We are a fairly new team working on Electrathon and we are having some trouble with our car. We can run at comparable speeds to the other vehicles for about 12-15 minutes, but then the vehicle batteries die. The motor is also very hot (so hot that it hurts to touch it) after the race. I was wondering if anyone has worked with or currently runs the Mars Brushless Motor (ME0201013001) and if you have experienced any problems with it. We have the motor paired with a Sevcon MilliPak, which is programable.
Would love to hear from people with experience in this field who have worked with these motors much longer than we have. Thanks in advanced.
ProEV said
Dec 16, 2012
Nick,
It could be a number of things.
The first thing you need is a way to measure amps. A clamp on ampmeter is one way. Or if you have an accurate volt meter that reads millivolts and a piece of wire of known resistance (Ohms) like a low Ohms precise resistor (available online for less than $1), you can read millivolts and calculate amperage.
Once you know your amp draw, you can start tuning. Different gearing? More air in the tires? Alighn the wheels? Etc.
Zaine Stapleton said
Dec 16, 2012
If your motor is hot to the touch look for loose connections. This is an easy way to waste your battery power is through loose connections. It's twice as hard for current to flow through a contact or battery lead if the wire is barely tight at all compared to a current that can flow easily through a tight connection.
This has happened to me twice. Once I was stuck for 20 minutes due to the controller being stuck in a bad spot. The other was after a race was over with that I won and noticed the controller and motor were both hot.
Zaine
Nick Gupta said
Dec 16, 2012
Right now, we have an ampmeter wired up and we are geared 1:3 on an oval track quarter mile track. The ampmeter is reading 56 amps when running at full throttle on straight aways, which I know is much greater than the other EVs. We have checked for loose connections. The problem that we are having is that we are pulling about 75% greater amps compared to other vehicles. obviously killing our batteries.
Zaine, what do you mean by the controller "being stuck in a bad spot"?
Zaine Stapleton said
Dec 16, 2012
Oh, it was in a place that was not very easy to get at in the car. Which meant that it was not easy to get tools into such a tight space to fix the problem, but that was my schools car. When I built my own car I made sure everything was very easy to get at incase something needed to be adjusted or whatever the case may be.
Zaine
ProEV said
Dec 16, 2012
Zaine's suggestion of looking for a loose connection is a good one. Start with everything cold. Do one lap. Feel all the connections and look for heat. Any where there is heat, you are losing energy.
If only the motor is hot and the connections are tight and clean, calculate what RPM and then search the Internet for efficiency graphs for your motor. Are you in the right range?
Also do not ignore the basics. Do your wheels rotate freely and are they all aligned? Is anything rubbing?
mhodgertt said
Dec 16, 2012
What type of motor are you using? We used to use 'Scott' and 'Pentad' motors and the one horse and even 1.5 Hp ones would get very hot and often burn up some of the windings. Then they would get hot quickly every time you used them. If you are using an eTek then I would think is has to be a very poor area of wiring, fuse, controller, etc. ---or bad bearings/brushes in the motor itself.
With the chain off does the motor spin easily? Mike
Nick Gupta said
Dec 16, 2012
We checked all of the connections for heat after running, and nothing was hot except the motor itself. Based on the graphs, our amp pull and rpms are within a percent or two of the motors peak efficiency. Our front wheels rotate freely, but may be slightly miss aligned. Would this cause enough of an issue to decrease the efficiency significantly, given that we are about 1/2 to 1/4 as efficient as other teams? How freely should the back drive wheel spin? When we apply a fair amount of force by hand, it will spin about 10 to 15 times, but it does not spin similarly to the front wheels.
The motor is a Mars Brushless motor, which is supposed to have similar performance to an eTek motor. The motor spins easily off with no chain - it is a smooth spin at least. However, I have no standard of comparison since I have not worked with electric motors before.
Thanks for all the help guys - really appreciate it!
