Re: Car Battery for post-season bot
 

hmm that seems wierd im gonna go do some more research and that and see what i can find out.

Re: Car Battery for post-season bot
 

I found this page:
http://www.tpub.com/neets/book5/18b.htm

I know it is mainly about AC motors, but do a search for "alternator" and this should come up:
"The construction of the synchronous motors is essentially the same as the construction of the salient-pole alternator."

So it's not the same as a squirrel-cage motor, but it still requires AC and would be a pain to power. :D

Re: Car Battery for post-season bot
 

I just did some research, and i found Bosch motors for generators. I saw that they had vey fast motors with low torque, and high torque motors with low speeds. They had high torque window motors. What if i take a normal windo motor from the kit and gear that way up to make the rpm way faster. Would that burn out the electronics and/or motor? I could not find the generators they make on their website, but i do know they make them for the old volvos. I want to get a pair of the generators for at max 120. The lowest price i found for one alone is 130. So, can i use the window motors?, and are there cheaper generators?

Re: Car Battery for post-season bot
 

that website that Elderon found is awesome!

They used DC generators on cars, which worked great, but they had a few drawbacks. They were somewhat expensive to build, and the commutator and brushes would wear out sooner or later and would have to be replaced.

An alternator is an AC generator that used diodes to rectify the AC to DC. They also use an induction armature (or rotor) which makes them less expensive to manufacture.

This is why you can use a generator as a motor, but not an alternator. The diodes in the alternator only let current out, not back in, and if you took the diodes out then you would need to power it with AC to make it run like a motor.

Its interesting to note that the EV1 electric car made by GM did have an AC motor, with electronics that converted the DC from the batteries to AC. I think the main reasons for doing that were the motor was lighter, less expensive, and easier to control.

But if you want a simple motor that runs on DC from a battery, then an old car generator or something like a wheel chair motor, riding scooter motor - those are the kinds of things to look for.

regarding the car window motors. I dont know how much HP you can get out of those. There are limits, any given motor will only take so much current before the windings melt, and you can only spin them so fast before they self-destruct. Also, if they use permanant magnets (like the window motors, CIMs, drill motors...) you can only drive the armature magnetic field to the point where the metal core material saturates. After that you cant practically get a stronger magnetic field, and any additional current you supply is turned to (copper melting) heat.

So as with everything else in engineering, the laws of physics impose limits to what you can do. You can only get so much HP from a motor before one of those laws maxes out and you either melt it down, or it rips apart.

Re: Car Battery for post-season bot
 

Why do other CIMs, not the FIRST ones, last a long time, yet the FIRST ones cant run that long, as stated earlier. It says on FIRSTWiki that they un a long time. Why cant i get a bigger battery, but use like 4 CIMs from the kit?

Re: Car Battery for post-season bot
 

Eric,
The smaller Chalupas are designed for powerful but intermittant duty on a trailer jack. The larger ones are designed for more prolonged duty on a scooter but have different power vs. RPM specs. The larger ones might be just perfect for your application.

Re: Car Battery for post-season bot
 

so this years large ones can work? I can order 2 more, as they are not as expensive as other ones. The only problem is the frying electronics. It happened once before, and how do i prevent it this time?

Re: Car Battery for post-season bot
 

Eric,
I assume you are speaking of the speed controllers. This is normal when the system draws too much current from the controller. If you make a mechanical design that runs the motors below 40 amps you shoul be fine. The thing that kills speed controllers is running the motors at near stall where the current is over 100 amps.

Re: Car Battery for post-season bot
 

so if i can rig the fuses in series with a 30 amp fuse instead of a 40 amp, would that cause the speed controllers to not fry. Is there any other option i have besides switching the fuses?

Re: Car Battery for post-season bot
 

you can use a 30 amp breaker instead of a 40 but it may trip more often, the bigger CIMs certainly last a while we ran our robot for a few hours and we use the bigguns for our drive and had no problems with them overheating

Re: Car Battery for post-season bot
 

The 40 amp breakers should be good to protect the Victors. The situations in which you are likely to burn out Victors are things like

having a drive train that can stall the motor. If the motor cannot turn it will draw its max current through the victors until the breaker opens. You keep doing this and the Victor will eventually fail.

having a drive train that is geared up so it takes several seconds for the motor to reach its top speed

having a driver who throws the motor from full forward to full reverse and back.

