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ROS will not work without wheel encoders?

asked 2015-12-21 16:51:48 -0500

tommytwoeyes gravatar image

Hello all,

Please forgive my ignorance. This is my first time building a robot using ROS, and I'm really, really eager to get it going.

I'm using the Wild Thumper 6WD platform/chassis with differential drive. Another user has just informed me that ROS will not work—that I won't be able to proceed with my robot build (as is my understanding of the implications of his statements)—without wheel encoders?

Is this true? Is there any part of the build process I can work on without having wheel encoders? The Wild Thumper chassis does not come with encoders out of the box, although they are available from Pololu. However the chassis itself was pretty expensive, for my student budget, ($250 usd) and while I was already planning to get a pair of those encoders, it will be several weeks, if not months, before I can afford to do so.

Please, any advice about how to proceed with other parts of the build that aren't blocked by a lack of wheel encoders (if it is, in fact, true that one can't build a working ROS robot without them), or any advice regarding work-arounds for this issue (if it is an issue), would be very much appreciated. Thank you in advance!

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answered 2015-12-21 18:11:18 -0500

ahendrix gravatar image

ROS is BIG, and there are a lot of different software packages within ROS. To say that you can or cannot use all of ROS without a particular piece of hardware is incorrect.

The core parts of ROS are pretty much hardware independent - you can install the core ROS packages on most x86 and ARM CPUs.

I'm not sure if there are packages that provide hardware support for your chassis or not; if you find those packages, they'll list any specific hardware requirements that they have, such as specific motors or encoders.

You will need encoders for closed-loop speed control and odometry.

Odometry is one of the key inputs to most of the localization and navigation packages in ROS, so it's generally recommended if you want to do navigation.

Without encoders or odometry, you can still write a ROS node which sends motor commands (open-loop), so that you can try driving your chassis using the standard ROS cmd_vel interface.

If you have a webcam or other sensors, you can also spend time setting up those sensor and getting their ROS drivers running.

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Thanks, that's good to hear. Based on the response I got from @Humpelstilzchen in the other post, I thought not having the encoders would preclude me from making pretty much any progress with this robot.

tommytwoeyes gravatar image tommytwoeyes  ( 2015-12-21 18:54:07 -0500 )edit

There aren't any ROS packages for the Wild Thumper per se, because it's just a bare-metal chassis. I'll try to find a package for generic motor control, and go from there. At any rate, I'm glad to hear I can at least keep making progress with this robot until I can get the encoders. Thank you!

tommytwoeyes gravatar image tommytwoeyes  ( 2015-12-21 18:55:39 -0500 )edit

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Asked: 2015-12-21 16:51:48 -0500

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Last updated: Dec 21 '15