Nick
Zaine Stapleton said
Dec 16, 2012
ProEV has a point to make. If your saying 1:3, that would mean you have your big sprocket on the motor and your small sprocket on the wheel. Most electric motors like it the other way around where it's 3:1 (small sprocket on the motor, big sprocket on the wheel.) This would also explain why your motor is getting way too hot because it simply does not have enough torque to move the car and it's payload.
Do you have pictures of how your motor is set up in the car by chance? That could be helpful so others can chime in with possible answers to your problem.
Zaine
-- Edited by Zaine Stapleton on Sunday 16th of December 2012 06:40:31 PM
ProEV said
Dec 16, 2012
Nick,
From what you are describing, it does not sound like the alignment or bearing drag are the problem but I always like to ask rather than make assumptions. For instance, when you say you are running a gear ratio of 1:3, does the wheel turn 3 times to ever turn of the motor or does the motor turn 3 times to ever turn of the wheel?
I have not worked with this motor but this posting suggest it is possible to connect the wires in such a way that the motor would run but with excessive current draw. http://endless-sphere.com/forums/viewtopic.php?f=16&t=3484
Have you tried limiting your current to 30 amps and see how far the vehicle will go?
Nick Gupta said
Dec 17, 2012
Right - so our gear ratio is actually 3:1 (my bad) - the motor turns three times for every time the wheel turns once. Sorry about the confusion.
Below are the pictures showing the motor and wheel as well as the controller.
To me it looks as if your motor is mounted so that it spins in a cw direction. Looking at the spec sheet for your motor says it has a ccw fan, and it may run a lot cooler if you swapped the motor to the other side and ran it ccw(someone can correct me if I'm wrong). Your motor may also be more efficient running ccw (not sure how much it would effect battery life), I know that mine does. I have run mine (ME0708) both ccw and cw and never got burning hot, but also does not specify fan direction on the spec sheet. I could be totally wrong here, but it may be something to try.
-- Edited by arcflash on Monday 17th of December 2012 11:44:58 AM
Nick Gupta said
Dec 18, 2012
We ordered the alternate fan this past week, so we will put it on soon to run in the CW direction. I have looked at the motor performance curves for CCW and CW, and they are nearly exactly the same. The only thing that needed to be adjusted was the phasing or timing on the motor, which we have reprogrammed for using the controller so it works in the CW direction. I do believe the fan will remove some of the heat, but I think that by cooling the heat that is forming in the motor is "masking the issue" given that the energy will still be used to heat the motor, but the fan will just cool the motor itself. The other issue is that I don't think the change in fan would alter the amp pull, which would still remain unusually high.
Thanks for all the help!
electrathon said
Dec 18, 2012
Here is my input to an issue that you did not ask for help with. Move the motor down! We set up the first car we ever made with the motor in almost exactly the same spot you did. Could not keep the car flat to the track durring hard cornering. Moved the motor as low as we could and could not get the car to lift after we moved it. Also, the shorter the rear chain is the less likely it will be to flip the chain off the sprocket durring hard cornering.
Unfortionatly I have no help for you with the overheat issue. The fan will draw more amperage once it is working properly, but the reality is that it is likely to be so little more you can not detect it. You are drawing way to much.
As to rolling resistance: Set your car on a tile floor (the hall of the school works great and roll it over a big sheet of paper (or smaller sheets taped togeather). You will quickly see if it is rolling true. This knowledge is off of the old Kung Fu tv series. "When you can walk across the rice paper without leaving a mark it will be time for you to leave".
Aaron
ProEV said
Dec 18, 2012
Nick,
Going back to the beginning of this thread, I am reminded that the problem is that if the vehicle runs at a competitive speed, it will only last 15 minutes. How confident are you that the batteries are good? Even at 56 amps, I would think the batteries should last longer than 15 minutes.
Charge them fully and then let them sit 8 hours. Do they read 12.8 volts?
Set your controller to a conservative maxium amp draw. If you are running Optimas, I would suggest 25 amps. Does the vehicle run for an hour?
bd64 said
Dec 19, 2012
So has anyone in Electrathon successfully used this combination of a Mars motor and Sevcon controller? I know they have been used in robotics and motorcycles but have never heard of them in Electrathon vehicles. I know some NE teams tried them without success.
