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by jwatte
Replies
9
Views
193

### Re: Dumb Idea: So like... what about jumpjets?

If you could actually bring that to the competition, all the drinks and food for you are on me for the duration.
No matter that open fire is against the rules and nobody would actually compete...
2. ## Thread: Parallel Robot kinematics

by jwatte
Replies
5
Views
165

### Question(s)Re: Parallel Robot kinematics

You say numerical analysis, but do you have trigonometry? Linear algebra? Calculus?

Assuming you know how to project from 3D to 2D (project along plane normals) the what you do is calculate the 3D...

by jwatte
Replies
9
Views
193

### Re: Dumb Idea: So like... what about jumpjets?

Funny you should say that ... I did the math on it a couple of years back, and I could strap two EDFs with angled actuators, AND a battery big enough to run them for a total of 40-60 seconds, onto...
4. ## Thread: Mech Warfare at Bay Area Maker Faire 2019

by jwatte
Replies
23
Views
3,584

### Re: Mech Warfare at Bay Area Maker Faire 2019

I just received the registration link by email (thanks, guys!) but I don't know when the last possible date is.
5. ## Thread: Parallel Robot kinematics

by jwatte
Replies
5
Views
165

### Question(s)Re: Parallel Robot kinematics

So, at the top there are three single-axis rotational joints, each set 120 degrees apart. They each establish a plane within which each "femur" rotates.

Then each femur has a parallel linkage of...
6. ## Thread: Parallel Robot kinematics

by jwatte
Replies
5
Views
165

### Question(s)Re: Parallel Robot kinematics

What, specifically, do you need help with? Do you have a sketch of the links and actuators?

In general, if you have 4 DOF but want to constrain 6 DOF (position + orientation) you're screwed,...
7. ## Thread: PhatomX with XL430-W250 servos

by jwatte
Replies
17
Views
2,634

### Re: PhatomX with XL430-W250 servos

No, I have not played with the data sendback. I look forward to hearing what you find!

by jwatte
Replies
1
Views
289

### Question(s)Re: Denavit–Hartenberg parameters

I just multiply out the transforms from the root using 4D matrices (graphs/physics-simulation style,) so I don't use that convention.
Also, I express the transforms using identity in the "servo is...
9. ## Thread: PhatomX with XL430-W250 servos

by jwatte
Replies
17
Views
2,634

### Re: PhatomX with XL430-W250 servos

Yes, that's correct! You should put in 3.3V to 5V on the red wire, ground on the black wire, and you will get out UART at 115200 bps, 8 bit bytes, 1 stop bit, no parity.
The protocol itself is easy...
10. ## Thread: More Mule then Rover?

by jwatte
Replies
247
Views
83,588

### ProjectRe: More Mule then Rover?

It's a robot controlled lift! Stylish!
11. ## Thread: How to use nrf24l01 wireless module with Arbotix-M Robocontroller & Arduino Mega 2560 r3 to communicate between each other?

by jwatte
Replies
3
Views
620

### Re: How to use nrf24l01 wireless module with Arbotix-M Robocontroller & Arduino Mega 2560 r3 to communicate between each other?

You need to make the appropriate connections to the NRF chip, which includes the SPI bus and the chip-enable signal.
Any available digital pin "ought" to work for Chip Enable -- it's a low-bandwidth...

by jwatte
Replies
3
Views
882

A status packet is a response with zero data. They're pretty much the same thing.
A command packet and an instruction packet are names for the same thing, too.

It can't possibly be the case that...

by jwatte
Replies
3
Views
882

I would not expect ser.readline() to return a proper response. The response packet has a very similar format as the command packet, and needs to be appropriately decoded.
14. ## Thread: Sync_write to multiple servos

by jwatte
Replies
3
Views
539

### Re: Sync_write to multiple servos

Is the problem in the servos, or with the board/sketch?
Is this a buffer overflow problem in the "serial tosser" code?
If you hook up a scope/logic analyzer to the servo TTL bus, does the 10+...
15. ## Thread: PhatomX with XL430-W250 servos

by jwatte
Replies
17
Views
2,634

### Re: PhatomX with XL430-W250 servos

https://github.com/jwatte/donkey_racing/blob/master/teensy_hat_firmware/FlySkyIBus.h
It's ten 16-bit integers with some surrounding framing information.

by jwatte
Replies
34
Views
14,193

### Re: Numa V2 - Quad Mech

Peanuts incoming:

For Onyx (RIP) I defined a "standard leg" where the coordinate system is "forward/back," "out/in," and "up/down."

