'Harder Than It Looks' Build

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wmoulds
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'Harder Than It Looks' Build

Post by wmoulds » Tue Feb 06, 2018 11:30 pm

First of all I love this forum for all the info I have gathered so far and thank you to Shakey, who I think it was, for telling people on Robot Wars how to get into battle robots by starting with Antweights. I grew up watching robot wars wondering where to start and how to get involved.

With not knowing a single thing to do with RC cars, robots etc all my knowledge I have scrapped from this forum. I have bought 2 pololu motors 600rpm with wheels and bracket, Dasmikro 2s6a, lemon rx, Devo 7e, small switch, turnigy lipo 2s 300mah, turnigy accucel 6 and jst cable adaptor for battery.

I waited patiently for all parts to come, the Dasmikro being the last component to arrive, excited I laid all the parts down figuring out which wire goes where, forgetting I had the battery still connected to battery leads, ended up frying the ESC when the wires moved. Gutted, so I ordered 2 more on the off chance something might go wrong again and the fact it takes at least a week to arrive from China.

Waited again for the ESC's to arrive. In the meantime I built a cardboard base for testing and I flashed the Devo 7e, with thanks to the guide on the Nuts and Bots website.

ESC arrived at the weekend, my dad is interested in robot wars and he is good at soldering so had him over tonight to help wire everything up. Wired the switch, cutting the red wire and inserting the switch, tested it on a motor, switch works. Wired this to the ESC, wired the motors and wheels to the ESC, wiring the negative to the first terminal, positive to 2nd terminal, negative from the second motor to the 3rd, postive to 4th. Then wired the first cable from the receiver, black to ground, red to VCC, white to signal 1, the second cable from the receiver I just soldered the white wire to signal 2. Made sure no solder or wires where touching. We connected these two cables to the ELE and AIL ports on the Lemon RX (Does it matter which signal wire goes to either one). Started the binding process, when binding one wheel was constantly turning at full speed, when binding had finished and I tested the controls the second wheel started to move but the ESC then started to smoke.

Thinking it has been ruined(?) we remove the wires and start to solder the 3rd and last ESC, being really careful about everything etc, it all looked very well soldered. Now being anxious we start it up, again one wheel is turning by itself and very fast, once we use the transmitter controls to move the other wheel the ESC starts to smoke again, but we turn the power off very quickly as to not cause anymore damage. We solder the black wire that we left out from the receiver to the ESC, this somehow fixes the smoking problem. I cannot for the love of trying seem to stop the one motor from constantly moving at full power in one direction. The 2nd wheel when using the transmitter only goes forward when pulling the knob backwards and nothing when pushed forward.

Is there something really simple I've left out that is causing the robot to not work or have I simply ruined the ESC again, possibly causing the BEC to be faulty or could it be just be pure bad luck with a broken motor? Need help badly as I've hit a brick wall. Thanks in advance.

Paulmchurd
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Re: 'Harder Than It Looks' Build

Post by Paulmchurd » Tue Feb 06, 2018 11:38 pm

If you can post a picture of all your wiring it would help us identify what is going on.

Most of the time from dasmikro faults I’ve seen on this forum is the soldering has created a short circuit some where.

wmoulds
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Re: 'Harder Than It Looks' Build

Post by wmoulds » Wed Feb 07, 2018 12:58 am

I'll try and upload photos in this message...

Image
Image
Image
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Image

The first picture shows the original way I had it wired, with just the white signal wire soldered from the second cable from the receiver. The other pictures show the way I have it now with all three wires soldered.

Paulmchurd
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Re: 'Harder Than It Looks' Build

Post by Paulmchurd » Wed Feb 07, 2018 7:28 am

You need both black reciever wires solder on but only 1red wire from then reciever cables.

I can’t see any major solder problems.

Possible faulty battery sending to much current. This chip can only take 9vaults I think.

Not sure, hopefully some of the electronic wizs will wake up soon 😁

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voorsk
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Re: 'Harder Than It Looks' Build

Post by voorsk » Wed Feb 07, 2018 10:44 am

It does all look okay. Nice looking soldering.

