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Topic: traction drive and steer concept (Read 1 time) previous topic - next topic

brywisco

Hi, please be forewarned that I am a complete newbie to arduino and am a mechanical engineer with just enough electrical knowledge to be dangerous. I am looking for some feedback to see if the arduino is something I might consider for an industrial control scenario.

That said, I am working on a design concept for a system to move loads that are on carts with casters. My idea is to use a single wheel that will both drive and steer the load. Picture a unicycle with 1 motor driving the wheel and a 2nd motor driving rotation of the seat-post. I hope that makes sense....
One vision I have is that the operator would use a 2-axis joystick to control the system. The drive wheel will always start from a 'home' position and we can define this as the wheel is pointed at 12 O'clock. If the operator simply wants to move the load straight forward, then he pushes the joystick straight forward and then fwd rotation power is applied to the wheel with no steering required. If a turn is initiated via joystick while the load is in motion, the steering motor would rotate the post to the required angle while the traction wheel is still doing its thing.
Now suppose the load is fully stopped and the wheel is back to the 12 O'clock steering home position. The operator now needs to pivot the load hard to the right (no fwd movement) so he/she pushes the joystick to the 3 O'clock position. In this case I picture that the steering motor would need to drive the wheel around to like the 3 O'clock position and THEN fwd drive could be applied to the traction motor.

The traction motor will have its own controller and will be looking for fwd/rev and analog speed signal. The steering axis would need to be a servo or stepper driven system. I am curious as to the feasibility of using an arduino as the controller to manage such a system. I really appreciate and look forward to hearing your input, suggestions, criticisms, etc.

WillR

#1
Mar 29, 2011, 05:24 pm Last Edit: Mar 29, 2011, 05:34 pm by WillR Reason: 1
This would make more sense in the Robotics forum. But sure -- why not?

Let me add this note:

Your questions are well thought out and specific -- so why not put them here?  :smiley-mr-green:
http://arduino.cc/forum/index.php/board,14.0.html

brywisco

Thanks, I have a controller pretty much for the traction motor, but I am hoping for some advice on the steering axis.
Note that this will likely be a 24V battery powered system.

TerryKing

Hi @brywisco ,

I think you have questions of an overall systems nature...

You have a couple of motion control systems. 

You have a human interface, probably both human input and real-time driving control, and possibly vehicle parameter display

You may have monitoring and control of vehicle power systems.

You might have location/navigation/collision-avoidance system interfaces.

You might have communications subsystems of some kind.

So the question, to start, may be "Is Arduino suitable for the system controller for such a vehicle?"

You probably need to outline the things that may restrain such a system:
- Number and types of interfaces to other devices and subsystems
- Computational requirements:
  - Program memory space
  - RAM and EEPROM memory space
  - Computational speed
- Availability of software libraries for most interfaces and functions

So, think about this stuff and continue the discussion??

A sketch of the vehicle and the degrees of freedom of the carts and overall vehicle would help...

You could start a subsidiary to market Arduino Bumper Cars  :smiley-roll:

brywisco

Hi Terry,

Now we're talking details!

The system in its most simplistic form will likely consist of the following:
24V battery pack - rechargeable
24V brushless 'hub' motor and its controller (traction drive)
24V stepper motor and maybe a gearbox (steering drive) - not sure about the power this will require yet, I am guessing about 3-8 amps(?)
    Note - I am also a little unsure about the need for an encoder on the steering drive.
24V linear actuator(s) - to couple the unit to the load itself
Load holding brake (releases when drive command is received from the joystick)
2-axis analog joystick
Control switches - yet to be fully defined, but for such things as on/off, enable, hitching, safety lanyard/ e-stop etc...
LED's - to indicate state of system (ex. on/off, enabled, hitched, issues, etc.)
Traction drive speed adjustment - for on-the-fly adjustment of driving speed for operator ease

The operator would dock the unit to the load and activate the hitching mechanism (electric actuator).
Once hitching is OK, the operator could move the load in any direction using the joystick. The operator would walk along with the load and guide it as needed.


This is still a somewhat 'top secret' project so I really do not have permission to post the actual prototype design drawing here. The first prototype will use manual steering (handlebar) and a simple thumb-type pot as the throttle. It will employ the 24V brushless hub motor for the traction drive. This will allow me to test and proof the overall concept and gather more detailed power data (like steering torque etc.). The prototype will also be manually hitched to the load at first.


TerryKing

OK, starting to get the picture. Operator walks.

?? Does the powered unit always PULL the cart on casters? Don't see how it could control pushing...

How many wheels / configuration does the power unit have?

OK: Late in Saudi Arabia -- back tomorrow...

brywisco

The unit will be able to push or pull the load due to swivel casters on the end we are hitched to and rigid casters at the far end of the cart. The hitching is analogous to actually bolting this drive unit to the cart, not merely a trailer hitch type system.

There will be a single wheel doing all the work (traction drive and direction - kinda like a unicycle arrangement) with a set of 'training wheels' to keep the whole mess upright when it is being wheeled around disconnected from a loaded cart.

brywisco

Well I am still scratching my head over this application.
I have at least ordered an Arduino Uno starter kit pro pack and book to start the learning curve.
I have also been looking at any info I can find on controlling stepper motors with a joystick. I understand the basic concepts, but am a little unsure at this stage exactly how much torque I will be needing. I do know I will probably need to be able drive a stepper in the neighborhood of 5A.
The interesting part will be programming the 'mixing' between traction drive and steering.
For example: say we are cruising along straight ahead at walking speed, and then throw the joystick full left or right. I wonder if it would be advisable in this case to have the controller back off the traction speed a bit before turning the wheel. This is making my head hurt. I need coffee now.

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