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Old 11-07-2010, 08:57 PM   #1
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Post Tough Car Question.

Hi,

Long story short, I have a team of people who are re purposing an RC car to be used in a race. Not any race, an autonomous RC car race (Think DARPA challenge on a miniature scale).

Anyways, the mechanical team has bought a "Kyosho-Inferno-VE-4WD" (sorry no link). Good looking car for our purposes.

My background is Electrical Engineering and I'm supposed to be finding some batteries to put on this thing to make it go. Here's the important catch.
We'll be adding some considerable weight to the car, 2x 500g cameras, and probably another 600-800g of control electronics. Also, were looking to splice the electronics and cameras into this battery also. The Mechanical guys concern is that the stock battery won't be enough to lug all of that around (I agree). However what they propose is absurd IMHO.

These Mechanical Guys think they need a 29V, 4000mah power source to run this thing. I think that's a load and I'm hoping someone on here with much more expertise than I can suggest some batteries for this project. I'm open to different configurations, multi-battery setups. Anything you think I need.

tl;dr: 1/8th scale car needs batteries, we're adding ~1.5kg of stuff to it, also. What batteries do I get? Price is important, but so is weight.

Much appreciated!
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Old 11-08-2010, 07:49 PM   #2
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WoW !! first thing we need to know is what top speed are you looking for?second, how long do you need it to run?
third what motor do you plan to use?
fourth what voltage do the cameras and transmitters opperate at.


as for batteries LIPOs are going to be the best for capacity vs weight.

the cheapest place i know to get them is hobbyking.com
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Old 11-08-2010, 09:37 PM   #3
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Sounds more or less like what I'm trying to do. (I got a much cheaper car and it's just me, not an entire team. )

I'm kind of curious -- where would you get a 29V/4000mAH battery? Are they thinking gel cell?? Whatever you get needs to have a high energy density.

Maybe you should do some experiments? Tape 1.5kg of dead weight on the car, and see what kind of current draw or battery run time you get out of the stock battery. And consider the effects of stop/start versus steady state driving. If the course is going to have a lot of slow down speed up stuff design the experiment accordingly. Is the course flat, or does it have hills, net altitude gain, etc?

In addition to the motor draw, try to estimate the amount of current draw from the control electronics (including speed controller if you are using it) and factor that in, along with margin, and the length of time on the course to come up with estimated battery capacity.

It might be interesting to do sensitivity analysis on weight vs runtime / current draw. Meaning you'd have to experiment with different weights, e.g., 0.5kg, 1.0kg, ..., 2.0kg. Might as well see what impact battery capacity has too. Ie, what yields longer runtime, adding a 2nd battery with 4000mAh capacity, or reducing weight by 0.5kg? Maybe the mech guys can come up with a more efficient motor. Or tires. Or something. I dunno.

Hope some of this helped...

Michael
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Old 11-08-2010, 10:58 PM   #4
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Quote:
Originally Posted by D-money View Post
WoW !! first thing we need to know is what top speed are you looking for?second, how long do you need it to run?
third what motor do you plan to use?
fourth what voltage do the cameras and transmitters opperate at.


as for batteries LIPOs are going to be the best for capacity vs weight.

the cheapest place i know to get them is hobbyking.com

+1.
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Old 11-09-2010, 05:18 AM   #5
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7S lipo is 29.4v charged (25.9v nominal). They are available - Hyperion G3-VX4200 - 7S, hope there's room, its a big battery -

http://www.rclipos.com/Hyperion_G3_VX.htm
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Old 11-09-2010, 05:41 AM   #6
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How long is the race?

I'm thinking that slow and steady might be the way to go or at least to begin with.
Does the cameras and control circuitry have to be powered by the main battery? I'd figure out the current draw of the extra equipment, nail down the control circuit then look at power. Figure the motor & esc draws about
20a, you'll have to measure the surge current with the car fully decked out, then see if the battery can supply it and the esc can deliver it.
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Old 11-09-2010, 05:52 AM   #7
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Default Gearing

If you are increasing the load one factor to consider is the gearing of your vehicle. Another factor to consider with the gearing is terrain. Hills and valleys will vary your formula much more than flat terrain.

I am a science teacher and the real world application of this technology in teaching problem solving skills is fascinating.
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Old 11-09-2010, 02:12 PM   #8
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Quote:
Originally Posted by D-money View Post
WoW !! first thing we need to know is what top speed are you looking for?second, how long do you need it to run?
third what motor do you plan to use?
fourth what voltage do the cameras and transmitters opperate at.


as for batteries LIPOs are going to be the best for capacity vs weight.

the cheapest place i know to get them is hobbyking.com
Ideally, we are only limited by how fast we can process images and figure out a path. However, looking how it will probably be controlled (constant velocity) we are aiming for 15-20km/h max. That would obliterate anyone at competition last year.

For the competition there is 2 events, (4 actually but only 2 performance ones) Drag Race and Circuit Race, for the Circuit race we finished in 10 minutes last year, but we probably want a runtime of 15-20 minutes so we don't have to take a penalty to change batteries again.

