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Upgrading My 1990 Miata Miata

7960 Views 140 Replies 13 Participants Last post by  ScythianNightingale
This will be the thread about my attempt at upgrading my working (albeit slow and loud) Mazda Miata conversion. Everyone's feedback and comments are welcome. I can take it. :)

First - about the car at present - the body is in great condition for being 30 years old. The top is new, all the lights and accessories work. It has a custom battery I made (mostly because I wanted to learn about the process) which is 21s (77V) and 136 AH. (10kWh). For V1 I used two 72V motors connected with the loudest chain on the planet. I have a Soliton 1 controller (340 V, 1000 amps) waiting to go in. I invite you to check out details on my website, here.

The other thing - I am a electrical engineering college student who likes doing things myself on the cheap - I am doing this project for the process and not as much the result. I didn't build my own battery (and my own spot welder, for that matter) because I thought I could do it better than Elon... So ditching everything and switching to a high voltage AC system is out of the picture.

The current plan:
- Acquire beefy forklift motor. (In progress, if you have had success with this and are in the DC area let me know)
- Remove the transmission and directly drive the differential. Add reversing solenoid for reverse.
- Extend the drive shaft and attach it to the motor. There is a universal joint on both ends of the drive shaft already.
- Possibly (see below) extend the C beam and attach it to the motor.

Here's my question for everyone - it is necessary or advised to balance the torque running through the driveshaft? We know that if my driveshaft is transmitting X amount of torque, an equal and opposite X torque has to somehow be transferred back from the differential to the front. The transmission presently has a C beam (see image below) that connects its output to the differential - the reaction torque is absorbed by this C beam.

One idea I had would be to extend this C beam forward to my motor, so both the drive shaft and beam would be attached to the motor. The motor would not exert torque on whatever is supporting it (aka, my 30 year old frame).

Thoughts on whether this is this necessary?

Here's an image of the output of the transmission. A driveshaft connects it to the differential. The C beam is attached quite heftily to the transmission and the differential housing.

Font Line Auto part Automotive window part Parallel

Other bits:
- I have access to basic tools. Lots of electronics stuff. No welding on site, but I know a guy.
- I plan to upgrade the battery pack from a 21s to a 40s after the forklift motor is good and secure. So if this first edition goes 40 mph, its ok.
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Discussion Starter · #81 ·
Updates

Yesterday the motor arrived - Warp 9. Yeah, costs more than a forklift motor (but not much more, I got it shipped for 1k). However, how much is it worth to have it work? It spins, plus there are technical drawings and performance data. So far looking good.

The motor came with some handy parts - a taper lock (Quick Detachable Variant) on the drive end with the accompanying hub to squeeze the tapers. Saved me 50 dollars. It also came with an RPM sensor on the non drive end as well as a mounting plate - don't think I'll need it but it sure made it easier to move around.

Automotive tire Motor vehicle Wheel Vehicle Automotive lighting


I bought the manual transmission output shaft a few days ago - it comes tomorrow. The idea is to cut off the relevant spline bit of the output shaft and weld it into the taper lock. Then I can taper lock the male spline that will go into the driveshaft onto the motor.

This is the "Sled". It will be mounted in front to the motor mounts and at the rear to a beam that will get welded to the bottom of the car.
Rectangle Automotive lighting Wood Font Parallel


I screwed a piece of wood that is in the spot where the welded cross beam will be. I laid the 1.5" sled rails down as well as the PPF - it will be lopped off at the appropriate length and bolted to the sled, similarly how it used to be attached to the transmission.

Automotive tire Motor vehicle Hood Automotive design Vehicle door


Hopefully I can be ready to start welding next week.
 

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Updates

Yesterday the motor arrived - Warp 9. Yeah, costs more than a forklift motor (but not much more, I got it shipped for 1k). However, how much is it worth to have it work? It spins, plus there are technical drawings and performance data. So far looking good.

The motor came with some handy parts - a taper lock (Quick Detachable Variant) on the drive end with the accompanying hub to squeeze the tapers. Saved me 50 dollars. It also came with an RPM sensor on the non drive end as well as a mounting plate - don't think I'll need it but it sure made it easier to move around.

View attachment 134750

I bought the manual transmission output shaft a few days ago - it comes tomorrow. The idea is to cut off the relevant spline bit of the output shaft and weld it into the taper lock. Then I can taper lock the male spline that will go into the driveshaft onto the motor.

This is the "Sled". It will be mounted in front to the motor mounts and at the rear to a beam that will get welded to the bottom of the car.
View attachment 134751

I screwed a piece of wood that is in the spot where the welded cross beam will be. I laid the 1.5" sled rails down as well as the PPF - it will be lopped off at the appropriate length and bolted to the sled, similarly how it used to be attached to the transmission.

