Motorizing a Model Boat

[PaPaPeng]

I am hijacking the guts from a miniature RC model boat toy ( see
http://www.sharperimage.com/us/en/s...DARGS=/us/en/include/standardheader1.jhtml.13
) to motorize the Revell S-100 Schnellboote that has three
propellers. (see
http://www.modelwarships.com/reviews/ships/dkm/s-boat/s-100-72/72-S-100-p1.htm
)

The Sharper Image mini-speedster boat is powered by two cellphone type
(I think) minimotors that has forward and reverse rotations controlled
independently from the RC transmitter. This is its steering
mechanism. There is no rudder. I think this is a great solution as a
separate channel for the rudder would involve a servo and its
associated installation complications, especially in a small model
such as the S-100.

The design question is the middle motor.

My idea is to feed each motor's forward signal into an OR gate and use
the output to power the middle minimotor. The mini-speedster's motor
has 3 wires, presumably fwd, rev and common. That way so long as one
side motor runs in forward the middle motor will run. The other
outside motor will be used to steer. If both side motors are stopped
or in reverse, the middle motor won't run.

Is the output of the OR gate enough to power a cellphone minimotor (2
NiCad cells power the everything in the mini-speedster.) Or do I
need to use that output to turn on a switch to a separate power supply
for the middle motor? Will the minimotors' power be drawn off too
much juice in supplying the OR gate's input signal? Any other design
considerations?

 

[Rich Grise]

I am hijacking the guts from a miniature RC model boat toy ( see

http://www.sharperimage.com/us/en/s...DARGS=/us/en/include/standardheader1.jhtml.13

All I got was a blank "search results" page.

) to motorize the Revell S-100 Schnellboote that has three
propellers. (see
http://www.modelwarships.com/reviews/ships/dkm/s-boat/s-100-72/72-S-100-p1.htm
)

The Sharper Image mini-speedster boat is powered by two cellphone type
(I think) minimotors that has forward and reverse rotations controlled
independently from the RC transmitter. This is its steering
mechanism. There is no rudder. I think this is a great solution as a
separate channel for the rudder would involve a servo and its
associated installation complications, especially in a small model
such as the S-100.

The design question is the middle motor.

My idea is to feed each motor's forward signal into an OR gate and use
the output to power the middle minimotor. The mini-speedster's motor
has 3 wires, presumably fwd, rev and common. That way so long as one
side motor runs in forward the middle motor will run. The other
outside motor will be used to steer. If both side motors are stopped
or in reverse, the middle motor won't run.

Is the output of the OR gate enough to power a cellphone minimotor (2
NiCad cells power the everything in the mini-speedster.) Or do I
need to use that output to turn on a switch to a separate power supply
for the middle motor? Will the minimotors' power be drawn off too
much juice in supplying the OR gate's input signal? Any other design
considerations?

It depends on the OR gate. You will probably want to use a discrete
transistor, or maybe 4, depending on the circuit.

An OR gate should draw an insignificant amount of current compared to
a motor.

Good Luck!
Rich

 

[PaPaPeng]

http://www.sharperimage.com/us/en/s...DARGS=/us/en/include/standardheader1.jhtml.13

All I got was a blank "search results" page.

Go to www.sharperimage.com and then do a search for "boats" on their
website.

 

[Tam/WB2TT]

Try to measure the motor current under load. What works at 24 or 64 ma won't
work at 200. Also, what is the battery voltage?

Tam

 

[PaPaPeng]

Try to measure the motor current under load. What works at 24 or 64 ma won't
work at 200. Also, what is the battery voltage?

Two NiCads. I presume 2.4Vdc. The wires are too teeny for me to want
to risk snapping them at this time.

The minispeedster's NiCad is charged from a 4 pack AA charger
(provided in the kit.) Takes 2 to 3 minutes to charge and runs for
some 10 minutes. Quite a little performer.

I am more inclined to use the OR output to switch on a separate
battery PS to the middle motor now.

Next question.

The TX range is around 30 feet now. How can I extend it? Will
connecting the Rx to real copper wire for the boat's scale antenna
work?

