DIY Electric Car Forums banner

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.
101 - 120 of 141 Posts

· Registered
Joined
·
46 Posts
Discussion Starter · #101 ·
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
Uhh... this is version 2. Version 1 took 1 year with a test battery pack and then another 6 months (really just waiting for the semester to finish) before I was driving with my custom battery pack. It was driving for all of last summer and last fall.

I took out the motors and transmission at around Christmas and have been doing this upgrade for the last three weeks or so.
 

· Registered
Joined
·
710 Posts
Just use some stock Miata motor mounts to hold the front of your sled. You can get competition mounts which are stiffer or just use stock ones. Either way the sled looks great. Leaves a lot of real estate for batteries and I love that you can use the stock driveshaft unmodified, at least that's what it looks like the plan is.
 

· Registered
Joined
·
5,397 Posts
Hi Everyone - Updates:
  • 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.)
He's already got it covered, seems to know what he's doing, he's stated his plans and goals, and is working to a plan after deciding to go with stock rubber engine mounts. Hence the metal plate brake-bending work at school tomorrow...

It's all coming together nicely, just a question of what he can get done before school starts.
 

· Registered
Joined
·
46 Posts
Discussion Starter · #104 ·
Today's Update: The exact sled position has been decided and mounts have been cut.

Rubber bushings are in to connect the sled to the rear cross brace.
Automotive tire Tire Motor vehicle Tread Wood


The PPF has been cleaned and cut and connected to the sled.
Automotive tire Wood Motor vehicle Gas Engineering




Overall Goal: Driving by Sunday

My optimistic schedule:
Monday: Test fit the sled several times as I line up for holes. Rear Rubber bushing holes drilled and test fit, PPF bolt holes drilled in sled and PPF. PPF cut to size. (Done)
Tuesday and Wednesday: Motor goes in for real! Front cross brace is bent and installed with rubber mounts, the adapter is assembled.
Thursday: What spills over from Tuesday, plus Controller mount and throttle.
Friday: Motor wiring, reverse solenoid if I feel like it, spin up the motor.
Saturday: Get the car out of the shop and drive it
Sunday: ...
Monday: ... get the car ready for storage, go back to school, and sleep until classes start on Wednesday. (lol)

Tuesday will almost certainly spill over to Wednesday... I expect either the adapter weld or the front brace bend not to happen.

Critical Paths:

  • Weld the spline shaft into the adapter. (Calling folks first thing tomorrow)
  • Bend the front cross brace (this: Green Urban design Grass Slope Circle
    ) (Doing this hopefully tomorrow, I have the measurements and access to the tool)

Also - thanks everyone for their comments and engagement...
 

· Registered
Joined
·
5,397 Posts
Get some spray wax the bodyshop guys use into the insides of those tubes before you close the ends off. Afterwards, drill a small hole and do the inside where the end closures are. Goes without saying you should ideally powder coat, or at least paint with a good chassis enamel, the fabbed pieces.
 

· Registered
Joined
·
46 Posts
Discussion Starter · #106 ·
Today's Update: Worked an 14 hour day today minus meals and am a day ahead of my previous schedule!

The motor is in for real and connected! Driveshaft and PPF connected, with rubber to the front and back cross braces.

The adapter is complete. It is very beefy and very straight. Or so I think... (Pic when it was out).
Automotive tire Machine tool Gas Engineering Machine


The front brace with the reversing contactor and RPM sensor.
Automotive tire Motor vehicle Automotive lighting Automotive exterior Bumper


Overall Goal: Driving by Sunday

My optimistic schedule:
Monday: Test fit the sled several times as I line up for holes. Rear Rubber bushing holes drilled and test fit, PPF bolt holes drilled in sled and PPF. PPF cut to size. (Done)
Tuesday and Wednesday: Motor goes in for real! Front cross brace is bent and installed with rubber mounts, the adapter is assembled.
Wednesday: Controller mount, throttle, reverse solenoid wiring
Thursday: Motor wiring, reverse solenoid if I feel like it, spin up the motor.
Friday: Get the car out of the shop and drive it
Saturday: ...
Sunday: ...
Monday: ... get the car ready for storage, go back to school, and sleep until classes start on Wednesday. (lol)
 

· Registered
Joined
·
5,397 Posts
Nicely done, kid

That sled looks like a nice heavy foundation for batteries. Not knowing your battery box details, I'd suggest getting that wiring crap off it so you can lower the box/cells/modules right down to those rails vs building yet another heavy structure suspended over it. It also will help pull the batteries back to the firewall so the car handles better....
 

