design of a great Hybrid H-bridge. The hybrid is a combination of relays and MOSFETs. The relays are for forward and reverse switching. The MOSFETS can accept a high frequency PWM for speed control. This design has been built (not just theory) and is currently powering one of BOA's great bots. Hopefully he will post a version of the PCB art - although it might be good to rework it so that the PIC is not part of the design, as others might be using different methods of control.
Original Author BaseOverApex robologist
Built By  
Max Current 15 Amps - limit by relay
Max Voltage 12 Volts to 15 Volts
Build Time 3 Days?
Pros strong, low cost
Cons not quicklyswitchable forward to reverse, limit by relay
Max PWM Frequency  
Features reverse flyback diodes, MOSFET driver
Parts List
Desig  Qty  Part#           Each  Total    Dist      Description
*K1,K2 2 PB897-ND $4.44 $8.88 Digikey Tyco PCLH-202D1SP,000 12VDC/75 mA coil, 15A relay
*Q1,Q2 2 IRFZ44NPBF-ND $1.89 $3.78 Digikey IRF IRFZ44NPBF 49A 55v N-chan FET TO-220
*Q3,Q4 2 P2N2222AGOS-ND 0.36 0.72 Digikey On Semi P2N2222AG 600mA 40v NPN GP BJT TO-92
*D1-D8 8 497-2753-5-ND $1.09 $8.72 Digikey STMicro STPS1545D 15A 45v Schottky rectifier diode
*U1 1 TC4427CPA-ND $1.05 $1.05 Digikey Microchip TC4427CPA 1.5A MOSFET driver
*C1 1 4035PHCT-ND 0.81 0.81 Digikey Vishay 220 uF 35 v Electrolytic Cap
* Total $23.96
Schematic Image:M_relayhp.jpg
BreadBoard Image:M relayhp B.jpg
Gerber Image:M relayhp gerber.jpg


I bought all the parts on the list above, all from Digikey, with the addition of some blank 2oz copper PCB boards and were quite happy when my parts arrived within 3 days!


Next, using PCB123 layout software (which is not only free, but worked quite well) transposed the schematic into a PCB layout. In general, I was able to keep most + runs to the outside and - to the inside. I think I did pretty well, only needing 6 topside jumpers. I must admit, it was a nightmare to keep all the componant's polarity straight as I went as things are mirrored or double mirrored (depending how you think about it) in terms of the top side of the board, bottom side and the fact the transfer is reversed when applied to the board. The picture below is of the final transfer I used.


This layout, printed with a printer using ink, was taken to my local copy-shop and Zeroxed as dark as it would go using a standard copier using toner. Next, I ironed the ever-living-shit of the transfer onto my blank PCB board. I was careful to go over each line one-by-one in addition to placing the iron over the whole transfer and putting my whole weight on it.

That would be:

140 Lbs

63.5 Kg

10 Stone

Happy that indeed the shit had been ironed out of it, I soaked-the-crap-out-of-it and then rubbed off the paper.



With a little scotch-brite (green scratchy pad (for dishes)) I removed the toner from the circuit lines, drilled and soldered away. The tiny little drill bit came from a model airplane shop, chucked-up in a dremel tool and was done by hand. Also, when setting the parts I seemed to run into a big phatty problem with the layout of the diodes. If you run into the same problem, well, here you go.


As you can see, I did have a few issues with some lines bumping each other but a cut-off wheel in a dremel and a very steady hand, I was able to tidy up everything.


And here she is!

Here you can see all the parts, the 2 green LED's are tied to the PWM input while the red LED's light with reverse.

Once again, much love and thanks to all who helped with this project. At the time of this post (and the video included) is of my first -low current- test. I hope to have some new videos up soon including this unit running the 2 DeWalt drill motors it was built for!


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I see the additional reverse protection diodes as useful if the FET reverse breakdown voltage is less than twice the supply voltage, otherwise I'd just use the FETs intrinsic diodes. As above, the OSMC if running a 36 volt pack or even higher up to 50v, is dangerously near that 55 volt reverse breakdown of the IRF1405s. If it was never to run more than 18 or so volt pack, the external TVS diodes probably wouldn't be needed.

This is getting more towards opinion, as I can't exactly spell out why that point is. I really prefer to provide a factual back-up as to why I picked the "double" figure, but can't lay my hands on it right now.  

Well, I really didn't mean to start anything with the McCain comment and don't want to get into anything here. It seems that here in the States things are SO polarized that we are all simply black or white, right or left or a 1 or a 0. I miss the middle. Again, I won't get into why I like my guy, maybe we should just use the dinner table rules.... No politics or religion. Or at least keep it confined to the Politics thread.

Bottom line: It would SUCK to loose any of my robot homies over something as silly as economic theory. Protection diode conversatinos are MUCH more important.

And in terms of diodes, I checked out the TVS diodes mentioned above. These seem like nifty little "surge protectors". I think Big Motor Board 2.0 should include them. I am really suprised how sensitive these FET's really are! When I was/am working with them, I was sure to ground myself out before touching them and tried to keep the soldering iron as cool as I could. It is suprising that something that can switch 50 Amps can be killed by a "carpet spark"! At anyrate, I really do think it was killed by some sloppy code and a "too quick" reverse while testing. I was using a ramp-up/ ramp-down chunks of code, I think it could have been as simple as a missed "pause". I am testing some new code using this guy which uses the same PWM/ out pins that I am using on the big bot. When my replacement parts get here I should have some solid, FET-friendly code to run. If I keep frying stuff on the second run, maybe some more protection will be in order...

How big of a resistor do you think should be used on the FET Gate?
Check the post just above . 10 ohm is about the minimum, might go as high as 50, but not higher for use with the TC4427 driver.. If you check the OSMC resistors, they are 150, but they are four 150 ohm resistors essentially in parallel. So the effective resistance the HIP4081 driver was seeing was 37.5 ohms. Ohms law 12v/37.5 = 300 mA forward current to average the higher reverse current (through the diode), to keep the HIP4081 cooler. If you don't use the reverse diode, you can have a smaller resistance for a greater current both ways, so that's why I went as small as 10 ohm.
So is this the driver you're gonna use with the wheelchair motors? Can it handle the Amps (24ish)?

i want to make a 10 amp motor control circuit just want to be able to drive it in both the direction two motors and ten amperes per motor any ideas pls help

If those TO-220 devices to the right of your main pic are voltage regulators in parallel, then you could have  a problem there.  Since the regulators aren't all exactly the same, the reg with the lowest threshold will take the full load until it burns out, and then the next lowest keyed reg will take the full load and so on.

High Current voltage regulation


If this is not the case then forget i said anything, it's too late in the night for me to read this massive page.