Car Battery for post-season bot

[Dad1279]

If you need more capacity, there are 'car batteries' that are sealed gell cells. Look at 'Optima' brand for one.

[EricRobodox]

yeah. thanks. now the engine/motor problem is my issue. thanks again for your guys's help.

[Al Skierkiewicz]

I agree with Tom that two stock FP motors with transmissions are the best bet for you. You might need to follow up with a little different transmission (final gearing) to make up for the fact that you are driving bigger wheels than what the transmission is intended for. The kit battery might getyou around the track but a larger version of the same battery might be a better bet. You can buy new ones but there are various surplus shops around that might have used or surplus devices for sale. You will need to check around in your area. Since this is for charity, a local battery shop or car parts outlet might be willing to lend you or donate a battery of more capacity.

[EricRobodox]

Im thinking of the 8 inche wheels, only because our team uses a 6wd on our comp robots and use 6's for the wheels. We have a lot of 8 inch wheels. If those are not good, what will be. And, is there a way i can integrate 2 fp motors together. We have like 4 of them. Or will 2 be enough? A car battery will do the work, im almost positive from my research, so that will be the bigger battery.

[KenWittlief]

I have seen people use old generators from car engines for small electric go-carts. Not alternators, it has to be a generator. VW bugs had generators up till around 72 or 73 (not sure the year they swithed to alternators).

There are two things that make these work well:

1. the are designed for a 12V application
2. they have a separate field winding that you can use to vary the speed. The stronger the field, the slower the speed (with more torque)

also they have fan belt pulleys already on the shaft. I would take a wild guess that you can get maybe 5HP out of one of these!

just to give you an idea, this is what they look like: the ground is through the metal housing, one connection is the armature, the other is the field

http://cgi.ebay.com/ebaymotors/VW-TY... 4644044QQrdZ1

[Al Skierkiewicz]

Originally Posted by EricRobodox

Im thinking of the 8 inche wheels, only because our team uses a 6wd on our comp robots and use 6's for the wheels. We have a lot of 8 inch wheels. If those are not good, what will be. And, is there a way i can integrate 2 fp motors together. We have like 4 of them. Or will 2 be enough? A car battery will do the work, im almost positive from my research, so that will be the bigger battery.

Eric,
The smaller wheels should be better. I was envisioning you modifying a regular wheel chair rather than building up from scratch. The FP motor and transmission is used on ride toys for 60 pound kids as a single unit. Two of these should be good for up to 120 and may work up to 150 pounds total weight. The larger Chalupa motor is used on a scooter type device. I repaired one once for a friend and rode it for several minutes. I am well over 200 pounds (no I'm not going to get scientific and give you an exact weight.) and it carried me at a relatively quick pace. It did have a safety device that required you to get the scooter up to speed before the motor could be engaged. It contained a centrifical switch that closed when the motor was spinning at more than the minimum speed. It used a simple toothed belt transmission to couple to the rear wheel.

[EricRobodox]

I cant find any lartger CIMs that will work with 12V. I found some at 24V, but i dont know if i can use Victor 883's, we have a lot and want to use since we cant use them in comp anymore. I dont want to blow the speed controllers out. The robot, kart, im looking at weighing about 90 pounds max. and the person weighing about 200 pounds max. So it needs to be able to push 300 lb. Of course, im using two motors. but i need to know if i wont blow up the victors.

Ken, does that attach to the wheel to recharge the battery while it runs? Im very new at electronics outside of FIRST and guitar electronics. That will charge the 12V battery, but if i get a 24V, do they make them?

[Al Skierkiewicz]

Eric,
I believe ken was indicating that a generator can be used as a motor and it already has a pulley attached and a few nice mounting brackets. The larger CIM motors in the kit this year are the ones I was talking about. (we call the chalupa) If speed is not important, I would think you could use two of those motors with a larger 12 volt battery and you should be OK for once around the track.

[EricRobodox]

well, im a little skeptic of using a lot of FIRST electronics because two years ago, i found this out today, that we tried building a go-kart and the electronics fried because of amp over heating the motors. Will the same thing happen with a lager battery. Thats why i want to get a car battery and bigger CIMs as the amps will be used and not fry the electronics. Thank god im not building without designing on this or i would have had an expensive problem. ahahah. thanks again for all your help.

[KenWittlief]

What Al said - you can use a generator from a car for a motor.

I dont see any reason why you could not run it at 24 V - it will have 4 times the power. The limiting factor on motors is the current level that melts the armature, and the max speed (that rips the windings and commutator off the shaft).

There are specs for the Victors on the IFI web site. I think they are rated for 12V only, but check for yourself, they might have other ones intended for other applications?

[EricRobodox]

so, if i used two, both a 12v, than i should be good right. Then i dont have to worry about getting new speed controllers. But will it push without over heating at 12v? If so, can heat sinks and fans cool it down enough? Also, mounting, is it easy to mount like the CIMs in the gear box? Also, can i buy them new at a cheap price?

[Al Skierkiewicz]

Eric,
If you correctly size the motor to wheel reduction the current in the motors will be low. The reason we have been suggesting a larger battery is the distance/time that it will take to get around the track. The best designs in our competition will get 3-4 matches from a single battery but there is rarely continuous current draw. With a larger battery, you should be able to run for a much longer and continuous period without worrying about the battery becoming discharged.
If the goal is to get someone around the track then a simple design should work fine. If the goal is to beat other teams around the track then that will require a little more design time and some better engineering.

[Eldarion]

Originally Posted by KenWittlief

What Al said - you can use a generator from a car for a motor.

I dont see any reason why you could not run it at 24 V - it will have 4 times the power. The limiting factor on motors is the current level that melts the armature, and the max speed (that rips the windings and commutator off the shaft).

There are specs for the Victors on the IFI web site. I think they are rated for 12V only, but check for yourself, they might have other ones intended for other applications?

The Victor 884 is rated to 15V stock, however I read somwhere that the limiting factor is the fan, and if you replace the fan with a 24V fan you can run it at 24V.

[Conor Ryan]

Originally Posted by Eldarion

The Victor 884 is rated to 15V stock, however I read somwhere that the limiting factor is the fan, and if you replace the fan with a 24V fan you can run it at 24V.

I wouldn't recommend over powering the victors, they are expensive stuff and I don't believe you can change it around. As you will see IFI has higher voltage PWMs running with only 24 volt (even 12 volt) fans, does that change what they are rated for? No.

Don't worry there are other solutions though, did you guys know that IFI makes stuff for a business and not just for FIRST?

Yes it's true! And they have Higher Voltage PWM's!!!
Victor 883 (6-30 rated 24 Volt recommended)
Victor 885 (6-30 rated 24 Volt recommended)
Victor 36HV (12-42 rated 36 Volt recommended)
Victor 48HV (12-60 rated 48 Volt recommended)

All the fans for the victors are available in 12 or 24 volt models, if your voltage is greater than 15 volts, I recommend bumping it up to a 24 volt model.

[Al Skierkiewicz]

Originally Posted by Eldarion

The Victor 884 is rated to 15V stock, however I read somwhere that the limiting factor is the fan, and if you replace the fan with a 24V fan you can run it at 24V.

The fan is not integral to the Victor but that is not the limiting factor. The FETs are different to handle the voltage spikes produced by a 24 volt motor. I believe the part number is 885 for the 24 volt version.