The IK solution then runs in terms of this standard leg, and...
17. ## Thread: Cobot Research and Development

by jwatte
Replies
1
Views
468

### Re: Cobot Research and Development

Looks awesome!

Make it bus away the table once it's empty, perhaps?

Sing and dance for birthdays? (and serve/cut cake?)
18. ## Thread: Mech Warfare at Bay Area Maker Faire 2019

by jwatte
Replies
23
Views
3,584

### Re: Mech Warfare at Bay Area Maker Faire 2019

I would love STL files!
Do these mount to the Double Eagle AEGs, or some other kind?
19. ## Thread: More Mule then Rover?

by jwatte
Replies
247
Views
83,588

### ProjectRe: More Mule then Rover?

That sounds exciting!

Curiousity killing cats:
How is the "L" part attached? Welded?
How thick is the plate that the bolts go through?
20. ## Thread: Mech Warfare at Bay Area Maker Faire 2019

by jwatte
Replies
23
Views
3,584

### Re: Mech Warfare at Bay Area Maker Faire 2019

Yeah, some kind of light preload on the feed seems needed. The design I've been using seemed to have a 10-15% dry fire / false load rate.
The twisty 1/4" spring feed seemed alright, although I don't...
21. ## Thread: PhatomX with XL430-W250 servos

by jwatte
Replies
17
Views
2,634

### Re: PhatomX with XL430-W250 servos

The U2D2 (and, to be fair, the USB2AX,) both are kind-of expensive for what they are: A \$2 chip on a board with some connectors.
Sure, the market might be only a few hundred, so you'd need a fair...
22. ## Thread: PhatomX with XL430-W250 servos

by jwatte
Replies
17
Views
2,634

### Re: PhatomX with XL430-W250 servos

I've had great luck with the FS-i6S controller/receiver: https://amzn.to/2T7pP5J The receiver actually spits out a simple protocol of reveived data over serial port, so you don't need to decode the...
23. ## Thread: How can I connect ROS with Unreal engine?

by jwatte
Replies
1
Views
925

### Question(s)Re: How can I connect ROS with Unreal engine?

I've only created Unreal plugins in Visual Studio. There, the integration is actually very nice.

I imagine if you have an exposed function in your plugin and you can call it from Blueprint, then...
24. ## Thread: More Mule then Rover?

by jwatte
Replies
247
Views
83,588

### ProjectRe: More Mule then Rover?

Interesting!

How do you figure out where the main flex is coming from? Do you have video from the sides while it's doing it?
25. ## Thread: More Mule then Rover?

by jwatte
Replies
247
Views
83,588

### ProjectRe: More Mule then Rover?

Only one way to settle this: Build TWO snow plowing mules, one with an aluminum bracket, and one with steel, and measure what the relevant bracket lifetimes are under equivalent workloads!
...
26. ## Thread: More Mule then Rover?

by jwatte
Replies
247
Views
83,588

### ProjectRe: More Mule then Rover?

Sure, aluminum will fatigue and break, but, you know, they make airplanes out of it. With enough safety margin, you'll be fine :-)

Anyway, if he wants to make another bracket because he enjoys...
27. ## Thread: More Mule then Rover?

by jwatte
Replies
247
Views
83,588

### ProjectRe: More Mule then Rover?

It's the torque, more than the power, that matters for your bracket. Think of it this way: A motor that is stalled develops zero power (at the shaft) but develops a lot of force at the mount!
You...
28. ## Thread: How to change the speed of the AX12a and Read its current speed ?

by jwatte
Replies
3
Views
647

### Re: How to change the speed of the AX12a and Read its current speed ?

The value range is documented in the manual for the servo. I don't remember the exactly values, but because it's a 2-byte register, the value range is higher than 0-255.
The "_L" and "_H" are the...
29. ## Thread: torque control for ax 12a

by jwatte
Replies
4
Views
831

### Question(s)Re: torque control for ax 12a

Yes, almost all motors of this kind have a continuous duty rating of 20-25% of the maximum instantaneous rating. It's a fact of physics.

