T_Y's Build Log

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T_Y
Posts: 128
Joined: Thu Mar 15, 2018 12:51 am
Location: York

Re: Hello, World! - A Newbie's First Robot

Post by T_Y »

It's been a while since the last update, due to the exam season rearing its head once more. :( I have not been idle, however...

Introducing Percussive Maintenance, the axe-bot of doom armed with an almighty 8.2g mini-spanner!

...okay that might be a bit of an exaggeration. :D

Image

I didn't realise during the design, but it does look a bit like Terrorhurtz, with the swept back angled front.

For this bot, I'm thinking of doing channel mixing on the Devo 7e and having separate ESCs for the drive and weapon (as the few dual channel ESCs I've found are quite expensive). I'm looking at using these ESCs for each drive motor and a VEX 29 for the weapon motors. I'm not sure about the wiring though.

The basic gist is:
- Battery is directly connected to each ESC (so they all get the full voltage)
- The LemonRx is powered by one of the drive ESCs
- Elevator and Aileron channels are mixed, and sent through the evelator - this signal is split between the two drive ESCs
- The weapon ESC takes its signal from the rudder, allowing it to swing forward and back
- Each drive ESC controls one drive motor. The Vex controls both weapon motors.

Here is a crude wiring diagram if it helps:

Image

Does that sound right?
Thomas

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peterwaller
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Re: T_Y's Build Log

Post by peterwaller »

If you use the same output for both left and right motor drives the robot can't turn.
When you use aileron elevator mixing you connect one motor drive to the elevator and one to the aileron.
The mixing then causes both outputs to change in the same direction with the elevator stick and in opposite directions with the aileron stick.

T_Y
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Re: T_Y's Build Log

Post by T_Y »

Ah right, thanks for that! I was under the impression that it somehow put both signals through the one connection. In hindsight, that doesn't make sense.
Thomas

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DieGracefullyRobotics
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Re: T_Y's Build Log

Post by DieGracefullyRobotics »

Also, I believe those ESCs are single direction only, hence the cheap price. They are designed to power a boat prop or car wheel in one direction whilst a servo rudder/rack does the steering.
Dave
Die Gracefully Robotics - Barely Even a Proper Team.

Paulmchurd
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Re: T_Y's Build Log

Post by Paulmchurd »

DieGracefullyRobotics wrote:
Fri May 11, 2018 6:17 am
Also, I believe those ESCs are single direction only, hence the cheap price. They are designed to power a boat prop or car wheel in one direction whilst a servo rudder/rack does the steering.
There are bi directional versions now. That include a switch for brake on /off. Less then £5 each as well. Just heavy!

Paulmchurd
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Re: T_Y's Build Log

Post by Paulmchurd »

DieGracefullyRobotics wrote:
Fri May 11, 2018 6:17 am
Also, I believe those ESCs are single direction only, hence the cheap price. They are designed to power a boat prop or car wheel in one direction whilst a servo rudder/rack does the steering.
There are bi directional versions now. That include a switch for brake on /off. Less then £5 each as well. Just heavy!

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DieGracefullyRobotics
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Re: T_Y's Build Log

Post by DieGracefullyRobotics »

I just found the bit where it says forward and reverse. Doh!
Dave
Die Gracefully Robotics - Barely Even a Proper Team.

T_Y
Posts: 128
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Location: York

Re: T_Y's Build Log

Post by T_Y »

Paulmchurd does bring up a good point about the weight. especially because I'll be running 2 of them plus the vex!

Did a bit more looking and found these ones from Micron Wings. They're much lighter at only 4 grams and smaller too, for just a few extra quid. No idea about reliability or reputation though.
Thomas

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peterwaller
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Re: T_Y's Build Log

Post by peterwaller »

I couldn't see where it says they are reversible, many designed for driving small model aircraft are one direction only.

Ant Ipodean
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Re: T_Y's Build Log

Post by Ant Ipodean »

We have been using the Bustophedon ESCs, and these ones:
https://www.aliexpress.com/item/JMT-20A ... 0.0.uqUWZr , with some success.

I have had a couple of failures with the Bustophedons, one DOA out of the packet, one recently had the BEC output fail inexplicably.

The JMTs have been fine so far and are a bit smaller and lighter - about 8g after removing the switch and some wire.
Make sure you order the JMT withOUT brake version.

Of course, a compact little dual ESC is ideal, if you can get one which is reliable/affordable/available ;)

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