P08205: RP 1 Motor Module First Generation
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Transcript of Dr Hensel Interview - 9-20-07

Transcript for Dr. Hensel Interview - 20 September 2007, Dr. Hensel's Office
Interviewer: Hello, my name is Jason Kenyon. I'm going to be building an RP1 Motor Module. I'm trying to get more information from you about what the project is about. The project is mainly about building the drive system for a larger robot platform. Is that correct?
Dr. Hensel: That is correct
Interviewer: What is your role in the project?
Dr. Hensel: My primary role is the sponsor of the project, so I am providing the financial support. The reason I'm providing the financial support is based on a history of looking at past senior design projects and looking at research projects that various faculty members have been involved with. Over the last 7 year I've seen several project teams need a robotic vehicle to do their project, but the robotic vehicle was not the focus of the project. So they end up trying to rush through the design of the robotic vehicle so they can get onto the main business of their actual project, and then 8 times out of 10 the fact that they rushed through the robotic design causes them a problem with the main project. The robots sometimes were so jerky that they interrupted the function of the main project. If teams had a smoothly operating robotic platform then the main portion of their projects would likely be more successful. So I said, "lets focus some teams on developing an open source open architecture robot so that at some point in the future, if a researcher or student team or club or whomever needs a robot, rather than designing the robot and then going on to work on their main project, here's the complete set of design specs and a bunch of parts that we may already have in-house, and just build your robot, basically assemble it, out of high-tech parts. So almost like a very sophisticated lego kit.
Interviewer: That makes sense. So, the ultimate objective of this project which you have pretty much have outlined is to make a platform for other teams projects. Now, this project that I'm working on, is this specifically going to be the motor module itself, just the drive system, and another team would be involved in making a platform that mates up to it?
Dr. Hensel: That's correct. So if you think about a vehicle like the skateboard concept that General Motors uses in their future vehicle design. Are you familiar with that?
Interviewer: Yes, it's just a drive system and then you place whatever body onto it right?
Dr. Hensel: Right. So think about a skateboard that has 4 wheels on each corner. But if each wheel had it's own motor and it's own suspension and steering system, and then you just drove it by wire, so you just provide power and commands to it, then each wheel can operate independently. And if you design each of those wheel properly, I should be able to take the left front wheel off, move it around and put it on the right rear wheel position or vice-versa. So the intent of these motor modules is that it's a modular, driven wheel that you can put into any position on the vehicle, tell what position it has, and it can then interpret it's commands in the appropriate context. So you can have 2 wheeled vehicles, 3 wheeled vehicles, tracked like caterpillar-type vehicles where you have 6 wheels on a side, you could put 18 of these on an 18 wheeler and make an 18 wheeled vehicle, or any combination thereof. So like a high-tech Lego.
Interviewer: Ok. Who are some of the other customers or guides or consultants on the project?
Dr. Hensel: There are 3 generations of this project or 3 sizes that we are looking at. There is one size of motor module that is nominally targeted at carrying a 1kg payload for the platform. There is another size that is targeted towards a 10kg payload, and another one for a 100kg payload. So that spans 3 orders of magnitude. Eventually we would like to go even smaller into a 0.1kg payload and even larger into a 1000kg payload, which is like a light pickup truck. A 0.1kg payload is about 1/2 a pound. So that is a pretty broad range of payload. So you are working on the 1kg payload Motor Module. The intent is that this motor module could be combined with other motor modules onto a platform, and that that platform should be capable of carrying a payload of 1kg, not every motor module. That is the way we defined the nomenclature of the projects. There are a number of faculty members that are involved with various aspects of the projects, either as consultants or guides or customers. Dr. Walter has been the faculty guide for most of the prior RP-series projects. He has done several projects in the RP10 and RP100 family. I don't know if he will be the guide for this particular project going forward because I would like to spread it out and get more people involved, but he has a tremendous history of experience that you may want to draw upon. Some of the customers or users of these robotic platforms, Dr. J. Yang in computer engineering has an application field where I would love for him to build like 20 of these robots and use it in his research. Dr. Ag Crissidis has a need for these kinds of robots for his research. There are many other student organizations that might be interested in having these robots available for their student clubs and activities as well. So it intended to be open to anybody who wants it to use it. We'd like to publish all the results on the internet along with all the manufacturing spec's so that a hobbyist or a high-school kid or other college students could make their own.
Interviewer: You had something you said about what exactly the specifications of the payload would be. So you are asking for a platform that carries 1kg, and the design that this project is intended for is making motor modules that would support a payload that carries 1kg?
Dr. Hensel: I'm thinking that the payload itself is 1kg. That 1kg payload would be carried on the robotic platform and then that robotic platform would be driven using 1 or more of these motor modules. So that is like 2 systems away from where you are designing. Your individual motor module may be able to carry a gross weight on it's motor module maybe of 1/2 a kg. So if you had 4 motor modules, then you would allocate 1 of those 2 kg's to the payload and one of the kg's to the balance of the platform.
Interviewer: So I should talk to Dr. J. Yang and Ag Crissidis?
