pic: kiwi vex robot

[TheNotoriousKid]

how does it move forward

[Greg Perkins]

Originally Posted by TheNotoriousKid

how does it move forward

Magic. Hahaha, I'm kidding; actually there are three "omni-wheels" that are located at 120 degrees from each other, and due to the angle of the wheels, when two are driven the third acts as a caster. It's all got to do with the vectors of the machine, and since I do not know the formulas off the top of my head, I cannot explain it in full detail. If you want, search "kiwi drive" or "holonomic drive' on delphi here.

[Greg Needel]

colin,

does this mean you are going to enter the vex comp at the Ra Cha Cha this year?


Greg

[colin340]

it works like a champ with some code from Tom Bottiglieri it should be allot easier to control as for computation I will problem not but team 340 is working on starting a 9th grade team

thank you tom Bottiglieri and Greg Perkins for advise

[billbo911]

Originally Posted by colin340

it works like a champ with some code from Tom Bottiglieri it should be allot easier to control as for computation I will problem not but team 340 is working on starting a 9th grade team

thank you tom Bottiglieri and Greg Perkins for advise

With Tom's permission, could you possibly post the section of code that makes the magic work? PLEASE!!!!

[Tom Bottiglieri]

Originally Posted by billbo911

With Tom's permission, could you possibly post the section of code that makes the magic work? PLEASE!!!!

Well credit needs to be given where it's deserved. I got the equations for my kiwi code from the living genious, Joel Johnson.

Anyway, here's what you need to do to make it work:

PHP Code:

//Make sure variables are unsigned ints... rollovers WILL occur with signed ints
unsigned int trans_x, trans_y, rot;

//Grab inputs (x,y coords in rectangular coordinates and rotation rate)
trans_x = 254 - PWM_in1; 
trans_y = 254 - PWM_in2; 
rot = 254 - PWM_in4;      

//Limit vector length to 127
trans_x = (unsigned int)(37+(254*trans_x)/359);
trans_y = (unsigned int)(37+(254*trans_y)/359);

//Assign and limit wheel outputs
wheel_1  = (unsigned char)limit( (((2*trans_x) + rot) / 3), 0, 254); 
wheel_2 = (unsigned char)limit( ((601 + rot - trans_x - (168*trans_y/97)) / 3), 0, 254); 
wheel_3 = (unsigned char)limit( ((161 + rot - trans_x + (168*trans_y/97)) / 3) , 0, 254); 


This assumes you have a limit function, which limits an input value to upper and lower bounds.

PHP Code:

signed int limit(signed int value, signed int min, signed int max) 
 { 
      if (value < min) 
      { 
           value = min; 
      } else if (value > max) 
      { 
           value = max; 
      } 
  
      return value; 
 } 


That should be all you need, and it should work. (It took me about 2 hours to figure out the variables needed to be unsigned. )

[billbo911]

Originally Posted by Tom Bottiglieri

Well credit needs to be given where it's deserved. I got the equations for my kiwi code from the living genious, Joel Johnson.

Anyway, here's what you need to do to make it work:

PHP Code:

//Make sure variables are unsigned ints... rollovers WILL occur with signed ints
unsigned int trans_x, trans_y, rot;

//Grab inputs (x,y coords in rectangular coordinates and rotation rate)
trans_x = 254 - PWM_in1; 
trans_y = 254 - PWM_in2; 
rot = 254 - PWM_in4;      

//Limit vector length to 127
trans_x = (unsigned int)(37+(254*trans_x)/359);
trans_y = (unsigned int)(37+(254*trans_y)/359);

//Assign and limit wheel outputs
wheel_1  = (unsigned char)limit( (((2*trans_x) + rot) / 3), 0, 254); 
wheel_2 = (unsigned char)limit( ((601 + rot - trans_x - (168*trans_y/97)) / 3), 0, 254); 
wheel_3 = (unsigned char)limit( ((161 + rot - trans_x + (168*trans_y/97)) / 3) , 0, 254); 


This assumes you have a limit function, which limits an input value to upper and lower bounds.

