This is how I have it wired currently.

 

This is how I have it wired currently.

I wrote in post #20:

Post your schematic, with all component values.

 

I would do it like this:

 

@Ron-

The Logic Level PMOS, is there an NTE equivalent?? NTE2371? This race is tonight, and I don't have a lot of source options. My local electronics supplier only carriers NTE products (and don't have any P-Channel MOSFETs in stock) and then there is Radioshack.

Could this be modified to accomodate an N-channel MOSFET? Otherwise, the closest I can come is a TIP42G (BJT). Would that work?

Jeremy

 

I don't know of a P ch logic level from NTE- so in despiration propose N ch NTE 2986, or a 5V relay, RS 275-243. Use Ron's parts for the rest.

 

Could the TIP42G substitute for the PMOS? Our supply shop here doesn't have any logic level MOSFETs in P or N in stock

Jeremy

 

It will drop about 1.75V C-E. - not great. FET would drop about .25 to .5 V. Do you have any relays?

 

None that could handle the current. I think I'll have to live with the voltage drop.

 

Actually,Vce(sat) should only be about 0.5V. Not as good as a MOSFET, but not too bad.
You can use PN2222A for the NPN, or the NTE equivalent.
See the attachment.

 

@Ron H & Bernard-

Thank you very much for your help with this project. I just got back from the race, where I took 2nd place overall. The winning car, used a rubber band to slingshot off of the start and the flat of the track wasn't long enough for me to catch up.

I was not able to get the circuit Ron posted to work on the breadboard, probably due to not having the PMOS chip???) and instead just wired a toggle switch to the power supply. Definitely not as elegant a concept, but it worked against all but the slingshot. One car used 3lbs of lead, another used a lead pipe, and yet another used a blower motor.

I have decided that I will simply build a car when time permits for the eventuality of another open class race. I will revisit the bump start circuit then, and add to it wheels on roller bearings and a geared drive axle (despite the decline in the track the torque was, in fact, problematic).

Again, thank you so much for the help. I really appreciate it.

Jeremy

 

Reminds me of when I was a kid. I had a toy army tank with a wind-up clockspring motor. It had a governor that made it crawl across the ground, up steep hills, etc.
For some reason, my dad took the governor out. That sucker would take off like a scalded cat!