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Author Topic: Looking to learn where to start  (Read 417 times)

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Offline lippyTopic starter

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Looking to learn where to start
« on: July 29, 2014, 06:41:05 PM »
Hello,

I've got a project I want to play with that will involve a robot that has a tray about 8x10" and can maneuver around the house via remote control.  Speed isn't a main concern, maximum load wouldn't be more than a few lb, and my maneuverability requirement is to easily go from hardwood to tile to carpet, maximum 3/4" transitions but nothing extreme, while maintaining the load relatively stable.

I do a good bit of playing around with micro-controllers and I have a 3D printer and access to a laser cutter.  In the past I've built a simple tank using a couple of continuous rotation sub-micro servos and a 3D printed chassis to chase my cats around, but that's about the limit of my robotics experience, so I wanted to ask for some advice here before I invest too much time/money in this project while going in the wrong direction. 

What I'm thinking at the moment is to use a Vex Robotics Tank Tread kit driven by a couple of stepper motors.  I have no idea about how to couple the steppers to the drive axle (is it acceptable/advisable to direct-couple this via a 'lovejoy' connector?) or if based on my requirements, is a tank just generally the wrong way to go and another form of robot would be better/cheaper to get off the ground?

Any advise/direction to documentation and resources would be greatly appreciated...Thanks for reading this far and I hope you're having a great day!

Cheers,

Roger

Offline bdeuell

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Re: Looking to learn where to start
« Reply #1 on: July 29, 2014, 09:55:43 PM »
From my understanding of your mobility requirements it doesn't seem like treads are necessary, you could probably get away with some wheels, they would need to be large enough and have some traction. Of course tracked robots can be very cool and if that is what you want to build it isn't the wrong choice...wheels are just simpler. The most basic robot construction is probably two driven wheels and a caster.

For mounting wheels, I am not sure what you have in mind but when i think of lovejoy i think of the shaft couplers with a rubber spider in the middle. These would work to connect a motor to wheel but the wheel would need to be mounted to its own set of bearings. for this robot you can probably make it light enough and get away with using the bearings in the motor (assuming your motor has decently sized bearings). In this case the wheel would be directly mounted to the motor shaft, probably with use of a hub of some sort.

As for motors you will probably want something geared. While you can easily drive stepper motors slowly without a gearbox they would have to be larger in size to provide sufficient torque. Selecting a motor with a gearbox will allow you to pick one that weighs less and still meets your torque and speed requirements. Weight is important because for every pound you add to your robot it will require more batteries and structure to support the weight which will also add more weight and require stronger motors...this turns into a vicious cycle. In addition to getting a geared motor i would recommend a standard brushed DC motor as it will probably be the easiest to control, (there are plenty of stepper controllers out there tho if you go that route). Also because it will be under remote control you probably don't need to use encoders or rely on the open loop position control of stepper motors, i.e. your eyes will provide the feedback to make course corrections.

Just some thoughts and very much my opinion, others may have different ideas.

Offline mklrobo

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Re: Looking to learn where to start
« Reply #2 on: January 23, 2015, 01:42:16 PM »
 :) Hello!
I would suggest investing time into programming the servos, along with identifying some
schematics. Parallax has some good starting robots, with manuals for basic programming.
The Avon microcontroller seems to be user friendly, with built in commands that take the headache
out of getting servos to work, with the interface worked out. Good luck!

Offline Schlayer

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Re: Looking to learn where to start
« Reply #3 on: January 24, 2015, 04:29:20 PM »
    If I were you, I'd forgo a micro controller altogether. You need to control two drive motors via remote control, and that is easily accomplished with a simple 2 channel radio receiver and transmitter. I agree with bdeuell on several of his points:
From my understanding of your mobility requirements it doesn't seem like treads are necessary, you could probably get away with some wheels, they would need to be large enough and have some traction. Of course tracked robots can be very cool and if that is what you want to build it isn't the wrong choice...wheels are just simpler. The most basic robot construction is probably two driven wheels and a caster.
As for motors you will probably want something geared.
etc...
    Geared motors are pretty useful, as with a remote controlled vehicle it's incredibly simple to operate them. I can't see a reason to use steppers, as that just adds a PWM component and complicates things. You could easily use a two joystick controller with two sub-$10 bidirectional speed controllers and two cheap gear motors, a ~$50 transmitter/receiver kit, and then be pretty much done with all of your electronics. Usually digital transmitters can be bought at a moderate price and give you a massive amount of control over an R/C system. You can get a $20-$30 analog controller instead, though I personally haven't found a 2 joystick transmitter for surface vehicles under $60.

Digital: http://www.rakuten.com/prod/neewer-fs-gt3b-2-4g-transmitter-w-receiver-combo-fly-sky-3ch-rc-car/276213605.html?listingId=380080984&sclid=pla_google_NeewerDirect&adid=29963&gclid=CjwKEAiAoo2mBRD20fvvlojj5jsSJABMSc7jeqFyoUR-shy0hms1x-pHGpNdxQlb2agrIuRhHbngyxoCp9Lw_wcB (This I've used personally and it can be used to control differential drive vehicles like you would a traditional car, with a steering wheel and throttle)

    Alternatively, you could use one motor to drive an axel on which you have both rear wheels, and mount your castor to a servo for steering, allowing easier use of the pistol grip transmitters like this: http://www.amazon.com/FS-GT2-Transmitter-Channels-Receiver-channels/dp/B007FSJM6S/ref=sr_1_1?ie=UTF8&qid=1422138401&sr=8-1&keywords=rc+car+transmitter
(FlySky just happens to sell transmitter + receiver kits that are easy to find and fairly inexpensive)

 


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