The next episode of probably a dumb question, but..

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Derek Dudge
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Joined: Thu Dec 07, 2017 9:32 pm

The next episode of probably a dumb question, but..

Post by Derek Dudge »

Hey again folks.

So my pondering about what bot to make next has me stuck on a couple questions that probably you guys can answer easy peasy. When the next project is decided, I want to use some different parts to my first push bot project. So I must think servo.

Can I connect 2 servos in parallel to each other to run from a controller such as nanotwo with only one servo plug, and have them activate in perfect tandem?

I'm thinking for lifting forks, or pincers, that kind of thing, a mechanism that has two prongs or arms or whatever moving in unison.


Next up. I don't think axe bot is next on my to do list, but I'm still curious about something. I see there are 180 degree servos, and that some folks modify regular ones to travel 180, but I also see some (looking at George's Axiom at ant freeze was where I first really noticed) using gear motors. Presumably that set up require its own ESC for the weapon to stop the motor wanting to keep rotating beyond 180? I assume the answer is yes, just haven't seen much talk about that when I have looked around here.

And finally (for now) a question about transmitter controls. This just an idle curiosity thing really. I'm looking at my devo 7e controls and of course Third Law just uses the right stick for driving with him having no weapons. Now the left stick, the gradual throttle one, I see as perfect for spinning up rotating weapons, and also as being good for pincers/grippers.

It seems a little clumsy to use that for an axe or flipper through. Anything wanting a snappy activation. And I saw at ant freeze a few folks had modified handsets to have a button where the top hold switch is, which looked a lot better for firing fast weapons

People with flippers and axes, how do you activate them? Make do with the stick or is the addition of the button basically mandatory? And is it an easy modification to do?

Cheers all in advance!
My robots:

Third Law (antweight) - push/ram bot
Manticore (antweight) - hammer bot
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MarkR
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Re: The next episode of probably a dumb question, but..

Post by MarkR »

You can parallel two servos, but don't expect them to behave identically to each other with respect to pulse-widths and positioning.

The ones with a small screw on the back to "tweak" the neutral position - you might be able to set them so they're about in sync. Others- good luck.

If you install them in the same direction, they will move the same way.

But if you wanted to fire a flipper with a pair of servos installed back-to-back, you'd probably need to run them in opposite directions, if you simply parallel them they'll both go the same way (clockwise / clockwise etc).

So if you have enough channels on the rx better to put them in different channels and program your fancy tx to drive those channels in response to the same input, but with opposite direction (and possibly different centre position). (I don't have that tx, I don't know their capabilities)
Robots: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?
Stacie - tidy flipper; 4wd driven by hair bands
Derek Dudge
Posts: 135
Joined: Thu Dec 07, 2017 9:32 pm

Re: The next episode of probably a dumb question, but..

Post by Derek Dudge »

Yeah I think I was not quite visualising it right. Would be easier if i had a couple servos to hand to fiddle with.

Good to know anyway that getting parallel ones to sync is difficult. Probably help me shoot a dumb idea down early. It sounds like I'd be better off planning around a single servo if I go with that idea I got floating around. Cheers.
My robots:

Third Law (antweight) - push/ram bot
Manticore (antweight) - hammer bot
Dazmund
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Re: The next episode of probably a dumb question, but..

Post by Dazmund »

In all honesty, I feel using the left (throttle) stick for a flipper is absolutely fine. I'm using a Turnigy S306G-HV and despite the flimsiness of my cardboard construction right now, it still has some great lifting capability on it.

And yes, you can connect two servos in tandem. The only example I know of doing this is Alex Shakespeare's orange flipper Space-Y, which connects the Turnigy servos I'm using to a 3D printed gearing system linking to the flipper (after looking carefully at its Robot Wars World Series cameo), and it has some serious kick to it. Yes, those Turnigy servos cost nearly £20, but you get what you pay for. As for hooking it all up, Alex is your guy for advice.
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Shakey
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Re: The next episode of probably a dumb question, but..

Post by Shakey »

Image

2 servos can be done and it's not so bad. Above is Space-Y using geared torque transfer and dual TGY306HV servos to produce a monstorusly power flip. The two servos are both connected to that middle gear, to stop them constantly fighting each other there is a bit of slack in each servos connection to the gear, at idle the gear can wobble a bit leaving the servos free to disagree by a bit without fighting but when it comes to a flip both servos will be putting the work in.

They both run off of the same channel (throttle). All I did to make them work together is a quick tweak to one of them. On one of the servos I simply swapped the outer 2 wires of the pot with each other and the same for the two 2 motor wires, this reverse both its feedback and turn direction. Changing just one is a fairly bad idea though the pink servos are forgiving for meddling as they are actually able to rotate 360 degrees, you can even trick them into 360 degree rotation by fiddling with the PWM signal (Accidentally learned this while messing with one and an arduino).

