Tag Archives: Building

A New Cannon

I’ve said it before and I’ll say it again: I was very pleased with Cannon’s second-place performance at Motorama. Still, its three fights against the eventual champion, Low Blow, highlighted some severe design flaws:

  • Exposed wheels. This is probably the single biggest flaw a robot can have.
  • The ball bearings pushing against the sides on big hits expand the beater holes.
  • There was no firewall; parts could be ejected from inside the robot into the blade.
  • Slow drive motors. 22.2:1s would have been a much better choice.

The scale was hardly Cannon’s friend, so figuring out how to add more material to the robot without adding any weight will be a challenge in and of itself. However, the first (and easiest) place to look is the wheel hubs. Cannon used aluminum “Dave’s Hubs” to hold its wheels on. Much lighter alternatives exist, such as the FingerTech Robotics Lite Hubs. Switching to the Lite Hubs will save over half an ounce off the next version of Cannon. That is more than enough to get started.

The next place I will look for weight will be the back of the robot. The old back weighed about 0.6oz and was made of 3/32″-thick garolite. Although stiff, garolite is about twice as dense as UHMW and is very brittle. The next Cannon will use a piece of (likely 1/16″-thick) UHMW that wraps around the back and protects the wheels. Kitbot creator Pete Smith gave me some UHMW bending tips at Motorama that should mean the clearance between the wheels and the UHMW is better on Cannon than it is on Coercion. Actually, I’m not sure Coercion actually has any clearance!

I put together a quick sketch of my thoughts for the next version of Cannon:

I am not a very talented artist.

I am not a very talented artist.

The new firewall will be bolted to the side rails, which will help to make the entire robot stiffer. I will make a groove in the sides so that the pieces fit together relatively snugly.

I also sketched the side rails (remarkably well). I think I might apply to art school if the whole top-ten school in the world thing doesn’t work out.

Note that the pockets are bigger and I have added holes for the firewall. Also note that the hole that will hold in the weapon bearing has been enlarged. This will allow me to put in a custom bushing, which will increase the surface area inside the hole and keep it from enlarging.

Note that the pockets are bigger and I have added holes for the firewall. Also note that the hole that will hold in the weapon bearing has been enlarged. This will allow me to put in a custom bushing, which will increase the surface area inside the hole and keep it from enlarging.

The next step will be to design the firewall and do more weight calculations. I’ll then need to order parts. Unfortunately (well…fortunately), I will be in Washington, D.C. from March 9th to the 16th, which isn’t conducive to robot design work, and over the next week, I’ll be busy getting ahead on schoolwork to get ready for my week off: not much will get done. Still, it feels good to finally put some of the ideas I have come up with on my blog.

Keep checking back–Bot Blast registration is up on the Builders’ Database. I’ll be taking Cannon, lolcat, maybe Coercion, and maybe Amatol if one of my friends wants to drive it.

Cannon’s Almost Done

I’ve run into quite a few problems with Cannon since I last posted, but I have also made a lot of progress. I’ll get you up-to-date:

  • Cannon’s beater (along with Coercion’s new blade) arrived
  • I realized that Cannon was about an ounce overweight. It had to go on a serious crash-diet.
  • The weapon shaft material has been changed from S7 to titanium. I ordered some Ti, cut it, and tried to thread it. Unfortunately, I had a rethreading die instead of a threading die: although it worked with unhardened S7, grade 5 Ti was a different story. I managed to make enough threads to put on lock nuts, and a good die will be arriving soon.
  • I reduced the weapon reduction from 3:2 to 1:1 by making a new weapon pulley.
  • I wired everything up.
  • I made some pockets in the back to reduce weight.
  • Cannon spun up.

All the weight-saving measures have brought Cannon down to weight without forcing me to resort to using the notoriously brittle FingerTech Lite Hubs instead of the good Dave’s Aluminum Hubs I had planned on using. I will have everything put together by the end of the weekend; I will only have to make a few spare parts and thread the ends of the weapon shaft a little more before Motorama (I only have one weekend left!). My next priority will be Coercion, which ought to be manageable enough.

Here’s a video of Cannon spinning up:

This thing is going to be a lot of fun at Motorama! I have always wanted an antweight beater ‘bot.

Cannon Build Update

Cannon has been coming along very well. I have spent the majority of my free moments–those not dedicated to studying for midterms or doing projects–getting Cannon together. Team Whyachi finally finished Coercion’s new 9.2oz, hardened S7 blade and Cannon’s 3.0oz titanium beater; I expect to have them here by Monday. The goal is to have Cannon in a place where I can plug in the beater and have a finished robot (but this is combat robotics, so that’s a very lofty goal indeed).

Since I last posted, I cut out the back and drilled the twenty holes that will hold Cannon together. I am using .375″ #6-19 button head plastite screws from McMaster-Carr, which are similar to the mind-bendingly strong ones that we used on Tough Nut last year. So far, everything seems to be holding up pretty well. I did the traditional “throw your frame down the stairs” test, and nothing broke. That means it will be super-strong in the arena, right?

The next steps in the build process will be to cut out and thread the ends of the weapon shaft, fashion a pulley for the weapon motor, drill and thread holes in the pulley I already have for the weapon, and then to get wiring. If I have time before Motorama, I will also harden Cannon’s S7 weapon shaft and Lolcat’s S7 weapon shaft. Lolcat’s bent at Bot Blast, so I do not have high hopes for its toughness against all the horizontal spinners that are registered for Motorama. However, the new motors I bought for it should provide a nice speed boost.

Here’s a front view of Cannon (note that I am waiting on shorter plastite screws from McMaster so not all the screws are in it yet):

It would look so much better with a weapon...

It would look so much better with a weapon…

Breaking Ground on the Cannon

My father’s health has improved a lot and I have a three-day weekend: it’s high time I started getting the new version of Cannon built. I have spent the last few days machining away and making small changes to my drawings. With the exception of the first side rail (on which I carelessly used a 1/4″ end mill instead of the 1/8″ end mill I told my GCode generator I would use), everything has gone surprisingly smoothly. There have been no bumps in the road.

Just kidding, this is combat robotics — where the probability of fire is about equal to the probability of success. Things actually have gone relatively smoothly. The biggest issue I have had during my time standing in my machine shop was that the power went out while I was making the top. Luckily, I was able to finish cutting the piece out with an X-Acto knife. X-Acto knives always seem to save the day.

As of writing (I am taking a break from working), I have a very nice looking pile of parts. I just need to cut the back out and drill 20 holes before I can wire up Cannon and take it for a drive. Before any kind of spinning takes place, I will need to create some pulleys on my lathe and make a belt. It looks like everything will somehow get done before Motorama, which is a big relief.

Here are some pictures of the build process so far:

This pile of parts has about a month to becoming a functioning, radio-controlled killer.

This pile of parts has about a month to becoming a functioning, radio-controlled killer.

The beginnings of a 3/8"-thick side rail for Cannon.

The beginnings of a 3/8″-thick side rail for Cannon.

The mill putting finishing touches on one of Cannon's rails.

The mill putting finishing touches on one of Cannon’s rails.

A finished side rail. It needs to be cleaned up a little more and get mounting holes drilled in it, but it is more or less complete.

A finished side rail. It needs to be cleaned up a little more and get mounting holes drilled in it, but it is more or less complete.