Total Newbie on a budget

[bitternboy]

A plug and play mixer would require no mixing on your transmitter, with channels 1 and 3 on the transmitters directly controlling the 2 used channels on the receiver.

I know it might be cheating but could you get hold of a ready to use V-tail mixing model for your tx? That would get you there straight away.

[Londonboii]

From the sound of it the physical mixer is just going to do what the program does.

I need to get ch3 left to control ch1 forward and ch2 in reverse, and ch3 right to control ch1 in reverse and ch2 forward.

So I think I'm trying to split channel 3 into 2 channels, with each one controlling the 2 in different directions. If that makes sense.

Maybe it would be easier to have each stick control a wheel and then I could turn by having one up and one down. But the left stick doesn't return to centre when released like the right. It sits where you leave it and it's not easy to centre without looking.

[Londonboii]

I'll look at what the v tail mixer does.

[bitternboy]

I know it might be cheating but could you get hold of a ready to use V-tail mixing model for your tx? That would get you there straight away.

That wasn't very clear of me. I meant - there must be a default tx programming file available somewhere with V-tail mixing taken care of. I'm not an expert in the slightest in programming that tx but I thought it might be a shortcut worth tracking down

Getting a physical mixer might be a bit silly as you say.

[Londonboii]

After looking a bit it looks like it's possible to mod the left stick to make it sprung, which will mean I can just operate each wheel sperately and I'll then just move them in opposite directions to turn.

Thanks for the help

[Londonboii]

I got the controls sorted by modding the left stick so it's sprung now.

Further questions:

I'm using 2 cordless drill motors and holding the wheels on with the reverse thread screws. They keep working loose. Anyone know how to prevent this or if there are stronger reverse thread bolts to hold them on with? The screw isn't made of the strongest metal and I've almost ruined one of the Philips heads.

Also looking forward to the weapon, I'm going to use a linear actuator to raise the lifting mechanism.

What do I need to connect the linear actuator to the receiver and control it? Something like what the escs do on the motors. Would a simple on/off do the job? Or is there something better for this?

I'll be using a switch on the transmitter to activate the lifter.

[bitternboy]

If you're keeping it simple and using a single switch for the weapon then a set of RC switch + relays would do fine (plus some microswitches for end stops if the LinAc doesn't have a limit switch of its own) to just flip it between the battery voltage in either direction. You'd have to do some simple circuit design to get the receiver signal controlling it properly.

Alternatively, you could get a reversible brushed ESC but if your not worried about controlling the speed then you'd be wasting some functionality.

[Londonboii]

Thanks.

If I use a mondeo seat height adjusting motor with the threaded rod arm as in the car would a brushed ESC similar to what I use on the motors for the wheels be all I need?

I think it has end stops when in the car as they stop at certain heights. But I'll look at that when I get it.

[bitternboy]

If what you salvage from the mondeo has some sort of end stop switches then possibly (assuming it's a suitable motor :P)

Bare in mind you don't just need physical end stops that stop the motor turning, they need to actively cut off power supply to the motor in their respective directions when the limits of the lin-ac are reached. The controller won't know when to stop on its own and will stall the motor at the limits of movement, which you don't want.

Lots of off the shelf lin-acs have this built in so you can drive them against their limits of movement and they won't stall, a bit like this:

[Londonboii]

I'm not too good with electric drawings, and haven't done much with relays.

But is that a drawing of 2 relays connected to the motor? So there would be a physical connection made at each end that tells the relays to cut off power to the motor once it's reached each end of travel?

Are they just standard auto 12v relays? Each point on the NC parts are the 4 pins on the relays?

[RogueTwoRobots]

They're just two microswitches, and each has a diode connected to it. This allows power to travel in one direction only. The idea being that when something reaches the end of its travel, it hits the switch which cuts the power to it, thus protecting the mechanical bits. But it only cuts power in one direction, allowing you to reverse/retract the motor to reset or reposition it. A microswitch at the other end of the travel will cut power there too. I fitted these on my featherweight grabber bot and they worked pretty well.

https://youtu.be/2TZ1lS8I-lg

[bitternboy]

That diagram shows the typical set up for using switches at the ends of travel to stop current flowing and letting the motor push it any further, sorry for being confusing :P

The ends with V+/- are the voltage you would be supplying from your ESC. The things labeled "NC" represent switches that are activated when the limit is reached, one for each end; NC stands for normally closed, so when it hits the end, they are opened.

The components represented by the arrow and line are diodes. Their function is to only let current flow in one direction.

The M in the circle is the motor driving the lin-ac.

Imagine the lifter is halfway up. Both switches are closed, so the diodes are redundant/bypassed and current can flow in either direction i.e. you can tell the ESC/relays to provide a voltage across the circuit in either direction and the motor can spin in either direction, raising it up or down.

Now the lifter hits the top of it's path, you don't want the motor to try and keep pushing because you'll break the mechanism or stall the motor. One of the switches is at the extreme however and is activated/opens. This means that if current wants to flow through the circuit it has to bypass the switch and flow through the diode instead of the switch. The diode won't let current flow in the direction that would result in the motor trying to push the lifter beyond its limit.

The other switch is still closed so it can still move back.

The same thing happens with the second switch and diode for the other limit.

Hope that's more helpful.

EDIT: Ah, got beaten to it :P

[Londonboii]

Thanks a lot both of you. I think I understand now.

Last silly question, what diode do I need?

I searched in maplin for the micro switches and they are simple enough, but search diode and a load of different types come up.

Is there a name for the type of diode in that setup?

[Londonboii]

Will this work? Using 3 pin microswitches.

If the diodes are needed, where would they go in this setup?

wiring.jpg

[R9000]

You do need diodes here, because otherwise, your linac will disconnect permanently when it gets to one end. Think of it this way: The diagram Bitternboy posted shows a circuit where there are two one-way paths for the current to follow, and a path for current to flow in either direction (if both switches are closed). Now if one switch opens (or disconnects), the current can only flow one way through the circuit now because the current is now forced across the diode that is connected over the switch. This means that, while the circuitry will stop your motor from trying to push the linac past its limits, it will still allow current to flow in the opposite direction so you can retract it.

Your diagram would stop the linac moving completely since it pulls both contacts of the motor to the same voltage, which then stops it (I think). You basically just need to make something like Bitternboy posted. The diodes you need can be fairly basic, you just need ones with a higher reverse voltage than you're running your motor at, and some that can handle the current through it (which you can measure while it's running). Also keep in mind that diodes introduce a small voltage drop when used (usually around 0.7-1V) but as long as your linac can move off the limit switch again, it'll be fine.
Something like this should do, but check your voltage and current as I said: https://www.arrow.com/en/products/1n...FQMM0wodY6MGTA

Oh, and don't get Zener diodes. They're not what you need here.