Nick Gupta said
Dec 19, 2012
I'm confident the batteries are not good. We have had them for three years and have charged them sporadically and often left them with no charge for up to 6 months. We will purchase the Optimas eventually, but I did not want to spend $800 on new batteries when the car is still pulling 56 amps. Right now, we are using four deep cycle wheel chair batteries capable of 18 amps in 1 hour. We are running them in series and parallel, so it is a 24V 36 amp system, which would be similar to that of the Optimas. However, given the condition of the batteries, I would predict they are able to only run for about 1/2 - 3/4 their max capacity, which would compensate for why the car is dying in 15 minutes when pulling 56 amps. My plan was to work the car down so it was reading about 35 amps on the straight away, then purchase new batteries, knowing that it will be worth the investment.
I will set the controller max to 25 amps, and will test again. May be a week before I can do this though
mhodgertt said
Dec 19, 2012
Nick, I did not see where you were from. If you are trying for 40+mph for the oval tracks in the NE or mid West,then aerodynamics may play a major role. This might be part of the problem. Also, if you are doing short track be sure you are not geared too high. Gearing too high will mean you are never into the most efficient RPM of the motor and if you have to slow down for tight corners you are way out of the efficiency curve and having to accelerate back up to speed. The only parking lot at our school without speed bumps is a very small rough one with top speeds of about 20 mph and 15 mph corners. Often a student will take a car out geared for 30+ mph and the batteries will die quickly and the motor is sometimes warm. My car has a fiberglass wolverine (school mascot) for a nose cone so on long fast tracks I am out of luck--anything above 35-38 mph and my amps spike too high. But on our parking lot races in the NW I seldom am out of the medal podium. These are won from 23 to 35 mph and aerodynamics don't play as big of role. My car (and I) are both over weight so I have made my car so I can take tight corners at higher speeds than any other car I have found. This way I don't slow down and speed up and don't waist as much energy on this which is large for my car (F = ma) with the large mass. Just some thoughts, Mike
bd64 said
Dec 20, 2012
I don't think there are any large oval tracks in Nebraska, but there is a small oval in Lincoln. Most cars geared at about 28MPH in the PowerDrive series faster at Hasting's road course which is similar to PIR.
mhodgertt said
Dec 20, 2012
The NE in my post was meant to stand for the North East where they do a lot of large ovals not Nebraska. Like I said I did not know where Nick was from.
ProEV said
Dec 20, 2012
Nick,
Running a 25 max current was more to check the battery capacity then anything else. Since you are using practice batteries, this does not seem necessary. Do you know how far off other team's lap time it is if you run a 30 or 35 amp limit (Optima users, is this the right limit?). It might be more repeatable to run a fixed current and try and improve laptimes rather than running a fixed lap time and try and watch current.
Zaine Stapleton said
Dec 21, 2012
30-40 amps is what most of use are running with redtops or yellowtops.
Zaine
Nick Gupta said
Dec 24, 2012
When we run 30-35 amps, we can only reach about 20 mph, rather than when we run 55, we can reach about 28-30 mph
Nick Gupta said
Dec 24, 2012
When we run 30-35 amps, we can only reach about 20 mph, rather than when we run 55, we can reach about 28-30 mph
bd64 said
Dec 24, 2012
It sure sound like you have problems with rolling resistance, alignment, both wheel and chain and aerodynamics rather than motor issues. You should be able to get under 1 MPH per amp on straight runs at about 30 MPH
mhodgertt said
Dec 25, 2012
Nick, I don't know the RPM for the brushless motor at 24 volts. But, like I said earlier, before I understood gear ratios I always had our team gear too high and we were out of the race too early as it was like driving in 4th or 5th gear. Try to drop to a 3.5 to 1 ratio or even slower (and see what the draw is and the speed at ~75% throttle. If the brushless motor's RPM is about the same as the original brush eTEK then you should be able to go about 23-24 MPH with less than 30 amp draw. For our cars we try to set our gearing so they are at about 500-800 RPM less than the specs. this way we can go faster at the first of the race but still have power and accelerate at the end. It also takes a lot less power to get up to race speed and you can accelerate better with less power when needed.