You said you tested the battery on one of the motors first.. the motors can only take 6v, but the batterys are 8v, so you maaay have broken one of the motors by doing that? Which one stopped working? If it's shorted out, it may explain the smoking. I'm not sure how much voltage they can take before going wonky.

I don't have that receiver, so I dunno if the connectors are on the right way around. Would having them on backwards (so signal and ground are swapped) cause an issue like this?

edit: also regarding receiver connections; you only need one connector with black (ground) and red (positive) attached. They all have to have white (signal) attached, tho, or else it won't do much controlling.

Have you tried switching the receiver channels around? Mine went really weird when they were in the wrong channels, altho I don't remember if one of the wheels was going round constantly.

Hopefully someone more experienced can provide a more definitive answer. :)

ooh, and welcome! :D
Team BLEEP Suspicious Houmous / Sprouting Potato / Fermented Melon

wmoulds
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Re: 'Harder Than It Looks' Build

Post by wmoulds » Fri Feb 09, 2018 5:47 pm

Thanks for your inputs. I'm going to try and swap the receiver channels around later to see if that makes a difference. Though I think you may be right about blowing the motors. I knew they were rated to 6v but thought they had a tolerance of above this, my logic was the ESC only regulated 6v to the receiver and allowed the full voltage to the wheels hence why I never thought attaching the battery to the wheel would have any bad consequence. But I believe the wheel that is not behaving is the wheel that I attached to the battery. Its a steep learning curve so mistakes are bound to happen I suppose. I'm going to order more parts later I think.

Couple of questions though. My battery is LIPO 7.4v 300mah 2s 35-70c, I connected it to my charger, went through the settings and choose balance charge @ 0.3a 7.4v 2s. Once charging it reaches 8.4v, is that meant to happen and would this extra voltage be causing damage to the motors/esc? Just a thought.

Also, I have one of the micro 9g servos MG90s. It turns 180 degrees, how does the mechanism work with the flipper... I assume once I push the throttle up on the transmitter this will engage the servo to turn, does how far I push the throttle determine how much the servo moves, does it reset its position or do I need to use the throttle stick to bring it back to position to be able to flip again? I understand this is a complete noob question but I literally can't find info on this anywhere.

Finally, I don't know where to post this but is there anyone from Northern Ireland here? I've been searching and can't find any antweight or any combat robot events here at all and was maybe looking to know if there is such events about or anyone who wants to battle, as that's the purpose of building the robot.

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voorsk
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Re: 'Harder Than It Looks' Build

Post by voorsk » Fri Feb 09, 2018 6:07 pm

I'm probably wrong about the motors. i thought the ESC limited voltage to them. i also didn't know you could make them turn by connecting a battery directly - i thought they had to be pulsed via an ESC to work?

i dunno about the batteries or servo.. I've got the same servo, so I'm interested too!
Team BLEEP Suspicious Houmous / Sprouting Potato / Fermented Melon

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Shakey
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Re: 'Harder Than It Looks' Build

Post by Shakey » Fri Feb 09, 2018 7:35 pm

There's a whole lot of misconceptions throwing around in here so... *cracks knuckles*
Paulmchurd wrote:
Wed Feb 07, 2018 7:28 am
You need both black reciever wires solder on but only 1red wire from then reciever cables.
Incorrect, you only need 1 of each and the 2 (white) signal lines. It's a dual ESC, both black wires are going from exactly the same place to exactly the same place (electrically). They're only both there normally for conventions sake.
voorsk wrote:
Wed Feb 07, 2018 10:44 am
You said you tested the battery on one of the motors first.. the motors can only take 6v, but the batterys are 8v, so you maaay have broken one of the motors by doing that? Which one stopped working? If it's shorted out, it may explain the smoking. I'm not sure how much voltage they can take before going wonky.

I don't have that receiver, so I dunno if the connectors are on the right way around. Would having them on backwards (so signal and ground are swapped) cause an issue like this?

