PDA

View Full Version : Comparing motors



DaveAK
03 February 2011, 1658
After I finish my bike I have a new project for the summer months. It will be a small tracked vehicle, so I'm looking for two motors. It's going to be slow speed, but needs a lot of torque. It will be run at 24-48V depending on motors. Taking a look at a couple of offerings I'm just not getting how to make a reasonable decision.

Compare these for me:

D&D SepEx as used by Tony: http://www.evdrives.com/dd_motors_170-512-0005.html

This D&D 512:5 is a Brush-Type, Shunt motor Capable of 2.2 KW continuous and 15 KW for 1 minute.

•24 - 72 VDC
•7/8" single-shaft base/face-mounted
•6.7" Dia x 8.5" Long
•Actual Weight 38 lbs
•Shipping Weight 43 lbs

CONTINUOUS RATING: @ 48 Volts
•3100 rpm
•2.8 ft lbs torque
•45 amps armature
•9.5 amps field
•2.3 HP

PEAK RATING:
•4500 rpm
•14.3 ft lbs torque
•350 amps armature
•20 amps field
•8.5HP

eBay offering: http://cgi.ebay.com/4-HP-24V-DC-VEHICLE-ELECTRIC-MOTOR-/230415376902?pt=LH_DefaultDomain_0&hash=item35a5d3a206

4 HP 24 VDC ELECTRIC MOTOR
45 AMPS NO LOAD
140 AMPS FULL LOAD
8000 RPM FULL LOAD
32 INCH POUND OF TORQUE
¾” DIAM. X 1 ¾” SHAFT WITH KEYWAY
MOTOR DIMENSION 4” DIAM. X 7 ¾”
SHPG 24 LB (ESTIMATED)


The eBay one has 4HP @ 24V vs. 2.3HP @ 48V. It has similar torque, but spins a lot faster. I would have to gear it down a lot more, so what effect would that have on torque? (I used to know this stuff.) Apart from the speed I feel it better suits my application, but I'm curious as to why it has more HP at a lower voltage.

How do you choose a motor for high torque and low speed?

lugnut
03 February 2011, 1906
eBay offering: http://cgi.ebay.com/4-HP-24V-DC-VEHICLE-ELECTRIC-MOTOR-/230415376902?pt=LH_DefaultDomain_0&hash=item35a5d3a206

4 HP 24 VDC ELECTRIC MOTOR
45 AMPS NO LOAD
140 AMPS FULL LOAD
8000 RPM FULL LOAD
32 INCH POUND OF TORQUE
¾” DIAM. X 1 ¾” SHAFT WITH KEYWAY
MOTOR DIMENSION 4” DIAM. X 7 ¾”
SHPG 24 LB (ESTIMATED)

It is a winch motor. Designed to pull in 100 ft of cable for a minute or two. And then cool down for an hour. It ain't going to do no bike :-(

DaveAK
03 February 2011, 1946
It is a winch motor. Designed to pull in 100 ft of cable for a minute or two. And then cool down for an hour. It ain't going to do no bike :-(
It's not for a bike. I had figured it to be a winch motor, but the write up implies 4HP continuous, with up to 9HP peak. So I guess the crux of the matter is what is 'continuous' when comparing these two motors, right?

Tony Coiro
03 February 2011, 2021
I'll let you know how my mini-sepex's work out. Just ignore the horsepower ratings, D&D's are really underrated (in my experience.) With some mods, I'll be shooting for +30hp per motor. And frankly, at that price, they really can't be beat.

DaveAK
03 February 2011, 2033
It needs to be reversible, and it needs to be cheap, (with a cheap controller). :) Looking at those etek knock offs it looks like they might do the job, but shipping is way too much for the one I found.

So if power=torque*rpm, give or take a little, I guess I just need to look at continuous HP at a given voltage. So what do I do with a torque constant of 1.14in-lb/amp? Use it to work out amp draw at particular speed?

DaveAK
03 February 2011, 2035
I'll let you know how my mini-sepex's work out. Just ignore the horsepower ratings, D&D's are really underrated (in my experience.) With some mods, I'll be shooting for +30hp per motor. And frankly, at that price, they really can't be beat.
Thanks Tony. I think the price you got is awesome, and it's in the ball park of what I want to spend, but then I'd need to find a couple of cheap sepex controllers. And they're not too easy to come by. I'm looking to see if I can find a series equivalent that's reversible.

Tony Coiro
03 February 2011, 2045
Yea, Curtis and Sevcon isn't cheap and I'd stay away from Kelly sepex (from experience). Alltrax DCX will reverse but I don't think it will regen (if you need that.) What about series wound reversing with some motorside contactors or big FETs? It's be a cheap and dirty way to do it.

DaveAK
03 February 2011, 2053
Yea, Curtis and Sevcon isn't cheap and I'd stay away from Kelly sepex (from experience). Alltrax DCX will reverse but I don't think it will regen (if you need that.) What about series wound reversing with some motorside contactors or big FETs? It's be a cheap and dirty way to do it.
Cheap and dirty is what I'm looking for. I don't need regen. A couple of series wound motors equivalent to your sepexs would be ideal, as long as they're reversible. I'd simply use a couple of reversing contactors.

Thanks for the warning about Kelly, I was just looking to see what they offered.

