Vintage Margay electric drift kart build

[JoelR]

Hi,

I'm very happy I found this forum and have been learning a lot the past couple of days.

My project: Convert an old Margay race kart to electric power (had a 5hp Briggs & Stratton) and make it purpose-built to drift like an adult-sized Razor Ground Force Drifter. Our paved driveway has a wide section we've been using for racing around cones. I'd like to purposely limit the kart's speed, grip and performance to keep the kart properly suited to this relatively small space.

My current plan:
Per Functional Artist's posts/references, I'm planning to buy most of my gear from Miguel @ Alfa Wheels on eBay.

Motor & Controller: 1500w brushless motor w/controller
Sprocket: 10 tooth "Power Curve" (originals are 12T (front) & 70T (rear))
Batteries: 4 x 12v 12Ah

I'm currently researching tires. The original tires are Bridgestone racing slicks: 5.5/11-5 (front) and 6.5/11-5 (rear) on Margay rims about 5" wide in front and 6-7" wide in the rear. None hold air well and have cracks so I'm looking for replacements on eBay. I'd love to be able to run used racing tires--sets of 4 spec tires are around $40 shipped but my wheels are rather wide for what I'm finding. On the rear I plan to install plastic sleeves like they use on drift trikes so my rear tire choice needs to be compatible.

I haven't researched throttle controls yet but would like to keep the original pedal and use something that can generate a signal for the controller.

I'm open to any tips, ridicule, etc.

Joel

 

[Budget GoKart]

Put a predator on a yard kart boom drift kart LOL mine will drift on dry pavement with a little weight transfer

 

[landuse]

Put a predator on a yard kart boom drift kart LOL mine will drift on dry pavement with a little weight transfer

He wants electric, so why are you suggesting a gas engine?

Welcome to the forum Joel!!

 

[Functional Artist]

Hello & welcome to the forum
Sounds kool

A pull throttle is probably what your lookin' for (~$25.00)

Heavy-duty cable pull throttle. Great for converting vehicles from gas to electric power. Body is made from tough reinforced nylon. Body dimensions are 5-1/8" long x 1-1/4: wide x 3/4" high. Body has four 0.16" ID (4.1mm) mounting holes that #8 machine screws fit through. Pull cable is 6" long and has a 0.06" (1.5mm) diameter. Cable pull distance is 1". Variable speed throttle is at zero when cable is released and at full when cable is pulled out 1". Cable has stopper that prevents it from being pulled out of the body. 35" long electrical cable. Wire colors: red, black, and white.
https://www.electricscooterparts.com/throttlesstandard.html

FYI: This thread has some info on throttles (starting on page 5)
http://www.diygokarts.com/vb/showthread.php?t=40239&highlight=throttles&page=5

 

[JoelR]

Put a predator on a yard kart boom drift kart LOL mine will drift on dry pavement with a little weight transfer

That's very tempting because it's so simple and effective. I'm curious about electric vehicles so this is a good project for my education.

 

[itsid]

I hate every word in this thread

A vintage Margay must NOT see an electric conversion and much less a predator!

It's an iconic race kart and spitting on it's heritage by installing a chinese clone or some battery powered boma is blasphemic!

That being said...
Cool another e-kart conversion I'm a big fan!
(just use something less relevant than a Margay please!... some old Tony or CRG perhaps
some of the generic looking oneofamillion is perfectly fine)

If you find old stocks of hardly or even unused slicks
you might get lucky and they hardend up to a point where thy are perfectly good drifters w/o any sleeving
(and they're mostly cheap too )

just check the DOT number.. anything 13 years or older is certainly a good chance if no perfect candidate.

And in case it's still too grippy, you have a nice cheap core for your sleeve to wrap around

'sid

 

[JoelR]

Sid,

Wow, thanks for your post! I guess I've taken this old thing for granted--I bought it used in about 1991 to enjoy on the recently-built Spokane ORV park kart track only to be turned away after my first lapping session for having such an old kart whose bumpers didn't match up to modern karts I was sharing the track with. From some brief Google research, I'd guess mine is a Margay Cheetah Mark III from about 1972 (same year I was born!). It's sat for over 25 years and I'd like to make it do something more useful than take up space.

My conversion plans at this point will leave everything intact/original (no cutting) and with your encouragement, I'll try to stick to this constraint so that someone more interested in vintage karts than me can properly restore it some day.

