6 ms·

Inside Haddington Dynamics and Their Groundbreaking Dexter Robot Arm

102 points by tlrobinson 8y ago

bitwize 8y ago
> There are no billionaire tech entrepreneurs riding Segways to meetings with angel investors, and there are no corporate PR-approved mission statements on the wall. Instead, you’ll find a small team of brilliant engineers who are using passion and innovative technology to design a very special robot called Dexter. That's, uh, that's exactly what a state-of-the-art robotics lab is supposed to look like. I used to work in one; place was a mess. Then they closed some big sales, moved to a shiny new facility -- and promptly got worse, that is, worse if your goal is to actually work on cool robots rather than edit elaborate specs on theoretical robots to get Major Defense Client to sign the contract.
neaanopri 8y ago
Haddington's arm is 5-axis, which is not enough to put a tool in an arbitrary position and orientation. To put a tool in an arbitrary position (3 DOF) and orientation (3 DOF), a 6-axis arm is needed. If their encoder technology is so good, why aren't they making a 6-axis arm and going right up against Universal Robotics? I'm not certain about this, but I believe that their arm does not have a final rotary actuator on the end of the arm. If the arm is used to hold a drill, for example, that does not matter. I don't know about the robotics community on hn, but I use the Universal Robotics robot arms for sensor testing. Sensor Testing requires 6 DOF. Current Universal Robotics arms go for ~50k, and for that you get a highly repeatable robot arm, which is also safe for operation near humans, and with a good UI. What is so hard about the final joint, Haddington? If this is a product decision, to go with a 5 axis first to get to market first, I disagree. At this moment, 5-axis robots seem more useful to manufacturing than to roboticists and robotics hobbyists. However, I would expect manufacturing to have long acquisition cycles, and to be more willing to select an expensive, yet proven, robotics company, than to take a chance on a cheap upstart, whatever their technology. However, if you can get a 6DOF arm to within the budget of a university robotics class or individual hobbyist, who will be willing to take a chance on an unproven robotics startup, then these people will build word of mouth about your design. Teaching the math of robotic manipulation requires a 6+ DOF robotic arm. Students who learned on a Haddington arm will go into industry knowing the Haddington interface. Furthermore, it's much more likely for a $3k arm to be within the discretionary budget of an engineering team than a $50k one. 6DOF or bust, I just don't get it.
- Animats 8y ago
  Haddington's arm is 5-axis, which is not enough to put a tool in an arbitrary position and orientation. To put a tool in an arbitrary position (3 DOF) and orientation (3 DOF), a 6-axis arm is needed. Their gripper option adds another axis.
letstrynvm 8y ago
It sounds impressive, but "FPGA supercomputer"? It's a few optical shaft quadrature decoding state machines and feedback to motor controllers. Describing that as a 'supercomputer' suggests there's a lot of marketing bs flying around. Still if its resolution really is 50 micron it should be able to, eg, mill useful pcbs with the right head.
- deckar01 8y ago
  > A supercomputer is a computer with a high level of performance compared to a general-purpose computer. https://en.wikipedia.org/wiki/Supercomputer https://en.wikipedia.org/wiki/Supercomputer By this definition any FPGA that has been correctly programmed is a super computer relative to a PC or non-parallel circuit performing the same task. Couldn't you mill a PCB a lot cheaper with a 3 axis machine? Edit: On the other hand, it would be nice to be able to probe a complex surface.
  - imtringued 8y ago
    Your definition is way too broad because it depends on the specific computer you're using as a comparison. Almost everything is a supercomputer compared to e.g. a raspberry pi zero.
- cbames89 8y ago
  I believe they have a version called electron which is doing smd placement.
- JamesMNewton 8y ago
  The encoder / motor controller logic is a bit more complex than that. Because the encoders are analog / digital hybrid they generate far more data than standard quadrature encoders. The FPGA is doing huge table lookups, ATAN2, PID, Dithering the motor driver, and all of that at 5 MHz end to end, so we have a 200ns response.
  - chaboud 8y ago
