A brutal apocalypse of twisted, tormented steel...

[superyob]

Or it could work. The following picture is of a project that my year 9s are working on. They are making a 'battle tank', using 2 starter motors and OHC gears and timing belts as tracks. I have doubts about the chassis being able to withstand the sudden torque of the 2 starter motors being used for motivation. I relayed this reasonable point to my year 9 group who have taken it upon themselves to ignore my hapless bedwetting concerns. Thusly I have instructed my seriously deranged students to not fire it up until I have covered every angle with video cameras. This thing is either going to shoot off into the distance at a rapid rate or self destruct in an ominous and spectacular paroxysm of apocalyptic rage and biblical scale destruction.

I have welded the cam gears to the starter motor pinion shafts as shown in the pics.

Update soon...

Hopefully...

[mike_nofx]

Got any system to vary the speed, those startermotors with no load are going to spin pretty damn fast...

[malazn mafia]

Also wondering what power source would be used to feed the immense appetite of two starter motors ?

[poppa smurf]

Hah! love it.....mad scientist stuff.

[superyob]

Originally Posted by mike_nofx

Got any system to vary the speed, those startermotors with no load are going to spin pretty damn fast...

No, I don't know of any variable speed rheostats that will work on a starter motor. Maybe someone can enlighten me on how that might work??? Trouble is they would have to be able to control current flowing through battery size cable and I am not sure such switches exist.

I spun the motors up after the cam gears were welded on just to show them how much speed they were playing with. Instead of fear and trepidation, I heard excited laughter...

[superyob]

Originally Posted by malazn mafia

Also wondering what power source would be used to feed the immense appetite of two starter motors ?

A car battery. But one starter motor will have to be isolated from the body so that its polarity can be reversed...

[JC]

Originally Posted by superyob

A car battery. But one starter motor will have to be isolated from the body so that its polarity can be reversed...

If you wire them in series, you will halve the speed, though you'd need to test that they will work on 6V each I suppose.

[pk2000]

i know its not your call but i would suggest using something like a single /pair of drills - you will have a few advantages :

1) you get a motor, controller, battery and gearbox/clutch all in one.
2) cheap - the cheaper the better in this case because the control circuitry and batteries will be way simpler/easier to control (and mate to RC circuits later)
3) you get a gearbox for low/high speed , and max torque clutch
4) the motor will be way smaller

got a few issues you will need to overcome using starter motors-

1) no load/light load speed control - they will spin till they pop from heat or rpm
2) stall will make them pull a huge amount of current - fire hazard at best- Fuse it at minimum
3) to control a series wound motor, your gonna need some proper circuitry a heavy PWM or similar system for speed + torque
4) common ground on case of motor
5) back EMF is gonna be fun on circuitry - flyback diode might work (diode across the solenoid )


-throwing them in series will share the voltage, but the full current will flow through both motors and cause some heat issues /battery issues and you wont be able to turn the tank!

Sorry about the lecture - good luck and chuck it on youtube for us to see!

[superyob]

Indeed I will pk2000. I am hoping for a spectacular outcome either way.

The students had to use materials that were readily available in or around the workshop. There are motors aplenty. I did also advise them to consider 2 heater fan motors as they can be controlled with a rheostat. They wanted the starters...

The positive trigger wires will have a switch so the motors will be able to be switched off easily, I hope

If I run the motors in series, can I still reverse the polarity on one motor??? Also, won't the first motor in line spin faster???

[Craig@AUDI]

That's the sort of crazyness us Aussie's are known for...love it!

[mike_nofx]

Originally Posted by superyob

No, I don't know of any variable speed rheostats that will work on a starter motor. Maybe someone can enlighten me on how that might work??? Trouble is they would have to be able to control current flowing through battery size cable and I am not sure such switches exist.

I spun the motors up after the cam gears were welded on just to show them how much speed they were playing with. Instead of fear and trepidation, I heard excited laughter...

I don't know too much about electronics to be quite honest.

I'm assuming some sort of adjustable voltage regulator is needed, 12V is probably too fast but maybe turning it down to 6-10V would slow it right down.

[.:4:.]

My only thought is to run in a similar fashion to a griller, you know the thing above the oven you use for grilled cheese on toast. Low is both elements (motors in this case) in series, and high is both in parallel. No real speed control. If it was rc car gear an electronic speed controller would fit the bill, but I doubt there is one able to fit the bill. In my line of work I tend to deal with 3 phase motors, and the basic ones like car park fans run a star delta setup, whether it be a soft start or a high low setup. The more complex things like industrial ac units are controlled by vsd's (again 3 phase) that do things like clip the sine wave to lower the voltage to control the speed. Brushless drills and rc cars etc that use dc batteries are forms of 3 phase motors that get the dc invered into square wave ac, then the speed controller can adjust the voltage to the user input.