In the meantime, I've ordered my motor, controller, batteries, throttle and sprocket and will move onto tire buying. Looks like some kind of servo/killswitch/etc. would make sense so I'll add that to my research list along with a source for wire and connectors too.

 

[itsid]

Wow rereading my post above it sounds way harsher than anticipated...
(wasn't as rough in my head when I typed it...)
Sorry for conveying the impression a violent purist comes jumping at your face

Anyways, thanks for keeping the Kitten intact
Please add "no welding" to the "no cutting" objective and everything will be violets in bloom.

If you have the original Margay three piece wheels, you may want to consider shelving those for drifting..
hitting a curb with them can turn out to be an expensive accident,
so some generic more modern kart wheels to take the abuse is a safer approach IMO
(In case you ever intend to resell the Margay)
Some guy recently tried to sell his Cheetah MkIII on ebay for 5k (I doubt he got that tbh)
but the last I remember being sold was around 3k IIRC
So after nearly 50 years it's still the same value as a new trackworthy race kart;
and you don't see such happening too often

Where do you want to put the batteries?
the lack of side pods on a cheetah suggest "steering column"
but then again 1.5kW smell like 8 20'ish Ah batteries at least *headscratch*

'sid

 

[JoelR]

Build update:

My motor, controller, batteries and #35 chain sprocket arrived today!

I didn't have much time to do more than mock-ups and a quick sprocket change.

I'd like to get some advice on battery capacity and placement:



Placement:
It looks like I can easily fit 4 12Ah batteries on the front floorpan. And I can fit 4 more behind the seat, 2 in front of the axle and 2 behind. If I was making a racing kart, I'd obsess about keeping the weight between the axles but since I intend to do some drifting, I'm thinking a higher polar moment would be beneficial to increase stability while locked in a slide.

Capacity:
Influenced by the Razor Ground Force Drifter that runs a 250W motor @24V using 2 7Ah batteries (and 30+ minute run time), I thought I was safely upsizing (while doing no math before hitting "Buy it now!") for my full-size kart running 1500W motor and 4x12Ah batteries. Digikey's calculator says I'll get about 5 minutes of runtime at full power. So, I'm thinking I'll order another 4x12Ah batteries and run 4 in front, 4 in back, wired as 2 48V packs in parallel for double the capacity. Is that a decent plan for a starting point? If all is well and it's lacking for run time, I can upgrade batteries to something more exotic and use the 12Ah SLAs on something else.

Fun note: while mocking up the rear battery placement, despite having the little terminal covers on, one of the batteries shorted across the axle briefly where the terminals peek out. Whoops! Well, at least I know I'm doing real science!

Rear Chain/Sprocket:


I'd like to use the existing motor mounting plate *with* an adapter plate (@Sid) for the electric motor but the alignment of the rear sprocket is off. I haven't tried yet but would like to slide the sprocket over to line it up but can't see how it stays put on the axle and key. If it has to stay put, I can cantilever the motor using a plate that overhangs the original mount. Suggestions?

Electrical Misc:
I'm open to suggestions for a solenoid/contactor/relay to provide a clean and safe on/off capability. I'm also looking for a suggestions for the battery cables and connectors.

Wheels
I'd like to take Sid's advice and put the original Margay 3-piece wheels on the shelf to preserve them. So I'll need new wheels. I'm clueless about the different standards and could use some help here so I get wheels that fit. I'm thinking much narrower would be fine for my back driveway.

 

[Functional Artist]

Placement:
I would try it with just the (4) 12V 12AH SLA's
...in the front
...& also in the back (mainly so you can get the "feel" of it)

Capacity:
48V 1,500W motor + (4) 12V 12AH batteries ="5 min run time" = BS

I recently ran (2) 48V 1,000W motors off of (4) 12V 12AH SLA's
...for nearly 30 min.

Here is the video (~12 min long & I cut out a bunch of just riding around)
https://www.youtube.com/watch?v=eLCojNpCPu0

Fun note: I once had a spiral bound notebook laying on one of these 12V 12AH SLA's
...I saw some smoke & noticed the metal spiral started glowing red

Rear Chain/sprocket:
The sprocket should be adjustable on the axle

I have also used a few different styles to mount these motors
http://www.diygokarts.com/vb/showthread.php?t=37442
https://www.youtube.com/watch?v=ffzQf7ppw5g

This set up holds the batteries & the motor in (1) nice-n-neat package
…& no cutting or welding
http://www.diygokarts.com/vb/showthread.php?t=37062
https://www.youtube.com/watch?v=zYWuGJTC0jQ&t=97s

Elec. misc:
Contactors aren't usually used on these small motors/controllers
...until you get in the over ~3,000W+ range

The key (on/off) switch will shut the controller/motor down.

