Camera, motor, kittens

Going through the workshop, making small improvements and sorting some things out.

For one, after several months of it bothering me, I knocked together a better mount for the angle-poise webcam.

Doesn’t look like much, but now the tilt is on top of the pan pivot rather than the other way around. The previous one was smaller but meant the image was only level when looking directly forward (along the line of the arm). Turning to show what I was doing to the left or right meant the image turned on it’s side. This way the image should remain level and I’ll be able to manuver the camera closer to the action.

In my sorting, I also scrapped some broken battery drills that either had dead batteries, broken chargers or damaged electronics. So I have four sets of low-voltage motors with reduction gearboxes and torque-limiters, and one electric screwdriver with just the motor & gearbox.

I haven’t checked yet, but Wikipedia suggests about the maximum torque you can expect from a battery drill is around 30Nm.

I’d been considering using them to make a large track-mounted robot arm, but at only 30Nm it’s unlikely they’d be able to make the arm move under it’s own power, let alone do anything useful.

If I packed out the torque control spring I could have them continue to run at higher levels, but I’ll still need more powerful motors I suspect. I’ll be looking into what’s cheaply available. Initial enquiries suggest radio-control vehicle motors won’t have enough torque. Steppers may be another option.

I’m envisioning something of a comparable reach to that of a human arm, so about 30cm between joints.

And finally, we still have some kittens looking for good homes.


The legality of using an electric cart

So I’ve been trying to figure out if it’s legal for me use these electric robot bases I’ve been making. This is only my research from today, so there may be flaws. Please feel free to correct me.

Electric bicycles & scooters in the UK are legal to use at age 14 without any licence provided the motor is only capable of 200Watts of power (or 250Watt if it’s a trike or tandem), limited to a maximum of 15mph under electric power and weighno more than 40Kg (60kg for trikes & tandems).

The junk-built “Thunderbird 1” would fall under that at the moment. A 120Watt motor and it’s built as a trike. It’d be lucky to hit 12mph with the wind at it’s back.

However, I do not want to ride T1; I wanted to add a guide-handle to it and use it as a power-assist cart to move heavy stuff around. This seemed a lot safer to me.

But this would also suddenly make it a class-K vehicle; “Mowing machine or vehicle controlled by a pedestrian”, which requires a UK driving licence to use. Mine is currently only a provisional licence.

I found a case where a poor sod who worked delivering milk using an electric hand-cart was told by the police that he wasn’t allowed to, and since he couldn’t get a drivers licence (could only read a licence plate at 21 yards, rather than 25) the dairy had to get him an assistant with a drivers licence to guide the cart while he walked alongside.

I can’t find the link right now, but it was the local MP bringing up the ridiculous state of the class-K licence in parliament and pointed out the man would have been fine to use a bicycle cart, or a horse & cart, all at much higher speeds (and potential risk) than a 4.5mph trolley. The matter ended after a lot of description by being dismissed in true government fashion. Paraphrasing; “Very nice, but that’s an extreme example, it’s not worth bothering.” “That’s ok, I can tell my annoyed constituents I tried, thanks!”

Then I look at the Road Traffic Act of 1988, section 189 which explicitly states “controlled by a pedestrian” is NOT to be treated as a motor vehicle. The same portion also defines the electrical-assist pedal-cycle as not a motor vehicle.

So a class-K is a vehicle as far as the driving licence is concerned, but not as far as the Road Traffic Act is concerned.

Fortunatly this section also defines what “controlled by a pedestrian” actually means;

  • is constructed or adapted for use only under such control, or
  • is constructed or adapted for use either under such control or under the control of a person carried on it, but is not for the time being in use under, or proceeding under, the control of a person carried on it.

Now here it gets very muddy. Remote-control vehicles.

The person driving a radio-control car is a pedestrian, but they have no physical contact with the vehicle. And the only specific example given in section 189 is that of lawnmowers (as well as the milkman case). This implies that the control by the pedestrian is considered to be by physical contact with the vehicle. And there is ample proof of larger & more powerful remote-control vehicles (EG: 5000 Watts) than I’m making being used without a licence (other than that for the radio system).

Now if, and it’s a dangerous to take an if when dealing with the letter of the law, this above paragraph is correct in it’s assumptions, we’re left with an absurd situation.

  • If I ride on Thunderbird 1, I have no legal issue.
  • If I guide Thunderbird 1 with a handle, I need a full driving licence or a provisional one with a fully licensed person present.
  • If I drive Thunderbird 1 via remote-control, I have no legal issue.

