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RC ESCs instead of an h-bridge. — Parallax Forums

RC ESCs instead of an h-bridge.

rwgast_logicdesignrwgast_logicdesign Posts: 1,464
edited 2013-02-05 10:40 in Robotics
Ok Ive been doing a ton and ton of back and forth and thinking about this, and ive come down to either a 4wd Rover5 with Dagu off road wheels and l298 h-bridges.

The second choice is a sting ray, but If i go with a 2 wheel bot like the sting ray I really want it to be compatible with the boe bot, that way I can use the plethora of information written for the boe bot to learn from. Theres even prop based boe bot tutorials on learn.parallax.com. I know the boe bot just isnt going to be enough for me in the long run though! So in order to make the sting ray more boe bot compatible ive been looking at every solution, including things like using an ATTiny to convert RC Servo Style pulses to true PWM and connecting that between the bs2/prop and the h bridge.

Well I ran across these http://www.hobbyking.com/hobbyking/store/__6455__Hobbyking_SS_Series_8_10A_ESC.html now if I were to buy two of these would these be suitable for driving the sting rays motors using the RC servo pulsing in the book? Also the sting ray motors are 4.5amp 7.2 volt, these ESC's are rated in cells, im not sure if that is lipo cells or what... but ill be using nimh, as Iv already built a nimh charger for this project and own a ton of 2500mah nimh cells

Comments

  • rwgast_logicdesignrwgast_logicdesign Posts: 1,464
    edited 2013-02-04 19:01
    Ok well that link was for a one way brushless ESC, hobby king isnt to descriptive.. but you get the idea, im looking for a comperable bushed esc that can do reverse. If I find one that should be totally BOE-Bot material compatible right?
  • msrobotsmsrobots Posts: 3,709
    edited 2013-02-04 19:23
    Parallax sells the HB 25 controller. They do what you want but are quite pricy... http://www.parallax.com/Store/Accessories/MotorServos/tabid/163/List/0/SortField/4/ProductID/64/Default.aspx?txtSearch=hb+25

    Enjoy!

    Mike
  • garyggaryg Posts: 420
    edited 2013-02-04 20:06
    From what I've been seeing lately on the RC Control websites, Brush type motors and ESC's are becomming farther and more
    inbetween than what they were a couple of years ago.
    It would appear to me that Brush type DC hobby motors will not be available in a few years.

    It's just a thought
  • rwgast_logicdesignrwgast_logicdesign Posts: 1,464
    edited 2013-02-04 20:17
    Ya, I know about the HB-25's and have even worked out a good deal on two of them, the reality is I just cant afford them right now along with a sting ray. Ive been looking at hobby kings stuff and I dont think any of there ESCs would be suitable for robotics, due to pausing before reverse. I may try e-bay too. I know the saber tooth motor motor drivers are set up like an ESC but they are also pretty pricey. Its amazing that if you want an RC speed control that is usefull for robotics the price jumps like crazy, when any of the HK stuff would work if they were to just reprogram the chip and cut a wire.

    Id been thinking about just doing a DIY ESC, something like a prop/avr connected to an h bridge that converted the RC pulse's to the micros native PWM, but thats a project with in itself as I cant seem to find a simple open source project with the code already written.
  • rwgast_logicdesignrwgast_logicdesign Posts: 1,464
    edited 2013-02-04 21:12
    Ok well how about this

    http://www.ebay.com/itm/RC-10A-ESC-Brushed-Speed-Controller-for-1-16-24-for-Car-Boat-Tank-w-brake-/251194596108?pt=LH_DefaultDomain_0&hash=item3a7c5d5b0c

    The main concern is I keep reading alot of ESC's have a safety feature that wont let you go from forward to reverse instantly, but this has tank in the recommended uses which uses differential drive.

    Now would I be able to basically plug two of these in to a bs2/prop then connect them to the sting rays motors and basically have a big/fast boe bot, or would I have some other issues I may be over looking?
  • ercoerco Posts: 20,256
    edited 2013-02-04 21:30
    Is it worth agonizing over for $4? Just get a 298 module and try it. Controls 2 motors. You'll use it somewhere.
  • al1970al1970 Posts: 64
    edited 2013-02-04 22:07
    Hi:

    "The main concern is I keep reading alot of ESC's have a safety feature that wont let you go from forward to reverse instantly, but this has tank in the recommended uses which uses differential drive."