I also agree that it sounds like you have a lot of drag. One way to check front alignment is to place a large piece of paper (butcher paper etc.) on smooth ground (smooth concrete like a shop or even smoother) so one wheel goes over it. With batteries in place and a drive sitting it so the frame is sprung as normal push the car over the paper and look for any movement (sideways or twisting) of the paper. Do this with the tires straight, then slightly turned right and then left and then fully turned. If everything is set up right the paper should not move. This is not an absolute but it is a very quick check to see it this is the problem. When the car is turning you should not hear any tire scrub or noise more than in a straight line.
Without the chain on you can also check your 'coasting' rolling resistance. Again have the batteries and driver in the car and give it a big shove. It should roll easily 50 to 100 yards in smooth level ground. You can also see if it will make a full 30-40' diameter circle with one big shove--do this for both directions.
For the gearing make sure that both of the sprockets run down the center of the chain and do not rub against either side of it. If it does then adjust the motor sprocket in or out. Also be sure that the motor and rear wheel/sprocket are exactly parallel. You can do this with a straight edge along both sprockets without the chain on. The sprockets should both touch the the straight edge at the front and back of each sprockets. If not one of the two is not lined up and that will cause a lot of drag.
We also pump our tires to 90-100 psi--more at Portland International Raceway that does not have as tight of corners. And we use 120 psi BMX Hookworm 1.95 tires which are fairly fat by most Electrathon standards but hold up on our tight corners. The higher tire pressure really make a difference in rolling resistance. The Clouds (top NW cars) ran a race last year where it was raining heavy and they lowered their pressure to about 65 psi and I won the race by several laps where if and when I beat them it is usually by less than a lap. They, for the first time ever, ran out of power with about 10 minutes left in the race.
Again I don't think aerodynamics make enough of a difference to matter until your speed are over 30 mph.
Good luck, Mike
drewjet said
Dec 28, 2012
Nick, with the chain off and full throttle, how many amps are you pulling? It should be no more than about 5 amps, if more than you may have a working but incorectly connected hall sensor.
Nick Gupta said
Dec 31, 2012
Ok - Thanks everyone for all of the advice so far! Unfortunately, our car is at the school, and I do not have access to it until next week. Some serious problems I have identified so far on the car are:
1) The tire PSI is around 35. We had problems popping tubes and the tires are rated for max PSI of 60. So, we will certainly replaced the tires with Maxxis Hookworms and work from there - hopefully pumping to 110 PSI (we aren't running at any tight tracks for the time being).
2) The chain and sprocket alignments may be slightly off - it appears our motor is at a slight angle and the sprocket, when not tightened, tends to ride to the edge of the motor shaft.
3) The front wheel alignment is off by a few degrees, so one wheel faces slightly in while the other is straight.
Andrew, for amp pull with no load, I'm not sure, since I am not with the car. I am hoping to get some time to work on it over the next week while we are off school. However, when we lift the car up so the rear wheel is not weight bearing and have a gear ratio of 3:1(3 on the drive wheel to 1 on the motor shaft), we are pulling 20.2 amps. I can't check the wiring over at the moment, but that will be the first thing I will do when I get to the car.
Thanks for all the help!! Really appreciate it!
drewjet said
Jan 3, 2013
20 amps is WAY TOO high! You are using almost 500 watts just to turn the motor. I think your hall sequence may be wrong. I just now am trying a brushless motor for my electrathon, I had it hooked up and the very first try it ran smooth. However, it was drawing 15 amps with nothing on it, not even a sprocket. I tried all the different combos and the I found one that was only drawing 2.8 amps, I hope to try and test it tomorrow on the road and see how it does compared to the brushed Etek.
ProEV said
Jan 4, 2013
Just to confuse things, here is another data point.
AC motor and Sykromotive controller. Full throttle and let current stabilize.
