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Question re: voltage regulators & lost amps

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

Reply to
Alex
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Phone wires are designed to send signals at 24V and up. You need higher voltage to minimize power lost.

You can change directions with the signal pair, not the power pair.

You need high efficency DC-DC step up/down switching regulators.

Reply to
linnix

More like 48vdc and a dc to dc converter down to 4.5 volts. Are the control signals going to be through that noisey cable?

greg

Reply to
GregS

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| | | | +--|~ -|--| -|---+---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

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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 | | | |--+--|
Reply to
ehsjr

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

Reply to
ehsjr

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.

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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:

Reply to
Alex

Does a person steer the vehicle via the big steering wheel on the front?

Ed

Reply to
ehsjr

Sorry, I realize I didn't describe what that thing is....you drive the car around with the steering wheel and a push/pull pot that acts as throttle and speed control, trying to run over various buttons mounted in the playfield. In the original 1950's version, the tether was an armored cable with 2 wire pairs (one pair for drive/direction of rear wheels and one pair for steering of the front wheels), which went in the top of the car with a slipring.

In my design, there are two pac-man style joysticks, each controlling the treads of my vechicle with only forward, reverse, or 'resting' for each tread (remember Battlezone in the arcades?). I have one microcontroller monitoring the state of the playfield buttons and illuminating whichever button you are supposed to drive towards, and it is connected to another controller that monitors the state of the joysticks and sends the appropriate commands to a Polulu dual micro serial motor controller, which send juice down the tether. This second micro also drives some relays hooked to a bank of 1970's pinball score reels.

You play until your 'fuel gauge' is on empty...the fuel gauge is a servo that slowly turns a pointer from 'full' to 'empy'. Every time you runover a lit button on the playfield, you get a little boost of fuel (i.e., a little more time on the clock).

--Alex

ehsjr wrote:

Reply to
Alex

Ok. That changes things considerably. As I understand it, you have two motors under independent control for both speed and direction. Each motor, independent of the other, needs to be "told" to go forward, go backward, and how fast (where 0 = stop).

To do that with your wires, you either must charge a battery on board the vehicle, or use the converter idea, using 2 wires to handle those chores. The converter could be either DC-DC or it could be an AC to AC with a rectifier and regulator. If you ran AC at 48 volts down the cable to a 120 to 12V transformer in the vehoicle, you'd get 4.8 volts AC. Rectified to DC and filtered, you'd have 6.7 volts DC. With a low drop out regulator, you'd get you 4.5 volts. The voltage drop in the wires would be 1/10th what it is now.

The other two wires can be used to control the vehicle, with a ucontroller on board. Don't know if you can fit the stuff in the vehicle. You need to specify the current that the motors draw to figure out the physical size of the transformer if you go with AC coming down the wires. DC-DC would be smaller. I stumbled on one in a catalog for $10.00 - if I can find it again, I'll post a link. Either way, you still need a ucontroller onboard the vehicle.

Ed

Reply to
ehsjr

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