TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot.  
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TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/18/2007 4:12:19 PM   
Lico Miami


 

Posts: 16
Joined: 4/23/2006
From: Miami, FL, USA
Status: offline 		I am using a 72 (spur) 16 (pinion) = 11.25:1 final drive ratio, but my Mamba M. speed C. is geting to hot. I am not geting all that final speed with 7cell (8.4V.4200.). Does enybody have a sugestion on gearing this car? I am disapointed with the temperature because I have planty take off but not so good final speed, so why 200 degrees F.?.

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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/18/2007 6:55:21 PM   
hands without shadows



Posts: 6039
Joined: 11/23/2005
From: denfield, ON, CANADA
Status: online 		What batteries are you using?

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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/18/2007 7:20:10 PM   
Lico Miami


 

Posts: 16
Joined: 4/23/2006
From: Miami, FL, USA
Status: offline 		7 Cell (8.4v/4200) I don't have it here so I can't tell you the brand.

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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/18/2007 7:23:07 PM   
cheech4



Posts: 6122
Joined: 2/24/2006
From: astoria, NY, USA
Status: offline
quote:

ORIGINAL: Lico Miami

7 Cell (8.4v/4200) I don't have it here so I can't tell you the brand.


this might be a stupid question but im gonna ask anyways, are you running deans plugs???

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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/18/2007 8:33:02 PM   
weracerc



Posts: 97
Joined: 12/15/2005
From: greensboro, NC, USA
Status: offline 		what are you trying to accomplish? racing or bashing? speed or handling? 11.25:1 FDR is way to high (low) depending on how you see it.......for racing we run 72/28, 29, 30, 31........brushed and brushless 13.5 we run 66/33, 34, 35 or 69/33,34,35 FDR's in the 4.85 - 5.15:1 area......

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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/18/2007 10:28:34 PM   
Access


 

Posts: 2505
Joined: 3/8/2005
From: , CA, USA
Status: offline 		My TC4 had a 3-cell/5700 setup and I was running pinions from 13-25 for speeds from 42mph to 65mph. My favorite gearing was 19/78 b'cos it was easy to keep all 4 wheels from sliding when accelerating in a straight line (any higher gearing and they would slip if you hit full throttle from a dead stop). Set a voltage cutoff starting at 0.9V per NIMH cell, set the timing to lowest, punch control to 10, and get a good heatsink and put a fan directly in front of the motor. I was using a 10W 14000rpm 12V fan in mine and this was vital to keep things cool.

Other than that it's all how you drive it. Don't worry if you can't beat the other cars top speed in the straights. Focus on your cornering, acceleration, and consistent driving. You will not win any races by setting up your car for top speed, unless you drag racing or on an oval track.

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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/18/2007 11:40:19 PM   
Slo-V Flyer



Posts: 2190
Joined: 2/23/2006
From: arlington, TX, USA
Status: offline
quote:

ORIGINAL: weracerc

what are you trying to accomplish? racing or bashing? speed or handling? 11.25:1 FDR is way to high (low) depending on how you see it.......for racing we run 72/28, 29, 30, 31........brushed and brushless 13.5 we run 66/33, 34, 35 or 69/33,34,35 FDR's in the 4.85 - 5.15:1 area......


With really tall gearing he is more likely to heat up the motor. Make sure nothing in the transmission is binding. The other reason the motor would heat up is if you have it geared with a pinion that is too large or maybe even too small. Have you tried a bigger pinion? That way the motor won't spin as fast. It is entirely possible you're pinion is too small, and so the 7700 motor is reaching it's max rpms and the bearings are actually spinning so fast it is heating up your motor?

It might sound weird, but try a larger pinion. Being a touring car, I think you might be too under geared for that motor like Weracerc mentioned.

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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/20/2007 2:30:19 PM   
Lico Miami


 

Posts: 16
Joined: 4/23/2006
From: Miami, FL, USA
Status: offline 		Yes I use deans, have you ever had problems with M.M. original Esc/motor conectors, would a bad contact cause heat? I am thinking on soldering Deans on Esc/motor wires also...

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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/20/2007 3:24:36 PM   
Slo-V Flyer



Posts: 2190
Joined: 2/23/2006
From: arlington, TX, USA
Status: offline 		No you don't need Deans for ESC/Motor wires... though it would be a wierd connection, since you only have 3 wires to deal with and Deans come with 2 pins each.... Those 4-5mm bullets are just fine for the Mamba motors.