The TGY306HV's are fast, faster than you can move the throttle stick. 2 together? No hope. So my transmitter has a couple of tweaks in the for of a 2 position switch and a microlever on the back. The signal from the throttle stick (analogue potentiometer, easy stuff) runs into the toggle switch which chooses between the signal (so normal operation) or simply 0v (telling the transmitter throttle is down no matter where it is). This then feeds into the micro lever that either passes on what the toggle switch selects to the transmitter or when pressed feeds a 5v (I think) signal (throttle high) tot he transmitter. I like this setup as it's instant trigger control on all throttle weapons and the toggle acts as a kind of extra safety thing for spinners where I can lock throttle to the down position. All this is so that the throttle channel goes from low to high instantly without following the relatively slow stick movement speed.

Of course you can do this via tranmitter if you have a smart one. I do it my way as after the initial wiring I never have to actually set it up for any model, the capability is always there. You could set your throttle to a low/high step response to counteract slow movement (though I still find using the stick clumsy and less responsive than my microswitch). You can mix your throttle into another channel (typically aux) but reversed to have 2 channels for dual servos.

For axes I recommend gearmotors and something like a Vex29. The ESC isn't necessarily to stop it going over 180 degrees, most are dumb and don't have a clue where the motor is. The ESC is there because it has to be. Stopping the motor when it has finished its travel can be a switch wired in or just good old fashioned manual control (my preferred). Typically fired off of rudder (being a centering stick that isn't used for steering).

A lot of the buttons on transmitters aren't often a modification but actually the throttle cut button (Again I find this awkwardly placed for weapon control). When bound correctly throttle cut forces throttle low, so you would typically reverse your throttle (so now throttle cut is effectively sending it high or flipper open) and typically then use throttle hold to hold the flipper down (Cut overrides all).
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GeorgeR
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Re: The next episode of probably a dumb question, but..

Post by GeorgeR »

Gearmotors are definitely the way to go for axes, as servos are a bit slow. In addition to Axiom, Baby Hell and the axebot that Shakey sells are both gearmotor axes. You obviously need an esc, but any suitable single channel drive one is fine, Axiom and Shakeys axebot use a Vex 29, which works well and is cheap.

For transmitter control the simplest way is to use the rudder channel (left stick left/right movement), when it's centered the axe is stationary, push one way to fire the axe, the other to retract. The other way is to use some kind of switch, i think Baby Hell uses a three way momentary toggle switch, up to fire, down to retract, with it staying still in the middle. On Axiom I've got a more complex setup, so i can switch between manual control on the rudder stick, or timed pulses that fire or retract the axe (i can explain further if your interested).

Modifying the transmitter can be a fairly simple operation, simple swap the wires from an existing switch to an alternative, mount it on the case, and your done.
As you have a devo 7e you can get more involved by adding two additional 3 way switches without loosing the originals, (there is even space to mount them as the 7e shares a case with the devo 6). Google "devo 7e extra switches" and you'll find plenty of info.

edit: It looks like Shakey beat me to it with the info!
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Derek Dudge
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Re: The next episode of probably a dumb question, but..

Post by Derek Dudge »

Wow, cheers guys, that's tons of info.

So linking via gears to combo servos like Alex described sounds crazy interesting, but also slightly ahead of where I see myself at for the next project. Actually my asking about linking the servos was more me picturing the front of something like King Buxton rather than a traditional flipper. I was curious how the prongs would be best powered, if they would have a servo each etc. Now I'm thinking a single linked lifter part (connected internally with prongs protruding) powered by a single servo would just be way easier.

The stuff about axes is interesting too. You know, it hadn't occurred to me at all that you might fire them from the sideways sprung/rudder control. Was just equating the direction it would move with forward and back on the stick. Doh.

This is all good stuff to know. Down the line when I'm next able to get things like a drive ESC and what not, I may take you up on further explanation about Axioms set up George. Right now I've got a page of terrible drawings of something that might look like a mini King buxtom, and another that would end up looking like Axiom and Third Law had a baby.
My robots:

Third Law (antweight) - push/ram bot
Manticore (antweight) - hammer bot
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MarkR
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Re: The next episode of probably a dumb question, but..

Post by MarkR »

Alex, that is really cunning, modifying one of the servos to run the opposite way by reversing leads to the pot, so you can run them off the same input channel :)

Mark
Robots: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?
Stacie - tidy flipper; 4wd driven by hair bands
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