Have you tried switching the receiver channels around? Mine went really weird when they were in the wrong channels, altho I don't remember if one of the wheels was going round constantly.
Motors don't really work that way. The 6V rating is a nominal rating, ie what it is expecting for normal use. They will more than happily take an overvolt. Chips dislike overvolts as it can break them down internally, motors dislike increased voltage as it produces extra heat. Extra heat however is needed in spades to kill motors so overvolting to 8.4v from 6v is fine. Even overvolting to ~12v is normally fine. For reference last time I killed a 6v N20 motor by overvolting it I had it up to ~26v for a minute or two before the heat was enough to kill it.

Having them backwards will just cause the ESC to read no signal, this usually presents as nothing happening.

Typically wheels constantly going round are a receiver not listening to its TX and falling back to non centre binds. Or the ESC ahs died on one side (sometimes the FETs die in such a way it simply just applies full power).
wmoulds wrote:
Fri Feb 09, 2018 5:47 pm
Couple of questions though. My battery is LIPO 7.4v 300mah 2s 35-70c, I connected it to my charger, went through the settings and choose balance charge @ 0.3a 7.4v 2s. Once charging it reaches 8.4v, is that meant to happen and would this extra voltage be causing damage to the motors/esc? Just a thought.
8.4v is the max charging voltage of a LiPo. They actually have 2 voltage ratings per cell, they are normally listed at their nominal voltage of 3.7v per cell which is where most of their capacity is. However they will charge up to 4.2v a cell. We use 2S LiPo's so 7.4v nominal and 8.4v max charge.
wmoulds wrote:
Fri Feb 09, 2018 5:47 pm
Also, I have one of the micro 9g servos MG90s. It turns 180 degrees, how does the mechanism work with the flipper... I assume once I push the throttle up on the transmitter this will engage the servo to turn, does how far I push the throttle determine how much the servo moves, does it reset its position or do I need to use the throttle stick to bring it back to position to be able to flip again? I understand this is a complete noob question but I literally can't find info on this anywhere.
MG90's are pure luck of the draw on how they behave, their made and knocked off by just about everyone and quality and behaviour varies wildly. The servo follows the throttle stick and that's it, so you need to return the throttle stick to low to set the servo back to low.
voorsk wrote:
Fri Feb 09, 2018 6:07 pm
I'm probably wrong about the motors. i thought the ESC limited voltage to them. i also didn't know you could make them turn by connecting a battery directly - i thought they had to be pulsed via an ESC to work?

i dunno about the batteries or servo.. I've got the same servo, so I'm interested too!
An ESC does not limit voltage, in fact the entire purpose of a modern ESC is to NOT limit it. Way abck when ESCs did work by simply varying the voltage to change the speed. Nowadays they work by rapidly turning the motor on and off at the full voltage. So for a half speed motor it simply alternates turning it on and off for equal amounts of time (This is done in the thousands of times a second range). A DC motor will turn fine with just a battery connected, the ESC is simply supplying it the power and they handle themselves.

Are you thinking of brushless motors? These need an ESC as the part of the motor that provides its self control (the brushes) is removed (as it is also the largest power limitation).

Lastly the soldering looks fine, my expectation is at some point either it just keeled over for no reason as some ESC's like to do or a short (whether by wires touching or an accidental solder bridge) has damaged a driver chip.

EDIT: It doesn't matter which way around AIL and ELE are just for testing, the ESC has no clue which one they are, only what speed they are saying.

Also the motor mounts aren't gripping the gearbox as they should, look on the inside of the mounts and you see 2 little notches, these lock onto the plate of the gearbox closest to the motor, this stops the motor moving side to side in the mount.
Nuts And Bots - For all your components and ready built antweights!

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AWS 44, 45, 49, 51 & 55 Winner - Far too many robots!

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peterwaller
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Re: 'Harder Than It Looks' Build

Post by peterwaller » Fri Feb 09, 2018 7:45 pm

On the battery front I always think it is confusing calling a 2 cell lipo 7.4v as fully charged it is as you have found 8.4v.
Even if your motors are rated at 6v they should be fine at 8.4v.
If you disconnect your motors from the controller and connect them in turn across the battery you can check if they work ok.
As to the servo although you can probably turn the arm through 180 degrees when operating it will only turn about 120 deg.
I am at the moment toying with the idea of writing a book about small combat robots and thought the section I have written on the operation of a servo might be useful to you as any feedback on it would be useful to me so here goes.

