Best Steering / Frame / Tractor Combo -- for Robotic-Electric.

[Phil Timmons]

What about differentials on the articulated design?

Great question. Since this is not really a road type vehicle -- I was planning on just letting it slip.

Any real "pulling" will likely be in a straight line, and then no differential is really needed.

For a relatively "light" vehicle do you think this would be a problem?

I could use (4) smaller motors and split the drive axle, like with the Zero Turn. All of these were planned to be a couple of 5 HP, but I have some smaller motors around, too.

Since I was going to build the Zero Turn first, and the Articulated is sort of a couple of nose-to-nose Zero Turns, I could use two Zero Turns tied together as a test . . .

 

[MossRoad]

If you have an articulated 4 wheel drive machine (like I do), it has to be able to do this:

- sitting still, turn the steering all the way to the left.
- as it turns, the two left wheels roll towards each other as the two right wheels roll away from each other.
- now turn the steering all the way to the right.
- the two right wheels will start rolling towards each other as the two left wheels start rolling away from each other.

How are you going to accomplish that with 4 electric motors?

Plus, you then have to consider the rate of movement at any speed or direction.

 

[Xfaxman]

What about differentials on the articulated design?

Great question. Since this is not really a road type vehicle -- I was planning on just letting it slip.

Any real "pulling" will likely be in a straight line, and then no differential is really needed.

For a relatively "light" vehicle do you think this would be a problem?

----------------------------------------------------------------------

I don't know, my articulated machine is has differentials and is big and heavy:

 

[RickB]

Here is the First Draft on Zero Turn.

Comments, Suggestions, OMGs all welcome.

Here are some notes ==

+ Steering Caster may be too much -- maybe more vertical?
+ Drawn with 20 inch tires. Frame is spaced to handle up to 24 inches.
+ Drawn with 1:5 Sprocket Ratio == motor nominal RPM is 1200 RPM.
+ Bigger tires may be better -- however, the larger the diameter, the more I have to gear down the sprockets.
+ Maybe the Drive Wheels should be "Front?" Lets it climb over things easier.
+ Over all dimensions are just what turned out. Trying to keep width under 3 feet to let it get through narrow paths, doorway, gates, etc. Could cut length down to 4 feet -- just trying to prevent it from flipping backwards with a pulling load.

Add on Edit -- Brakes. I am planning on using VFDs as load regeneration to stop either or both motors -- BUT -- I see I still need Emergency and Parking Brake(s). Looks like the left and right split axles may be the place to put those.

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View attachment 701638
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View attachment 701639

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View attachment 701640

Caster angle isn't 45, it's zero. Measured through the center of the yoke shaft going up through the bushing mount in the frame.

 

[Phil Timmons]

If you have an articulated 4 wheel drive machine (like I do), it has to be able to do this:

- sitting still, turn the steering all the way to the left.
- as it turns, the two left wheels roll towards each other as the two right wheels roll away from each other.
- now turn the steering all the way to the right.
- the two right wheels will start rolling towards each other as the two left wheels start rolling away from each other.

How are you going to accomplish that with 4 electric motors?

Plus, you then have to consider the rate of movement at any speed or direction.

SUPER. Let me go down your list?

So for making this discussion practical, let me tag the tires?

Front Left = FL
Front Right = FR
Rear Left = RL
Rear Right = RR

================================

Now the tricks each motor can do.

All the motors are controlled by Variable Frequency Drives. This allows them to go fast, slow, stop, reverse, and either “coast” or even electrically brake, or stop and hold in a position. So let's say with 4 wheel independent drives.

Here are some general functions:

+ Fast Forward (travel) -- with a speed range up 1200 RPM – at 1:5 that makes a max axle RPM of 240 RPM. 20 Inch Diameter Tire at 240 RPM = 3.14 x 20 x 240 inches per minute, or about 14 Miles per hour (Max). Or about 17 Miles per hour, if 24 Inch Tires, like yours.

+ Fast Reverse (travel) -- the other direction, same thing

+ Slow Forward (for slow travel) this can go down to near zero.

+ Slow Reverse (for slow travel) again, down to near zero.

+ Bump Forward (mini pulses or turns to bump any tire forward)

+ Bump Reverse (mini-pulses or turns to bump any tire reverse)

+ Lock (hold its position)

+ Braking (slow the coasting motion, forward or reverse)

+ Freewheel -- since the Gear / Sprocket Ratio is low (1:5) it can reverse spin the motor in a free-wheel fashion.

==============================

Putting this all together . . . Scenarios – from your list . . . .