    How huge is huge? The rest of the chain sounds pretty straightforward, even at 5MHz. That's not to say that an FPGA is wrong for the application, but nothing in that list screams "must use FPGA" to me. However, the whole program screams "get to market, then iterate" to me, which is a very effective way to move forward with a product like that. Note: I've shipped products doing continuous signal processing on DSP, GPU, CPU, SoC, and FPGA. (MCU eventually... Give me time.) I did the mental swag on the described processing chain... Out of curiosity, how big is your FPGA?
cjnicholls 8y ago
July 2014. The article is a little out of date to have a title of Groundbreaking.
Animats 8y ago
Where did they get a shaft encoder with over a million counts per rev? 130K is considered "ultra precision" in encoders.[1] The article misses the point. The purpose of the high resolution sensing is not positional control. It's for force feedback. Here's the spec page for the robot, with more info.[2] (But too much hype. Seeing "In the loop, On the loop, Out of loop, Big Data Roadmap" on a data sheet makes me think "phony".) Also, it's not $2,999. It's $4,888 for the base kit, and $9,800 complete and assembled. You don't have a usable robotics system at that point - you need another computer to control it. The FPGA is just motor control. Still, that's better pricing than Universal Robotics, which starts around $35K for a mechanically comparable system. There's no reason these things should cost more than many cars. They're not that complicated. It's mostly volumes being low. That problem took down Rethink Robotics. I have a $400 3-axis uArm on my desk. This is a low end robot with RC servo grade motors. I built a six-axis force feedback end effector out of a Space Navigator for it. Controlled by ROS. The functionality is there; the precision and useful life are not. [1] https://www.mouser.com/new/broadcom/avagoAEAT9000/ https://www.mouser.com/new/broadcom/avagoAEAT9000/ [2] http://hdrobotic.com/tech-hub/ http://hdrobotic.com/tech-hub/
- cbames89 8y ago
  The FPGA enables higher sampling rates, which allows for the finer resolution when paired with a lookup table which contains systematic error.
- letstrynvm 8y ago
  > Where did they get a shaft encoder with over a million counts per rev? The article says they put the encoder directly on the motor, before gearing it down. So the effective resolution after gearing is magnified. But the encoder moves much faster accordingly, hence the need for higher speed / fpga decoding.
  - Animats 8y ago
    No, the article says "Dexter’s optical encoders are placed directly on each joint, and have resolutions that aren’t possible with any other control system." The usual approach is an encoder on the motor, before the gear train. They probably have one too, so they can see what the motor is doing vs. the joint. Remember, none of this is rigid under load.
joshu 8y ago
The reason encoders go on the motor and not at the far end of the gears is because inexpensive gearing has backlash, which will cause the motor to dance back and forth to keep the encoder at a specific point. So how are they solving the gearing problem? Harmonic drives are expensive and patented.
- cbames89 8y ago
  I have a Dexter. They have harmonic drives from China which were deemed out of spec for normal usecases but are fine for the 3kg realm. Their latest version is running a custom cycloidal gear system.
- JamesMNewton 8y ago
  1. The encoders on the Dexter arm are at the joints because that gives us the ability to compensate for backlash in the drive system. 2. The motor dance issue happens because the feedback loop on most control systems isn't fast enough. With the FPGA, our control loop is 5 MHz / 200nS so we can correct before an oscillation has time to happen. 3. Our encoders give more than 1 million CPR (clicks per revolution) so we can sense an error before it has time to become an issue that might lead to oscillation. (2 and 3) are the real magic of the arms design 4. Yes, Harmonic drives are hell. And they are not actually free of backlash, it's just "soft" e.g. they bend slightly. At this point, they are the best solutions, but we have prototypes of a cycloidal drive that costs less (in quantity) and gives us better performance. There are issues to work out, especially related to smoothness and wear, but we are making progress on it.
boxcardavin 8y ago
I've been following these guys for a while and I really like their approach. In our lab we've done a lot of work to improve control of cheaper BLDC motors (low gearing) to mimic human control and compliance, and these guys are using similar methods to achieve accuracy. Most engineers just decrease tolerances to improve accuracy but using a blunter instrument and making it accurate with good software is an approach that leads to much much cheaper systems and robots. Drones are a good example, quadcopters are inelegant and somewhat inefficient flying machines but their cheap and blunt hardware comes alive with good control theory and software.