Servos

The servo is the device that translates the signals from the radio control system into physical movement by the use of an electric motor. The motor output goes through several sets of gears each reducing the speed but increasing the power of the drive. The final output shaft is mechanically joined to an output arm and a feedback potentiometer. The potentiometer is connected to a circuit that generate a 1.5 ms pulse when the pot is central, a 1 ms when the pot is turned about 60 degrees one way and a 2 ms pulse when turned about 60 the other way. There is a circuit that compares the feedback pulse length to the pulse coming from the receiver and by sending direction and speed information to the motor drive circuit causes the motor to drive until the feed back pulse matches the receiver pulse. This creates a closed loop system so the movement of the output arm moves proportionately with the transmitter joy stick. The bigger the difference in the pulses the faster the motor turns so as it approaches the required position it slows down to reduce the chances of overshooting the mark.
Image
Looks like Alex got there before me.

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voorsk
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Re: 'Harder Than It Looks' Build

Post by voorsk » Fri Feb 09, 2018 8:32 pm

ooh - sorry for my bad info. just realized i forgot to mention I'm a noob too, and was really just speculating on possibilities (was hoping the question marks would indicate i didn't actually know) :oops:

i have learned lots, tho - thanks guys!
Team BLEEP Suspicious Houmous / Sprouting Potato / Fermented Melon

wmoulds
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Re: 'Harder Than It Looks' Build

Post by wmoulds » Thu Feb 22, 2018 11:24 pm

Hey folks, just an update to where I am in case it may help someone else in the future.

I had bought a robot from nuts and bots for a few reasons, 1 so I could battle two robots, 2 use it as a benchmark and 3 use it as a learning tool. It has succeeded already in helping me to troubleshoot my own robot. I binded it with my Devo 7e and low and behold the right wheel kept spinning at speed and the controls didn't make sense, just like my own robot. Whats the odds, so that got me thinking 'whats the common part between the two?' - the transmitter. So I re-flashed it tonight, followed the instructions exactly once more and binded it up to the nuts and bots robot and boom it worked, needed a little bit of trimming to get it working better but basically working as it should do. I tried binding again to my robot but no luck, the same problem was occurring, the dasmikro does look slightly damaged on one of the FETS so I reckon that's the problem like Shakey mentioned, that full voltage is bypassing it and going straight to the right motor. So I've ordered another dasmikro and hopefully I'll get it soldered up perfectly and this should solve the problem. I'll report back soon.

Peter, thanks for the info on servos. I did find it interesting and very helpful. A book on small combat robots would be very beneficial to many people I would suspect, myself included. Who is your target audience? I am able to comprehend the passage you wrote now, but I feel a month and a half ago I would need it put into layman's term before I understood it, though I suppose you can ease people in with the book and have a good learning curve throughout.

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peterwaller
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Re: 'Harder Than It Looks' Build

Post by peterwaller » Fri Feb 23, 2018 9:55 am

You have hit upon the problem if it is too technical it will only be understood by those who probably don't need it but because I understand it I have trouble deciding what a youngster or complete newcomer can comprehend. I think at the moment it is coming out as you have said maybe a little too complex for starters but I have put in a large section on different types of antweights with plenty of example photos and cad drawings of robots I have built so should at least give people ideas on what is possible. There is also a chapter on useful components so that should help starters. Anyway its a work in progress and I have no illusions of it being a best seller but just hope it can be of help to those involved or starting out in this great hobby.

Derek Dudge
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Re: 'Harder Than It Looks' Build

Post by Derek Dudge » Sat Feb 24, 2018 3:40 am

Shakey and Peter - cheers for writing those posts out! Not my thread but regardless that was all very interesting and informative.
My robots:

Third Law (antweight) - push/ram bot
Manticore (antweight) - hammer bot

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