Jonathan Oxer
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Blog > Terran Rover: steering success!
>> Terran Rover: steering success!
Fri, Feb 27th 8:53am 2009: Tech Toys
You know that moment that comes while you're in the process of modifying something, and you put the cutters around the piece of plastic or wire or whatever, and just before you squeeze the handle there's a flash of "anticipatory buyers remorse" where you realise you're about to do something irreversible? No? Oh well, maybe it's only me. The original steering mechanism used a steering arm that was quite long with a cam on the servo to move it, providing significant mechanical advantage. The new servo I've put in though is incredibly powerful and doesn't need any extra leverage so I cut up a new servo horn and the original steering control arm and combined them into a custom horn that will move the steering rods directly. The problem is that the forces involved are rather large and the pieces I had to join are rather tiny so I was worried that they wouldn't hang together. In the end I clamped them together in the right place and cross-drilled with a 0.95mm PCB drill, then screwed them together with the smallest bolts you've ever seen in your life:
I put in two bolts in each direction then snipped off the excess length with wire cutters. They are seriously small: think about the diameter of a dressmaker's pin, and even that's bigger than one of these. I then covered the bolt ends with Araldite, which I also put all around the joint edges. I would have liked to get it between the plates but it wasn't possible to do that and still bolt it.
This morning before work I attached the horn to the servo and fitted the steering rods. This shows the steering assembly upside-down before the bottom cover was fitted:
Then with the cover fitted it all looks exactly like it did from the factory, except that now it's using a standard servo that I can control directly from a PWM output of an Arduino.
I plugged it in and ran a loop on the Arduino to swing the steering from side to side. Success!
Next I need to reassemble the chassis with the steering and I'll be ready to start fitting sensors.
You know that moment that comes while you're in the process of modifying something, and you put the cutters around the piece of plastic or wire or whatever, and just before you squeeze the handle there's a flash of "anticipatory buyers remorse" where you realise you're about to do something irreversible? No? Oh well, maybe it's only me. The original steering mechanism used a steering arm that was quite long with a cam on the servo to move it, providing significant mechanical advantage. The new servo I've put in though is incredibly powerful and doesn't need any extra leverage so I cut up a new servo horn and the original steering control arm and combined them into a custom horn that will move the steering rods directly. The problem is that the forces involved are rather large and the pieces I had to join are rather tiny so I was worried that they wouldn't hang together. In the end I clamped them together in the right place and cross-drilled with a 0.95mm PCB drill, then screwed them together with the smallest bolts you've ever seen in your life:
I put in two bolts in each direction then snipped off the excess length with wire cutters. They are seriously small: think about the diameter of a dressmaker's pin, and even that's bigger than one of these. I then covered the bolt ends with Araldite, which I also put all around the joint edges. I would have liked to get it between the plates but it wasn't possible to do that and still bolt it.
This morning before work I attached the horn to the servo and fitted the steering rods. This shows the steering assembly upside-down before the bottom cover was fitted:
Then with the cover fitted it all looks exactly like it did from the factory, except that now it's using a standard servo that I can control directly from a PWM output of an Arduino.
I plugged it in and ran a loop on the Arduino to swing the steering from side to side. Success!
Next I need to reassemble the chassis with the steering and I'll be ready to start fitting sensors.[ Back to top ]