Just a sprocket, no chain. 6.75 amps at 49 volts = 330.75 Watts (RPM 5760)
This seems like a ridiculous amount of power just to spin the motor. Is it because the motor is inefficient with high RPM and no load?
With chain and rear wheel and tire spinning free 8.25 amps at 49 volts = 404.25 Watts (RPM 5490)
This looks to me like 74.5 Watts goes to bearing drag and chain drag.
mhodgertt said
Jan 4, 2013
How tight is your chain? I like to have mine just a little loose so that there is less friction on the bearings of the motor. Too tight adds to the drag.
Nick Gupta said
Jan 5, 2013
Andrew, what sequence did you use for the wiring? Currently, we are using the sequence shown in the drawing to be paired with our Sevcon controller, but that seems to not be doing the trick. Did you alter the wiring from the schematic that explains how to wire the motor to the controller?
Also, our chain has about an inch of play in it. I looked into how tight motorcycle chains should be, and this is how I decided on how much play should be in it. Is this too tight compared to others?
Thanks for all of the help!
ProEV said
Jan 5, 2013
Nick,
Did you take a look at the link I posted for 'how to determine the wiring for a brushless motor'?
http://endless-sphere.com/forums/viewtopic.php?f=16&t=3484
Testing what you have might be more effective than guessing from different motors.
The same is true for chain tension. Your chain might be different size or design.
Measure chain droop. Get a current reading at full throttle, spinning free off the ground. Loosen the chain. Measure chain droop. Get another current reading. Better or worse?
I do not know if a free spinning wheel test will tell you what really matters, drag when running but it could give you a starting point.
Nick Gupta said
Jan 7, 2013
Cliff, when I initially looked over the article, and the only problem was that our motor is larger than the one they are using in the picture, meaning that the magnets are much stronger. We have no way of actually opening up the motor to follow the wires, so I cannot determine which of the wires are hall sensor power wires. Because of this, it creates so many more combinations of wires to check. Rather than checking about 36 combinations, it would be 210 possible combinations. However, I just did some research online on the motor, and based on this drawing of the motor: http://www.evassemble.com/pdf/motor/ME0201013001-Model.pdf, in the bottom right hand corner it shows a chart pertaining to the connections. It shows GND (0) as black and V(+12) as red, so I think it would be correct to assume that those are the hall sensor power wires. I will test all 36 combinations soon, and let you know how it goes.
stan r said
Jan 9, 2013
When the Marrs brushless came on the market a few years back we tried them in Nebraska for 1 year. I don't think anyone ever got one to[perform properly if at all. Then the Marrs brush motor came out & for our purposes at least, took the bruahless motor's place. The brush motor motor more closely mimmicks the Etek. Any electric motors most efficient rpm is wide open. If you want 30 mph then choose gears that let your motor run wide open at that speed. Also, Nebraska does have a 2miles + track at Hastings, Ne.
drewjet said
Jan 26, 2013
Nick, this is how I do brushless motors. Connect up the three phase wires in any order. I then use a 5 amp circuit breaker to power the controller so in case the wrong order is hooked up it will pop the breaker before it over currents the controller. Hook the red hallwire to the + out of the controller, this should already be there since you currently are able to run the motor. Hook up the black hallwire to ground from controller, again this should already be done. Now in any order hook up the 3 hall sensor wires from the motor to any 3 hall wires out of the contoller. Use the throttle gently. The motor will either spin nice and smooth and use around 2 to 5 amps or it may spin smooth but use high amps(which is what I think you have) or it will stuter badly and may not even turn and use real high amps. If low amps and correct direction you are done. If high amps or stuter hall wires are wrong. There are 4 combinations to try one of them should give smooth rotation and low amps, if the direction is wrong, but runs smooth and low amps reverse any 2 phase wires and repeat until you get smooth running and low amps.
One other possible issue is if it is 60 degree hall sensors spacing or 120 degrees, You need to know what the motor is, I am sure that should be readily available, and then make sure the controller is set for the right spacing
ProEV said
Apr 4, 2013
Nick,
Did you ever solve your high current draw problem? We were amazed to discover that our power usage more than doubled when our bearings went bad at the ASU race in Febuary. With good bearings, our hubs seem to be ambient temperature after a 1 hour race. That race, they were warm to the touch.
