Wednesday, October 1, 2008

Chain Drive

With less than a week to go before we need to submit the robot for safety approval, we are still missing 2 vital components.

1) A drive mechanism to deliver power from the motor to the wheels.*
2) A frame to mount all the other components on.
*see update for details

Now, since there is so little time left, I am going to assign everyone on the team to do their best to get what we need. If you are going by a hardware store, or hobbyco, please drop in and see what they have. Everyone needs to search the internet for "drive chain supplier" or "drive chain catalog" etc, and see if they can find anything suitable. Anything that might be useful needs to be posted here, or call me if you have any questions.

Drive Mechanism
After a lot of discussion, I think that a chain drive is superior to a V-belt or gears. They are easier to adjust and more compatible with our design, but if you have reason to think otherwise then let me know. We need two sprockets and a compatible chain:
  • The diameter of the motor shaft is 13mm. Therefore, one sprocket needs to have a 13mm inner arbor.
  • The diameter of the rear axle is 15mm. Therefore, the other sprocket needs to have a 15mm inner arbor.
  • Having said that, BUY SPROCKETS WITH A SMALLER ARBOR! We can always drill it out if it is too small - too large and we have to mess around with bushings and crap. Get 10mm or even smaller if you can.
  • There is no need for anything other than a 1:1 power ratio, but if you must get sprockets with different numbers of teeth, get more teeth on the axle sprocket.
  • Our robot has about a bit more than 50mm clearance from the axle to the ground. Therefore, do not buy a sprocket with an outer diameter larger than 100mm.
  • The chain needs to be at least 200 + 200 + 2*pi*100 = 1028mm. Longer is better. Make sure that the chain is easily adjustable. has a section on how to choose a chain (pp 29-30). In all honesty though, it is a complex procedure so you are probably better off using your judgment.

We need a chassis that is at least 300mm x 400mm. At this stage, if we have to make it out of wood - so be it, but we need to have something to mount all our parts on! Once again, I'm throwing this task out to everyone - think about what you have in terms of tools and materials... THEN MAKE IT!

I am currently working on the remote controller (which I finally picked up), the speed controller, the steering and the power system (AA batteries FTW!). The only thing we don't have is a fuse box, but I'm willing to put that into the non-essentail pile.

Thanks to everyone who has helped with this robot. We are almost at the end!


I spent friday walking around the city, looking for sutiable stuff. I tried hobbyco, but they don't have anything strong enough for our purposes. I went to a few bike repair stores, and eventually came away with two sprockets and a matching chain.

The catch is that the sprockets will need some work to fit around our axles. I need somebody to help me out by building two bushings out of wood or something, so that we can fit them on the motor and axle.

The sprockets look something like this (I'll take a photo of the actual ones when I have my camera):

The rings that I bought have the dimensions: A = 35mm, B = 57mm.

What I need from one of you is to build something that allows us to connect this to the shaft. Something like this:

Sunday, August 17, 2008

Motor and Competition Info


On Monday, I will be in the workshop from about 9am till 4pm. I will be bringing all the parts in and putting together what I can. If you have some free time, come down and help out! (If you can't find me, call me). I will leave most of our stuff down there so that we can work on it during the week - let me know when you are available to help.

Here are the specifications for the motor so that we can fit the frame around it. I still can't figure out how to get the flywheel off, but since we need it to use the belt drive that fit's around it, I'll be leaving it on for the moment.

Finally: is "Dreadmill" a good name for a robot?

Monday, July 21, 2008

We have got to use this motor

Thanks to everyone who came on Thursday, and Friday. For those of you who weren't there, here is an update:

On Friday, we found an old treadmill that we took apart to get the bearings. We managed to get 4 heavy duty ball bearings (which I am very excited about, since it saved us a trip to the bearing shop), and some axles that fit nicely into them. There was another surprise in the treadmill as well:

A 230V 2.7hp DC motor.

Now, my first reaction was a negative one. For one thing, the motor weighs about 8kg (although a lot of this weight is from the flywheel). Also, we would need many, many battery cells to run it at 230V. And using our current steering design, we would need a second one to run the other wheel. Overall, it would be too much weight.

