Team Dudge build diaries.

[Derek Dudge]

From hobbytronics. They were more expensive than some I saw on ebay but I didn't want to wait weeks for shipping.

I have been fiddling around trying figure out how to mount the motors up. And i have a plan now.

Kinda a stroke of luck, that turned onto their side, the mounts that came with the motors are almost spot on tall/wide enough to have the peg where i need it so the wheels are halfway up. It's very damn close. Within a mm. I'm not gluing anything until i have the wheels to double check, but at most a sliver of plasticard or something might have to go under.

I gotta stick a bracket to each mount to do it this way.

I attached a picture of a hasty mock of what I'm thinking. Please excuse, I had to draw the lines on my phone.

My plan: is yellow line needs to be cut/filed away a bit, so it fits underneath the lid.

Green lines will be hot glue, attaching the mount to the bracket and then all of it to the chassis.

Blue line will be a removable plasticard or tape flap, to stop the motor moving around inside the mount, but allow the motors to still be removed if they get damaged etc, since the mount and bracket will be stuck down.

So.. I guess my question is, you guys think those hot glue joins will be strong enough?


russian photo sharing

[MrEnDo]

I wouldn't of thought hot glue would be strong enough, maybe epoxy glue?

[peterwaller]

I normally mount my motors using the two threaded holes in the face plate.
You need the mounting to have a 4.6mm hole for the shaft bearing and two 2mm holes 4.5mm either side for the mounting screws which are M1.6 by 4mm long. Don't make the screws any longer as they can reach the gears and lock the motor.

[MarkR]

I see that there are various motor mounting options; I like the idea of using a plastic (maybe 3d printed, or bent polycarb) mount, then making "wrap around" wheels which overlap the gearbox.

I saw that technique on a youtube video, it looks like quite a neat idea to save length on the gear motor.

Create a hollow wheel that can slide all along the shaft then wraps around the gearbox.

But most of my parts for antweight haven't arrived yet, I've not built one before (but I have built bigger non-combat robots)

[Phil_8]

Trim those bolts to save a load more weight too!

[Derek Dudge]

It shouldn't be too long now before I'm ready to move on to wiring up Third Law. I plan on ordering the rest of the parts I need later this week and am mostly done fiddling with the chassis and armour.

Before I get there though, I've a few potentially dumb questions I want to double check about. I *think* I know the answers but would just like to check. Better a few silly Qs now than ruined components later, right?

First up - I want to include a switch. Presumably between battery and ESC would be best place for it. However my esc is a nanotwo that already has a nice easy red plug connection for the battery. I figure I'd be best leaving battery side alone, so changing batteries without any faff is still easy. So, ESC side of the plug connection - I just cut the red wire and splice in the switch?

Next up - I want to incorporate a few LEDs. I read a little about it, and am aware best practice is to include a resistor with them. The formula on the site I was reading tells me a 200ohm resistor would be what I need for the battery and lights I plan to use. So, I can just wire the resistor with three LEDs I wish to use in series? Or will they be dim done this way?

Also where in the overall circuit would you guys hook up LEDs? Can I combine the switch and the lights into one series, and wire them all in betwixt battery and esc in one go?

Finally, is there any recommendation of which wire to buy? I see on ebay that it's available right down to 1mm thick, which would be awesome for weight saving. This stuff will be good for ants? Any potential pitfalls I'm missing here?

When I ordered the ESC Alex explained about connecting 3rd and 4th motors for my 4wd to the first pair, so all good there. Just those few niggling queries to double check on and hopefully I'll be good to go.

Cheers in advance!

[MarkR]

About LEDs - diodes have a "forward voltage", which is the amount of voltage they will drop (almost independent of current) - this is the opposite of a resistor which has a constant resistance.

So if you wire several LEDs in series, calculate the forward voltage (1.8V seems typical for some red LEDs; it's significantly different on high-brightness ones or different colours), then calculate the amount of current you want.

So for example, if you want 100mA (this drives some LEDs too hard, and makes others really bright!), and want 2x 1.8V LEDs, then the drop is 3.6v. using the 5v output of your regulator (aka BEC) there will be 1.4v remaining, so you need a resistor which will drop 1.4v at 100mA (V=IR ; R = V/I) so about 14 Ohms.

A bigger resistor allows less current, which makes the LED dimmer.

Putting 2 or more LEDs in parallel with a single resistor is a bit error-prone, because if their electrical characteristics aren't absolutely identical, one will take a lot more current than the other.

In general, either wire them in series with a single resistor, or in parallel each with its own resistor.

Hope it makes sense

leds.PNG (44.37 KiB) Viewed 9811 times

[Derek Dudge]

Cheers for the reply. Although sadly I confess I'm still a tad unsure here. So the ebay store I ordered a few leds from (blue ones with higher forward v than red it seems) gives me the following numbers

Forward volt 3.2 - 3.8

Forward current 20mA typical 30mA max.

You mention the voltage in your example being 5v from regulator. This part is where I'm falling down. I'm going to use the 180mA turnigy batteries (7.4v) that folks regularly recommend on here, and Rorys ESC. Where between these do I find what regulated voltage the LEDs would be getting?

I found this calculator online and entered info from battery and the LEDs (just 2 though, I'm now assuming the higher forward voltage from the blue diodes means I should just use two) and got this back. But i had to enter the 7.4v for battery as I'm not sure about the regulated value you mentioned.

[MarkR]

Some of the speed controllers, (I don't know about Rory's) have a built-in regulator, known in RC-speak as a "BEC" or "Battery Eliminator Circuit" - because traditionally its role was to eliminate the need for a second (receiver / servo) battery on a RC car. Antweight robots usually use the regulator to power their RX and any other low power stuff. The regulator usually produces 5v.

The advantage of using the regulator is that it always makes 5v, but a 2S Lipo pack will put out somewhere between 8.4 (fully charged) and 6v (dangerously flat)

I think you've realised this - but you can't put multiple LEDs in series if the total forward voltage will be higher than your supply voltage. If you're using blue leds with a forward voltage of 3.8 or something, each will need its own resistor.

If you would feed the leds from a variable voltage, they will also have variable current, so they will be brighter when the battery is higher - maybe that's a feature so you can easily see when the battery gets low?

[Derek Dudge]

Ok, yeah that's making a bit more sense now. Cheers!

That's seems like it's not a bad idea really, letting the lights dim as the battery discharges. I understand letting the lipos run down fully can ruin them, some kind of early indicator I'm playing around with the bot for too long would be great.

So, wired in parallel but before the ESC so it's unregulated is where I want them? Cheers again, that's helpful!