    I don't understand why you think this is a bad thing! If you are using a gearbox motor that is using 10 amps; you want your motor to come to a stop before you go into reverse! If you didn't, your gearbox would have broken gears in no time. You would also fry your motor controller in no time. Remember that your controller would not only have to handle the watts that you are giving it when you put it in reverse but also all the watts the motor has stored when it was moving forward.

    Al
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-02-04 23:38
    erco wrote: »
    Is it worth agonizing over for $4? Just get a 298 module and try it. Controls 2 motors. You'll use it somewhere.

    Agreed!

    I don't think it's worth bothering to use an ATTiny to convert hobby servo pulses to PWM signals. This is trivial for the Propeller to handle.

    I've been actively working on code to control four motors with one cog. I'm pretty sure it works just fine. I'll post an updated version in the Rover 5 thread tomorrow. I'm using the code with L298N motor controllers in one robot and Pololu's MC33926 boards in another.

    Right now the code uses three I/O pins per motor but this should be able to be reduced to two pins per motor with a little additional hardware (an inverter (or maybe diodes (right erco?))).

    Code for controlling two motors with PWM (with a Propeller) is very common.

    I do agree that CR servos are easier to use than regular DC motors but not by much. While I think the HB-25s are nice motor controllers, I don't think they would be the best use of your limited robotics budget.
  • rwgast_logicdesignrwgast_logicdesign Posts: 1,464
    edited 2013-02-05 00:59
    :/ Im sorry guys I wasnt really agonizing over the price of the controllers, only trying to find a fairly cheap way to be able to use all the BOE-Bot examples with the sting ray. If i drive a straight PWM signal to the stingray the code will be much different than whats in the all the BOE Bot documentation, while Its not to big of an issue to just use modify the BOE Bot code to work with a non rc style motor control system, its still a bit of a hassle, not to mention, the bs2 is totally left out as a learning tool without buying/building some kind of PWM or ESC module, unless I totally leave out speed control.

    So do you guys totally disagree with using something like this

    http://www.ebay.com/itm/RC-10A-ESC-B...item3a7c5d5b0c

    i    nstead of just using a standard h-bridge?
  • ercoerco Posts: 20,256
    edited 2013-02-05 08:28
    Duane Degn wrote: »
    (an inverter (or maybe diodes (right erco?))).

    Inverter is the way to go. IIRC you'll fry the 298 if your code accidently makes both inputs high.

    I just got my ghetto mecanum bot running last night with twin 298s... that thing's a hoot. Working up a video.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-02-05 10:15
    rwgast_logicdesign wrote: »
    If i drive a straight PWM signal to the stingray the code will be much different than whats in the all the BOE Bot documentation

    rwgast, I'm cleaning up my four motor PWM code right now in order to post it to the forum. I'll add a method with same type of interface as the servo method so instead of using -1000 to 1000 speed setting wth zero as stop, the method will accept input like a normal servo with 1500 as stop.

    This should make using code for the BOE-Bot easier to use with an H-bridge motor controller.

    I also don't see anything wrong with the speed controller from ebay. It would save you one or two I/O pins per motor.
    erco wrote: »
    Inverter is the way to go. IIRC you'll fry the 298 if your code accidently makes both inputs high.

    I just got my ghetto mecanum bot running last night with twin 298s... that thing's a hoot. Working up a video.

    I'll add inverters to my next parts order.

    I want to see that video!
  • ercoerco Posts: 20,256
    edited 2013-02-05 10:40
    Duane Degn wrote: »
    I'll add inverters to my next parts order.

    Check this 4069 hex inverter from RADIO SHACK: 99 cents, free ship. Now you're barkin'! http://www.ebay.com/itm/NTE4069-CMOS-Hex-Inverter-High-Voltage-Type-NTE4069-/360571143242
    Duane Degn wrote: »
    I want to see that video!

    Me too. Might have Youtubed it yesterday, but for a sick toddler puking through the night... but the delay bore unexpected fruit. I shall produce a video, the likes of which have never been seen before!

    ... on my Youtube channel anyway.
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