RC control for skid-steer 'robot' 3D printed dinosaur kit

[cokerian]

Hello,

I have developed a self-build, 3D-printed 'robot' dinosaur kit. It is not at all robotic to be honest -it's just a simple skid-steer toy, as shown further below.

It is presently controlled through a long 'umbilical' cable which is not really ideal and involves the user dealing with a lot of wires. So I am seeking advice about how to convert to an RC system.

More details below if you are interested...

The device moves using skid-steered rotating claws and the head/neck/jaws lunge and bite.

Two are shown fighting in the video below (an earlier design that used the motor from a cordless drill and was not 3D printed, but it functions in the same way).

There are four rotating claws. Those on one side rotate in the same direction and each side is controlled by an on-off-on, DPDT slider switch:

This provides simple skid steering.

In addition, a micro-switch is used to operate the biting-lunging action of the head and jaws operated by the trigger shown above.

The claws are rotated by 'economy' 6V motor gearboxes which have a built-in 200;1 gearbox.

Four such motors move the neck-head-jaws assembly using simple cranks:

The image below shows the assembled device with the controller and umbilical.

As you can imagine the long length of wires involved is annoying!

So I would value thoughts on how to convert it to an RC system. I have done a bit of research into possible off-the-shelf solutions, but they all relate to the use of servos rather than simple on/off switches.

One other issue is the electromagnetic 'noise' generated by the motors. Someone started looking into this for me and they were thinking of an infra red system but said that the amount of noise generated was a problem.

Ok, any help much appreciated -thanks in advance.

 

[KlausST]

Hi,

In electronics we use numbers with units to design ..
But in your post I see not a single number describing the problem.
* Not battery voltage, not motor count, not motor current ... nothing.

Also I miss the control system information. How many channels to control, how to control (ON/OFF only or speed control, one or two directions...)

I recommend to write down a list (not much words) of all requiremets.

Klaus

 

[BradtheRad]

I owned an R/C airplane with 4 channel transmitter. Four control signals are broadcast every 1/50 second. The onboard receiver splits these up into 4 individual pulses. Each pulse varies from 1mSec to 2mSec in length.

You don't have to install servos. You can derive your plain On-Off signal by building a circuit which detects some midway pulse length (say 1.5 mS). An RC type timer is adequate. So while a pulse lasts less time, a wire is low. If a pulse lasts longer, the wire goes high. A Schmitt trigger is suitable for this job in the sense hysteresis maintains either state.

 

[D.A.(Tony)Stewart]

Hello,

I have developed a self-build, 3D-printed 'robot' dinosaur kit. It is not at all robotic to be honest -it's just a simple skid-steer toy, as shown further below.

It is presently controlled through a long 'umbilical' cable which is not really ideal and involves the user dealing with a lot of wires. So I am seeking advice about how to convert to an RC system.

More details below if you are interested...


View attachment 193932

View attachment 193931

The device moves using skid-steered rotating claws and the head/neck/jaws lunge and bite.

Two are shown fighting in the video below (an earlier design that used the motor from a cordless drill and was not 3D printed, but it functions in the same way).

There are four rotating claws. Those on one side rotate in the same direction and each side is controlled by an on-off-on, DPDT slider switch:

View attachment 193935


This provides simple skid steering.

View attachment 193936

View attachment 193937


In addition, a micro-switch is used to operate the biting-lunging action of the head and jaws operated by the trigger shown above.

View attachment 193944

The claws are rotated by 'economy' 6V motor gearboxes which have a built-in 200;1 gearbox.

View attachment 193940

View attachment 193941

Four such motors move the neck-head-jaws assembly using simple cranks:

View attachment 193942

The image below shows the assembled device with the controller and umbilical.

View attachment 193943

As you can imagine the long length of wires involved is annoying!

So I would value thoughts on how to convert it to an RC system. I have done a bit of research into possible off-the-shelf solutions, but they all relate to the use of servos rather than simple on/off switches.

One other issue is the electromagnetic 'noise' generated by the motors. Someone started looking into this for me and they were thinking of an infra red system but said that the amount of noise generated was a problem.

Ok, any help much appreciated -thanks in advance.

can you create a schematic with the remote control with values?.