View attachment 134753

Hopefully I can be ready to start welding next week.
I like your "sled" - I would recommend some rubber in the mountings either motor to sled or (easier) sled to chassis
 

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Yeah, costs more than a forklift motor (but not much more, I got it shipped for 1k). However, how much is it worth to have it work? It spins, plus there are technical drawings and performance data.
- Forklift motor is as cheap as free. At most it's 20% the price of what you paid.
- The forklift motor you would've found almost certainly would have worked just fine and you could've tested it with a spare battery. It's not a grandfather clock that fell down the stairs, it's a motor with a 1/4" thick shell and 1" thick end caps. So, zero added value there.
- A forklift motor would also spin. This is what motors do. No modifications were necessary to accomplish this.
- Technical drawings aren't worth anything really, and, every forklift motor I've ever looked at I was able to find technical drawings of just fine, either by google or just by asking for them. You have successfully avoided having to measure, or to use google.
- Performance data on the Warp9s are generally marketing wankery. Not worth anything. And, whatever they're worth, you'd get the same out of any random motor the same size yanked out of a forklift... because it's the same thing. What performance data are you needing? Take motor. Use motor. Done.

...

So, what you've done is pay $1000 for a motor worth $200. The $800 difference is in not having to look around for one. Which is just fine, but I would've figured you were more of a type to need to save money than to be buying shortcuts to a little bit of effort. Else... why are you doing a DC build if you've got money to waste for convenience?

Hopefully I can be ready to start welding next week.
Congrats on moving forward on your project. It's an exciting step.
 

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He paid $1000 for a motor that sells for $4000 now.

He can always his his money back for it, so that means it's costing him $10 a year in lost bank account interest 😂

The car's also worth more than one with "found it in a scrap pile", because...motor salvage value again.

Kid's clearly got some scholarship money he's spending, so it's either spend it on a decent motor or on hookers and blow.

And you just know the hookers would just go out and buy themselves a Hyper9 to EV convert Big Daddy's Caddy.
 

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He paid $1000 for a motor that sells for $4000 now.

He can always his his money back for it, so that means it's costing him $10 a year in lost bank account interest 😂

The car's also worth more than one with "found it in a scrap pile", because...motor salvage value again.

Kid's clearly got some scholarship money he's spending, so it's either spend it on a decent motor or on hookers and blow.

And you just know the hookers would just go out and buy themselves a Hyper9 to EV convert Big Daddy's Caddy.
I agree with remy - $1000 is not a bargain - but its a lot better than $4000 and the old DC motors are getting scarce mow
 

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Discussion Starter · #89 ·
You're running outa time - doesn't school start next week? 👨‍🎓
UMD has a pretty long break - School starts 25th; I'll go back the 24th. So I'll aim to have it all assembled for the first time by the 18th - two weeks, and then 5 days for breaking and fixing.

the old DC motors are getting scarce mow
This is exactly what I found... I figure in 2010 it wasn't worth buying a new DC forklift, but it was worth repairing one. Now we are getting to the point where the DC forklifts are dying and they aren't worth keeping around to repair other DC forklifts - I heard from several shops that they remove and sell motors for their cores.

Another thing - I searched in Baltimore - maybe in such a commercial hub it is easier to transport a motor core and melt it back down to use the copper again. Maybe in the middle of nowhere there are still loads of DC forklifts just sitting around. But I tried and I couldn't find one.
 

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Discussion Starter · #90 ·
Sled is assembled - bolt holes are in the right spot and everything fits together. Tomorrow is hopefully welding day for both the cross beam on the car and the sled (towing the car with the tractor to the neighbors who has a lift and a welder).

Train Rolling stock Wood Motor vehicle Mode of transport


The todo list:
- Weld Sled (Tomorrow)
- Weld Cross Beam (Tomorrow)
- Bend metal plate that will connect engine mounts to sled in the front (Asking around... maybe by tuesday?)
- Cut and weld section of transmission driveshaft into old motor adapter. (Asking around... maybe by tuesday?)
- Mount and wire controller (As soon as the sled is in for good... Sunday?)

My optimistic and totally not achievable goal is wheels spinning by the end of next week.
 

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Discussion Starter · #92 ·
Where is the rubber?
Good question. Rubber mounts that would allow the sled to move with the diff were originally part of the plan, but I spoke to someone with a lot of experience with gas miatas. He said that rubber mounts are on stock cars to make the car feel softer and more beginner friendly. He also said that one of the first things people do to upgrade their cars is to remove those mounts if they are ok with vibration. He said the mounts primarily absorb noisy frequencies and not to protect the car.

I am aware though that rubber mounts help reduce instantaneous spikes of force that could otherwise break my stuff. If I change my mind I can add them up front between the engine mounts and the sled as well as in back between the cross beam and the sled.
 

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Good question. Rubber mounts that would allow the sled to move with the diff were originally part of the plan, but I spoke to someone with a lot of experience with gas miatas. He said that rubber mounts are on stock cars to make the car feel softer and more beginner friendly. He also said that one of the first things people do to upgrade their cars is to remove those mounts if they are ok with vibration. He said the mounts primarily absorb noisy frequencies and not to protect the car.

