V Rex won't walk forward, tips over

I recently tried to build the Vex IQ V Rex. At first, I had a hard time with steps 100 and 108, connecting parts of the leg, but I was able to “fix” that. Now, when I run it, the robot won’t walk forward. The legs move, but the whole things tips forward.

Any ideas in terms of what I may have done wrong, or how I could try to fix it? Thanks.

Hi RawlingsCFA,

We’re sorry that you have encountered this problem. V-Rex uses a unique leg geometry design - the linkages for each leg need to be oriented exactly opposite to each other. If the linkages are not angled exactly opposite to each other, the legs will not be synchronized and V-Rex may fall over while attempting to walk.

The most important detail to check are the angle orientation of the four 1x3 Shaft Lock Beams that power the leg linkages. These need to be carefully aligned to each other to ensure the legs walk properly. I have attached a photo, with these parts highlighted, showing correct orientation of these parts.

The important detail is the angles of the 1x3 Shaft Lock Plates are the same on the left and right legs, but that the left and right legs use the exact opposite mounting holes. For example, the front 1x3 Shaft Lock Beam on the right side is attached to the leg using the top hole, while the front 1x3 Shaft Lock Beam on the left side is attached to the bottom hole.

A higher resolution version (without the added text) of the attached image is available here:

If you have any additional questions, please feel free to contact our technical support folks at support@vex.com or by calling +1-903-453-0802 for additional assistance.


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    V-Rex - Orientation of 1x3 Shaft Lock Beams for proper leg movement - 950px.jpg