A flat motor.

chorl2 Comments

I got some flat motors the other day.

They’re seriously flat motors.

For a really flat robot.

It’s been a while since I’ve updated Pop Quiz, which has been in much the same form since the end of 2005. That makes it my longest-lived bot ever!

For revision 2, the blade height will be dropped from 0.8″ to a bit over 0.6″. The chassis height will be lowered from 0.5″ to 0.375″.

This requires extensive customization on almost all levels. The only stock gearmotors I can use are Sanyo micromotors, which are about .380″ tall, but unless combined with an additional gearup on the output, will not offer satisfactory speed.

So I’m going a different way.

This is a custom 3:1 gearbox design for a Mabuchi slot car motor, the square kind. I got a bag of 30 of these surplus a little while back.

3:1 straight off these motors at 14 volts will make the bot travel over 9000 miles per hour. However, I plan to inject some big N50 magnets in place of the ceramic ones in there now, greatly increasing the magnetic flux within the core and hopefully dropping the voltage constant enough such that 3:1 is actually sort of manageable, especially with wheels 0.5″ in diameter. The target speed is about 4 feet a second, which is incredibly zippy, but only if it works out. Extensive testing of this setup will occur.

The gears are metric module 0.4 things from SDP-SI, which is about 64 pitch. Aligning them will be such a royal pain in the ass that I don’t want to think about it at the moment.

The housing is a chunk of aluminum channel or rectangular tube, machined to taste. Four modules will be made for 4 wheel drive. Each module should be around 2/3 ounce according to Inventor.

Wepon motor in place. Oddly enough, the version of PQ’s motor that worked unquestionably the best was the original hacked hard drive motor with its 2504 stator and ball bearings! The later custom motors just never quite matched up to it. So I’ll be using a HDD stator again in a custom housing, with ball bearings – no more of this bushing crap that plagued the current weapon motor.

The axial flux one had ball bearings, but didn’t fare any better because its torque output was so low.

The flat motor stators in the picture are 28mm diameter x 3mm tall, but only 9-poled. I have another set of HDD motors which have 28mm x 4mm stators with 12 poles, allowing the use of a dLRK winding, which have been designed into the above motor.

This is, of course, the fun part. Ground-to-blade height of a hair over .625″. It could be less, but running the blade to close to the body results in self-eating.

The top of the frame is exactly half an inch from the ground. The ground clearance around the wheels is a bit less than 1/8″.

Overall, the parts rundown is:

  • Banebots 3-9 controllers for drive. The Scorpion Minis inside Pop Quiz at the moment are workable, but the BBs are more compact and lighter. I’m not too concerned about thermal issues with the Banebots controllers since PQ shouldn’t be doing any pushing anyway. I might revert the decision if they can’t handle the…
  • Frankenmotors, former slot car motors with giant magnets attached to them. I wish they had carbon brushes.
  • A GWS Pico receiver. The Cirrus 4 channel micro Rx that I use in PQ at the moment is actually too big to fit inside the frame! Spektrum makes a 2.4ghz receiver that I can use, but it is of the airplane type and does not return signals to neutral in the event of transmitter signal loss. Even though PQ is pretty close to takeoff when running, I’d prefer it stay on the ground.
  • 14.8 volts of 430mAh lithium polymer cells, rated for 10-15C. I want to run high voltage, low current this time around, so 6 amps should be plenty (14.8v and 6 amps is still a solid 80+ watts!)
  • A random 10 amp controller from United Hobbies. The ESC I have in PQ at the moment is 10 amps, but this one can run 4 cells. I bet it’s not as plushy as they make it out to be.
  • A 12 inch waterjet-cut titanium blade.
  • Lots of carbon fiber! Instead of using heavy 1/16″ fiberglass (Garolite) plates, I wanted to see if the lighter, stiffer carbon fiber material can be used in slightly thinner section (.041″). The weapon motor is supported from both sides this time, so I can probably run .021″ material on the bottom to increase clearance.

More to come! This is a summer project, since my attention is focused on the scooter and … classes (yeah, I think) at the moment.

Bot on.

Re(Snuffles Reloaded: Update)

chorl

There’s plenty in the imaginary part of the update, but you can’t see it anyway.

Hey, this thing looks kind of familiar… It’s the extend-o-pack, with 4 4000mAh lithium polymer cells in place. No, they’re not shorting on eachother, despite the precarious appearance of the tabs.

The Deans connector cutout is a snug fit and should hold a female Deans in place firmly with some CA glue. I need to remember to undersize slots and holes for the LASER cutter by a few thousandths to account for its kerf (since it cuts on the line).

Here’s how it was built.

This is sacrificial vehicle #2, another junked scooter that was sitting around MITERS. I’m not sure if it’s an older generation or what, but there are quite a few structural differences compared to the new A3 model I’m converting. It’s certainly beefier in the folding joint (0.1″ formed steel plate!) and brake area, and there is more material in the chassis.

Efficient re-engineering or corner-cutting?! The world may never know.

The plan is to cut a 12 inch segment out of the chassis and use it as the extend-o-pack body.

After a trip to the bandsaw, this was what remained. It was much like partitioning a fish for cooking – remove the tail, remove the head…

…and clean the middle. Oddly enough, with the parts that remain, I could make a very innovative vehicle.

Here, the side flanges that used to form the upper deck have been milled off, and in a previous unpictured operation, the mounting ear holes drilled.

It might have been better to mill with each flange facing upwards, since the cutting head is always at the same height as the vise above the table, but the vise might not be aligned with the table axis. I tried centering it in as well as I could, but across 12 inches of travel there was still .003-.005 of deviation, enough to have a flush-cut flange at one end but a very light remnant of it at the other.

Oh well, I’m not that good… yet.

After trimming the flanges off, I milled the remaining channel down to the design height of .606 inches, which is just enough to clear the two cells with some breathing space above. I did this in order to minimize the ground clearance hit – these things aren’t known for their great terrain ability, and I was only going to make it worse by sticking batteries under it.

Here’s one of the LASER cut acrylic endcaps installed. They are retained by some drops of CA wicked into the cracks between acrylic and aluminum and one screw on each side.

The waterjet-cut mounting ears have also been installed. It turns out I was off by exactly 2mm on the width of the channel, so dumping all 4 blocks in the same vise and running an endmill through at 1mm solved the problem and made it a slip fit onto the bottom of the chassis.

The other endcap with connector cutouts! On the right side is the last leg of the height-trimming cut where the milling cutter went Z-axis Tokyo Drift on me and ended up slipping lower. Oops. Crank the drawbar a bit harder next time?

And here it is installed. It actually looks quite elegant, with the exception of the other side where there is a small gap from the milling cutter slipping.

This whole assembly slides onto the chassis tube and the mounting screws grab the small flange on the underside to hold it in place. There’s lots of potential for “slide-on accessories”, actually.

So, with my Maxamps order on the way (two more cells to fill in the insides!) I need to get going and design the internal mounting structure. I suspect that it will also be a “slide-in” thing, but from the front – mounting via the four holes at the front.