Having had some time to think about it, I've changed my stance. We have GOT to use this motor! 2.7hp! That's more than 2kW!! Here are some of our options:

Idea 1: We can use the motor to power our weapon. No messing around with springs or screws - we can run the entire thing electro-mechanically. We can get bursts of high voltage using a bank of capacitors: We can charge them in paralell and then discharge them in series:

This will allow us to get pulses of power at 5x our base voltage. This means we can power the flipper almost directly off the motor, making our build a lot simpler. We will still have to port the heavy motor around, but we don't have to worry about lots of batteries to keep it running constantly.

Idea 2: The above idea is a good way of sticking with our original design, but if we do a bit of a redesign we can make far more efficient use of having such a powerful motor.

First of all, we won't be able to find a matched motor to power the right side of our robot, so we will need to use this big motor to power our rear drive wheels, while using a rack and pinion system to steer. There are a few advantages to this:
  • One motor of this size is more power than we will need to move the robot (pretty much irrespective of weight). A second one to power the right wheel would be total overkill.
  • The remote control that we are getting is designed to operate servo-motors, not continuous motors. Rack and pinion steering is servo-friendly.
  • We already have this motor. Why spend money on two big matched motors, when we could just buy a single small servo to steer?
But what about getting enough power to run this beast? Here comes some maths:
  • First of all, we tested the motor and it will turn with as little as 12V.
  • With 4 x 12V cells in series, we can drum up 48V - about one quarter of the total capacity.
  • 2.7hp = 2.01kW; therefore we would be delivering 0.42 kW just to drive around. This is an enormous amount of energy, especially for such a small robot. We would be able to out push any other robot with this (for reference, our previous plan was 2 x 12V x 2A = 96W).
  • Operating at 0.42kW, for say, 20 minutes means that our batteries will have to have a total capacity of 0.14kWh - 35Wh each if we use 4 cells.
  • Assuming that each cell will operate at 12V, this means we are looking for cells with a mere 2.9 Ah rating.
Of course, we might need to use a different number or type of cell, depending on what we can find. However, these numbers are very reasonable and achievable.

Idea 3: Here is the kicker: What if we combine both of these ideas?

We are running the motor below capacity (about 1/4). If we get 4 capacitors, and charge them up as shown in part 1, we can deliver quick, high voltage bursts of 100% operation.
All we need to do is weld a big metal spike to the front of our bot, and we have a death machine that can stab holes in any robot.

Update: Found these.

Friday, June 27, 2008

Workshop Robot Building

Hey, since its the holidays we should arrange for some time to build our robot.

What days can people go into the workshop?


Before we can collect the controllers, we ALL need to sign a terms and conditions agreement and give it to Sarah. Since most people don't have any major commitments, I am going to suggest that we meet THIS THURSDAY (17th July) at the Royal for dinner (7pm). I'll print out a copy for everyone to sign, and we can have a progress meeting then too. Let me know if you can make it (facebook or email me if you have to).


Wednesday, May 28, 2008

Soldering as an alternative to welding

I was just thinking about robot stuff to avoid doing my System Dynamics and Control assignment.

I've been doing a bit of soldering for an electronics assignment (which I nailed, by the way), and I realised that I am already quite handy with a soldering iron - so I decided to explore the advantages of using soldering as an alternative to welding.

  • Welding is generally stronger than soldering as a method of joining metals, however a large factor in determining the strength is the quality of the join. This means that a well done soldered joint might be stronger than a poorly done weld.
  • Soldering does not require bulky or expensive equipment - allowing us to quickly perform repairs at events and things.
  • Welding can sometimes warp a part or joint because of the extreme temperatures. This can also lead to stress concentration areas.
  • The solder used in electronics is a very soft and low strength type of solder. Other solders such as plumber's solder, aluminum solder and high tin solder are much stronger. This table contains a few types, and their strengths. A particularly attractive choice was a 90% tin solder with a tensile strength of 8000psi = 55MPa.
Anyway, I thought I'd just throw the idea out there. There is no point in using welding in places where extra strength is not required, so soldering might be a good option for certain parts.

