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  • I'm building an autonomous mobile robot for my FYP. differential steering is the technique I'm using to steer the unit. wheels configuration is as follow: two drive wheels in the rear each one has its own stepper motor and one caster wheel in the front. the robot is supposed to navigate on tiles covered floor and wheels are made of plastic not rubber. i have no localization method for my robot. so its important to me to know whether I'm going to face complications due to wheels slippage and skidding or not. and how to reduce these effects.
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  • Differential

    Member • Mar 12, 2009

    Let's say your device makes a complete round. Then there would be 2 circles of different radius but with same center made by two rear wheels. Now, circumferences of these circles will be different. So inner wheel has to rotate at relatively lower speed than outer wheel. But this relation will depend upon turning radius.

    How do you achieve this?
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  • Ashraf HZ

    Member • Mar 12, 2009

    Yeah, there will always be a risk of wheel slippage when using the differential method. You MUST have some sort of feedback, and not rely on programming the wheels to turn the robot a specific direction.

    Do you have a certain budget limit?
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  • momin

    Member • Mar 13, 2009

    by feedback you mean localization aren't you ASH?
    Localization is a very challenging task for me and i don't have time for such complicated techniques. lets say that budget is not a problem, what do you have in mind?
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  • sauravgoswami

    Member • Mar 14, 2009

    well promixity sensors or motion sensors can be customised for localisation,well if you wheels with spikes skidding wont be an issue of-course i am talking in terms of surface!!!
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  • Ashraf HZ

    Member • Mar 14, 2009

    Well, in terms of turning accuracy.. you can use compass modules 😀 Very easy to interface with microcontrollers.

    #-Link-Snipped-#

    At Sparkfun, its about $60, and has a 0.5 degree resolution.

    In terms of positioning, you can use the sensors that saurav has mentioned. However, I have not personally done any positioning systems for robots at all yet. I would use GPS for larger distances, but it is totally useless in a small playing field.
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  • momin

    Member • Mar 14, 2009

    i never knew that such digital compasses exist, i think they will sense the heading perfectly.
    in term of positioning, i was thinking roller mouse. a computer mouse will read the motion even if the wheels didn't spin. optical mice are an option too; what do you guys think.
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  • Ernesha

    Member • Mar 15, 2009

    yeah but i dont think the movement will be that smooth
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  • Ernesha

    Member • Mar 15, 2009

    bile robots are increasingly being used in high-risk rough terrain situations, such as planetary exploration and military applications. Current control and localization algorithms are not well suited to rough terrain, since they generally do not consider the physical characteristics of the vehicle and its environment. Little attention has been devoted to the study of the dynamic effects occurring at the wheel-terrain interface, such as slip and sinkage. These effects compromise odometry accuracy, traction performance, and may even result in entrapment and consequent mission failure. This paper describes methods for wheel slippage and sinkage detection aiming at improving vehicle mobility on soft sandy terrain. Novel measures for wheel slip detection are presented based on observing different onboard sensor modalities and defining deterministic conditions that indicate vehicle slippage. An innovative vision-based algorithm for wheel sinkage estimation is discussed based on edge detection strategy. Experimental results, obtained with a Mars rover-type robot operating in high-slippage sandy environments and with a wheel sinkage testbed, are presented to validate our approach. It is shown that these techniques are effective in detecting wheel slip and sinkage.
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