 

[cokerian]

Hi,

In electronics we use numbers with units to design ..
But in your post I see not a single number describing the problem.
* Not battery voltage, not motor count, not motor current ... nothing.

Also I miss the control system information. How many channels to control, how to control (ON/OFF only or speed control, one or two directions...)

I recommend to write down a list (not much words) of all requiremets.

Klaus

There were some numbers mentioned actually Klaus but I'll make it briefer for you...

Number of legs: 4
One motor-gearbox per leg
Four motors driving the head-neck

Three circuits: let side, right side & head-neck, motors wired in parallel

Control is on-off-reverse (no speed control)

Thanks

 

[cokerian]

I owned an R/C airplane with 4 channel transmitter. Four control signals are broadcast every 1/50 second. The onboard receiver splits these up into 4 individual pulses. Each pulse varies from 1mSec to 2mSec in length.

You don't have to install servos. You can derive your plain On-Off signal by building a circuit which detects some midway pulse length (say 1.5 mS). An RC type timer is adequate. So while a pulse lasts less time, a wire is low. If a pulse lasts longer, the wire goes high. A Schmitt trigger is suitable for this job in the sense hysteresis maintains either state.

Thanks!

--- Updated Tuesday at 1:13 PM ---

can you create a schematic with the remote control with values?.

Thanks Tony

Wiring for the left and right motor circuits:

And for the crank motors:

The wiring for each slider switch:

 

[D.A.(Tony)Stewart]

Missing values of motor resistance, supply voltage

 

[cokerian]

Missing values of motor resistance, supply voltage

Thanks Tony,

Battery : 12V
Motor resistance: not sure. I tried measuring with a multimeter but it registers nothing (presumably because it's at zero load?). I checked online and found this: '..Pass a test current through the wire: the value of the test current should be selected according to the nominal winding current. The test current should not exceed 10% of the nominal winding current...' (link). So I can do that if needed.

 

[betwixt]

When you say "measures nothing" do you mean it measured zero Ohms, like the probes are touched directly together or there was no measurement at all like the probes are not connected to anything. There is something suspicious about reading nothing at all, regardless of loading.

The ideal method is to apply the motors rated voltage and connect a multimeter in series with one of the motor wires using the 'Amps' or current range. Start with the meter on the highest current range and drop it if necessary. I'm guessing you should see something like 75mA with the motor idling and considerably more if you try to stall it.

Brian.

 

[D.A.(Tony)Stewart]

Thanks Tony,

Battery : 12V
Motor resistance: not sure. I tried measuring with a multimeter but it registers nothing (presumably because it's at zero load?). I checked online and found this: '..Pass a test current through the wire: the value of the test current should be selected according to the nominal winding current. The test current should not exceed 10% of the nominal winding current...' (link). So I can do that if needed.

Wrong assumption. DCR is an ohmmeter value in Ohms with a locked rotor.

 

[cokerian]

When you say "measures nothing" do you mean it measured zero Ohms, like the probes are touched directly together or there was no measurement at all like the probes are not connected to anything. There is something suspicious about reading nothing at all, regardless of loading.

The ideal method is to apply the motors rated voltage and connect a multimeter in series with one of the motor wires using the 'Amps' or current range. Start with the meter on the highest current range and drop it if necessary. I'm guessing you should see something like 75mA with the motor idling and considerably more if you try to stall it.

Brian.

Thanks Brian,

I meant without power the resistance is zero (1 ohm and 10 ohm ranges).

The motor gearbox is a generic item sourced from China and I have no idea who manufactured it. But it seems that various companies make these such as 'Pro-Elec' and 'PXC' For the PXC version (found here) it states that the 6V no-load current is 70 mA. So resistance = 85.7 Ohms. But I did the test as you described. At 6V it is 0.11A and at 12V it's 0.16A. I think the 200:1 gearbox does provide quite a bit of loading even when not used to drive anything.

I don't know if it's relevant here but each motor-gearbox has a simple adjustable slip-clutch to prevent stalling.

Wrong assumption. DCR is an ohmmeter value in Ohms with a locked rotor.

Thanks

 

[D.A.(Tony)Stewart]

I expect the motor DCR to be ~5% (with gear drag) of the no- load impedance or 10% of the full load impedance otherwise with no gearbox DCR is near 1% of no load impedance.