Dr. Hensel: Right. Dr. Yang is a computer engineering faculty member. I would hope that he would be a customer or a user of the product. Dr. Crissidis would be a user of the product. Dr. Walter would be a user of the product. The multi-disciplinary robotics club could be a user. I would hope that the high-school FIRST robotics organization might look at this and say "that's cool, we could use that". I think it would be really cool to publish these out there and then they could put these motor modules one on each corner of the FIRST robot and then it's done.
Interviewer: Yes, FIRST is really big on the kits.
Dr. Hensel: Right now they are using some proprietary motor controllers. Victor motor controllers that are like $80 each. Well if we could develop an open architecture open source motor controller that's not copyrighted and not patented, it's not proprietary, then perhaps we could lower the cost of participation in that club for students. In the 100kg motor module we actually used motors that are very similar to the SIM motors that are used in the FIRST kit. We went with a 24V version rather than a 12V version but that is the only basic difference.
Interviewer: Will this project be referencing past project in that we will be using their designs and just scaling them down or are is this going to be a total re-design just smaller.
Dr. Hensel: Both. My goal is to re-use design knowledge from one team to the next as much as practical. I want to promote the idea that a new design team stands on the shoulders of the students teams that have come before them. Not that they take as written in stone what the student team did before them, but at the same time I don't want them to start over with a clean sheet of paper every time. So we are going to take the best features and move them forward, and improve on the findings of things that didn't work in the past generations. So I would view this as an evolutionary design, not a revolutionary design. As the design evolves, my hope is that we would have a single design concept that would be applied across 4 orders of magnitude of vehicle sizes. That is a very difficult task. If you think about an 18 wheeler truck, the drivetrain in that truck is very different than the drivetrain in a vehicle that a 5 year old kid would drive around in their driveway as a toy. We don't want that. We want the same architecture across 4 orders of magnitude.
Interviewer: So like if it was designed like this (making a sketch with motor, bevel gear and belt down to a wheel, similar to the configuration seen on both the 10kg and 100kg motor modules today), would you make something like this and just shrink it? Do we eventually want to be able to do that?
Dr. Hensel: We want there to be certain elements of the design that are constant themes across all 4 orders of magnitude of size. For example, I think it is very appealing to have an azimuthal angle that has an infinite number of degrees of rotation. That's really cool.
Interviewer: You mean you can spin the wheel all way around right?
Dr. Hensel: Yes, an infinite number of times so it's not like I can go +180 degrees to -180 degrees, I can go +1000 degrees minus 10000 degrees so I can just sit there and spin all day long.
Interviewer: Right. Because if you wanted to go from this angle to this angle and the maximum turning stop-point is in the middle, you don't want to have to turn almost 360 degrees all the way around to reach that point, you want to just turn right to that point.
Dr. Hensel: Correct. And that has some very severe implications relative to controls. You have to count your angles and degrees so you can tell where the wheel is turned. Obviously it has some pretty neat challenges involved in it. The other thing is that when you stand back and look at the 1kg, 10kg, and 100kg motor module, it should be immediately clear to the casual observer that they are cousins of one another. At the 100kg motor module, you may have steel and titanium components and spur gears. At the 10kg you may have aluminum components and bevel gears, and at the 1kg you may have plastic components and a belt drive. But somebody should be able to say, "oh, they are using a belt here instead of a bevel gear, but it still has the same drive concept". That is what we are striving for.
Interviewer: Along with the infinite turning of the wheels, is there anything else specifically about these projects that you liked?
Dr. Hensel: There were a number of features that we've identified as good and bad features as a result of the debriefs on all the different senior design projects. Last academic year we asked every single student team to go through lessons learned and recommendations for future groups and things they would have differently if they were starting over. This happened the last week of the course. We asked them to go back and say, "tell us what you would do differently". So there are reports like that in each of their archives for 7 or 8 groups last year. Those reports have not yet been compiled into a single cumulative set of learning yet, but there are 8 individual ones. So if you were to read each of the findings and look at common themes, there may be some contradictions. One group may have said "this was a bad idea", so you have to dive into why. There were certain things that came out very strong as a consensus amongst all of the teams, so I recommend that you compile all that stuff. Dr. Walter has a platform group that is working this fall. They may also be doing some of that consolidation and reflection right now, so you may want to talk with his platform group. I don't remember if they are Fall-Winter or Fall-Spring, but there are a next generation 10kg platform team. They are taking stuff from last year and moving the 10kg device forward a little bit. You could then move forward from them into the 1kg size scale. I want to encourage and promote cross-team collaboration. I want to inhibit or discourage cross-team competition. I would like nothing better than to have 6 teams work very closely and leverage one-another resources and share software, designs, etc. and make each other stronger because of that. So it is not a competition, it is a collaboration. I think that is something I would like you to emphasize in your project plan, because even though you can say that, as students get invested into their project which is human nature, you fall into a mode of "not invented here", "wasn't my idea" or "I spent all my time doing this stuff, why should I share it with you?". Last year for example there was some conflict between the teams where one said, "We bought this battery out of our budget for our team, and now it turns out we don't need the battery so we are going to send it back". Another team said, "but we need the battery!". So the first team was going to send it back and pay a restocking fee and the other team was going to turn around and order it again, lose a 1.5 weeks. That is ridiculous. It's all my money and I'm the customer, so I got really upset about that. You're together folks! There are certain resources that we should buy once and share across the teams. I don't want to introduce that parochial view into the teams.