Nick Gupta said
Apr 5, 2013
We were able to get the no load current down to about 3 amps, but we couldn't get to 1500 rpms on the motor. We ended up up buying an etek and just installed it in the car today. Hoping for better results when we take it out to the track this weekend!
We are a fairly new team working on Electrathon and we are having some trouble with our car. We can run at comparable speeds to the other vehicles for about 12-15 minutes, but then the vehicle batteries die. The motor is also very hot (so hot that it hurts to touch it) after the race. I was wondering if anyone has worked with or currently runs the Mars Brushless Motor (ME0201013001) and if you have experienced any problems with it. We have the motor paired with a Sevcon MilliPak, which is programable.
Here is the link to the motor:
http://www.evassemble.com/index.php?main_page=product_info&cPath=17_18&products_id=130
Would love to hear from people with experience in this field who have worked with these motors much longer than we have. Thanks in advanced.
It could be a number of things.
The first thing you need is a way to measure amps. A clamp on ampmeter is one way. Or if you have an accurate volt meter that reads millivolts and a piece of wire of known resistance (Ohms) like a low Ohms precise resistor (available online for less than $1), you can read millivolts and calculate amperage.
Once you know your amp draw, you can start tuning. Different gearing? More air in the tires? Alighn the wheels? Etc.
If your motor is hot to the touch look for loose connections. This is an easy way to waste your battery power is through loose connections. It's twice as hard for current to flow through a contact or battery lead if the wire is barely tight at all compared to a current that can flow easily through a tight connection.
This has happened to me twice. Once I was stuck for 20 minutes due to the controller being stuck in a bad spot. The other was after a race was over with that I won and noticed the controller and motor were both hot.
Zaine
Zaine, what do you mean by the controller "being stuck in a bad spot"?
Oh, it was in a place that was not very easy to get at in the car. Which meant that it was not easy to get tools into such a tight space to fix the problem, but that was my schools car. When I built my own car I made sure everything was very easy to get at incase something needed to be adjusted or whatever the case may be.
Zaine
If only the motor is hot and the connections are tight and clean, calculate what RPM and then search the Internet for efficiency graphs for your motor. Are you in the right range?
Also do not ignore the basics. Do your wheels rotate freely and are they all aligned? Is anything rubbing?
With the chain off does the motor spin easily?
Mike
The motor is a Mars Brushless motor, which is supposed to have similar performance to an eTek motor. The motor spins easily off with no chain - it is a smooth spin at least. However, I have no standard of comparison since I have not worked with electric motors before.
Thanks for all the help guys - really appreciate it!
Nick
ProEV has a point to make. If your saying 1:3, that would mean you have your big sprocket on the motor and your small sprocket on the wheel. Most electric motors like it the other way around where it's 3:1 (small sprocket on the motor, big sprocket on the wheel.) This would also explain why your motor is getting way too hot because it simply does not have enough torque to move the car and it's payload.
Do you have pictures of how your motor is set up in the car by chance? That could be helpful so others can chime in with possible answers to your problem.
Zaine
-- Edited by Zaine Stapleton on Sunday 16th of December 2012 06:40:31 PM
From what you are describing, it does not sound like the alignment or bearing drag are the problem but I always like to ask rather than make assumptions. For instance, when you say you are running a gear ratio of 1:3, does the wheel turn 3 times to ever turn of the motor or does the motor turn 3 times to ever turn of the wheel?
I have not worked with this motor but this posting suggest it is possible to connect the wires in such a way that the motor would run but with excessive current draw. http://endless-sphere.com/forums/viewtopic.php?f=16&t=3484
Have you tried limiting your current to 30 amps and see how far the vehicle will go?
Right - so our gear ratio is actually 3:1 (my bad) - the motor turns three times for every time the wheel turns once. Sorry about the confusion.