PHP Code:

signed int limit(signed int value, signed int min, signed int max) 
 { 
      if (value < min) 
      { 
           value = min; 
      } else if (value > max) 
      { 
           value = max; 
      } 
  
      return value; 
 } 


That should be all you need, and it should work. (It took me about 2 hours to figure out the variables needed to be unsigned. )

Now I know why I like Tom (oh yeah, and Joe too ) so much!!

The problem is, now I have to go buy some omni wheels for this weekends project

BTW. Do you know how the constant values were determined (ie. 37, 359, 601, 168, 97, 161)? Also, I see you are using PWM_in4 for the rotation value. I assume this is off the left stick X-axis. Knowing these can help me modify this stuff for future projects.

Thanks again!!!!

[s_forbes]

I like that design! It's so compact and sturdy, good job!

[colin340]

Originally Posted by s_forbes

I like that design! It's so compact and sturdy, good job!

yes this is so much better then my old frame it's very stiff and compact

[billbo911]

I just got this working this morning. I tried for hours last night to code it with EasyC. Apparently doing the math wasn't so easy with EasyC. I'll figure it out later today. What you see it the video is coded with MPLAB in about 20 minutes.

Vex Kiwi Drive

[billbo911]

Originally Posted by billbo911

I just got this working this morning. I tried for hours last night to code it with EasyC. Apparently doing the math wasn't so easy with EasyC. I'll figure it out later today. What you see it the video is coded with MPLAB in about 20 minutes.

Vex Kiwi Drive

As I mentioned earlier, I was working on getting this coded using EasyC v2.0. Well I finally got it working. The math is the same, the process is a little different, but it works. Oddly, the bot works smoother with the code done in MPLAB than it does with the code from EasyC. Anyway, I'm attaching the .hex, .bds and .ecp files from EasyC in the hopes someone else can use them. They are in a .zip file, so download and do what you will with them.

[Francis-134]

Originally Posted by billbo911

As I mentioned earlier, I was working on getting this coded using EasyC v2.0. Well I finally got it working. The math is the same, the process is a little different, but it works. Oddly, the bot works smoother with the code done in MPLAB than it does with the code from EasyC. Anyway, I'm attaching the .hex, .bds and .ecp files from EasyC in the hopes someone else can use them. They are in a .zip file, so download and do what you will with them.

I noticed that your code uses a lot of custom c blocks to do the math. May I suggest using the "assignment" block, located in program flow in order to cut down on the labor. Perhaps it will work better as well.

[jgarbers]

Originally Posted by billbo911

What you see in the video is coded with MPLAB in about 20 minutes.

If I may ask - are you using the "Student Version" of the C18 compiler with MPLAB? If not, what compiler are you using? I'm trying to figure out what's appropriate to buy above and beyond what comes with the stock Vex Programming Kit... I've already bought the easyC v2 upgrade, but I'd like to be able to just edit source code.

Thanks!

[billbo911]

Originally Posted by jgarbers

If I may ask - are you using the "Student Version" of the C18 compiler with MPLAB? If not, what compiler are you using? I'm trying to figure out what's appropriate to buy above and beyond what comes with the stock Vex Programming Kit... I've already bought the easyC v2 upgrade, but I'd like to be able to just edit source code.

Thanks!

Excellent question.
I am one of the more impatient people in this world. I couldn't wait for the programming kit to be released through Radio Shack. So, when I found out that there was a possibility to purchase a prototype programming module directly from IFI , I jumped at it. It came with the cables, circuit board (unhoused) and a C-BOT CD which included MPLAB 7.0, C18 and IFI loader. These are all licensed to me and not part of my FRC teams programs. I have since then upgraded all three applications to the most current versions that work with FRC, and they still work with Vex. This allows me to use my laptop with the team to help them in programming and fiddle around with my Vex system as well.
I added EasyC when I bought the kit on sale, then later purchased the 2.0 upgrade. Now I can program in either environment. Honestly, I really like EasyC, it is amazingly powerful for a module based programming environment and is extremely easy to teach noobs the basics of robot programming. I can quite literally have a complete novice programming a Vex bot to work autonomously in less that ten minutes. On the other hand, MPLAB offers a lot more flexibility and advanced programming ability. I am not versed well enough in C to use MPLAB exclusively, but I have to admit, I can do some things in MPLAB much faster than I can with EasyC.
So, what do I recommend? Definitely keep EasyC. Only add MPLAB/C18/IFI Loader when you have mastered the use of EasyC and started running into limitations that require you to program directly in C. I know others will have different opinions, and listen to what they say as well. I base mine on my experience and knowledge level in programming. Weigh others opinions on their experience and ability as well. That will give you the truest measure of "What you should do".

