Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: pomprocker on January 13, 2009, 01:39:26 PM
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I just had an idea come to mind regarding my caster problem I've had for a while.
I have a round robot base, with 3.5" foam wheels on both sides. On the front and rear I have omniwheel casters.
Here is an out of date 3d model:
(http://a41.ac-images.myspacecdn.com/images01/19/l_e01f8d4cbec864d4ef6f4c47ef29a748.jpg)
The problem was the suspension. I read up on Admin's one-piece suspension tutorial, but that won't work for me, because I really don't have the resources to design something like that, and besides my robot is truly in development, and the weight will be ever changing.
The second thought I had was to use an R/C suspension type system. But that is to complex, and requires engineering.
I ended up coming up with something on my own using small compression springs, and a long bolt, and that was a flop!! total garbage.
Then I just had this idea of a way that the robot itself could control the height of it's own casters. It would also be able to 'lean' forward and backward.
The idea:
One could mount two servos, one in front and one in back with sail arms.
The servos would have to be strong enough to hold the weight of the robot when leaning, and fast enough to catch itself if need be (that way if both casters are in the up position, then it would be using its balancing functionality) The servo arm would also have to be strong in that not only to support weight, but when the robot is turning it will exert forces on the sides trying to bend the arm.
Also, if a gyro/imu/accelerometer is also used, the robot can tell when it is level, and if not it can level itself with these omniwheel casters on a servo.
Another thing, if the designed weight of your robot in development increases, you just upgrade the servos and servo arm.
Does anyone know of any servo and servo arm specs that would be a could starting point for me? My robot base has a 9" diameter btw. not sure how much it weighs. I do however plan on stacking it and adding two arms, and a robot vision system.
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Hi,
If you move the centre of gravity (CG) towards one "end" where a caster is placed, you can skip the suspension. Suspension is good for keeping friction on all 4 wheels (or 6 or more) but it won't change it's driveability in a significant way, assuming the average slow speed of <6 km/h.
Better to move eg. the battery pack around, to keep the CG in check on steep inclinations.
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On the front and rear I have omniwheel casters.
You don't want both caster wheels to contact the ground at the same time. Make it so one is just a few millimeters higher than the ground. You'll get a bit of rocking, but you won't need the suspension system.
Or use velcro/foam tape to attach your caster wheels. The give from this loose connection will give a slight suspension.
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so you don't think it would be useful to have front and rear casters height controlled by servos (with servo savers) ?
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Hi,
Here's a bit of text for you: http://That.Homepage.dk/PDF/Suspension.pdf (http://That.Homepage.dk/PDF/Suspension.pdf)
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Thanks that was a good read...now if what i am thinking is correct, giving the robot the ability to learn forward and back would also shift its CG correct?
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Yes, but if it's just a couple of mm, it wont matter much, as you won't be able to climb steep hills with a design like yours anyway - just keep the heavy stuff low and "centered".