Thursday, May 15, 2008

Workshop Initiation Reminder

Hey, for those of you still reading the blog, just a reminder that workshop initiation is next Friday 23 May.

Looks like we're going to be allowed to the student workshops after all.

Monday, May 12, 2008


After many setbacks and trips to the hardware store, I've finally managed to cut the stock steel tubing into pieces that we can use for our frame. One of the main purposes of this blog is to document our progress so that we don't make the same mistakes again. To that end, here is a quick summary of what I did do, didn't do and should have done.

With the exception of stone, metal is probably the most difficult common material to work with, and one of the hardest things that needed to be done was to cut the tube at a reasonable 45 degree angle. The tool I had to use was a small, hand-held 350mm circular saw.

The initial plan was to cut each piece from the next at alternating angles (diagram, top) to minimize the total number of cuts. I needed to figure out a way to clamp down the stock at a fixed angle with respect to the direction of cutting. I ended up using part of a phone book placed on the edge of a table to lift the saw up to the top of the tube. Then I taped the tube to the table at the correct angle with the part to be cut hanging over the edge. I could then run the saw along the edge of the table and cut a straight line through the overhanging part. Long lengths were hard to clamp in this way, so I ended up chopping the stock into sections first (diagram, bottom). A table saw would probably have been the best tool to use for this.

- Use the right type of blade: Initially, the only circular saw blades I had were designed for cutting wood. I made a test cut to see if I could use it, but it just skipped across the surface and shredded the walls - definitely not appropriate. To cut metal, use a fine toothed blade with suitably hard edges. For thick metal, you may even have to use an abrasive blade.

- Measure twice, etc: I used a pencil to mark the places I wanted to cut, but this was hard to see against the steel. I wrapped masking tape along the lines to make it more visible. I also did a quick double check just before I cut to avoid stupid mistakes (ie, cutting on the wrong side of the tape)

- Perform a test cut first: To see how the width of your blade will affect your finished product. I also tried to leave a little extra material on the ends since it would be easy to sand down the ends a bit instead of having to cut a whole new length if it was too short.

- Use a high rotation speed and a low cutting speed: This will minimize the wear on your tool, and result in a better finish. There is really no reason not to do this, unless you are in a huge hurry.

Sunday, May 4, 2008

Chassis Design

The frame for the chassis is going to be built from 16mm stainless steel tube. At present, it is simply a rectangle with inner dimensions of 300mmx400mm, but we will definitely extend it into a trapezoidal shape, and we can add reinforcing beams if necessary.

I stumbled upon this site while I was looking for metalworking circular saw blades. It has some good tips and info.

Check the comments for progress updates.

Monday, April 28, 2008

Warp 3 Sir?

I know we were all a bit disappointed that our robot didn't work for the first event, but now that we have had a bit of a break it is time to get going again.

I thought I'd get the ball rolling by revealing what I've been working on over the last week. Speed controllers are essential if you want to have any level of control over the robot. Especially if you are using more powerful motors, you need to be able to operate them over a wider range of speeds than "OFF" and "WARP 8".

Obviously, the poor-man's solution to this problem would be to simply put a variable resistor in series with the motor which could be used to limit the amount of voltage that was dissipated across the motor. However, this has the negative aspect of continually draining maximum power from the battery, giving it a shorter operational life than a red-shirt.

Speed controllers work by creating a pulse-width-modulated signal. The actual process of generating a PWM wave with an appropriate duty-cycle is a little bit complicated, but at it's basic level PWM is just a square wave with a fixed period, but the on and off times vary depending on how much current you want to supply to the load. To further abuse the star-trek analogy, a 20% on - 80% off wave would merely stun, whereas setting your phaser to 90% on - 10% off would most certainly kill. This means that no power is wasted when the motors are operating at a low speed, but they are still capable of working at their full capacity when the tap is fully opened.

Anyway, I've put together a PWM speed controller that uses two transistors and two MOSFETS, which should be able to deliver up to 20A at a voltage range of 7-40V. Unlike pre-assembled speed controllers, which I've been unable to find for less than $100, this one cost a measly $20. Stay tuned for pictures.

