Powering Propeller and Motor on the same lines

RobertW

I was wondering, is it possible to power a Propeller and a motor on the same lines / buss?· I am thinking about something like putting a Propeller inside of a model locomotive.· This would result in all power coming from the two·rails but would need to power both the Propeller and the motor inside of the locomotive.· I understand that the power to the Propeller would need to be regulated to 3.3V, etc.· I know that this is basically·how DCC works for those of you familar with model railroading.· Would this setup work, or is it not recommended?· I don't have enough of a electronics background to answer this myself.· Also, what would be recommended for driving the motor.· I believe they are lower voltage.· Maybe 10-15V.· I was thinking of something like a H-bridge to get forward and reverse, etc.

Thanks
Rob W.

P!-Ro

I tried it once and the rc car is still sitting to be worked on after I got annoyed when (due to the motors power surge?) the propeller jumped lines in the code and sent the car out of wack without any sensor polling. But what I did for the power control is I cut off all of the components on the circuit board except for the h bridge and I soldered wires to it so I could control it with my pe kit. If you want I can try and take a pic of that real quick.

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RobertW

A pic would be nice to see. Does anyone have a recommended h-bridge IC? I found a LMD18201 which may be overkill. I'm not sure.

P!-Ro

It's somewhat dark, but you should be able to see it. It has four wires coming from it. They are ground, 8v, forward transistor, backward transistor. You can use the pwm object to control the speed.

edit: thats a bad pic. let me get a better one

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RobertW

Thanks for the pic. You suggested that a motor power surge caused the trouble with your car. Is there a way to control this? Is this something that a diode would help solve?

P!-Ro

This one should be full size. sorry about that

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P!-Ro

RobertW said...
Thanks for the pic. You suggested that a motor power surge caused the trouble with your car. Is there a way to control this? Is this something that a diode would help solve?

I'm just assuming here since it showed all the signs such as it was jumping out of my loops randomly and every time it happened·it was accelerating. My advice is to either use batteries that can deliver high current or use two seperate batteries for controlling any servos and the main main motor and for controlling the prop.

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RobertW

Thanks. I was wondering if it would be a better design to keep the motor and the propeller on a seperate 'power supply'. I will need to look into this some more.

Timmoore

I have used 2 batteries and 1 battery. I found as long as the 1 battery is well charged and can deliver the current needed and you noise surpress the motors (caps across the motors and ferrite cores on the motor wires) you can run with 1 battery but when the battery gets low you will get resets when the motor pulls a lot of current. If thats a problem either use 2 batteries or get the prop ot monitor the battery and stop if too low.
In term of h-bridge depends on the voltage/current - I have used l293d, l298, tb6612 and mc33887. l293d is good cheap and simple for low power upto ~1a per motor also handles 2 motors. the l298 is also cheap and handles 2 motors, needs external protection diodes and upto 2A per motor. tb6612 is good for low power < 1.2A and does 2 motors, MC33887 is good for 5a but only 1 motor and needs a touch more to interface to prop (2 resisters per io pin). The tb6612 has a max voltage of 15V but all the others will do 10-15V without problem.

P!-Ro

Hey Tim, how do you connect the motor wires to a ferrite ring? Do you just wrap it around a few times? If so I just might try that since I have some lying around from old computers.

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Timmoore

Pi, if the ring is small just feed the wire through the center of the ring, if the ring's larger wrap it round a couple of times - through center round the ring and back through center. I normally then put some electrical tape over it to stop it moving and protect it. Do this close to the motor.
In terms of caps, a cap across the motor leads as close to the motor as possible. and if possible a cap from each motor lead to the motor case (if its metal). The 2nd only work for some of the larger motors and if you have a big soldering iron, I dont normally bother and haven't had many problems.
The other thing to do is twist the motor leads together from the motor to the motor controller.

Toby Seckshund

As well as the spikes coming off the motor when it is running there are the deep gulps of energy to get then started. A quick reversal and the motor will be a complete short cct to the supply. How about a small rechargable cell for the Prop which is charged from the main power source, it should only have to cope with a few seconds at most. Perhaps a "supercap" ? then the prop has it's own UPS.

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Style and grace : Nil point

RobertW

My goal is to still work off the power supplied by the rails but I may need to install a small battery to power the Propeller.· The more I think about it, I don't think I can only use a simple 2 rail system.· I will need a third rail for a signal to the Propeller. Dah!· At that point to add a fourth rail to power the Propeller may not be that much more effort.

Rail 1 - power for motor
Rail 2 - power for Propeller
Rail 3 - Propeller signal
Rail 4 - ground for motor and Propeller

I don't expect any sudden motor rotation changes.· The locomotive would run similar to a subway or transit system.· Pull into the station, pause, leave the station, etc.

-Thanks