Please excuse me if I break rules... I'm new here

I'm designing a robot for Battle-bots (Look it up on YouTube if you don't know what this is)
So; I currently have a frame made out of 2x4s and a huge flywheel from an old stationary bike.
Yesterday I talked to my schools auto-tech teacher and picked up a old car starter motor (He says it still works...)
Considering that the wheel is 45kg with a diameter of 11 inches and the sprocket mounted on it is about 3 inches in diameter...
How much current will I draw from my battery and what kind of battery should I look at?
I am not really comfortable going over 100 amps (just because it isn't my shop)
So considering all of the above factors; where do I go next?

P.S.
I do understand how dangerous this much mass going at these speeds is; so please don't pull a yahoo answers and say 'You need help kid.'

 

How much current depend on the size of the motor sprocket. Even if you told me that I still couldn't help with the current needed

I will be looking out for the battle(s) though.

 

Well I just got it and don't have it with me but I would guess about an inch diameter
As for the current needed do you just not know this well or you need more information?

Also I have a widely known YouTube channel at https://www.youtube.com/channel/UCv3yhZZVnequR9prMnnD7ZQ
There's nothing relevant there right now but I will try to keep an update log of some sort

(Three subs makes me a YouTube star right?)

(edit)
I know its very premature; but any name ideas

 

As for the current needed do you just not know this well or you need more information?

I have no information about the current draw of starter motors. It is presumably also going to depend whether the motor is from a small petrol engined car or a large diesel engine.

 

P.S.
I do understand how dangerous this much mass going at these speeds is; so please don't pull a yahoo answers and say 'You need help kid.'

LOL I get it, but...
Be aware that a starter motor is a series wound motor, and as such, its speed with no load will ramp up from 0 to [theoretically infinite] whatever speed it takes for the motor to self destruct, almost instantly.
With your flywheel attached, it will ramp up from 0 to [theoretically infinite] whatever speed it takes to destroy your flywheel, a little bit slower than "almost instantly" but still fast enough that you probably don't have time to react before the room is peppered in shrapnel. Even if you limit current to 100A, the flywheel controlled by a series motor will probably still be destroyed, but it will just take a couple more seconds before it happens. Even with a limit of 10A, the speed will probably still trend slowly toward infinity (destruction).

This is the nature of series-wound motors. They need a load to regulate their speed, and a flywheel isn't much of a load once it's up to speed. I seriously encourage you to employ some speed feedback and a controller of some sort, to keep the speed below a safe level.

Alternatively, there is probably some very low amp limit at which the inertia of the flywheel combined with mechanical losses in the motor equals the input power, and it will reach a steady state. But this very low amp limit probably won't be enough to get it started.

All that being said, I doubt you will find the info you're after. Automotive OEMs don't publish datasheets on their starter motors, that I've seen. I think you will have to find the information that you want empirically. Do some tests, find out what kind of torque you get for how many amps you put in.

 

@strantor beat me to it.
The starter motor is not a good choice, some recent ones are PM, which should work.
Older ones have the wound series field.
Max.

 

Starter motor is not good for what you want to do as said it will run from O to self destructs
Plus it will kill your batteries in about the same time get a wiper motor.

2x4s for frame and and spinning a 100 pounds
Those 2x4's better be welded steel frame.

 

You also need to show some of the mechanical constraints to get an idea as to what motor size you may need.
What is the anticipated rpm at the motor shaft?
Max.

 

@strantor @MaxHeadRoom
Thank you for the information, I would like to note that the flywheel weighs more than I do and is made of hardened steel...

Considering your precautions, would it be safe to use the motor only to get the wheel up to speed and then use it (as a generator) to regenerate battery charge, then get the wheel back to speed and so on?

Again, thanks for your time

PS. @strantor wow! thanks for putting in the time to write such a long message - especially on a newbie like me <3

(edit)
the RPM of the shaft is unbeknownst at this time but I will update you tomorrow when I have the chance to test it (carefully starting and about half an amp)

 

Alot depends on the amount of energy stored in the flywheel and what is required to expend it, the charging is going to require some expending of energy.
You cannot make a perpetual motion machine!
Max.

 

When stalled, which it will be when trying to get a flywheel moving, a starter motor may draw at least a couple of hundred Amps. Check Automotive web-sites for examples.

 

Considering your precautions, would it be safe to use the motor only to get the wheel up to speed and then use it (as a generator) to regenerate battery charge, then get the wheel back to speed and so on?

I've never attempted to turn a starter or any other series wound into a generator, but I suspect it will not be very effective, as the only source of magnetic flux I see being the residual magnetism left over after the starter is deenergized. If possible, it might make sense to separate the field and the armature and power them separately. This would give you much better control over speed, as well as regeneration. Although I don't see the point of regeneration, assuming the wheel is meant to spin constantly.

What you could do for a simple speed control is a sensor which cuts out the starter once desired speed is reached, and turns it back on once it drops below a threshold, with some hysteresis. Maybe a centrifugal switch, although it would take some creativity to implement it.

 

What you could do for a simple speed control is a sensor which cuts out the starter once desired speed is reached, and turns it back on once it drops below a threshold, with some hysteresis. Maybe a centrifugal switch, although it would take some creativity to implement it.

This is essentially what I was trying to say I was just hoping to gain some battery charge in the process
@MaxHeadRoom
Yes; I know I cannot make a perpetual motion machine, but I can come close enough to extend my battery life for a good while right?

also; creativity I have. Its the actual knowledge that I lack at the moment

(edit)
'hysteresis'
I had to look that one up
Thanks for the new vocab!

 

This is essentially what I was trying to say I was just hoping to gain some battery charge in the process
@MaxHeadRoom
Yes; I know I cannot make a perpetual motion machine, but I can come close enough to extend my battery life for a good while right?

If you use regenerative braking it will put some energy back into the battery, but that energy will come from the rotation of the flywheel and so it will slow down. Then you will need to use energy from the battery to speed it up again. And repeat...
Each of these cycles will lose energy.

It would be better to switch off the motor when the desired speed has been obtained. The flywheel will now slow down gradually. When the speed has fallen by some small amount, turn on the motor again. And repeat... This will lose less energy.

 

@AlbertHall
Gotcha;
also, I will be starting to post updates on progress as of tomorrow on my YouTube channel so check it out