A few considerations:
  • One speed controller can control a single motor, so if we use a two motor drive system (independent left and right wheel control) I'll have to put together another one. Not that it's a problem - it will just cost another $20.
  • Although the circuit is supposedly rated to 20A, operating at full capacity for an extended period of time is likely to burn out the MOSFETS. Phil, keep this in mind when you are buying the motors - less might be more when it comes to the power that they require.
  • I would like to find a way to guarantee that both of the wheels turn at the same speed when we give them the same input signal (ie, full forwards on both will not list lazily to the left). It would be nice to have some way of dynamically adjusting the gain on each of the output channels so that the person driving doesn't have to be continually compensating. Any ideas?
I hope that everyone else is going well with their tasks. We'll see each other on Thursday, but if anyone wants to meet before hand, let us know and I can show off my circuit =)

Live long and prosper.

Monday, April 14, 2008

Batteries and other stuff

Hey, as the first deadline approaches, I'd thought I'd give this blog a go (since I've actually remembered to look at the bookmark now heh).

Firstly, regarding power, we have to use dry cell batteries as Sarah pointed out in an email a whole while ago. I've already discussed with most of you guys my suggestion to go for the sub-C cell type battery to power our robot as these are readily available and fairly good value for money. Plus I've got a pack and the gear to charge them (so we save a bit of money there).

There are a couple of places off the net to get them really quickly and reasonably priced.

These sub-C batteries have a reasonable amount of punch and current (since afterall, they are used for RC cars). We can get batteries that have a capacity of holding 4000mAh, or 3600mAh which is almost double the amount of charge that you can normally find on drill batteries.

I'm thinking of sourcing a couple of used battery packs (6 cells, 7.2volts) for now and seeing how we go. I think we might need to go in the direction of one pack for movement, and one pack for weapons (I'm thinking that two motors will draw alot of current). Also we can pull the packs apart to make new packs with different amounts of cells and change the shape of the pack itself. Right now we just have to get our robot moving and I already have a pack for that.

If anyone else has suggestions for batteries, please post up!

Another problem that we need to figure out (for later down the track) is how exactly we are going to control our robot. We can easily buy a 4 channel remote (2 for driving and steering, another 2 for weapons) but we need to figure out how we are going tackle the problem of figuring out an interface between our motor/weapon system to the receiver unit. At the moment, I'm clueless to how these receivers actually work. We could just probably find some servos to stick on them for the weapons at the very least.

Monday, April 7, 2008

Meeting time

Some of us are (or will be) having trouble getting to the 5:00 meetings on Thursday. Can everyone reply to this post with the times that are best for them. Those of us who can still make it to the regular meetings should go, but it would be good if we could all meet up at least once a week.

In other news, the first minor robot competition will be in about 2 weeks. By then, we need to have:

  • A chassis
  • A power source (batteries)
  • Two drive motors (and applicable gearboxes)
  • Tank treads (or wheels)
The other thing is that it looks like it might be a while before the uni will allow us to use their workshop to start building, so can everyone please post what tools/facilities they have access to? In the short term, we might have to do quite a bit of work at home.

Also, I hope that you are all going well selling chocolates and shares!

Peas out -

Friday, April 4, 2008

Making Tracks

Here are various methods for making scale sized tank treads

My Feet Hurt

Wednesday, April 2, 2008

Stalins Hammer

Time to throw my ideas into the ring. Please don’t see this as me trying to step on anyone’s toes or ideas.

In my viewing experience, some of the most successful Bots didn’t have or use any fancy weapons to beat the others, they used brute strength to man-handle the other contestants into those fiery pits or ram them up against the wall.

The design I’m thinking of is very similar, using a battering ram and high torque motors to bash the opponent into submission!

Taking into account the Australian Rules of Battlebots, specifically the one not guaranteeing a perfectly flat arena, my idea is too use tank treads to power the machine, in a dual configuration ala The Mammoth Tank of Command & Conquer fame to lower the resistance and power draw from the batteries. It also takes from Alex’s idea of having the drive wheels above and below the chassis Alex raised good point about having to change the steering 50% of the time, this can be solved using this a bit pricey but well worth it?