I am aware though that rubber mounts help reduce instantaneous spikes of force that could otherwise break my stuff. If I change my mind I can add them up front between the engine mounts and the sled as well as in back between the cross beam and the sled.
He is talking bollocks
The soft engine mounts are to stop the low frequency vibration from the pulses of an idling engine
The much stiffer mountings I am talking about are to stop the much higher frequency of vibrations from your motor and from the road

Stiffer mountings are a good idea - but bugger all to do with "more beginner friendly" - solid mountings are a bad bad idea
 

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Duncan's Silver Hammer

Not only a mangled title from a Beatles song about a deranged [DC forklift motor] maniac, but hammers are how you test structural response and tune vibration out...

You'll find a LOT of vibration coming from a motor unless you are really good at sinewave synth at 30kW - with brushed you are a victim of pwm, though. The hockey pucks are a good idea, imo.
 

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Discussion Starter · #95 · (Edited)
Ok, I'll add them. I think I'll use something like this - I could easily add them to the front and pretty easily add them between the sled and the cross beam in the back.

In other news ... it's welded!
Motor vehicle Gas Engineering Asphalt Machine

The cross beam on the bottom of the car is done as well. My neighbor welder said it was hard to weld the 1/4" beam to the paper thin miata frame... but then at the end he did a few aggressive pull ups on it... he probably weighs 250 lbs. I also added a 4*2*.25 plate just below the carpet by the seats that bolts the cross beam to the floor of the car.

The todo list:
  • Weld Sled
  • Weld Cross Beam
  • Add plate to strengthen the cross beam
  • Bend metal plate that will connect engine mounts to sled in the front (Asking around... maybe by tuesday?)
  • Cut and weld section of transmission driveshaft into old motor adapter. (Asking around... maybe by tuesday?)
 

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with no or stiff rubber isolators you can expect a your bolted on assembly to experience higher g force. so 250# hanging on it is no test. I would look at 3X minimum and as high as 5X with the suspensions. At the least I would add a spreader plate opposite your sheetmetal mounts so it doesn't rip out. I think if you can use the hard mounts for the old trans and motor that would be the best start.
 

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I use rubber mounts like those - BUT mine are always in compression - in compression they are great - in tension or sheer not so good

Remember they need to take the torque loads - and more importantly the acceleration loads as the car goes over bumps - also side loads but they are probably less
 

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Discussion Starter · #98 ·
Hi Everyone - Updates:

The sled is in for the first time ever! Super exciting.
Motor vehicle Electrical wiring Electricity Gas Auto part


It fits. I also got the adapter back from the machinist (this evening), all I need to do is weld the spline shaft inside it - the machinist added chamfers so that should be easy. The part he made is easily the nicest part on the whole thing.

Wood Gas Engineering Machine tool Auto part


And yeah, I am sure that it is straight. The hole in the center is so precise that it actually can hold suction with the spline stub... lol.

Wood Gas Auto part Machine Household hardware

Another picture of the parts. I will cut down the spline shaft so it doesn't protrude from the adapter.

A few days ago I tested my controller with my motor at 24 volts... everything worked well. I got live data to go from the controller to my microcontroller that will send that to my touchscreen on the car.

  • Weld Sled
  • Weld Cross Beam
  • Add plate to strengthen the cross beam
  • Bend metal plate that will connect engine mounts to sled in the front (Found one at UMD I can use, will go bend on Tuesday when they reopen.)
  • Cut adapter
  • Weld adapter (???, should be easy with how good the hole in it is)
  • Cut sled rails to correct lengths and drill holes to mount on rubber. (Tomorrow)
  • Wire the controller for real with reversing solenoid for low power reverse (controller supports lower power reverse). (I have the switch in the dash, though!)
  • Cut and connect the power plant frame.
I am going back to school next Monday, so officially I have 7 days left. If I don't finish... I only live 30 minutes away from school. It seems doable - the only aspects left to do that are outside of my control are the welding of the adapter, but that doesn't require anything special.
 

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I am going back to school next Monday, so officially I have 7 days left. If I don't finish... I only live 30 minutes away from school. It seems doable - the only aspects left to do that are outside of my control are the welding of the adapter, but that doesn't require anything special.
looks at being 3 years into his conversion and only just starting the actual electric vehicle part of it

I hate you.

Best of luck. Remember that when you're "almost done", you've got 80% of the work left, you just don't know it yet :p
 

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Focus on school when it starts out vs following the Call of the Syrens who smash ships on rocks.

You'll have lots of time to work on the car when semester is behind you. Resume goes in the trash compared to other candidates -- nobody looks at, "finished cutting the sled rails on my Mazda vs doing Karnaugh maps" as an excuse for a crap GPA.

Blitz it for this 7 days, then put it away.
 
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