Interviewer: The Gleason foundation is not the customer?
Dr. Hensel: The Gleason foundation provides an annual gift to the ME Dept in support of our programs. I am using that gift that they make to our department to support this project. We are recognizing the financial support the foundation provides to support the environment, but it's not that the Gleason foundation will take these results back. They could and that would be great, but primarily they are making a philanthropic gift and I am choosing to use it for this.
Interviewer: When we go to the Robotics lab to look at the robots maybe you could show me some specific things you like, don't like and would improve in the 1kg robot.
Dr. Hensel: Absolutely. I think it would be easier to do with the hardware in front of us.
Interviewer: Was there any specific thing that the previous projects failed to complete in terms of goals and customer needs?
Dr. Hensel: Yes. From a couple of perspectives. I gave a set of customer needs on day 1 a year ago in the fall. We did a launch and I went in and met with 6 teams at the beginning of the fall quarter and they did a group interview of me in the Xerox auditorium. They got questions from the 100kg and 10kg payload and motor module. I put a huge job on their plate, so I never expected them to solve all these problems in the first year. I expected from the beginning that this was going to be a multi-year development effort. I would like to see a really nice robust, solid system done in 3 or 4 years. We are in the 2nd year of that now. The biggest frustration that many of the groups had was that they took on more than they could chew. I tried to be very clear with that from the beginning. I said, "I know you're not going to do all of these things. Pick those things that you can do and commit to getting them done". I had numerous conversations with them. For example, there are Victor motor controllers commercially available that you hook up to a motor and you're done. So having a motor controller is not critical to having a motor module that works. We can put a commercial motor controller on it this year, get the module to work, and now we know what all of the power characteristics are in that motor module. THEN maybe it would be time to develop an open architecture motor controller. They tried to do too many things in parallel, and as a result didn't finish many of them, or they finished them in somewhat of a slipshod manner. In prior senior design projects, a team typically built a single prototype of their device. Last year was the first year that many of our teams had to build multiple copies of their project. I think that was a very positive learning experience. Building four is a lot different than building one. When you build just one there is a lot of craftsmanship in making it work. When you are building four, yes there can be craftsmanship involved, but the req't of the craftsmanship has to make it back into the design. When you're building just one, often-times that craftsmanship doesn't propagate back into the design drawings. On the drivetrain last year, they had some things about how they were retaining the wheels and the gears on the axles. The first one they made, they had a lot of axial slop in the powertrain. In the second on that they made 3 days later, they put some different E-clips on it and use a little different way of doing their retainer, and the third one they built was still a little different, and the fourth etc. So you look at them and there are no two that are the same. That is a negative. But it is a positive in that every single one got just a little bit better. And that is great. I liked that evolution, but the fact that there was so much evolution within a short period of time showed that there was a lack of design fore-thought. You now this year have the benefit of 6 teams that spent an entire year working on this project. That works out to easily 8 man-year of development on this project last year. It would be a shame to start all over and not build on what they learned. They have a very nice list of things that have to be fixed. My hope is that at the end of this academic year when we have 4 copies of this RP1 motor module, they are all identical and I can't tell them apart. Then we have a good design. This is definitely moving closer to the productization. If this became more of a product and less of a project, we are at the right transition.
Interviewer: What is the budget for this project?
Dr. Hensel: I havn't set one yet. I am going to be looking to you during the fall quarter to scope out what a reasonable budget is. Last year we had 8 projects focused on robotics projects and I allocated almost $20,000 for that. So we spent a lot of money last year. I don't think we will have to spend nearly that amount of money this year because we have already bought a bunch of motors and batteries and hardware that we can and should reuse. I don't have a pre-concieved idea of what the budget is. There is no way I could spent more than 20k. I don't think it needs to be anywhere near that. I don't want to tell you it's 3k today and you try to scope that out and leave something really important off the table. It is probably more in the neighborhood of 3-5k as opposed to 15-20k, but if you make a compelling case that it needs more or less than that then I am pretty flexible. By the end of the fall quarter we should have that specified.
Interviewer: Let's move into the Robotics lab to look at the hardware.
Notes taken during the preceding visit to the Robotics Lab to look at the previous projects:
Smaller turntable - both the 100kg and 10kg teams used same turntable, way too big for 10kg module
Easier maintenance and repair
Robustness
Ruggedization - possible drop test
Minimize weight - robots are very big and heavy for what they have to carry
Smaller size or size appropriate to payload capacity
Option for multiple wheels
More professional-looking
More focus on platform-module interface
Easy belt or other drive piece replacement
Simple and easy to assemble and disassemble - you need to disassemble a lot to get at parts that easily break or wear out
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