Tri-wheeled Omni-bot – Update II

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Peter McKinnon from Rotacaster pointed out from looking at my last update the  I’ve managed not to take into account that for proper Rotacaster Omni-wheels action to work on myOmni-directional robot, the wheels have to always remain parallel to the ground. When the legs were raised & lowered independently, or together  the wheels where never parallel to the floor. My initial response to Peter was thank you for bringing it to my attention & it will be an easy fix.

How wrong I was!


Omni-Bot Mark II Raise Up

Yes, I initially thought a quick half-hour mod would do the Trick but this failed completely and introduced a number of new problems. It was amazing the difference with the way the arm behaved in and out of the bot. After about 10 hours of bad language I decided to ditch the old leg design & try again. This resulted it the wheels contact surface remaining parallel to the ground at all times, but because I had to introduce another universal joint and a set of knob gears the result was a lot of noise and very unreliable movement.


Omni-Bot Mark II Lowered Down

In the end, I completely demolished the original robot and started afresh. After a lot of experimentation I decide to also ditch the shaft and universal joint drive for the wheels and go for a direct drive solution. The result is a bot that tracks well without and horrible noised and the wheels remain at an optimum to the ground, no matter the height the Robot Body is from the ground. This new version is also stronger and the Arms function better as well. The new Omni-Bot Mark II is also a 100mm wider when lowered to the ground compared with the Mark I version.

To finish the Omni-Bot Mechanically and Electronically, I am waiting on a few parts to arrive. The most important is the Lego version Rotatacasters which will enable it to move in other directions besides in a circle as it does now. I am also waiting on some PowerFunction XL-Motors to replace the M-Motors presently being used. This will increase the torque available to raise and lower the legs and hopefully I can gear the drive up to improve the speed of movement. I considered using a second NXT Brick and three NXT Motors, but wait is a consideration so I’ve decide that the PowerFunction parts are they way to go. It also makes programming a little easier. I am also waiting on some extra PowerFunction Infra-red Receivers so I can independently control each arm.

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