Below are the pictures showing the motor and wheel as well as the controller.
To me it looks as if your motor is mounted so that it spins in a cw direction. Looking at the spec sheet for your motor says it has a ccw fan, and it may run a lot cooler if you swapped the motor to the other side and ran it ccw(someone can correct me if I'm wrong). Your motor may also be more efficient running ccw (not sure how much it would effect battery life), I know that mine does. I have run mine (ME0708) both ccw and cw and never got burning hot, but also does not specify fan direction on the spec sheet. I could be totally wrong here, but it may be something to try.
-- Edited by arcflash on Monday 17th of December 2012 11:44:58 AM
Thanks for all the help!
Unfortionatly I have no help for you with the overheat issue. The fan will draw more amperage once it is working properly, but the reality is that it is likely to be so little more you can not detect it. You are drawing way to much.
As to rolling resistance: Set your car on a tile floor (the hall of the school works great and roll it over a big sheet of paper (or smaller sheets taped togeather). You will quickly see if it is rolling true. This knowledge is off of the old Kung Fu tv series. "When you can walk across the rice paper without leaving a mark it will be time for you to leave".
Aaron
Going back to the beginning of this thread, I am reminded that the problem is that if the vehicle runs at a competitive speed, it will only last 15 minutes. How confident are you that the batteries are good? Even at 56 amps, I would think the batteries should last longer than 15 minutes.
Charge them fully and then let them sit 8 hours. Do they read 12.8 volts?
Set your controller to a conservative maxium amp draw. If you are running Optimas, I would suggest 25 amps. Does the vehicle run for an hour?
So has anyone in Electrathon successfully used this combination of a Mars motor and Sevcon controller? I know they have been used in robotics and motorcycles but have never heard of them in Electrathon vehicles. I know some NE teams tried them without success.
I will set the controller max to 25 amps, and will test again. May be a week before I can do this though
I did not see where you were from. If you are trying for 40+mph for the oval tracks in the NE or mid West,then aerodynamics may play a major role. This might be part of the problem. Also, if you are doing short track be sure you are not geared too high. Gearing too high will mean you are never into the most efficient RPM of the motor and if you have to slow down for tight corners you are way out of the efficiency curve and having to accelerate back up to speed. The only parking lot at our school without speed bumps is a very small rough one with top speeds of about 20 mph and 15 mph corners. Often a student will take a car out geared for 30+ mph and the batteries will die quickly and the motor is sometimes warm.
My car has a fiberglass wolverine (school mascot) for a nose cone so on long fast tracks I am out of luck--anything above 35-38 mph and my amps spike too high. But on our parking lot races in the NW I seldom am out of the medal podium. These are won from 23 to 35 mph and aerodynamics don't play as big of role. My car (and I) are both over weight so I have made my car so I can take tight corners at higher speeds than any other car I have found. This way I don't slow down and speed up and don't waist as much energy on this which is large for my car (F = ma) with the large mass.
Just some thoughts,
Mike
I don't think there are any large oval tracks in Nebraska, but there is a small oval in Lincoln. Most cars geared at about 28MPH in the PowerDrive series faster at Hasting's road course which is similar to PIR.
Running a 25 max current was more to check the battery capacity then anything else. Since you are using practice batteries, this does not seem necessary. Do you know how far off other team's lap time it is if you run a 30 or 35 amp limit (Optima users, is this the right limit?). It might be more repeatable to run a fixed current and try and improve laptimes rather than running a fixed lap time and try and watch current.
30-40 amps is what most of use are running with redtops or yellowtops.
Zaine
I don't know the RPM for the brushless motor at 24 volts. But, like I said earlier, before I understood gear ratios I always had our team gear too high and we were out of the race too early as it was like driving in 4th or 5th gear. Try to drop to a 3.5 to 1 ratio or even slower (and see what the draw is and the speed at ~75% throttle. If the brushless motor's RPM is about the same as the original brush eTEK then you should be able to go about 23-24 MPH with less than 30 amp draw. For our cars we try to set our gearing so they are at about 500-800 RPM less than the specs. this way we can go faster at the first of the race but still have power and accelerate at the end. It also takes a lot less power to get up to race speed and you can accelerate better with less power when needed.