30. ## Thread: Mech Warfare at Bay Area Maker Faire 2019

by jwatte
Replies
23
Views
3,584

### Re: Mech Warfare at Bay Area Maker Faire 2019

That's 10 minutes from where I live and 5 minutes from where I work, so ... yeah, I'll have to be there. I'll borrow my daughter's AX-12 based 'mech. (Onyx has donated too many pieces to be...
31. ## Thread: C program for AX

by jwatte
Replies
3
Views
748

### Re: C program for AX

Yes, a zero bit is sent as wire-to-ground on the TTL UART bus. It works fine to wire a microcontroller UART straight to the servo, EXCEPT when the servo tries to send a response back, the...
32. ## Thread: XL430-W250 Stop moving randomly

by jwatte
Replies
6
Views
1,223

### Re: XL430-W250 Stop moving randomly

Are you sure it's the motor? If so, is it signaling an error? (Not reading status back is in general a bad habit, because it makes debugging harder.)

If you hook up a scope or logic analyzer on...
33. ## Thread: Dynamixel MX-64T Torque control with Arbotix

by jwatte
Replies
2
Views
709

### Re: Dynamixel MX-64T Torque control with Arbotix

Have you enabled torque with register 24?
34. ## Thread: torque control for ax 12a

by jwatte
Replies
4
Views
831

### Question(s)Re: torque control for ax 12a

If the servo cannot get to the desired goal, it will generate an error to tell you this. The practice of "set a goal position that is not achievable" is not generally useful for controlling these...
35. ## Thread: XL430-W250 Stop moving randomly

by jwatte
Replies
6
Views
1,223

### Re: XL430-W250 Stop moving randomly

Not really. The main question is if you have command response turned on; if so, you may have to wait for a timeout if the servo didn't get the packet (because sometimes it's slighlty slow to...
36. ## Thread: Puppet Master/ Slave setup

by jwatte
Replies
4
Views
1,097

### Re: Puppet Master/ Slave setup

Is the theory that you have two robots, one to capture the pose, and one to play it back?
That would require software.
The user "tician" on this board used to support a graduate art program that...
37. ## Thread: Sinusoidal Servo control using MATLAB

by jwatte
Replies
3
Views
850

### ProjectRe: Sinusoidal Servo control using MATLAB

I don't know how fast Matlab can run -- can it run at 100 Hz itself? If not, then you're going to have to live with whatever it can do ...
38. ## Thread: Sinusoidal Servo control using MATLAB

by jwatte
Replies
3
Views
850

### ProjectRe: Sinusoidal Servo control using MATLAB

The best you can do is to send a very high speed stream of updates -- say, 100 Hz -- for where you want the position to be.

Let the control algorithm and damping inherent in the servo then drive...
39. ## Thread: Puppet Master/ Slave setup

by jwatte
Replies
4
Views
1,097

### Re: Puppet Master/ Slave setup

The RoboPlus software that comes with the Dynamixel series of servos can do some of those things without programming.
You have to read the instructions, which are sometimes hard to just FIND, and...
40. ## Thread: Dynamixels AX-12A on OpenCM 9.04 + OpenCM 485: how to send instruction packets

by jwatte
Replies
3
Views
840

### Question(s)Re: Dynamixels AX-12A on OpenCM 9.04 + OpenCM 485: how to send instruction packets

Here's my setup code for OpenCM 9.04:

void DxlIO::begin() { afio_remap(AFIO_REMAP_USART1);
afio_cfg_debug_ports(AFIO_DEBUG_FULL_SWJ_NO_NJRST);
gpio_set_mode(PORT_TXRX_DIRECTION,...
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