But any way, no, bad wire connections will NOT cause the motor to heat up. The wiring will heat up at the point where the connection has the most resistance, e.g. like at the battery/ESC connectors if you run Tamiya connectors. The only reason a motor will heat up is if the motor has too much of a load on it, has too much voltage/amps going through it, or in some cases spins realllllly fast and heats up the bearings though I'm not sure about that.

Did you try a larger pinion to see if it heats up more or less? Did you check for binding in your transmission? Also, are you running the Mamba ESC with Low (or Lowest) timing?

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(in reply to Lico Miami)
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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/20/2007 4:12:05 PM   
Lico Miami


 

Posts: 16
Joined: 4/23/2006
From: Miami, FL, USA
Status: offline 		Thanks for your time with me, I am using deans plugs, my car is free and thare is no binding. My setings are low timing and normal punch control..., about gearing: 72/16 is what I have now, I tried 72/18 before. I figured that my final dreve ratio is 11.25:1 and the roll out ratio is: 0.725.
Considering M.M.7700 and 7cells/4200 battery, what do you think about my gearing? I like final speed, but I realy don't like the heat, The esc, is easily geting 200.F.
I am sorry for my poor english, I am Brazilian living in US.

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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/20/2007 5:46:08 PM   
Lico Miami


 

Posts: 16
Joined: 4/23/2006
From: Miami, FL, USA
Status: offline 		Weracerc, Thank you for your help, note that 11.25:1 is my final drive ratio, my gear ratio is 4.5:1 (72/16t). so if I go up to 5.0:1 5.5:1 I will end with less top speed. I like top end speeds, I do not race on the track. So what do you sugest for top end with my 7700 M.M. and 7cells, 8.4v./4200?, Do you think that the only way to go faster will be with a 6900 motor and 11.1 volts? or is ther anybody that can reach 60mph. with 7700 motor and still keep temps resonable low?

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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/20/2007 5:59:19 PM   
Access


 

Posts: 2505
Joined: 3/8/2005
From: , CA, USA
Status: offline 		"Undergeared" and "Overgeared" are relative terms in the brushless world. What castle suggests is that you gear for the top speed you want provided that you are not overheating anything.

In general, if the ESC is heating up much faster than the motor, it is undergeared. If the motor is heating up much faster than the ESC, it is overgeared. But if you use the rules above, sometimes the only way to make a setup work is to undergear it and to cool the ESC with some kind of fan. In many setups, the motor is nearly encapsulated or not entirely accessible while the ESC can generally go anywhere. Hence it is much easier to cool the ESC, also, an undergeared setup is more efficient (generates less heat overall) than an overgeared one and runs longer.

"But any way, no, bad wire connections will NOT cause the motor to heat up."
Actually they could. This is brushless and delta-wound so one bad connection would cause two poles to be impacted. Two bad connections would case all three poles to be impacted, but not evenly. Either way this could throw off the balance of the motor and/or force the remaining pole to work even harder. Once an electromagnet gets near/into saturation (ie. is working too hard), the waste heat will increase.

If you want to talk speeds with the mamba I have radared 65mph with a 3-cell/5700KV setup and 25/75 gearing (same car). With NIMH and a 7700KV motor a reasonable speed would be ~50mph. People have reached 100mph+ but not in that car. The 100mph+ was in a drag racer and only for a short time.

< Message edited by Access -- 9/20/2007 6:04:06 PM >

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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/20/2007 6:58:44 PM   
Lico Miami


 

Posts: 16
Joined: 4/23/2006
From: Miami, FL, USA
Status: offline 		Thank you Access, I think that the only way to get grater speeds will be with a 5700 or 6900 motor and 3cells lipo. (geard properly). I think that my problem can't be solved.
I have high temps with 8.4v. so I can't go with a lager pinion to increase speed... If I solve the temp. problem I have to loose final speed (smaller pinion), so I gess I will have to go with the 5700 or the 6900 with 3 cells (biger Pinion) to be able to get around 60s, correct? thank you again!

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RE: TC4 11.25:1 final Drive Ratio and Mamba 7700, to hot. - 9/20/2007 7:27:26 PM   
Access


 

Posts: 2505
Joined: 3/8/2005
From: , CA, USA
Status: offline 		It's hard to say without all the information (ie. high temps where? The motor, the