(Need Advise) RC ESC or L298?
xnonox
Posts: 6
This is my robot
I need to control 4 omni direction wheels separately.
Well, I had 2 HB-25 , but I dont have the budget to buy 2 more
I can either do 4 RC esc (reversible) or two of L298 (something like this)
the question is how well can BS2 handle the output for four esc or two L298.
I am familiar with the esc using "PULSOUT" , but how do I control L298 using BS2?
I need to control 4 omni direction wheels separately.
Well, I had 2 HB-25 , but I dont have the budget to buy 2 more
I can either do 4 RC esc (reversible) or two of L298 (something like this)
the question is how well can BS2 handle the output for four esc or two L298.
I am familiar with the esc using "PULSOUT" , but how do I control L298 using BS2?
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Comments
Do you know how much current your motor pull?
I've use these H-bridges a lot with small motors. I think the L298 you linked to works the same way as the H-bridges I just linked to.
You control the H-bridge by driving certain pins high or low. You can kind of think of it as if your microcontroller is powering the motor directly. When the uC drives a pin high the H-bridge drives one of its lines high but with a higher voltage and much more current. They're not hard to use.
I've used these to drive small stepper motors.
I have a Roboni-I robot which I replaced its guts. I use one of these $2.35 chips to drive both of the robot's motors.
So the main question is: how much current do you motors need? The $2.35 H-bridges can drive up to 1 amp.
Duane
The L298 works alright but it should have some extra components installed to help protect it. I believe that part needs 4 extra diodes on each H-Bridge at a minimum. I prefer the LMD18200 chip which has been a bit more robust in my projects and requires less external parts.
There are a couple different ways to control H-Bridges but chips like the LMD18200 make it really easy. One pin sets the direction (low for one way and high for the other). Then you use one other pin to turn on the H-Bridge to make it go in the selected direction. low is off, High is on 100% and use PWM for any speed in between. I think this is one of the easiest ones to control.
Robert
I just looked up the LMD18200 chip on Digi-Key. Wow, that's an expensive chip. $17.78. It looks like it can control only one motor; is that right?
The current sensing and thermal sensing is pretty cool.
You must use some pretty big motors to need these. They can use up to 55 V at 3 A (peak 6 A). I don't think I have any motors that need near that much power (not yet anyway).
I'm pretty sure the SN754410 chips I linked to have internal protection diodes so extra diodes aren't needed. I think the LMD18200 would probably be overkill for xnonox's bot. Especially since xnonox has indicated not wanting to spend a lot of money.
I know some motor controllers can be paralleled. I'm not sure if the SN754410s can be. If they can, then one could double the amperage available by using two.
Duane
I haven't use them with the Basic Stamp 2 but I have with the Propeller. I'm sure I have some Propeller code I could share if you want it. (I'm willing to share any and all my Propeller code if anyone wants it.)
I've read in the SparkFun comments that these chips can be paralleled (stacked on top of each other). There's some debate whether or not these need external diodes. I haven't had any problem not using external diodes.
Sounds like diodes on the output pins is a safer design when using the SN754410...
I think most of the reversible ESC has a brake function.
if you want to control from forward to reverse, it will brake first then you have to release the handle (neutral position) , pressing the handle in reverse direction the second time, then it will go to reverse.
is it true for every reversible ESC?
if true , is there a way to bypass the function when programing?
Thanks for the response
Hello Duane,
I'm usually building larger robots and why I've been using more of the LMD18200 chips lately. They are very robust chips. And yes, one per motor. When you mentioned the L298 it makes me automatically bring up the LMD18200. I've used the L298 with no issues for some applications but when testing for another I blew the top right off one. The LMD18200 handled that one just fine.
If you have smaller motors then the TI SN754410 chips can be an excellent choice. You can double them up for more capacity and you don't need extra diodes. They are also pretty easy chips to work with. When I stack those I add a thin coating of heat sink grease on the top of the lower chip and also on the bottom of the upper chip. I then install a small DIP heat sink on the top chip and sandwich them all together. If you want an example on how they are wired you can look at the schematics for the motor section for the Handyboard which is available free online.
In 2008 I wrote a series of articles for SERVO and one of them it specifically covers upgrading an H-Bridge based on the L293. The progression was:
L293
SN7544410
2x SN754410 (stacked w/heatsink)
L298
2x LMD18200
I took another look at the SN754410 data sheet. On the bottom of page 2 there is a equivalent circuit schematic. Under "Typical of All Outputs" there are diodes between VCC2 and Output and between GND and output. This is one reason why I didn't think the chips needed external diodes.
However on page 6, Figure 3 "Application Information" shows eight external diodes. Time to fire up the soldering iron and find my bag of diodes.
Thanks for setting me straight.
@Robert, I've subscribed to Servo for several years now. I'm betting your article is where I read about stacking motor controller chips. Thanks for helping me with my electronics education.
When you say "You can double them up for more capacity and you don't need extra diodes." Do you mean I don't need to add a second set of external diodes or I don't need external diodes at all? As I mentioned above, I think Ron is correct about external diodes being a good idea with SN754410 chips.
The description on page 1 of the data sheet says "The device is designed to drive inductive loads such as relays, solenoids, dc and bipolar stepping motors. . ." This description is another reason I thought external diodes weren't needed.
Duane
You don't have to add any external diodes when using the SN754410 chips in either a single or stacked configuration.
Glad I could help.
Robert