Re: Question re: voltage regulators & lost amps

Wow, I guess this won't be as simple as I thought...
A couple of key points I forgot to include:

1) This will be kind of a kiosk, intended to require little to no
operator intervention. That's why I want to send drive power through
the tether instead of using batteries inside the vehicle.
2) I have removed all the guts from the vehicle, including the i/r
receiver and board. All that remains are the drive motor and the
batteries; the batteries are serving only as ballast, they aren't
powering anything. The current traveling down the wires will serve only
to power the two drive motors...there are not distinct signal and power
wires...just wire-pair 1 to motor 1, and wire-pair 2 to motor 2.

Here is a picture of what I'm trying to accomplish. I didn't include
this orginally because it is a fairly silly idea...but I can't bring
myself to believe that this machine cannot be recreated by a tinkerer
in his basement.

http://www.pinrepair.com/arcade/motora17.jpg

The vehicle I am using is NOT a Plymouth Belvedere, but rather a
tracked vehicle that requires only the two above-mentioned drive
motors...no complicated steering mechanism required.

Thanks
--Alex


ehsjr wrote:
ehsjr wrote:
Alex wrote:

I have a small motorized vehicle, designed to be I/R remote, that I
want to control via a microcontroller, DC motor controller, and a
tether (suspended above it). Since it has to be able to turn in circles
inside its 'pen' without tangling up the tether, I am using a telephone
handset cord with a pivoting cord-detangler mounted in the top of the
vehicle. The weight of the cord is low enough that is does not impede
movement, but just enough that it will twist the de-tangler when
necessary to avoid getting all knotted up.
The vehicle is meant to run on 4.5V, which I'm sending through the 4
wires in the tether (two wires for each of the two drive motors). The
problem is that I lose all my amperage through that 6 feet of tiny
wires. (As it is all coiled up, a 6' handset cord is the perfect
length.) I can get SOME response by sending 12V through the tether, but
I'm not sure that's so good for those tiny motors.
I realize that my problems would be solved if i were using
appropriately-sized wires, but I want to give a shot at using the
ready-made simplicity of a handset cord and this Radio Shack detangler.
Can anyone think of a way I can send 12V through these wires,
regulating them down to 5V on the other end, but turning those unused
volts into more amps? I thought of just using a couple of off-the-shelf
voltage regulators inside the car, but each of the drive motors must be
able to turn forwards or backwards, so the polarity of the juice I'm
sending through the wires will be changing whenever I change direction;
I don't know if that would eliminate voltage regulators as a solution,
or even if they would give me more amps with the lower voltage.
My knowledge of electrical theory isn't what it should be, so please
excuse what I'm guessing could be a pretty newbie question.

Thanks
--Alex


If you decide to follow the idea mentioned in the thread:
(paraphrasing) "Run 48 volts with a DC-DC converter at the end."

You can control direction this way:


TopA --------+----+
| | BR1 DC-DC +-------------------+
--- | ---- ------ | Ry2-1 Ry2-2 |
D1\ / +--|~ +|--| +|---+---o --- o---|--+
--- | | |48 4.5| <--|Mot|--> | |
| +--|~ -|--| -|---+---o --- o---+ |
[R1] | ---- ------ | |
D2 | | +----------------------+
+-->|--+ |
| | |
| [Ry2] |
| | |
TopB--+------+----+

Top represents the supply connection at the top. When A is + and
B is - the relay Ry2 will energize. When A is - and B is + it won't.
The bridge rectifier will steer the 48 V to the DC-DC converter
in the correct polarity. For the relay, use RLY-467 from
http://www.allelectronics.com/
For that relay, R needs to be 1000 ohm, 1 watt.
Note that the relay can switch no more than 2 amps
to the motor.


The problem with the approach is the cost of the DC-DC
converter. If you can get it cheap - great. Otherwise,
here's a better answer: run the vehicle from rechargeable
batteries. Charge the batteries via the tether. You
can easily control the direction without the bridge and
DC-DC converter, still using a relay, but this time driven
by a transistor. You have 4 wires - two are used for
charging the batteries, and one more is used to control the
direction relay, and one to control the on/off relay.

D1 ------
+ 24V+-->|----tether-----|LM317 |--------+
| ------ |
[2K] | [7R] Ry1-1
| | | <--- +
+----+ +-[3R]-+-----------+-------+-----o
| | | | | |
[470R] | 5.1v [Zd] [Batt] [Ry2] |
| | | | | D2 | D3
Gnd -+--------tether--+------+--- ---+--->|--+--|<-+
| | e\ / | |
+----+ | --- NPN [Ry1] |
| | | | | |
o o +---- | --- ----+-----+
S1 / /S2 | e\ /
o o | --- NPN
| | | |
| +--tether---[470R]-------+ |
| |
+-------tether---[470R]--------------+


The relays this time are catalog # RLY-452. When S1 is open,
relay Ry1 is de-energized, so no power is available to the motor.
Close S1, and the relay energizes, making power available to the
motor. S2 has the same effect on Ry2. Ry2 is wired the same way
it was in the previous diagram, except that where it connected to
the + from the DC-DC converter in the prior diagram, it now
connects to the Ry1-1 point. The 24 volt DC wall wart supply is
left plugged in all the time. The 7 ohm resistor sets the
charging current for the battery pack to about 180 mA. When the
pack reaches 5.1 volts, the zener diode begins to "steal" current
that would otherwise continue to charge the pack. When the pack
reaches 5.6 volts, it charges at about 10 mA, and it can stay on
that charge rate forever with no damage. You can charge a 4 cell
pack to the charge termination voltage of 1.4 volts per cell (5.6)
and then keep it on a very low charge rate as long as you want.

The zener is cat # 1N4733 the wall wart is cat # DCTX-2450
They don't sell a 7 ohm, but you can put a 2.7 ohm in series
with a 4.3 ohm. The 3 ohm as well as theh 2K and 470 are all
available. The resistors are 1/2 watt. Diodes D1, D2 and D3
are cat # 1N4004 and the transistors are # PN2222A. They
also have switches and NiMh or NiCd batteries.

Ed

I forgot the heat sink. With the charging circuit using the
LM317, you need a large heatsink. Change the 24V wall wart to
a 9V wall wart and the 2K to 470 ohms for operation without
a heatsink.

Ed

.

Relevant Pages

  • Re: ezilla to accept ladder packs
    ... My 2 pairs of matched 3300mah batteries give me ... I recon if that guy moved his esc to the front of the chassis, ... where the receiver was and running 2" long wires to the motor, ... replaced the motor and battery wires. ...
    (rec.models.rc.land)
  • Re: Looking for some ideas for DC motor control
    ... I thought that a PWM speed control would be best because the ... motor torque will be close to constant. ... this is because there two wires to the wirefeed gun. ... put a relay coil in series with the motor power wires with the relay ...
    (sci.electronics.basics)
  • Re: adding relay to AC fan circut
    ... blower to start when the fan in the AC does. ... wires go to solenoids on the PC board. ... one of the three wires from the relay. ... I would like to understand better how the motor is being controlled by ...
    (sci.electronics.repair)
  • Re: Bummer.... Re: Car stereos: some inneresting fyi
    ... Is the car itself acting as an antenna, ... operates this motor, but I don't hear a relay. ... "Seems to require *duplicate* hots (from hot wires at slightly ...
    (rec.autos.tech)
  • Re: Looking for some ideas for DC motor control
    ... motor torque will be close to constant. ... this is because there two wires to the wirefeed gun. ... wires as power wires for the motor. ... put a relay coil in series with the motor power wires with the relay ...
    (sci.electronics.basics)
Loading