Further to this I find some more explicit descriptions on the Suffolk Police website that states;

  • The term MPV (mechanically propelled vehicle) is not defined by legislation, but will include, for example, child-sized motorcycles, quads and all motorised vehicles as defined in the Road Traffic Act 1988. Note the exceptions from the definition of motor vehicle contained in section 189(1)(c) of the Road Traffic Act 1988 i.e. grass-cutting machines, certain vehicles controlled by pedestrians, and specified electrically assisted bicycles.
  • An MPV becomes a motor vehicle when it’s made or adapted to go on roads.
  • MPVs have to be registered, taxed and insured.

I think this just told me that a childs electric ride-in car (a 4-wheeled vehicle, not a bike or trike) would have to be taxed & insured.

I know I’m being facetious there.

Though there’s another loop-hole in all this mess that recently saw a man prosecuted for riding a Segway in the UK. Why is the Segway illegal to use on public land? Because it doesn’t have pedals, apparently. Quoting from the Legalise Segways website; “The Highway Act of 1835 renders the Segway PT illegal in the UK on pavements. They cannot be used where bicycles can (even electric bicycles) because they do not have pedals – and they cannot be used on the road as a motor vehicle because they do not meet any kind of permitted type approval in the UK. The only place they CAN be used is on private property (and only with the land owner’s permission).”

Their mention of the electric bicycles is a bit of a mistake I feel. Although I can’t find Segway literature listing motor power, a user forum post from 2002 however says the Segway uses two 2HP motors. So nearly 3000Watts.

With the electric-bike/trike law an absolute 250Watt limit, using the comparison here seems to provide their campaign with an immediate Achilles heel. I would be far more concerned that the Segway is fifteen times more powerful than the highest rated electric-assist bicycle, rather than it lacking pedals. (of course the Segway needs that power for rapid high-power adjustment in balance, rather than speed or loading)

But the pedal issue is why electric scooters are illegal. They’re solely electrically powered, not power-assisted. And despite being popular gifts for kids, illegal to use on anything other than private land in the UK.

Now to close with a couple of bits of speculation;

  1. The law relating to electric MPVs (but not motor vehicles) seems to take the attitude that the electric motor is solely for the purpose of assistance where the person is physically unable. Bicycle power-assistance, invalid carriages, electric wheelchairs, etc. Actual use as an independent low-risk/low-cost device for the able-bodied does not seem to be a consideration.
  2. With Thunderbird 2 looking at 360Watts of power, it should be legal to use as long as I don’t ride on it, control it wirelessly, don’t run it fast and don’t act like a cock to draw attention to myself. The whole area of new MPVs seems to be a sprawling grey-area where there’s a lot of interpretation involved on the behalf of the legal services. While this seems to sit ok as not-a-passenger-vehicle or a pedestrian-assist/controlled vehicle, it’s still an unusual variety of remote-controlled-vehicle which could invite legal wrangling. The additional robotic components will likely exacerbate that.
  3. While I can’t find specific mention, there’s some suggestion that using an RC vehicle to carry anything (person or cargo) turns it back into a motor vehicle. Which would rather stump one of the original intentions for the damn things.

If I were to make an amendment to the rules though? For a start I’d scrap the motor-wattage rating completely (Hell, scrap the ICE size limits too), but keep the speed limits on them.

It doesn’t matter if your motor is a hundred or a thousand watts; if it’s limited to twelve or fifteen miles per hour you’re only going to go that speed. The only thing it’ll effect is how much load you can carry and how quickly (or if) you can get to that top speed.

Final thought: While cat-K seems to be included on full licences by default, as many of the other categories require specialised testing it seems to imply there is a specific test or portion of test to get licensed to “drive” a push-lawnmower. I wonder if it’s possible to get a licence for JUST that?

Also, I’m aware that while not a legal necessity, public liability insurance is advisable when using powerful RC vehicles in public.

Buster: Chapter 1 in essense

From page one, the book is memory filled. I’m glad to have it because there’s no other way I could remember the details.
Published 1976, Buster the robot is described as “one of the most unusual machines possible in the context of modern technology” and that he “Represents the highest-order machine that technology can produce today”. And I believe it.

It’s a strong contrast to the book itself, as the glue holding the pages in is cracking and the first 14 of them are threatening to come away entirely.

