Team MedBots

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Max
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Re: Team MedBots

Post by Max »

Thanks Rory, as I understand it each individual channel gives out a pwm signal as you said but obviously the tx isn't sending 6 separate signals but instead send a single signal with the information for all 6 channels on it (known as PPM). I'm interested in accessing this signal as it allows me to monitor all 6 channels on a single pin of the arduino. As an arduino only has 2 interupts I need to do this to monitor more than 2 channels efficiently.

On a lot of receivers there are ways of accessing this PPM signal by soldering on an additional wire.
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peterwaller
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Re: Team MedBots

Post by peterwaller »

The answer is not a lot.
I just hooked up a lemon receiver to a scope and there appears to be no signal at all on either of the two points you mentioned.
I know that on many of the DelTang receivers you can program them to output all the channels sequentially on one pin if that is what you are after.
I see while I was doing that things have moved on so maybe the deltangs are what you want.
Rapidrory
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Re: Team MedBots

Post by Rapidrory »

My ESCs use a single interrupt to monitor two signals, and this could be easily extended to monitor all 6 channels. Only one channel is high at any one time, so it's possible to trigger the interrupt when there's a change in state of each channel.
Rory Mangles - Team Nuts

Robots: Nuts 2 and many more...

NanoTwo Motor Controllers: https://nutsandbots.co.uk/product/nanotwodualesc
Max
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Re: Team MedBots

Post by Max »

Ah thanks Peter, looks like the deltang is what I need, just a shame it costs as much as 6 lemons!

Rory- that's interestting to hear, I've been searching for information about using an arduino and an rc receiver with more than 2 channels and the usual response is 'this could easily be extended beyond 2 channels' but never alludes to how! I will look into it further as clearly there must be a way!
Max
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Re: Team MedBots

Post by Max »

That didn't take long, found a helpful piece of code here:
http://forum.arduino.cc/index.php?topic=91909.0

Monitors all 6 channels and uses interupts rather than pulseIn.

I'll start off using that and if I run into problems will invest in a deltang.

Thanks all!
Max
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Re: Team MedBots

Post by Max »

Rapidrory wrote:You want a setup like this (just a random pic of google image):

Image

the Fet needs to be on the low side of the circuit.

Also, you may want to drive it with more than 5v at the gate as I've found that they can get warm even just driving ant motors..
I've hooked it up just like the diagram with 3 motors, mosfets and Diodes. But I have noticed something peculiar. When I have the gate pins of the MOSFET disconnected but plug in the battery initially the motors are stationary as you would espect. But then each one starts to slowly accelerate up to maximum speed. When you pull the pin down to ground the motor stops but once you disconnect the gate the motor slowly starts up again. Spooky.

It's not a big problem as once it's all connected to the arduino the gate will be naturally pulled to ground when it is not set as high. But nonetheless does anyone knowing why this is happening?
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peterwaller
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Re: Team MedBots

Post by peterwaller »

The gates are very high impedance and will slowley charge up you need a pull down resitor between the gate and 0v it can be quite high say about 47k but the value isn't critical.
It will also help to provide protection against damage casued by static.
Max
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Re: Team MedBots

Post by Max »

Ah ok, I'll add in resistors.

Does anyone know a good source of the 10:1 HP micro metal gearmotors? Obviously technobots does them but they are fairly pricey.
Rapidrory
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Re: Team MedBots

Post by Rapidrory »

HPs are always pricey unfortunately... I did find some 10:1 LPs for a ~£2 a while back, but they're unlikely to be very useful.. I think you'll just have to bite the bullet and shell out for the pricey ones...
Rory Mangles - Team Nuts

Robots: Nuts 2 and many more...

NanoTwo Motor Controllers: https://nutsandbots.co.uk/product/nanotwodualesc
Max
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Re: Team MedBots

Post by Max »

Hmm that's a shame. Trying to decide what will work best for the melts brain, 3 of those 10:1 HPs which would give me 900rpm for the robot and increased stability due to the 3 wheels or go for a single high power motor and just one wheel. The 900rpm is under no load so I would expect that to drop a lot.

I'm struggling to find a suitable high power motor that wouldn't need a gearbox, I think 50grams is probably the maximum weight I can afford for the motor. Found this:
http://pages.ebay.com/link/?nav=item.vi ... 1153655398
Which due to the larger wheel size would give a theoretical maximum of 16,000 rpm which is obviously way to much. I fear it may not have the power to get moving on a 50mm wheel and even if it does it will be under massive load so draw silly current.
Can anyone think of a better alternative motor?
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