I also agree that it sounds like you have a lot of drag. One way to check front alignment is to place a large piece of paper (butcher paper etc.) on smooth ground (smooth concrete like a shop or even smoother) so one wheel goes over it. With batteries in place and a drive sitting it so the frame is sprung as normal push the car over the paper and look for any movement (sideways or twisting) of the paper. Do this with the tires straight, then slightly turned right and then left and then fully turned. If everything is set up right the paper should not move. This is not an absolute but it is a very quick check to see it this is the problem. When the car is turning you should not hear any tire scrub or noise more than in a straight line.
Without the chain on you can also check your 'coasting' rolling resistance. Again have the batteries and driver in the car and give it a big shove. It should roll easily 50 to 100 yards in smooth level ground. You can also see if it will make a full 30-40' diameter circle with one big shove--do this for both directions.
For the gearing make sure that both of the sprockets run down the center of the chain and do not rub against either side of it. If it does then adjust the motor sprocket in or out. Also be sure that the motor and rear wheel/sprocket are exactly parallel. You can do this with a straight edge along both sprockets without the chain on. The sprockets should both touch the the straight edge at the front and back of each sprockets. If not one of the two is not lined up and that will cause a lot of drag.
We also pump our tires to 90-100 psi--more at Portland International Raceway that does not have as tight of corners. And we use 120 psi BMX Hookworm 1.95 tires which are fairly fat by most Electrathon standards but hold up on our tight corners. The higher tire pressure really make a difference in rolling resistance. The Clouds (top NW cars) ran a race last year where it was raining heavy and they lowered their pressure to about 65 psi and I won the race by several laps where if and when I beat them it is usually by less than a lap. They, for the first time ever, ran out of power with about 10 minutes left in the race.
Again I don't think aerodynamics make enough of a difference to matter until your speed are over 30 mph.
Good luck,
Mike
1) The tire PSI is around 35. We had problems popping tubes and the tires are rated for max PSI of 60. So, we will certainly replaced the tires with Maxxis Hookworms and work from there - hopefully pumping to 110 PSI (we aren't running at any tight tracks for the time being).
2) The chain and sprocket alignments may be slightly off - it appears our motor is at a slight angle and the sprocket, when not tightened, tends to ride to the edge of the motor shaft.
3) The front wheel alignment is off by a few degrees, so one wheel faces slightly in while the other is straight.
Andrew, for amp pull with no load, I'm not sure, since I am not with the car. I am hoping to get some time to work on it over the next week while we are off school. However, when we lift the car up so the rear wheel is not weight bearing and have a gear ratio of 3:1(3 on the drive wheel to 1 on the motor shaft), we are pulling 20.2 amps. I can't check the wiring over at the moment, but that will be the first thing I will do when I get to the car.
Thanks for all the help!! Really appreciate it!
AC motor and Sykromotive controller. Full throttle and let current stabilize.
Just a sprocket, no chain. 6.75 amps at 49 volts = 330.75 Watts (RPM 5760)
This seems like a ridiculous amount of power just to spin the motor. Is it because the motor is inefficient with high RPM and no load?
With chain and rear wheel and tire spinning free 8.25 amps at 49 volts = 404.25 Watts (RPM 5490)
This looks to me like 74.5 Watts goes to bearing drag and chain drag.
Also, our chain has about an inch of play in it. I looked into how tight motorcycle chains should be, and this is how I decided on how much play should be in it. Is this too tight compared to others?
Thanks for all of the help!
One other possible issue is if it is 60 degree hall sensors spacing or 120 degrees, You need to know what the motor is, I am sure that should be readily available, and then make sure the controller is set for the right spacing
Nick,
Did you ever solve your high current draw problem? We were amazed to discover that our power usage more than doubled when our bearings went bad at the ASU race in Febuary. With good bearings, our hubs seem to be ambient temperature after a 1 hour race. That race, they were warm to the touch.