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We are building a mobile robot which will use two motors in a differential drive configuration to maneuver and move around, and we want to choose the right driver IC or transistor circuit for the job of controlling these motors and providing enough current. Our motors are rated at a power of 14W (link at bottom) and we will be using an 11.1V lipo battery to power them. We might be changing our battery setup once we get this thing built and tested.

So I am looking for a motor driver IC or transistor configuration which can provide enough power / current for our motors. The way I understand it, the L298 provides 2 amps max per channel, which I guess would work for us since the 14 watts / 11.1 volts = about 1.3 amps max current draw, is that correct?

We are also curious, the stall current of these motors is rated at 11.5 amps. I'm assuming that this means that, should the motor stall, it will then draw 11.5 amps of current until it begins moving again as it should. Should we use a transistor configuration / driver which allows for higher current draw than 2 amps then? There is a chance that, while operating this robot, it might bump a wall or something which would result in a temporary stall in the motors being able to freely spin. Forgive my questions please, I am still fairly new to this stuff.

If the L298 wouldn't work for us, I was looking at something like this: https://www.sparkfun.com/products/10213 . We would need four of these since we need each of the two wheels to go forward or backward. So two wheels x two directions = four semiconductors. Again if this isn't right, please feel free to suggest something better.

Thank you so much!

Chris

This is the motor we are planning on using (two of them.)
https://www.andymark.com/NeveRest-p/am-neverest.htm

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    \$\begingroup\$ You need a minimum of 4 transistors per motor if you want to have reversing with a single-ended battery supply. \$\endgroup\$ – Dwayne Reid Sep 14 '17 at 3:05
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    \$\begingroup\$ There are dozens or even hundreds of Integrated Circuits and pre-packaged modules that will control your motors. Google is your friend. Check out Pololu, Adafruit, Sparkfun, Seeed Studio, Banggod, many other suppliers. \$\endgroup\$ – Dwayne Reid Sep 14 '17 at 3:08
  • \$\begingroup\$ You must define the moving mass, acceleration and maximum velocity to optimize your power train. Then use a half bridge configuration with PWM and a dead-band during PWM switching or just buy something that works if you cannot. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Sep 14 '17 at 3:26
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If you use L298 then a protection against the stall current is needed, "over current protection".

And the stall current 2 x 11.5A have to be checked against the C rating on the LiPo batteries so you don't overload the batteries. Look for "Discharge rate characteristics" for your battery type.

And @Dwayne Reid s comment about 4 transistors per motor is also known as a H-bridge, ref.: https://en.wikipedia.org/wiki/H_bridge

And 14 Watts is rated at 12V not 11.1V. So calculate the resistant for the motor and then you can calculate the watt at 11.1V.

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  • \$\begingroup\$ Thanks guys for the replies. I know that motor control is a very, very widespread application of transistors and so I know there are lots of things that will work for us. So I guess my question is - could you guys give an example of an h bridge which would work with these specific values? I am only familiar with the L293, and to a lesser extent the L298. But if there is a similar DIP IC which we can use that would solve everything. Also our robot is about 3 lbs and wheels are 2.9" diam. Our system will have to handle the stall current, correct? Likenwhen the robot moves from a dead stop? \$\endgroup\$ – user108391 Sep 14 '17 at 20:52
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    \$\begingroup\$ I am not trying to be lazy, I checked adafruit, sparkfun, and mouser looking at transistors. Im just not sure which parameters to look at I guess. I am assuming source to drain current has to be at least our stall current? And also that it can handle the max dissipation of our 11.1 V lipo at the stall current ~12 A, so maybe 130 watts? Am I approaching this the right way? Or are there fundamentals I am missing here. Finally (sorry for my curiosity) does it matter if it's a QFET vs other types of FETs? Kind of an amateur in this area, haha. Thank you all \$\endgroup\$ – user108391 Sep 14 '17 at 20:56
  • \$\begingroup\$ If you want to be lazy, you should search for a "ESC motor controller Raspberry Pi" and choose one for your current rating. \$\endgroup\$ – MatsK Sep 14 '17 at 22:18
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    \$\begingroup\$ Thanks MatsK. I looked into that after your post, but since we have two motors and two directions each, I think I would need 4 ESC's, and so that would not work for my particular application. I ended up buying some TIP102, TIP107, TIP120, and TIP127 darlington transistors from Mouser last night, along with a few N type and P type power MOSFETs. I'm going to build an h-bridge and test it out with these, and am pretty sure at least one of these combinations will work. Any further comments are welcome, but thank you everyone for your input! Have a good weekend Chris \$\endgroup\$ – user108391 Sep 15 '17 at 21:42

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