Monday, March 31, 2008
I've been mates with Alex J for a whiles now, and for almost that amount of time we’ve wanted to build a robot, that’s why he’s invited me to join, I hope that’s ok.
Just a clarification, I don’t have those motors Alex mentioned, but I've sourced them from a scooter repair place, Ill get the full Specs for them tomorrow, they will be $80 each.
- Dave has decided that we are better off using a two motor system to drive opposite wheels instead rack and pinion steering.
- I have looked all over the internet and parts beyond and have been unable to find a small automatic gearbox. The only way to get them is as part of a hobby nitro car etc. This means we will need to probably buy or design a speed controller to regulate the motors.
- We needed to get a preliminary design in for the robot. This really only needs to be cosmetic so that Sarah has something to put up on the site. We ended with a flipper-like weapon that attaches at a pivot at the back of the robot like a skid loader. This is not the final design - just something that works for the moment.
- Chris (our newest member) has got some old electric scooter motors that should provide more than enough power for drive purposes.
- I have had a brainwave about the chassis, but I will post the details up when I'm done with horrible System Dynamics and Control stuff. Probably tomorrow.
Thanks to everyone who came to the meeting. Once again, I implore you to set this as one of your homepages so you can keep up with what is happening.
Tuesday, March 25, 2008
Rear Wheel Drive
Dave, the first thing we need to sort out is the drive shaft diameter. There are too many unknowns to go about calculating it, so the best thing to do is have a look at some other battle bots and try to estimate what they use (maybe here?). At a guess I would say that we are looking at around 10mm, but see what you can find. I also need you to look into some kind of gear/chain/belt drive that we can use to get power from the motor to the wheels. Have a look on the interslice and see if there is somewhere local we can get these sorts of parts from.
Once we have decided upon the shaft diameter, we need to look into bearings. Blake, I think you would be the most qualified to look into the model and type of bearings we should use. Try to find somewhere that we can get them from locally. Outer diameter isn't that important, but remember that our robot could weigh as much as 20kg (or more, with armour), and might need to push/lift another robot of similar weight.
Finally, we do need wheels, but lets see if we can salvage these from something second hand. Everyone look around for old toys or pram wheels, etc.
Ok, Alex C is in charge of finding and purchasing batteries. At this stage, it is uncertain what voltage our drive motor will operate at, so that means we prefer many smaller cells over a few big ones:Once again, find out what the best sorts of batteries for us are, and see where we can purchase them from.
Motor and Transmission
I am currently looking for cheap cordless drills or electric skateboards that we can use for motors and gear reduction. I am also trying to find a place where we can get a small 2 or 3 speed automatic gearbox, but I haven't had much success. In the immediate future, only the motor is important, so we can always upgrade the transmission module later on. Once I have found something suitable, I will put all the details in another post.
This is one of the most difficult parts to design, since it needs to be able to accommodate all sorts of parts that don't exist yet. I suggest that we use a meccano-style set of parts that can be bolted together in different configurations if the parts change. Remember that we still haven't decided on a weapon or steering system, so we need something that is flexible. Phil, I hope you are up to the challenge.
Sarah has moved the due date for the concept of the robot to Tuesday, which gives us a bit more time. We need to schedule a quick meeting on Monday and talk about what we have achieved and what the final robot will (probably) look like. There is a very good chance we will change the design along the way, so what is really important is that we at least have some half-baked concept drawings to hand in. =)
Update - I forgot to mention it, but what I really need from everyone is a shopping list of things that we need. We may be able to salvage them, but we will probably have to buy a lot of stuff. Put all the parts that you will need in your post, and we will organise who will buy what from where once everything is complete.
Monday, March 24, 2008
Also, it's very important to find a way to un-invert our robot, in case it gets flipped. Incorporating this into the wheels/steering could save a lot of weight. If anyone has any ideas about this please share them.
Sunday, March 23, 2008
One of the first things that we need to decide on is how we are going to approach this problem. Nobody on this team has any experience with building combat robots – or any sort of robots for that matter. This means that we don’t have a good idea of the areas that need the most work, or the problems that we will face during the build.
I would like to suggest that we design and construct this robot in small pieces (modules) to allow the design to evolve over time. In my experience, projects never work out the way that you think they will, so it is critically important that we keep our options open during the execution of this project. The following diagram is an example of the different subsystems that need to be engineered:
Using a modular approach gives us a number of advantages:
- Each module can be allocated to a single person, dividing up the work.
- Modules can be upgraded easily without having to redesign other parts of the system.
- Repairs are made easier because modules are isolated and can be tested separately.
- Each team member gets experience at designing an entire product from start to finish.
However, designing a robot in modules has some drawbacks as well:
- Crafting the interfaces between modules requires very good communication between team members.
- Peer review of components is essential to ensure that they are well engineered.
- The overall design process is more complex, but it is divided amongst more people.
I feel that this approach is suitable for us because the choices you make in the early stages of a project don’t come back to haunt you later when you realise you didn’t fully understand the situation. In my experience, this design strategy is a little more difficult at the start, but saves a lot of time later on due to its flexibility.
Please tell me what you all think.
Saturday, March 22, 2008
1) If you have something to contribute, make a new post and share the details of your design. You can upload pictures, links to research and diagrams.
2) When someone makes a new post, make a comment and tell them what you think of their idea. Give them advice, support or constructive criticism.
3) When you finish working on an element of the robot, use this space to post your progress and keep everyone informed of how things are going.
Try to use this space like an informal log book. Posts can be edited at any time, so don't worry about making mistakes or draft posts.