Something similar to the stock motor will be used. Which is:

550 Size Motor
2040KV
Continuous Current 85A
Peak Current 160A

The cameras are 3W each, ran from 6-12V DC. (2 of them)
All the other electronics I'll do my own power regulation. But it will be ~12V and half an amp.

I know I need to look into LiPo batteries for this. I just don't know if its worth it to get 2 in series, 1 big one, 2 in parallel whats the best way?

Quote:
Originally Posted by shimniok View Post
Sounds more or less like what I'm trying to do. (I got a much cheaper car and it's just me, not an entire team. )

I'm kind of curious -- where would you get a 29V/4000mAH battery? Are they thinking gel cell?? Whatever you get needs to have a high energy density.
I think they are full of it when they claim they need something that big. I think they read 2-4S LiPo as 2-4 regular batteries. The electronics are taking up no more than 10W at any time, which is a drop in the bucket compared to the motor on the car. Also, if you need help with what you are doing, PM me, theres 10 Electrical and Computer engineers in this room.

Quote:
Originally Posted by C&B RC View Post
How long is the race?

I'm thinking that slow and steady might be the way to go or at least to begin with.
Does the cameras and control circuitry have to be powered by the main battery? I'd figure out the current draw of the extra equipment, nail down the control circuit then look at power. Figure the motor & esc draws about
20a, you'll have to measure the surge current with the car fully decked out, then see if the battery can supply it and the esc can deliver it.
Race will be as short as we can run it in. 3 laps at maybe
200m/lap. The drag race being shorter.
We can run any configuration of batteries. So long as we are within the dimensions, we can add a Lead-acid car battery trailer if needed.

Quote:
Originally Posted by MC1357 View Post
If you are increasing the load one factor to consider is the gearing of your vehicle. Another factor to consider with the gearing is terrain. Hills and valleys will vary your formula much more than flat terrain.

I am a science teacher and the real world application of this technology in teaching problem solving skills is fascinating.
GEARING! Yes, I dont have any experience cutting gears but it will be done by the mechanical people I'm sure. (Screwed us last year, 20% slope and no power) The track this year sounds like it will be pretty flat with a couple of obstacles. Like a hill and tunnel. Most of the competition is actually finding a good algorithm to find the track and plan a route.

--------------

tl;dr: With a motor with these specs:
550 Size Motor
2040KV
Continuous Current 85A
Peak Current 160A
and an extra 10-15W of electronics on top, plus 1.5kg of weight,
what kind of battery setup and batteries should I find? Specifically voltage, mah, and discharge rates I want to know.

Thanks!
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Old 11-09-2010, 08:28 PM   #9
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I did a little digging, check out these threads and look at GSMnow's comments. He has done his homework. In general a higher voltage results in lower current draw as expected but also less energy waste(heat). Also, the ME's should weight balance the loaded chassis. A balanced chassis will be easier to control, less compensation cycles.

Brushless motor current draw


1/8 ELETRIC QUESTION

http://www.rctech.net/forum/electric...nges-pita.html

Survey: 1/8 Electric buggy run times.

4s is the max you can run with the stock esc if you got the RTR version. If your Course runtime is 10 min a 4s might do it. A big question is the course dirt, carpet, asphalt? The last link discusses runtime and as you can see typical is 15min -20min on a 4s lipo. These guys are runnin in the dirt running with motor rpms about 30k. You'll be carrying more weight but running at a slower speed. I would think you would gear it for torque on the course track and speed on the drag run. If you're running on-road, get different tires.

I can also bounce some ideas off my engineering group too cool a project.
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Last edited by C&B RC; 11-10-2010 at 11:28 AM.
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Old 11-10-2010, 02:16 AM   #10
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Quote:
Originally Posted by WorstNameEver View Post
Hi,

Long story short, I have a team of people who are re purposing an RC car to be used in a race. Not any race, an autonomous RC car race (Think DARPA challenge on a miniature scale).

Anyways, the mechanical team has bought a "Kyosho-Inferno-VE-4WD" (sorry no link). Good looking car for our purposes.

My background is Electrical Engineering and I'm supposed to be finding some batteries to put on this thing to make it go. Here's the important catch.
We'll be adding some considerable weight to the car, 2x 500g cameras, and probably another 600-800g of control electronics. Also, were looking to splice the electronics and cameras into this battery also. The Mechanical guys concern is that the stock battery won't be enough to lug all of that around (I agree). However what they propose is absurd IMHO.

These Mechanical Guys think they need a 29V, 4000mah power source to run this thing. I think that's a load and I'm hoping someone on here with much more expertise than I can suggest some batteries for this project. I'm open to different configurations, multi-battery setups. Anything you think I need.

tl;dr: 1/8th scale car needs batteries, we're adding ~1.5kg of stuff to it, also. What batteries do I get? Price is important, but so is weight.

Much appreciated!
LiPo = 3.7v cell
LiIon = 3.6v cell

Several flavours available and bullet connectors and you could hook up in series if you need to keep a low profile, or buy two 14.4v lumps or hookup IDX in camera's at work as well (you did mention price though) so RC shops online will have everything you're after, get some interconnects while your at it.

500g camera's?? Really, that's heavy and can only wonder how big they are, get some heavy springs too or you'll bottom out, shoulda bought a baja or 1/5th scale
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