Tony Coiro
03 February 2011, 2339
We had a sepex cart in evgrandprix (electric gokart race at Purdue) running a Kelly and the field strength had a minimum of like 10A. You would turn the kart on and within a few minutes, the motor would start getting warm, even if it hadn't spun. Spent hours going through manuals, on the phone with Kelly and looking in the programming and nothing would change it. We had the 72V 600A model, something like the KDC model I think, it was almost a year and a half ago. Eventually switched to a Sevcon PowerPak and it worked like a charm. If you're looking for cheap and dirty, I remember a conversation I had with Remote Contact about the possibility of using two series controllers to run one sepex........ I mean, I've heard worse ideas before. :D

Remotecontact
04 February 2011, 0917
You're testing me, right?

Tony Coiro
04 February 2011, 1003
You're testing me, right?

Lmao, I wish I could've got a picture of your face during that, it was magical.

EVcycle
04 February 2011, 1012
We are always testing ...someone around here RC. :)

DaveAK
04 February 2011, 1108
Hmmm. I can get two of the 48V Sevcon PowerPaks for $250 a piece, and then two of the D&D SepEx motors for another $250 each. That's stretching the budget, but a good price for the quality of the kit, (and I have a Sevcon calibrator).

Shipping is always the problem though.

DaveAK
04 February 2011, 1113
And the Sevcons can be set up as master/slave, although I don't know if this will allow me to have them going different speeds and/or direction.

Interesting. Veerry interesting.......

DaveAK
04 February 2011, 1904
OK, looks like I'm going with the D&D from EVDrives and a couple of Sevcon controllers from eBay. Spoke with Carl at EVDrives and he's willing to send USPS Parcel Post which really keeps the cost down. He's also got the speed sensors for them, which is an added bonus!

I really shouldn't be doing this, but ..... :D

dice23
04 February 2011, 1943
was just hanging out at d&d yesterday. i used to run a 6.7 in my dragbike,now my golf cart has a special one vic did for me. vic is a good friend of mine and having them in my backyard sure help. i ran my 6.7 at 201 volt one day,but 168 with a few mods really worked nice! very easy to work on would have been great for a street bike.not really sure why anyone would want to use a sepex though? no performance...unless you don't care?

DaveAK
04 February 2011, 2047
SepEx gives me regen braking. It's a low speed/high torque application. Two of these motors will give me just the performance I need.

larryrose11
05 February 2011, 0654
DaveAK, You pull the trigger yet?
I believe I have something you may want for a tracked EV. A RoboTek ax2550. It is a dual channel motor controller, with reversing built in. It is for a battle-bot. 120 A / Chanel (30 sec), 60A for 1 hr. Thermally self limiting. A possible issue is the 40V max on the unit
http://www.roboteq.com/brushed-dc-motor-controllers/ax2550-ax2850-dual-120a-brushed-dc-motor-controller.html
The sweet part for you would be the interface. It is set up for tracked vehicle stuff already. Left / right blending and all that. I even have the special cables that allow you to use an RC style input. I need to do a final testing to make sure its all working.

DaveAK
05 February 2011, 1132
Thanks for the link Larry, I'll check it out. I'm not a very patient man though, so yes I have already pulled the trigger on the motors. I should have thought of you crazy battle-bot guys!

larryrose11
05 February 2011, 1408
You could always send them back. I would think that a PM motor would be your best bet for efficiency, series Wound for monster torque, since it is a low speed setup.

DaveAK
05 February 2011, 1424
I got such a good deal on them though, and the controllers too. They might not be the absolute best for my application, but the price is hard to beat. Plus I know the Sevcon controllers reasonably well and I can use some of my (as yet undeveloped) bike tech on them. The nature of this project is very much experimental, and if I decide I need a better drive system I'll be able to make a much more informed decision. If I do switch them out I'll probably be abloe to recover most of the money I'll have invested.

And I hate cancelling orders or sending things back, especially in this economy.

So, are series wound motors that much better for torque than shunt wound?

larryrose11
05 February 2011, 1719
Series vs shunt? All depends on speed. With series wound, it will generate monster tq, but it falls off pretty quick with speed. If you keep the armature current a constant, and decrease the field current, the motor has less torque, butr will also generate less back EMF, allowing it to spin faster. The idea setup is to have the field current some multiple between 0-1 of the armature current. This 0-1 multiplier needs only to be a function of speed. The details of this function depend on the motor.
As an example, I worked it out for something like the ADC9 a bit back. The ratio should be 1 (armature and field are the same) up to about 900RPM, then decreasing to about 10% by 5000 RPM. I programmed it all a bit back into Simulink as part of grad school. I can make it available to anyone who is comfortable in the Matlab / Simulink environment.

Remotecontact
05 February 2011, 1817
Thanks for the link Larry, I'll check it out. I'm not a very patient man though, so yes I have already pulled the trigger on the motors. I should have thought of you crazy battle-bot guys!

Now that you mention it. Battlebots Pro 2011 competition is in Miami this year and I'm entering with my robot Witch Doctor. Here's a fight from last year and a video of this year's testing, launching a 45lb aluminum frame into the air.

http://www.youtube.com/watch?v=8XElkUqzMz4

http://www.youtube.com/watch?v=QxVz3EryThc


I'm going to try to have some live streaming video of the event incase anybody is curious about how a battlebots event rolls.

/end shameless rant on my robot

DaveAK
05 February 2011, 1847
Yeah, like I said, crazy! :D