102 points by tlrobinson 8y ago

> There are no billionaire tech entrepreneurs riding Segways to meetings with angel investors, and there are no corporate PR-approved mission statements on the wall. Instead, you’ll find a small team of brilliant engineers who are using passion and innovative technology to design a very special robot called Dexter. That's, uh, that's exactly what a state-of-the-art robotics lab is supposed to look like. I used to work in one; place was a mess. Then they closed some big sales, moved to a shiny new facility -- and promptly got worse, that is, worse if your goal is to actually work on cool robots rather than edit elaborate specs on theoretical robots to get Major Defense Client to sign the contract.

neaanopri 8y ago

Haddington's arm is 5-axis, which is not enough to put a tool in an arbitrary position and orientation. To put a tool in an arbitrary position (3 DOF) and orientation (3 DOF), a 6-axis arm is needed. If their encoder technology is so good, why aren't they making a 6-axis arm and going right up against Universal Robotics? I'm not certain about this, but I believe that their arm does not have a final rotary actuator on the end of the arm. If the arm is used to hold a drill, for example, that does not matter. I don't know about the robotics community on hn, but I use the Universal Robotics robot arms for sensor testing. Sensor Testing requires 6 DOF. Current Universal Robotics arms go for ~50k, and for that you get a highly repeatable robot arm, which is also safe for operation near humans, and with a good UI. What is so hard about the final joint, Haddington? If this is a product decision, to go with a 5 axis first to get to market first, I disagree. At this moment, 5-axis robots seem more useful to manufacturing than to roboticists and robotics hobbyists. However, I would expect manufacturing to have long acquisition cycles, and to be more willing to select an expensive, yet proven, robotics company, than to take a chance on a cheap upstart, whatever their technology. However, if you can get a 6DOF arm to within the budget of a university robotics class or individual hobbyist, who will be willing to take a chance on an unproven robotics startup, then these people will build word of mouth about your design. Teaching the math of robotic manipulation requires a 6+ DOF robotic arm. Students who learned on a Haddington arm will go into industry knowing the Haddington interface. Furthermore, it's much more likely for a $3k arm to be within the discretionary budget of an engineering team than a $50k one. 6DOF or bust, I just don't get it.

Animats 8y ago
Haddington's arm is 5-axis, which is not enough to put a tool in an arbitrary position and orientation. To put a tool in an arbitrary position (3 DOF) and orientation (3 DOF), a 6-axis arm is needed. Their gripper option adds another axis.

letstrynvm 8y ago

It sounds impressive, but "FPGA supercomputer"? It's a few optical shaft quadrature decoding state machines and feedback to motor controllers. Describing that as a 'supercomputer' suggests there's a lot of marketing bs flying around. Still if its resolution really is 50 micron it should be able to, eg, mill useful pcbs with the right head.

deckar01 8y ago
> A supercomputer is a computer with a high level of performance compared to a general-purpose computer. https://en.wikipedia.org/wiki/Supercomputer https://en.wikipedia.org/wiki/Supercomputer By this definition any FPGA that has been correctly programmed is a super computer relative to a PC or non-parallel circuit performing the same task. Couldn't you mill a PCB a lot cheaper with a 3 axis machine? Edit: On the other hand, it would be nice to be able to probe a complex surface.
- imtringued 8y ago
  Your definition is way too broad because it depends on the specific computer you're using as a comparison. Almost everything is a supercomputer compared to e.g. a raspberry pi zero.
cbames89 8y ago
I believe they have a version called electron which is doing smd placement.
JamesMNewton 8y ago
The encoder / motor controller logic is a bit more complex than that. Because the encoders are analog / digital hybrid they generate far more data than standard quadrature encoders. The FPGA is doing huge table lookups, ATAN2, PID, Dithering the motor driver, and all of that at 5 MHz end to end, so we have a 200ns response.
- chaboud 8y ago
  How huge is huge? The rest of the chain sounds pretty straightforward, even at 5MHz. That's not to say that an FPGA is wrong for the application, but nothing in that list screams "must use FPGA" to me. However, the whole program screams "get to market, then iterate" to me, which is a very effective way to move forward with a product like that. Note: I've shipped products doing continuous signal processing on DSP, GPU, CPU, SoC, and FPGA. (MCU eventually... Give me time.) I did the mental swag on the described processing chain... Out of curiosity, how big is your FPGA?

cjnicholls 8y ago

July 2014. The article is a little out of date to have a title of Groundbreaking.