Buster is set out in a three-stage project (accordingly titled Buster I, II and III), in which the same machine is further added to and modified, increasing it’s abilities.

The Buster I phase warns that it will be the most expensive, dealing mostly with converting/building the driveframe, power supply, control systems and so on. Basically building Buster up as a tethered remote control vehicle, going up through the stages of; going from brute-force power switching to logic-level control, adding speed variation control, self-centring steering, and finally converting the controls over to binary.

The Buster II stage starts working on the autonomic reflex system and “brain”.
I’m rather excited that it talks of them separately, indicating lifelike concious and autonomic motivators.
The section also adds sensors and reflexes, as well as low-battery self-monitoring and an alarm to alert the owner of this, which is also used if Buster gets stuck somewhere.
After this comes the cutting of the umbilical controls, and making some form of audio control system (though it mentions the transmission format being compatible with then-current regs for data links between telephones and CB radio systems. This seems rather esoteric now! I had no idea CB radios were often hooked up to telephones.).

Buster III starts by adding the impressive-sounding “tracking function” which ties in with giving him goal-seeking abilities. This then ties in with the hunger alarm, and allowing Buster to seek out his charging station to plug himself in.
I seem to recall from the first time I read the book that this had some sort of contacts on sprung arms. Guess we’ll see when we get there.

Yes, I’m not re-reading the book up front, I’m taking it as it comes (well, chapter by chapter).

By this point Buster should be able to run around by himself, bumping into things, hurtling into empty spaces, and charging himself up when needed.
Beyond this point it talks of the icing on the cake; optional extras and so on. Things like line-following and other variations.

There’s also mention of a theoretical Buster IV, adding microprocessor control on top of the reflexes and goal-seeking. Perhaps these would be analogous to reflexes, instincts and concious learning?

The staged construction and review layout of the book sounds perfectly manageable.

And ultimately it points out that you need to choose some of the design choices at each stage yourself. It’s a recipe, not a design.

It also notes that “despiking” capacitors are omitted on all schematics. Will have to remember that.

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into to re-purpose DW blog account.]

Buster: Car and batteries examination

So here’s the lil fella I picked up for £3..

This little mock quad-bike is pretty lightweight. There’s some metal framework for the axles, but the rest is all a moulded plastic body. I’d be worried about it taking the weight of extra parts if it wasn’t designed to cart around reasonably large children.
The rear drive wheels are pretty worn, and all are the cheap hollow plastic variety.
They’re a lot wider and with less grip than the ones on the original Buster’s frame as best I can judge from the few photos. I’ll keep it in mind as it may have issues with drive and steering.

The rear wheels have separate drive motors, driven together on a static axle. Cheapest design, but running the motors together should be fine.

Controls are pretty simple. Two sealed 6v lead-acid batteries, a two-button toggle for forward and reverse, another for fast and slow (seems to switch the batteries from serial to parallel connection, so 6v to 12v) and a foot pedal switch to make it go.
The controls on the handlebars are purely for show. There’s nothing in them beside a horn powered by a separate set of AA batteries.

I should be able to strip off a few odds and ends, but as it’s a monocoque they’ll be a limit. And since I’m running out of space here, my Buster will need to be able to be stored outside.
I suspect the control electronics may be a bit smaller, even using as close to 1970s parts as I can. Maybe if I upturn a plastic bin on them that’ll be sufficient rainproof housing.

I was quite excited to find it used two 6v batteries, as that’s what Buster was designed to run on. However when I measured them they only read 2.27v each.
Lead-acid batteries are also not meant to be concave.

My charger wouldn’t read it as needing the charge. Rather wish the charger gave out more information on battery status. Charging complete has the same indication as being unable to charge.

As a last-ditch effort I pried the sealed cover off one of the batteries and found three rubber caps. On pulling one off there was a characteristic sucking noise. All the cells were under vacuum. So I suspect the car may have been left out in hot sun for a long time, and literally boiled the batteries dry. So when they cooled the covers were sucked on.
With nothing to loose I grabbed a bottle of demin water and proceeded to refill the cells with a syringe through the tiny vent holes.

Sadly, that didn’t work. Even after a few days for the plates to re-wet, the readings didn’t change at all. Due to construction there’s no way of getting electrolyte back out again to check the gravity. At this point though it’ll just be simpler to spend the £20 buying a new set of more powerful batts.

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into to re-purpose DW blog account.]