 

[Tim Wescott]

I am hijacking the guts from a miniature RC model boat toy ( see
http://www.sharperimage.com/us/en/s...DARGS=/us/en/include/standardheader1.jhtml.13
) to motorize the Revell S-100 Schnellboote that has three
propellers. (see
http://www.modelwarships.com/reviews/ships/dkm/s-boat/s-100-72/72-S-100-p1.htm
)

The Sharper Image mini-speedster boat is powered by two cellphone type
(I think) minimotors that has forward and reverse rotations controlled
independently from the RC transmitter. This is its steering
mechanism. There is no rudder. I think this is a great solution as a
separate channel for the rudder would involve a servo and its
associated installation complications, especially in a small model
such as the S-100.

The design question is the middle motor.

My idea is to feed each motor's forward signal into an OR gate and use
the output to power the middle minimotor. The mini-speedster's motor
has 3 wires, presumably fwd, rev and common. That way so long as one
side motor runs in forward the middle motor will run. The other
outside motor will be used to steer. If both side motors are stopped
or in reverse, the middle motor won't run.

Is the output of the OR gate enough to power a cellphone minimotor (2
NiCad cells power the everything in the mini-speedster.) Or do I
need to use that output to turn on a switch to a separate power supply
for the middle motor? Will the minimotors' power be drawn off too
much juice in supplying the OR gate's input signal? Any other design
considerations?

I would be inclined to just use two motors and either leave the 3rd prop
off entirely or mount it so it's free to spin. If fidelity to scale
were truly important you'd be pondering how to get a rudder in there.

 

[Tim Wescott]

Two NiCads. I presume 2.4Vdc. The wires are too teeny for me to want
to risk snapping them at this time.

The minispeedster's NiCad is charged from a 4 pack AA charger
(provided in the kit.) Takes 2 to 3 minutes to charge and runs for
some 10 minutes. Quite a little performer.

I am more inclined to use the OR output to switch on a separate
battery PS to the middle motor now.

Next question.

The TX range is around 30 feet now. How can I extend it? Will
connecting the Rx to real copper wire for the boat's scale antenna
work?

The low range is probably a combination of low TX power and a sleazy
receiver. Changing the antenna material probably won't make a big
difference. Increasing the antenna length may help, but if the RX is
highly tuned it may make things worse.

If you really want serious hobbyist-quality performance from the thing
you need a hobbyist-quality RX, not a toy.

 

[PaPaPeng]

The low range is probably a combination of low TX power and a sleazy
receiver. Changing the antenna material probably won't make a big
difference. Increasing the antenna length may help, but if the RX is
highly tuned it may make things worse.

The 30 ft range is pretty good as is for what I am using the plastic
model for. I'll probably experiment with a regular RC Tx to see if
the range will improve.

If you really want serious hobbyist-quality performance from the thing
you need a hobbyist-quality RX, not a toy.

I already have the regular RC equipment. First the regular equipment
takes up too much room and is complicated to install, what with the
motors, batteries, servos, linkages and speed control. Plus its more
than $150 in the hole for starters.

The SharperImage unit is genuinely miniature, completely self
contained and the power units (cellphone minimotors) are ideal for
scale speeds. $19.95 buys a kit with two complete boat systems to
race each other with. The Rx is good enough to discriminate the
channel separation for these two boats. Where else can you get any RC
unit for that price.

I would be inclined to just use two motors and either leave the 3rd prop
off entirely or mount it so it's free to spin. If fidelity to scale
were truly important you'd be pondering how to get a rudder in there.

To get enough speed (small scale props) and to avoid the drag from a
dummy middle prop I prefer to power all three. The beauty of steering
with props only is that I can avoid rudder control (3 in the s-boote)
which takes one channel. To maintain scale fidelity and to avoid drag
during turns my proposed solution is to link the 3 rudders and use a
weighted pendulum that will position the rudders into/with the banked
hull's inclination..

 

[Rich Grise]

I would be inclined to just use two motors and either leave the 3rd prop
off entirely or mount it so it's free to spin. If fidelity to scale
were truly important you'd be pondering how to get a rudder in there.

If fidelity to scale were truly important he'd be pondering how to get
_three_ rudders in there. Did you check the link?

Cheers!
Rich