A circuit breaker seems to be the easiest way of shutting the whole system down
...or if you use a simple fuse, just pull the fuse

 

[JoelR]

How does this look for a switch/circuit breaker in one?

https://www.amazon.com/Tocas-Circuit-Breaker-Trolling-Waterproof/dp/B01F76VJKQ

I like the surface mount style and heck, the yellow even goes with my kart frame!

 

[Functional Artist]

How does this look for a switch/circuit breaker in one?

https://www.amazon.com/Tocas-Circuit-Breaker-Trolling-Waterproof/dp/B01F76VJKQ

I like the surface mount style and heck, the yellow even goes with my kart frame!

Yup, something like that

Personally, I like the panel mount style
...this way the terminals & cables are hidden, behind the panel (out of sight & touch)

https://www.ebay.com/itm/Car-Circui...MP-E96-/113010789596?var=&hash=item1a4ff7ccdc

 

[JoelR]

Question about charging -- Any recommendations for a charger and charge connector? I'd like to charge the whole pack at once.

Also, do I need to hook up the controller's lock/switch, brake, or other wires for a basic forward-only setup? I'm shooting for a simple "get it up and running" configuration first.

 

[Functional Artist]

For my (4) 12V 12AH SLA's, I have been using a charger like this:
https://www.ebay.com/itm/120-240-to...=15244668519965c79868a67244acb85af919df31b198

These threads show a few different configurations for connecting these systems.
Cotton Candy (48V 1,000W brushed motor)
http://www.diygokarts.com/vb/showthread.php?t=39760

Torsk (48V 1,000W brushed motor)
http://www.diygokarts.com/vb/showthread.php?t=38905

Damien (48V 1,800W brushless motor)
http://www.diygokarts.com/vb/showthread.php?t=40084

Sorry, their kinda long
...but, very detailed

Basics: (IIRC for your type brushless system)
Battery to controller: + & - (power in)
Motor to controller: (3) thick wires & (5) thin wires (power out)
Lock, key: (2) thin wires (to on/off switch)
Forward/reverse: (3) thin wires (signals the controller to rotate the motor in forward or reverse)

 

[JoelR]

Thanks FA for the info, you've been a great resource for me.

Build Update:
I ordered crimp spade connectors, a crimping tool, a switch-type circuit breaker, charger and a charger socket.

I mocked up a motor mount using 8020 15 series (1.5") beams. It allows for no drilling (Sid, I'm talking to you) and a lot of flexibility for positioning things. Plus, I feel like a big kid working with that stuff--like LEGO or Erector set!




I'm trying to keep the wiring away from and out of the plane of the chain (It would be nasty to break/drop a chain and have it short your mains!) I'll probably make a chain guard to help with that and to keep gunk off the wiring.

I did hit a snag tonight trying to move the rear sprocket over to line up with the motor. I removed the 4 nuts that appear to squeeze a split aluminum collar into the hub (which must be tapered inside) to pinch the axle. In anticipation, I applied a liberal dose of Kroil penetrating oil yesterday and added lots more today but to no avail. I can't get a good angle to tap on it near the shaft, can't get a good prying position without using the bearing as my fulcrum (seems like a bad idea). I've tried rubber hammer, gentle pry bar, gentle pickle fork, wooden dowel w/metal hammer, etc. I also wire brushed the axle thinking it would help to be clean where I want it to slide. I also saw 2 tapped 1/4-20 holes in the collar and tried driving bolts into them thinking they might exist to force the collar out once they hit bottom. Nope, nothing. HELP!

 

[Functional Artist]

Very welcome

Axles & hubs have really tight tolerances (so, just a little corrosion can create a lot headaches)

Did you remove the axle from the kart?
...it's a PITA but, usually easier to get to & deal with a stubborn sprocket hub

Then you can slide a (proper diameter) piece of pipe over the axle
…& apply the pressure right where its needed

 

[JoelR]

Sprocket Hub Removal

I found some pics online of the same basic sprocket hub. As you can see in these pictures...