And finally the chassis/design, build the weapon into the chassis so the battering rams are tied directly in and there is no central compression point when something gets rammed.

Brought too you by Caffeine,

Tuesday, April 1, 2008

Image of Initial Robot Design

Hey guys,

I know this is kinda late, but it's still technically Tuesday night, and I've been busier than I thought I would be so I didn't get to get your critique and suggestions. I probably could have done a more refined job if I had more time, and have added a few more things just to make it look meaner (I was thinking a pirate flag). But notice I did end up putting racing stripes on to increase its aerodynamic something-or-other (I'll ask Dave to put in a big word in here later since he's the aero dude in the team).

This blog was brought to you by Philip Gun

More than meets the eye

Ok, I'm done being eaten by my assignment, so I'm ready to share my brainwave for how to build the chassis. I only got about 2 hours of sleep last night, and I think I've got bird flu so right now the only thing keeping me functioning is copious amounts of amphetamines - I make no guarantees about the coherency of this post.

Right, down to business. In it's current state of design, our robot has no fixed form. We have no assurances about the availability or effectiveness of parts, only the vaguest idea of what the rules are, and we all have different ideas about what would make a good robot. As I have mentioned in previous posts, the best way to deal with this is to incorporate this flux into the design itself.

The chassis is the hardest part to design in this capacity, because it needs to accommodate all of the other parts within it. Since each module is unknown and subject to change, the chassis needs to:

  • Expand or contract in volume to encase parts of any size.
  • Provide mounting points at any location to support parts.
  • Be strong enough to support heavy parts or contain reaction forces.
  • Not be unnecessarily heavy or bulky.
I suggest that we make the chassis like a roll cage out of metal tubes and Y-joints. If we use bolts to hold the assembly together then we can re-configure it's size and shape to whatever we need. We can drill holes in the tubes without compromising much of their strength to join them together, and of course we can always cut longer tubes shorter if we need to.

  • Like lego or meccano, we can reconfigure parts of the chassis without having to buy/design an entirely new one.
  • We can easily extend mounting points by adding Y or X -joints to the scaffold.
  • Strength can be easily increased in a number of ways:
  1. Cross-beams can be added to distribute the load from places
  2. Rigidity can be increased by reinforcing corners and joints
  3. We can upgrade all or part of the chassis - from hollow aluminium to solid aluminium to iron to steel
  • Weight can easily be reduced in places it isn't needed.
Remember that the chassis is not armour. It's primary purpose is to provide mounting points for all the other modules. Once we have got all the pieces working together, we will have several upgrade options available to us: some can be used to strengthen parts of the structure and lighten others. Most importantly, we can continually re-use the pieces, so it won't cost us a fortune!

If anyone has comments or suggestions, please let me know. I will try to get my hands on some suitable material by this Thursday, so that we can use the time in the lab productively. I hope you will all come along to help out!

Monday, March 31, 2008


Hi yall,

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.

Status Update

Several of us had a de-facto meeting at lunch today. Here is a quick update for those of you who weren't there:

- 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

Parts and Labour

OK everyone, here is a quick list of what needs to be done before next Thursday. It is very important that we have the parts we need by the next meeting so that we can use the time properly.

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.

Design Drawing

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


I've been thinking about the steering design, and it looks like it may be too complicated to get steering to powered wheels, so maybe we should start with two-wheel drive (back wheels) for now, and modify it later if we want.

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

Modular Design

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:

  1. Each module can be allocated to a single person, dividing up the work.
  2. Modules can be upgraded easily without having to redesign other parts of the system.
  3. Repairs are made easier because modules are isolated and can be tested separately.
  4. 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:

  1. Crafting the interfaces between modules requires very good communication between team members.
  2. Peer review of components is essential to ensure that they are well engineered.
  3. 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

Congratulations on purchasing your RoboBlog2008!

When working as a team, it can be difficult to make sure that everyone gets the time they need to express their ideas. The purpose of this blog is to create some shared space that everyone can contribute ideas and designs to, and then allow others to comment and critique on your posts.

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.