Space Kart - Project Updates

Automotive
#81

So that turned out to be the case, within 30 seconds of around 1/3 throttle the motor fried and I saw a small puff of smoke, then we kept the system energized and tried the throttle again to see what was going on and blew up the ESC. Then we plugged in the spare ESC without diagnosing the issue and suprise, that blew up also.

The cheap electric goal is out the window anyway, so I’m going with awesome electric, and purchased an off the shelf 8hp brushed motor kit to put on the kart, so we can try again next saturday. The equivalent brushless kit would be double the cost, and efficiency and longevity aren’t big requirements for this use case.

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Space Kart Fail
#82

Awesome. Do you have a link to that 8hp motor kit you ordered? I’m curious for my own projects.

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#83

And most importantly, is the 3d printed coupler going to be used…
breath bated…

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#84

It’s the Motoenergy ME0708, apparently it’s the equivalent to an etek motor that several famous spinner battlebots used to power their spinners in the past. We will be running at 36 instead of 48 volts (since we are using a 4 10s lipos instead of building a 6 6s lipo pack which would be more cost for same capacity) so it will be less powerful than the max sustained 8hp at 48v. Will be going from a 26 tooth sprocket directly on 7/8" motor output shaft to the 57 tooth main axle sprocket for a 2.2 gear reduction to get our target 1,000 rpm axle speed at top speed of 30mph.

Is anyone familiar with a motor performance curve like the following? It’s not immediately obvious what the horizontal axis means, do they run it up to full speed and then just steadily increase the load?

Will be using an Alltrax AXE 4834 controller, which we can program to limit it to less than its 300 amp max output, seems prudent to start at 50-100 amps.

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#85

The voltage stays at ~24v, so I’m guessing they keep voltage steady, vary load, and those are the other numbers gathered at that voltage and load…
But I suck at graphs, so hopefully someone else will chime in…

#86

Those types of graph are usually speed vs. torque, but I admit to being a bit confused by that one.

http://www.vexforum.com/attachment.php?attachmentid=6043&d=1336704320

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#87

I was going to mention an etek motor because I remember them being used in Battlebots (Team Nightmare uses one for their blade http://www.robotcombat.com/nightmare.html). I had the cheaper “EV Warrior” motors which were still 1.5hp at 36V.

Still if that’s correct 3/4 the voltage if it directly relates to HP is still 6hp (I’m assuming equivalent to gas engines), which is pretty impressive on a go kart.

That’s a pricy kit, I guess that came out the space kart budget?

#88

My recollection is that electric motor power should relate to the square of voltage, in an ideal sense, because both RPM and torque vary linearly with voltage.

#89

We already spent the money raised from the class, I’m buying and donating this kit so that we will have something worth the time we have invested so far.

Currently I’m researching more on the relationship of the voltage and motor output power, this is the data provided on the motoenergy website:

Product Description
This ME0708 is a Brush-Type, Permanent Magnet DC motor with very high efficiency. Capable of 4.8 KW continuous and 15 KW for 1 minute. For voltages from 12 to 48 VDC input and 100 amps continuous (300 amps for 1 minute). Designed for battery operated equipment. For more information, see the Drawing below. Motor weight of 28 pounds.

  1. Armature Resistance Line to Line is 0.010 Ohms.
  2. The number of brushes is 8.
  3. The maximum recommended rotor speed is 5000 rpm.
  4. Voltages from 0 to 48 VDC input.
  5. Torque constant of 0.13 Nm per Amp
  6. The Inductance Phase to Phase is 0.06 Milli-Henry.
  7. Armature Inertia is 180 Kg Cm Squared.
  8. Continuous current of 100 Amps DC.
  9. Peak current of 300 Amps DC for 1 minute.
  10. Weight of 28 pounds.
  11. Peak Stall Torque if 38 Nm.
  12. This is an Open Frame, Fan Cooled motor.
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#90

“EK20 high performance electric motor rated at approximately 18 HP (Comparable gas-powered karts rated at approximately 6 HP)”

Found this quote

Myth busters build they used a golf cart motor and power handler.

If you guys are interested in one I can call a couple shops that specialize in golf carts. Possibly see about a donation from ez-go

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#91

I couldn’t actually find a motor for sale called the EK20. Why would a golf cart shop donate supplies to us? Just advertising a completed project?

#92

I can think of a number of reasons that a shop might donate a used motor to us. Starting with “That sounds like a cool project”… I would suggest taking @Robert_Davidson up on his offer to call around and see about a donation.

#93

http://www.sellfaster.com/planogolfcarts/

This place had a used motor out of a 2008 golf cart for $250 he hung up before I found out if that comes with the power controller

It also had regenerative breaking not sure if you guys have thought about using it

#94

Looks like the new motor wont get here by tomorrow, they said it would ship by wednesday but no tracking number yet :rage:

I will have a 12x12 1/8" aluminum plate that we can mill into a motor mount for when the drivetrain does arrive, also to improve our steering and prevent the binding we got last week, (it is using small qa1 cfr3-4 rod ends http://www.qa1.net/catalog/motorsports/#100 with 0.190 inch ID holes) we just need to get some longer 10-32 bolts and some 7/32" (.014 wall thickness) aluminum or copper tube to make very narrow bushings so that the tie rod doesn’t hit the washers we were using

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#95

Stop the presses! The DMS Space Kart needs to be just like this…

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#96

Forgot to take pictures but we milled the motor mount and improved the steering this past weekend, the new motor should be arriving any day now that I ordered it from a different supplier.

The new BOM cost is about ~1,700, we went from a $200 120amp brushless motor and $250 250amp controller to a $450 300amp brushed dc motor and a $400 400amp controller. We also saved some money since the new motor will connect directly to the main drive sprocket instead of going through an intermediate shaft (which cost about $100 in parts)

https://docs.google.com/spreadsheets/d/1zwMJlGWFvijT2UEXvyGlNasunnBot3TR4t7g41upT9M/pubhtml

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#97

Also http://www.evdrives.com is awesome, got a call from the owner and a good deal to bypass a backordered part so everything is in the mail now!

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#98

A 30 pound chunk of metal is fairly substantial, I probably need to beef up the wooden motor mount structure, may try to make it to DMS late tonight to start wiring up the motor.

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#99

So close, just some wiring left to do. We should start taking bets on what will fail first on this hastily thrown together test vehicle, I’m thinking either the non speed rated tires exploding at 30 mph or the front steering knuckle attachment pulling out (3 3" wood screws hold each front wheel on to the chassis)

Will probably also have to fine tune the alignment of the motor mount to the rear axle, I think the motor mount is leaning with the top out a couple degrees.

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#100

Ssssssssmoke’m ifyagot’em!