Robotic drive & ste...
 
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Robotic drive & steering systems, (caster trike, steerable trike, steerable car, tank style)


WhitneyDesignLabs
(@whitneydesignlabs)
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I am starting this topic to discuss pros and cons of various conveyance and steering techniques. I have yet to execute any designs and fear I may be over thinking this. However, I know me, and once I develop a certain method, it will likely evolve and grow in size, and if I am forced to go back and start all over, it could take the wind out of my sails. So my thought is to learn and develop one style, and stick with it.

Over the years, I have collected a variety of gear motors, steppers, subassemblies and kits. My thought is to start with a smaller robot, then keep upscaling it, but with all core logic and code, more or less unchanged, just evolving and improving. I want to start with remote (radio) control, with eventual goal of autonomous.

I have the little "car" robot kits with the yellow wheels. Not wanting to leave well enough alone, and just build one stock.... My first thought on those, discard the trike castor design, morph two together, and make it 4wd, tank steer. Then I thought I should add tank tracks. This still hangs on pegboard, untested.

But then I came across an aluminum frame, bike-wheel, 80s vintage, electric trike chassis at the salvage yard, with built in differential. So now I am thinking of 2wd trike, with steering mechanism. I took the time to completely model this frame, wheels, and gear ratio in SolidWorks. That is as far as I got.

Then I came across the motor, axle, differential and wheels from a mobility scooter, at the salvage yard. So now I am thinking smaller steerable trike to test, first. Then later upsize it to the the 80s bike trike platform.

Then I started to think about pros and cons of tank steering vs trike or traditional car steering. Tank (what its the technical name for this kind of mobility and steering?) style vs front steering wheel(s). Presumably tank style is far less efficient, but better traction for uneven surfaces. I may want this project to eventually evolve to a 4 wheel electric vehicle.

Then it occurred to me, what if we had a trike style, with differential (single rear motor), a steering motor, and then made the front steering wheel power driven, too. So 3 wheel drive, with traditional trike steering. If we could turn the steering motor/wheel 90 degrees, and then drive only the front wheel, we could turn almost in a circle, not quite like a tank, but rotating around center of rear axle.

Then I had a thought, what if we used the front drive motor of said 3wd trike, for regenerative braking, when needed.  Run rear and front motors for normal use, and in normal corners. And run only front wheel to make very tight turn arounds. Would this be the least compromised, best of all worlds? Short turning radius, more efficient than tank style, and regenerative braking as well.

Again, my thought it to start small, maybe bench top test robot, and get bigger as the project grows, with eventually possible human cargo.

How difficult are the autonomous steering algorithms for tank style, vs steered front wheel(s)?  For pure human radio control, who cares. But I want the mechanical platform to be compatible with future AI and autonomous functions (not just line following, but GPS, LIDAR, collision avoidance, waypoint navigation etc). 

Obviously, this is a LONG term project, or series of projects. But I want to tip toe down the correct path from the get go. 

Thoughts?

PS.  other than in the title of this post, I forgot to bring up the caster style trike, using two rear motors, which, the way I consider it, is essentially the same as "tank" style driving.

PPS. I forgot to mention, I have the 48v front drive wheels from a GEM electric car (the ones you always see in Sci-fi movies) in my shed. So this re-purposed drivetrain might become the biggest iteration of everything mentioned above.

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WhitneyDesignLabs
(@whitneydesignlabs)
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Joined: 8 months ago
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Topic starter  

Some pics for reference.

robot1
robot2
robot3
robot4
steeringmotors

 I didn't refer to the last picture in my post above, but it is my bin of steppers and DC gear motors to choose from for the steering motor.

BTW, the GEM motor axle assembly is unique in that the GEM cars were front wheel drive and front wheel steering. If you look closely at the pic, you can see the wheels turn like a normal car, but are electrically driven drive wheels, also. Could be an interesting build....(it is a terrible picture, sorry...if anyone is interested, I will drag it out of the dirt, and line it all up straight, so you can visualize its operation better)

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robotBuilder
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@whitneydesignlabs

I personally don't like those flimsy yellow toy robots. A medium sized robot can potentially do useful stuff beyond testing sensors and AI and there is plenty of room to add things.

My robots use a laptop controller and thus are remote control from the get go via a wireless keyboard or remote LAN or internet control from another computer. I can use the on board webcam to control it visually when it is out of sight.

The ideal robot base would be a small second hand (or new if you can afford it) electric wheelchair. It comes with all the electronic motor control circuits and battery charger.

From decades of experience:  Trying to build a robot base out of junk parts is a sure way to take the wind out of your sails and can in the long run cost you a lot more money than doing it right the first time.

If the robot is going to work on a farm then you would go for the four wheeled vehicle.

Most of the work is 99% software and is the part most hobby robot projects never really get to and yet it costs nothing but time and the ability to program.

IMHO

 

 

 

This post was modified 7 months ago by robotBuilder

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WhitneyDesignLabs
(@whitneydesignlabs)
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Posted by: @robotbuilder

The ideal robot base would be a small second hand (or new if you can afford it) electric wheelchair. It comes with all the electronic motor control circuits and battery charger.

I agree. You are going to kick me.... Our local DAV thrift store recently had one of those 4wd wheel chairs, for $500. (retail about 12-15k USD) Only issue was dead batteries. I drooled, and kicked the tires, but didn't have $500 to spare. And it sold. Consolation is that a limited-mobility human is now actually using it.

From decades of experience:  Trying to build a robot base out of junk parts is a sure way to take the wind out of your sails and can in the long run cost you a lot more money than doing it right the first time.

Point taken. I think junk parts are my strong point. I have sought out stuff like this, as a kid, way before I had access to microcontrollers, as an adult. Money I don't have, but the electronics are now a drop in the bucket. And the tinkerer in me wants to make neat stuff from old bits and bobs. I am also somewhat driven to upcycle stuff, philosophically, and save it from the landfill, or melting furnace.

If the robot is going to work on a farm then you would go for the four wheeled vehicle.

Not farm, but ideal operation could handle unknown, rough terrain, snow, rain etc.

Most of the work is 99% software and is the part most hobby robot projects never really get to and yet it costs nothing but time (and brains).

Duly noted. Hence why I want to start development on a platform that can grow and evolve, but the fundamentals are unchanged.

IMHO

Thank you. I will spend some time reading your posts and learn more about your robot projects.

 

 

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robotBuilder
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@whitneydesignlabs

 Consolation is that a limited-mobility human is now actually using it.

Something I have thought about when looking for a used electric wheel chair.

Really I think the needy should be given a nice new one 🙂

 

This post was modified 7 months ago by robotBuilder

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