[Joel J]

Originally Posted by billbo911

Now I know why I like Tom (oh yeah, and Joe too ) so much!!

The problem is, now I have to go buy some omni wheels for this weekends project

BTW. Do you know how the constant values were determined (ie. 37, 359, 601, 168, 97, 161)? Also, I see you are using PWM_in4 for the rotation value. I assume this is off the left stick X-axis. Knowing these can help me modify this stuff for future projects.

Thanks again!!!!

Here's the "documentation." Its in the PBASIC file that I used to program the KIWI drive 229 did a year or so ago.

'KIWI Code Overview
'------------------
'
'Vx, Vy, and w are on the interval [-127, 127], but the inputs p2_x, p2_y, p1_x are on the interval [0, 254], 
'so we compensate by setting Vx, Vy, and w to the shifted version of the input:
'
'	trans_x = p2_x
'	trans_y = p2_y
'	rot 	= p1_x
'
'	Vx = trans_x - 127
'	Vy = trans_y - 127
'	w  = rot - 127
'
'The kiwi system is characterized by the equation:
'
'	[ Vx ]		[  1	 	-1/2		-1/2	  ]	[ V1 ]
'	[ Vy ]	=	[  0		-sqrt(3)/2	sqrt(3)/2 ]	[ V2 ]
'	[  w ]		[  1		1		1	  ]	[ V3 ]
'
'	[1x3 matrx] = 	[3x3 matrix] * [1x3 matrix]
'
'where L is a length constant, Vx, Vy, and w are the system translation velocity components, and the system 
'angular velocity, and V1 is the wheel velocity vector at angle 0 degrees, V2 the wheel velocity vector at 
'angle -120 degrees, and V3 the wheel velocity vector at 120 degrees.

'
'Solving this system for V1, V2, and V3 yields the following equations of motion:
'
'	V1 = (2Vx	      + w) / 3
'	V2 = (-Vx - SQR(3)*Vy + w) / 3
'	V3 = (-Vx + SQR(3)*Vy + w) / 3
'
'(NOTE: These equations operate on the assumption that the magnitude of the desired velocity vector can be 
'no greater than 127. That is, the hypotenuse of the triangle formed by the trans_x and trans_y variable 
'cannot exceed 127. To ensure that this condition is met, one has to convert the rectangular 
'coordinates (trans_x, trans_y) into polar coordinates (V_desired, theta), limit V_desired to 127, then 
'back-calculate the new values of trans_x and trans_y based on the new value of V_desired and the already 
'existent theta. The code that does this has been placed exactly before this large block of text.)
'
'(NOTE: UPDATE! The Basic Stamp doesn't like the math required to make the previous note a reality, so I
'am using a crude solution: I scale down all input values by 127*SQR(2) to ensure that the largest vector 
'magnitude doesn't exceed 127.)
'
'The output from each equation (V1, V2, V3) is on the interval [-127, 127], but the desired outputs, 
'drill_1, drill_2, drill_3 are all on the interval [0, 254], so we compensate by setting drill_1, drill_2, 
'and drill_3 to the shifted version of V1, V2, and V3:
'
'	drill_1 = V1 + 127
'	drill_2 = V2 + 127
'	drill_3 = V3 + 127
'
'And that's it! Plug in all the variables, and we end up with the equations of motion that follow 
'(note: fractions were expanded out to compensate for the integer based calculation done by the stamp):

'Motion equations