Keep in mind the breakers are intended to protect you wiring and Victors from shorts. If you repeatedly overload the breakers (so they click click click all the time) you are over stressing your entire motor drive circuit (including the Victors).

Re: Car Battery for post-season bot
 

So, if i take 4 large CIMs (i buy two more, as well as 2 per side equaling 4), and wire them up for the drive, and since i will be running it on a flat rubber track, they wont stall. If i design it right, than i wont bun anything out right? But what if i want to take it full speed? (on the straight-aways :) ) I know you mentioned you have taken full speed and has taken time to do that, but are you refering to stall in the since that there is a force causing the motor to stop with power going in?

Ken, "Keep in mind the breakers are intended to protect you wiring and Victors from shorts. If you repeatedly overload the breakers (so they click click click all the time) you are over stressing your entire motor drive circuit (including the Victors)."

It protects the victor on the other side of the victor from the motor. Does it protect the victor when the motor is causing the victor to smoke/spark from over heating? No, need explaing if it does, just a yes or no answer because i can figure out both senerios if it does or doesnt protect the victor on the motor side.

Re: Car Battery for post-season bot
 

Eric,
Stall means that the motors are so loaded that they cannont turn, even when full power is applied. If you design the mechanical system such that the motors are turning very slowly when full power is applied you are drawing more than either the motors or the speed controllers are designed to supply. JVN or Paul Copioli or Andy Baker can give a better description or a better design criteria for your use. If you look at the power curves for the motors, you will notice a point at which the motors are the most efficient, are at stall or at no load. On these curves are the tested currents for each of these conditionsl. A designer chooses wisely the point on the curve he wishes to operate by selecting the final RPM delivered to the wheels and the correct gear or pully reduction that will put the motor into a specific point on the curve. (not at or near stall and hopefully closeer to the most efficient point on the curves or printed specification.
Although the breakers are thought to protect the motors and/or the Victors, they are in fact chosen to protect the wiring from damage. If you were to consult the wire tables from the NEC (National Electrical Code) you would find that a #12 in free air with intermittant duty can be protected by a 40 amp fuse or circuit breaker. In conduit or in continuous duty that current must be reduced to prevent damage to the wiring. It is easy to see that breakers protect wiring, since many of the more powerful motors supplied in the kit are capable of well over 40 amps when heavily loaded or near stall. When the Victor fails, the circuit breaker trips to protect the short from drawing so much current in that branch that the wiring starts a fire.

Re: Car Battery for post-season bot
 

Thanks Al, I think i may want to have direct drive though to the wheels. But if not, can someone help a little bit more with the curve, i think i understand what you are talking about, as my next paragraph explains. Is it the one on the spec sheets on FIRST, or a different curve. I know the pm i want. I want around 850, which with 8 inch wheels is 20 miles an hour or so, if outside factors did not limit it. I think the large CIM is at 1600 rpm at 40 amps. Well thats what the spec sheet shows. It also has 210 torque of oz-in.

Now, looking at the graph, http://www2.usfirst.org/2006comp/Spe..._FR801-005.pdf
I want about 200 oz-in of torque to give just about 1700 rpm, which is perfect for gearing 2:1 to get my desired speed. The only problem is it is 35 amps, which i dont know how to achieve this. I think this set up wont stall the motors, as well as allow a fast ride with a lot of torque.

Re: Car Battery for post-season bot
 

WHOA! I would NOT want my grandma flying around the track at 20 mph on a handcrafted powered chair! If you are still using this for the same purpose (Relay For Life) I highly suggest you don't let your machine ever come anywhere close to that speed! Seeing as the normal walking pace is ~2.5 mph, you should probably try to keep your machines output topped out at about 4 or 5 mph (in case their partner wants to run.)

If you directly couple a Fisher Price gearbox to a 12" Pnueamatic wheel, (One of these assemblies on each corner), your nominal speed will be about 3.25 mph.