Animats 8y ago

Where did they get a shaft encoder with over a million counts per rev? 130K is considered "ultra precision" in encoders.[1] The article misses the point. The purpose of the high resolution sensing is not positional control. It's for force feedback. Here's the spec page for the robot, with more info.[2] (But too much hype. Seeing "In the loop, On the loop, Out of loop, Big Data Roadmap" on a data sheet makes me think "phony".) Also, it's not $2,999. It's $4,888 for the base kit, and $9,800 complete and assembled. You don't have a usable robotics system at that point - you need another computer to control it. The FPGA is just motor control. Still, that's better pricing than Universal Robotics, which starts around $35K for a mechanically comparable system. There's no reason these things should cost more than many cars. They're not that complicated. It's mostly volumes being low. That problem took down Rethink Robotics. I have a $400 3-axis uArm on my desk. This is a low end robot with RC servo grade motors. I built a six-axis force feedback end effector out of a Space Navigator for it. Controlled by ROS. The functionality is there; the precision and useful life are not. [1] https://www.mouser.com/new/broadcom/avagoAEAT9000/ https://www.mouser.com/new/broadcom/avagoAEAT9000/ [2] http://hdrobotic.com/tech-hub/ http://hdrobotic.com/tech-hub/

cbames89 8y ago
The FPGA enables higher sampling rates, which allows for the finer resolution when paired with a lookup table which contains systematic error.
letstrynvm 8y ago
> Where did they get a shaft encoder with over a million counts per rev? The article says they put the encoder directly on the motor, before gearing it down. So the effective resolution after gearing is magnified. But the encoder moves much faster accordingly, hence the need for higher speed / fpga decoding.
- Animats 8y ago
  No, the article says "Dexter’s optical encoders are placed directly on each joint, and have resolutions that aren’t possible with any other control system." The usual approach is an encoder on the motor, before the gear train. They probably have one too, so they can see what the motor is doing vs. the joint. Remember, none of this is rigid under load.

joshu 8y ago

The reason encoders go on the motor and not at the far end of the gears is because inexpensive gearing has backlash, which will cause the motor to dance back and forth to keep the encoder at a specific point. So how are they solving the gearing problem? Harmonic drives are expensive and patented.

cbames89 8y ago
I have a Dexter. They have harmonic drives from China which were deemed out of spec for normal usecases but are fine for the 3kg realm. Their latest version is running a custom cycloidal gear system.
JamesMNewton 8y ago
1. The encoders on the Dexter arm are at the joints because that gives us the ability to compensate for backlash in the drive system. 2. The motor dance issue happens because the feedback loop on most control systems isn't fast enough. With the FPGA, our control loop is 5 MHz / 200nS so we can correct before an oscillation has time to happen. 3. Our encoders give more than 1 million CPR (clicks per revolution) so we can sense an error before it has time to become an issue that might lead to oscillation. (2 and 3) are the real magic of the arms design 4. Yes, Harmonic drives are hell. And they are not actually free of backlash, it's just "soft" e.g. they bend slightly. At this point, they are the best solutions, but we have prototypes of a cycloidal drive that costs less (in quantity) and gives us better performance. There are issues to work out, especially related to smoothness and wear, but we are making progress on it.

boxcardavin 8y ago

I've been following these guys for a while and I really like their approach. In our lab we've done a lot of work to improve control of cheaper BLDC motors (low gearing) to mimic human control and compliance, and these guys are using similar methods to achieve accuracy. Most engineers just decrease tolerances to improve accuracy but using a blunter instrument and making it accurate with good software is an approach that leads to much much cheaper systems and robots. Drones are a good example, quadcopters are inelegant and somewhat inefficient flying machines but their cheap and blunt hardware comes alive with good control theory and software.