#1 - sitting still, turn the steering all the way to the left.
#2 - as it turns, the two left wheels roll towards each other as the two right wheels roll away from each other. (do you mean while traveling and in motion?)
#3 - now turn the steering all the way to the right. (I am going to assume, still traveling, as otherwise, this is same as #1, just switch the sides)
#4 - the two right wheels will start rolling towards each other as the two left wheels start rolling away from each other. (like #2, this is sort of a description, not really a function)

​	FL​	FR​	RL​	RR​
1​	Bump or Slow Reverse	Bump or Slow Forward	Can Freewheel	Can Freewheel
2​	Slow Forward	Fast Forward	Slow Forward	Fast Forward
3​	Faster Forward	Slower Forward	Faster Forward	Slower Forward
4​	Same	Same	Same	Same

 

[Phil Timmons]

Caster angle isn't 45, it's zero. Measured through the center of the yoke shaft going up through the bushing mount in the frame.

okay. I follow the pivot bearing is straight up and down -- but what about the ideal angle between the center bearing of the wheel, and where the bottom of the pivot is attached?

sample pictures >>> Caster - Wikipedia

 

[Phil Timmons]

I don't know, my articulated machine is has differentials and is big and heavy:

View attachment 702135

Thanks. Also you have the ability for the connections between the front and back section to swivel -- so all 4 wheels stay in contact with the earth on un-even ground.

I figured I might try to avoid that feature to start, but maybe I should do that, as well, as it will put less stress on the frame pivot bearing(s).

 

[MossRoad]

SUPER. Let me go down your list?

So for making this discussion practical, let me tag the tires?

Front Left = FL
Front Right = FR
Rear Left = RL
Rear Right = RR

================================

Now the tricks each motor can do.

All the motors are controlled by Variable Frequency Drives. This allows them to go fast, slow, stop, reverse, and either “coast” or even electrically brake, or stop and hold in a position. So let's say with 4 wheel independent drives.

Here are some general functions:

+ Fast Forward (travel) -- with a speed range up 1200 RPM – at 1:5 that makes a max axle RPM of 240 RPM. 20 Inch Diameter Tire at 240 RPM = 3.14 x 20 x 240 inches per minute, or about 14 Miles per hour (Max). Or about 17 Miles per hour, if 24 Inch Tires, like yours.

+ Fast Reverse (travel) -- the other direction, same thing

+ Slow Forward (for slow travel) this can go down to near zero.

+ Slow Reverse (for slow travel) again, down to near zero.

+ Bump Forward (mini pulses or turns to bump any tire forward)

+ Bump Reverse (mini-pulses or turns to bump any tire reverse)

+ Lock (hold its position)

+ Braking (slow the coasting motion, forward or reverse)

+ Freewheel -- since the Gear / Sprocket Ratio is low (1:5) it can reverse spin the motor in a free-wheel fashion.

==============================

Putting this all together . . . Scenarios – from your list . . . .

#1 - sitting still, turn the steering all the way to the left.
#2 - as it turns, the two left wheels roll towards each other as the two right wheels roll away from each other. (do you mean while traveling and in motion?)
#3 - now turn the steering all the way to the right. (I am going to assume, still traveling, as otherwise, this is same as #1, just switch the sides)
#4 - the two right wheels will start rolling towards each other as the two left wheels start rolling away from each other. (like #2, this is sort of a description, not really a function)

​	FL​	FR​	RL​	RR​
1​	Bump or Slow Reverse	Bump or Slow Forward	Can Freewheel	Can Freewheel
2​	Slow Forward	Fast Forward	Slow Forward	Fast Forward
3​	Faster Forward	Slower Forward	Faster Forward	Slower Forward
4​	Same	Same	Same	Same

Good grief you're making it so overly complicated!

Just use differentials and either 1 motor driving a transmission that drives both differentials, or two motors with one driving each of the differentials. Then you'll only have to match the speed between the two motors.

The way you have that set up in that chart, you'll be skidding wheels all over the place and/or it will be quite jerky.

 

[RickB]

okay. I follow the pivot bearing is straight up and down -- but what about the ideal angle between the center bearing of the wheel, and where the bottom of the pivot is attached?

sample pictures >>> Caster - Wikipedia

That angle is immaterial. You could build it any way you want and if the wheel axle is the same offset distance from the center of the pivot the wheel will act the same.

 

[Phil Timmons]

Good grief you're making it so overly complicated!

Just use differentials and either 1 motor driving a transmission that drives both differentials, or two motors with one driving each of the differentials. Then you'll only have to match the speed between the two motors.

The way you have that set up in that chart, you'll be skidding wheels all over the place and/or it will be quite jerky.

Yeah, it does sounds rough, but with just 8-bit control -- and usually using the first bit as Forward or Reverse -- that leaves 7 bits (or 128 levels) for speed adjustment.

So when you tell any given motor which direction to go, it might be [1xxx xxxx] for Forward, or [0xxx xxxx] for Reverse. And so like maybe Maximum Fast Forward would be [1111 1111]. Or half speed Reverse would be [0011 1111] -- it is just basic binary coding. Since the sensors also tell the actual rotation speeds of each wheel, this becomes a "Closed Loop" control and lets you know if things are slipping within Microseconds. Fastest Mechanical reactions are in Milliseconds, so the control system is about 100 to 1000x faster than the equipment can fight.

With 8 bits controllers, this is about a $25 Control System -- and it runs everything. And the control system is part of the overall system, because this is intended to able to tie back into a networked system.