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Motor driver booster

  1. Mar 16, 2004 #1
    I'm trying to build one of those mini sumo robot's as a project and I have a working drive circuit. I'm trying to control it with my parallel port on my computer that way I can write control programs and change behaviour relatively easily however my circuit has quite a few losses and I was wondering if anyone had any advice for it. The values for all the components are just estmates because I don't have the actual motor yet and the multimeters in the circuit are the "motors" while I was using a program to digitally test it. From what I can tell the motors I want to use have a resistance of 6 ohms when stopped and can handle a maximum voltage of 8.4 volts safely. ( I was trying to get the car to run around on 6v and then have the option to boost at an additional 3v that makes 9 which is slightly over the maximum for the motor but will only be for short times.) (all the logic pins at the bottom and the ground are the PP interface). Thank for any help.
     

    Attached Files:

  2. jcsd
  3. Mar 16, 2004 #2
    The jpeg open up tini-tiny almost unseeable but it looks like your running two motors with independend Full H-Bridge controllers. Have you thought about using H-Bridge IC's? I made an RC airplane speed controller using a PIC and a Vishay H-Bride. The ESC worked well, and didn't consume much power (lots of power is good when your bot is bumping against another bot)

    Here, take a peep at this, or something like this: http://www.vishay.com/docs/71326/71326.pdf

    The bottom three are pretty good (or so I've found in the small applications I've made).

    Also, do you have any motor restrictions?
     
  4. Mar 16, 2004 #3
    yeah it is just an H bridge controller however because I don't have infinite access to IC's and the like and alot of access to transistors I figures it would be the best way to go and since its a bit of a project I wanted to build as much of it as possible from scratch. As to your comment about motor restrictions, there is a specific motor and gear combination that I need to use. sry about the jpg the restrictions on file sizes are quite exstensive. What I am more interested in are changes to the H-bridge design or the booster design most of the circuit doesn't consume power except for the diodes. One of the diodes is bypassed when I trigger the addition power but for some reason my electronics simulator only put power to one of the motors when I didn't have the diodes at the power in to the H-bridge.
     
  5. Mar 16, 2004 #4
    They're actually very cheap and if you're doing it for a "school project " you can request free samples. They usually send samples out no problem, no questions asked. I got a handful of picks for a robot project about 6 months ago as a matter of fact. I droped my request and 24 hours later "knock, knock, knock, FedEx".

    What do you mean by losses? Are you popping transistors, or just consuming more power than expected. If the latter is the case, what frequency are you runnning your bridges at, or are you simple turning on a lege and leaving it on to drive the motors?
     
    Last edited: Mar 16, 2004
  6. Mar 16, 2004 #5
    I'm sorry, I just saw that your simulating these. Use an input frequency of 4kHz to 8kHz on the enable line, and use inductors to simulate the motors instead of meters. That shoud improve your simulated effeciency.
     
  7. Mar 16, 2004 #6
    I do intend to build the circuit so any suggestions I would hope work practacally and I'm hoping to just ledge trigger the transistors that would be simpler however if it would improve proficientcy I could have the PPort oscilate. By consume I mean that there is a 1V voltage drop over the diodes which is 1v less to drive the motors not to mention heating up the diodes. however that "school project" option seems intersesting as it really is a school project one question however is that US or Canada because I live in BC.
     
  8. Mar 17, 2004 #7
    one final thing it seems that the H-bridge IC uses a pulsed input and I'm not to thrilles about putting a pulse generator in the circuit I would rather keep it nice and simple and small.
     
  9. Mar 17, 2004 #8
    You want to run an H-bridge with a pulsed input. It makes the whole circuit a lot more effecient. Transistors are on less thus they don't get as hot. The 4kHz to 8kHz is filtered by the motor inductor so the motor really doesn't "see " the pulsing. H-bridges are very inefficient when simply switched on to go and off to stop. You should be able to set the desired frequency from your Parallel Port. 8kHz is nowhere near the data transfer limit. I haven't had a parallel port in years, so I can't help you there, but swing by here:

    www.beyondlogic.org

    also, subscribe to the piclist and ask around ther. A guy by the name of Bob Blick prowles around there. He had (might still be up) a web sight that talked a little about H-bridge theroy. If you ask a question on the Piclist, you'll usually get a lot of good helpful informat.

    for some good info on parallel ports. Also, go to visheys web site and search around there. They have a good knowledge base and they address H-Bridges. You just have to look for the information. Als google search it.

    As far as the samples go, I don't see why they wouldn't ship something your way. You might have to say your a company requesting a sample for a prototype.

    Well, good luck.
     
  10. Mar 17, 2004 #9
    thanks for your help i'm sure my bot will kick some ass.
     
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