There are 2 threaded, thru holes in the collet. I can't think what else these would be used for except as a built-in way to force the collet out of the hub. I think I'm going to try again with a wrench on these after the penetrating oil has soaked overnight. If that doesn't work, I'll remove the axle and try my impact driver--some vibration ought to help. Maybe some heat too.

<forgot to hit send -- went to shop and...>

As described above, I cleaned out the 2 holes w/compressed air to remove any grit, added some white lithium grease to each 1/4-20 button head cap screw and drove 'em home(slowly with an allen key). With the reduced friction and increased certainty that these were put there for just this purpose, the screws bottomed out and look at this!

The collet finally budged!


After tapping the sprocket away from the collet, I got enough room to gently pry the two apart. The collet was still seized to the axle so I drove a screwdriver into the gap and that did the trick. YAY!



Unfortunately (and I'm kicking myself I didn't see this earlier), the sprocket cannot line up with the motor without slightly hanging the motor over the edge of the mount. Moving the sprocket did make a nice difference in how much, though. One thought occurred to me--would it be possible to flip the sprocket around so the bolts/nuts are swapped? If so, I might be able to push it even closer to the rt-hand bearing and tighten the nuts on the collet on the left side. I can't think of a reason why the sprocket couldn't be flipped.

 

[itsid]

First: thanks for being carefull with the kart

then, don't worry too much about battery life for now, yes 5min at full power..
but let's be honest.. you will need full power for seconds to induce a drift
and the rest will be more in the realms of 30%

twin 48V packs however are a good idea.
not for the increase of capacitance, but for a reduced level of amp drawn per cell
those tabs do not look very eager to spit 30'ish amps your way let's say
cutting that in half is certainly a safe approach

Since you have the controller likely somewhere 'half way'-ish between the two batpacks a same length power line makes a more even spread.

your taper locking hub is awesome
and it can be installed facing in or out as you need (taper left or right doesn't matter)
I'm not sure you can move the sprocket from one side to the other though,
check if it has recess on both sides that the sprocket bore would tightly lock on to,
if so, no problem;
if not.. stick with the sprocket on the side it's on.

I know flipping the clutch would make installing the locking taper difficult,
you'd need to remove the axle bearing to make room and slide it back on afterwards.
Also with the nuts on that side you might not gain much anyways *shrugs*
but with bearing flangettes like yours you might be able to have the flangettes inboard of the bearing retainer.
(that might buy you a few mm)

I have a hard time remembering how the original enginemount looks tbh
[how's it attached, how much it can be moved etc]..
care to post a pic of the entire rear end so we can see the motor mount in the grand scheme of things and how's it attached,
maybe we spot a place to buy another few fractions
(daylight is of great help as well.. dark garage with bad lighting never helps seeing things much less making things visible on photos )

'sid

 

[JoelR]

Motor Mount

After several iterations, I decided that my nifty 8020 beams were not yielding a motor mount solution I liked so I got a scrap aluminum plate and made an adapter.


I explored several options to enable easy, straightforward mounting considering that the fasteners holding the adapter to the stock mount (I still owe Sid some pictures of that) might end up under the motor. I wanted to avoid relying on tapped holes in the aluminum plate if possible, probably and irrationally due to the high vibration I'm used to with gas engines. The solution I came up with (which looks dead simple now but wasn't obvious to me at first) uses 5/16-18 button head cap screws (same as the 15 series 8020 beams), nylon locknuts and only 2 tapped holes at the back of the motor. If these pull out, I'll use countersunk bolts underneath the plate, rivnuts or helicoils but I doubt that'll be necessary.



I'm happy with how it came out, seems strong and easy to work on and all 8 fasteners are the same except that the screws in the tapped holes also use washers as spacers.

Now I'm onto battery and controller mounting and soon battery cable making if Mr. Amazon Prime will deliver the crimping tool. ;-)

I would love to get some help finding cheap wheels that will work. My front wheels mount on 5/8" spindles and rears mount onto the 1" axle. So far, all wheels seem more expensive than expected and until I'm more familiar with compatibility, I'm hesitant to make a purchase.

 

[landuse]

I would love to get some help finding cheap wheels that will work. My front wheels mount on 5/8" spindles and rears mount onto the 1" axle. So far, all wheels seem more expensive than expected and until I'm more familiar with compatibility, I'm hesitant to make a purchase.
View attachment 109221

DO NOT by dolly wheels from Harbour Freight!! We see them so often and they break within minutes of kart riding

Someone will be able to give you some good ideas on tyres if you wait a bit.