Spinning Tortoise Melty Beatle

Anyone? Anyone? Bueller?

Alex is a wiz kid with electronics....Alex?

Probably simple for you.....

If you are not familiar with how melty works, here's the deal

one or more motors spin the entire bot. the controller uses input from the throttle, elevator and aileron channels to know what to do. Throttle controls how fast the bot spins, while elevator and aileron control direction...typical fwd/rev and left /right.

There is no speed controller, the controller turns the motor(s) on or off....using darlington transistors, mosfets or relays (depending on current requirements)

So far, everyone has only used brushed motors and with the available shared code, the motor(s) are either fully on or fully off, no in between or pwm or anything.

to actually move, drive or translate, a motor is turned off at the right time during the spin, so as to cause the bot to move off in a direction.

If you need more info, google 'open melt' or translational drifting.

So the question is simply this: Can you use brushless motors/controllers in this situation? and if so, how would you do it?

btw: no one has succeeded so far ...to the best of my knowledge

Nice solution, but not sure if it would work.

so this gizmo requires that you keep the existing speed controller and just take the negative wire to the motor and connect itto the the gizmo???

Or did I miss something?

So is it Alex FTL ?

Actually, you're so wrapped up in your current obsession that you're probably not thinking about this at all, but my discussion with jeff was about how I think that I can make it work without much effort.

It's based on how a pwm signal works compared to how the brushed version works.....really simple solution.

You didn't really lose anything..just didn't figure it out....yet

I have everything I need to see if it works in a 3.

I should do something with it soon.....I'd really like to see this in a 12 or a 15 with a pair of monsters.

I still think you've found a way to alter the input signal to a brushless ESC - that's the easiest way to do it I can think of.

Jeff L wrote:

I still think you've found a way to alter the input signal to a brushless ESC - that's the easiest way to do it I can think of.

You are somewhat curious, aren't you??

If you really want to know, I'll tell you, but I'll do it by asking questions...until it hits you in the face.'

You've read the above posts, so you know that Rich Olson's melty code causes the motors to be either completely ON or completely OFF, right?

And I am hoping that you know a bit about pwm?

If so, then how does pwm work (for rc) ?

PWM signals are made by comparing potentiometer states to a set waveform, providing power in a direct on state if the state is greater than set values on the waveform (the opposite of this is true for an off state). Considering that, if you altered the timing of the waveform the potentiometer is compared to you could do some very weird little things.

You're killing me again....

rc pwm signals are as follows: the pulse duration is supposed to be between 1 and 2 milliseconds long

2ms = full forward
1.5ms = neutral
1ms = full reverse

frequency for rc pwm is 50Hz or 50 times per second or once every 20 milliseconds

In melty, the motors are either fully on or fully off.

assuming forward direction....

fully on = 2 ms pulse fully off = 1.5ms pulse

So, for the brushless esc to function using the melty code, it has to see a pulse of either 2ms or 1.5ms

Conveniently, we already have a source for the pulses...the receiver

If we set the gearswitch to ON and the flaps (aux channel) to neutral, then the signals at those receiver pins will be 2ms and 1.5ms respectively.

Route those signals thru a SPDT relay (highspeed) to the esc and...

tada...instant melty style on/off control of a brushless esc and motor

Using a second relay or a NAND gate IC and a second esc/motor can be controlled as well.

There is a least one possible problem here tho.....the pwm frequency of 50Hz

At 3000 rpm, the ESC would only be able to see 1 pulse per revolution (or every 20ms).

I have this working on the bench but just haven't tried it in the bot yet.

Will this work? other options?

Anyone? Jeff? Alex? Bueller?


Future possible expansion: Hit the gear switch and now you're running in reverse. Haven't thought about it much more, but I'll bet that only 1 motor could be reversed which = driving like a standard bot as well...

hahahahahaha im totally out on this one

this where i go to alex

Cody Harris wrote:

hahahahahaha im totally out on this one

this where i go to alex

I'm no electronics guru...just a 'master of hack' and creator of puffs of smoke from electronic components.

I tried to hand it to alex, but I think that he punted...

Interesting workaround. I guess from what I understand of what you wrote, it should work (electronics are not my forte). Still, if you weren't hurting for weight I'd just use a really small microcontroller to do the work for you. Drop in three or four channels as inputs, add a bit of code, and it'll be foolproof for any speed. The only thing is I have no experience programming microcontrollers, but from what I know about their function [and programming in general] tells me there is no reason it couldn't be done that way.

the melty hardware already includes a microcontroller.

the 'hack' is so as to be able to interface with a typical brushless esc....which are bult to rc pwm standards.

I don't see any problems with the workaround.

After all, even if you tried to turn a motor on and off at a much faster rate, I don't think that any existing and suitable motor could respond that quickly.

You mentioned a relay.

Mechanical or Solid-state?

What I'm thinking is: if the brushes are failing due to spin, the mech relay will not work either.

Also, I suspect that the 1pulse/rotation is likely to be a problem.

Luck to you
*actually, in your case I have come to realize that luck has got nothin to do with it

Actually, the latest brushed version seems to be hanging in pretty well, well enough that I wouldn;t hesitate to compete with it.

Brushes themselves have not been a big problem, it's really come down to the location of one motor, which could be resolved without all that much effort.

regarding relays: no standard mechanical relay (that I've found) could switch fast enough for this. there are several IC options. I do hav e a cheap small solution, but I'll bet that you already guessed that.

I don't know the exact numbers, but I am assuming that the current small contingent of melty's don't translate well or at all, over 500 to 1200 rpm. Higher numbers meaning much less translation.

I don't think that many or perhaps anyone has been following this that closely, but an experiment with Robot Power's Scorpion chips, did prove to be rather interesting. the difference betwen thusing those chips and regualr mosfets or ss relays, is that when the motor(s) are shut off, a bit of dynamic braking occurs (by design of the chips/ regenerative braking).

This is one of the reasons why possible brushless braking might prove to be interesting, especially in heavier bots.

As stated earlier, how fast can a brushed or brushless motor react to on/off pulses?

1 pulse per rev happens at 3k rpm, which is extremely fast, probably way too fast for melty, so the long term plan is a larger diameter swing and lower r's....making an insect class melty probably not the best candidate in that respect.

message to self

I have brushless melty up and running on the bench!! will test in robot soon...

Very interested to hear the results. . . .

when you say one pulse per revolution, is that revolution of the bot or revolution of the wheel? Or are they the same?

Dan Curhan wrote:

when you say one pulse per revolution, is that revolution of the bot or revolution of the wheel? Or are they the same?

per rev of bot or at 3k rpm 20ms

Now that Spinning Tortoise has been converted to brushless motors and escs, it is undergoing some more tweaking of the code.

I am working on having the bot maintain rpm while translating. Once the speed is locked , the brains with adjust things accordingly, in order to maintain rpm.

I don't have it down 100% yet, but I am seeing improvements.

When going over rough spots, it used to have a tendency to slow down over rough spots and then suddenly spring off in a direction at a higher speed. Now it is just rolling over the rought spots while maintaining speed!!!

Once I get this totally tweaked, it should be much more predictable and obviously more effective.

I wish we had video of the pre-event attempt to calibrate this bot....I thought that the arena was going to come apart!!!

I knocked the poly carb pieces right off the wall, but had to run it un-calibrated for the entire event.

I slowed down the cal speed after the event and it moved very well.

Possibly the scariest 3 pounder I've seen....it hits REALY hard.

Terrible results on paper, but the future looks very good