[mik]

That thing is going to do a serious mono .

[pk2000]

RE series wiring - assuming the motors are the same (and similar temp) and wiring can handle it, they should spin the same speed.

If you want to have them run independently you will have to control them independently

A resistor element (like .:4:. mentions a heater element or big *** resistor pairs) to limit current feeding 2x DPDT switch like shown here might be the cheapest way to have some control - at the expense of power wastage.

ie car battery -> fuse -> resistor *-> switch for left ->motor
-> switch for right ->motor

(* = wiring splits into 2)

A single phase vsd will work if you have one that can handle 2hp or so and remove the solenoid - a newish drill control circuit works in the same way.

I'm not even sure a starter can be reversed - id test that first, i have a feeling the brushes will hate that and go on strike in sort order.

[superyob]

I did test the starters by reversing the polarity and they spun backwards with no obvious trouble...

[superyob]

Originally Posted by pk2000

-throwing them in series will share the voltage, but the full current will flow through both motors and cause some heat issues /battery issues and you wont be able to turn the tank!

Each starter will have its own switch to control it. I doubt however, that anyone will be able to keep up with it to control it...

[Pis-ton broke]

Originally Posted by .:4:.

The more complex things like industrial ac units are controlled by vsd's (again 3 phase) that do things like clip the sine wave to lower the voltage to control the speed.

i understand that many variable speed drives (vsd) in industrial automation operate at 24v after a transformer has stepped it down, so its getting closer to 12v. we used to jump start cars and trucks with 24v all the time.

in the machinism is there a spot to allow for slippage?

[superyob]

Originally Posted by Pis-ton broke

i understand that many variable speed drives (vsd) in industrial automation operate at 24v after a transformer has stepped it down, so its getting closer to 12v. we used to jump start cars and trucks with 24v all the time.

i the machinism is there a spot to allow for slippage?

No, not that I am aware of. As soon as voltage is applied everything is driving at 100%. (Is that what you meant?)

Is there anyone out there (with superior electrical knowledge to mine) who can see any problem with one car battery running both motors on opposite polarities? The motor with reversed polarity would have to be isolated from the chassis but that's the only problem that needs to be addressed I think???

[Tonz]

Have this well videoed,
your principal is going to either love you for bringing fame on the school or .........
totally reject you as a misfit degenerate teacher who coerces his students to crazy and stupid adventures that will lead to death and injury

Bring it on

Youtube will love you.

[Pis-ton broke]

Originally Posted by superyob

No, not that I am aware of. As soon as voltage is applied everything is driving at 100%. (Is that what you meant?)

=yes.

change the tires to bald ones, and use a flat battery, no worries.

[superyob]

A previous attempt by last year's year 10s. Unfortunately they misjudged the distance between the drive and driven cogs and had to try to cut and shut a fan belt...

https://www.youtube.com/watch?v=--v8gJQ106s

[Work Horse]

I think your students are on to something!

This is a battle tank.

I believe the speed could be controlled by adding more load to the starter motors.

A series of gears and axles powered by the tracks should be attached to large rotating knives at the front of the tank.

Speed control would be achieved by placing objects in the path of the tank.

[falconhell74]

I would use separate batteries and put a variable rheostat in each circuit that way you can start at low rpm and also be able to turn it like a skid steer bobcat by varying the voltage separately.

[superyob]

Originally Posted by falconhell74

I would use separate batteries and put a variable rheostat in each circuit that way you can start at low rpm and also be able to turn it like a skid steer bobcat by varying the voltage separately.
image

Will these work with a starter motor?

[falconhell74]

The rheostat will vary the voltage so less voltage less rpm , I cant see why not.

[olfella]

How long do you want them to run for? and that would depend on the capacity of the batteries. Therefore putting a resistance in line would be counter productive. How about some sort of pulsing switch - so you regulate the speed that way.

[superyob]

Originally Posted by olfella

How long do you want them to run for? and that would depend on the capacity of the batteries. Therefore putting a resistance in line would be counter productive. How about some sort of pulsing switch - so you regulate the speed that way.

olfella, could you please show me a pic of what you mean?

[olfella]

Originally Posted by superyob

olfella, could you please show me a pic of what you mean?

You may have to knock one up. I envisage something like a cam driven by a small motor and it opens and closes contacts. I will give it a bit more thought. But then you could control the speed of the series starter motors by the speed of the cam, which in turn could be driven by the rheostat.

[olfella]

I am trying to think of things the kids can make up themselves. So how about a wiper motor arm opening and closing the circuit? The interment delay could be the speed control?

[X-AHH]

It may be worth having a talk with the people who operate this business.

https://www.motiondynamics.com.au/

They sell similar products to what you need and might be willing to help out since it's for legitimate educational purposes.