· Registered
Joined
·
5,397 Posts
Can you mod those mounts to use bolts pointing downwards?

Nut comes off, you might lose a mount your way, and the stud eats into a lot of underhood volume (length of bay x height of bay x the stickout) if a box sits on the rail.
 

· Registered
Joined
·
46 Posts
Discussion Starter · #109 ·
Today's Update: Controller mounted, wheels spinning! Reverse working, screen runs with live (great latency too) data about amps, power, voltage. Controller has reverse signal as well.

Here's a video of the (not) first spin... props to camera man Dad.

Motor vehicle Automotive exterior Vehicle Gas Auto part


Noise is primarily coming from the differential... After a 1 minute 2000 RPM unloaded test, it was the warmest part of the whole system (via inspection with one of those thermal guns). My only guess is that the fluid in there needs to be replaced or topped off.

Not knowing your battery box details
No battery box at the moment, sticking with the batteries I got, which is a DIY 21s20p out of 26800s (6.8Ah each) ~10kWh. They are where the gas tank used to be. In the future I will be tripling the battery situation (not DIY...) to a 60s pack, I'll stick with 130AH. My charger and controller both do up to 300V.... might as well use it. Motor only takes 175 max, but the soliton can limit that kinda thing. 60s at the same AH would be 28kWh... maybe 100 miles... perfect.

Tomorrow I need finish up securing the wiring, reassemble the center console, secure the throttle and get it out of the basement. Don't worry, I fully expect something to break. It always does.
 

· Registered
Joined
·
5,397 Posts
Heat in the diff is normal - churning, squeezing, and shearing a lot of viscous lube.

That heat is demonstrating part of the conversion's inefficiency due to keeping the original drivetrain. You'll notice racecars and some trucks, have fins on the diff cover to cool the lube down and the serious guys use pumps and radiators.
 

· Registered
Joined
·
8,530 Posts
A bevel (including spiral bevel) gear drive, as typically used in a longitudinal transaxle but also in some rear final drive units of front-engine AWD vehicles, is efficient. 95% to 99% efficiency is typical; that's still up to 5% of the transmitted power being dissipated as heat, but it's not a cooling problem. This is comparable to the loss in a parallel or planetary gear set as found in an EV transaxle.

A hypoid gear drive, as typically used in separate final drives of longitudinal powertrains (front engine, rear drive), is significantly less efficient. 90% to 95% efficiency is typical; that's still not enough transmitted power being dissipated as heat to be a cooling problem in most applications, but the lube oil does get warm and cooling fins are common on final drive housings.

A limited-slip differential uses friction in a clutch system to transfer drive torque from the faster-turning wheel to the slower-turning one; this dissipates significant energy as heat, in addition to the loss in the gearing, but only when turning a corner or spinning a tire. The combination of hypoid gearing and LSD in severe operating conditions often leads to the need for active cooling, which means a pump and heat exchanger for the lube oil, but street driving is not a severe operating condition.
 

· Registered
Joined
·
46 Posts
Discussion Starter · #117 ·
Success!

I haven't put an update up because I have been driving this car so much! It feels great. Originally power was low but it was because the minimum controller input voltage was too high (65 V). But at 800 motor amps, that car moves! A fun amount of acceleration.

Up to 30 miles an hour it's perfectly silent (loudest part is the diff) - above 35 when I let off on the accelerator a noise starts - I am still looking for the cause. When I keep the power on the noise does not appear.

On friday I finished up everything under the hood and put the center console together. I also painted all the custom parts with a anti rust + rust sealing paint - thick rubbery stuff that looks pretty good. Saturday morning the car came out and was driving - all of yesterday I was alternating between charging the battery and tuning the controller.

My charger is having issues... it's one of those EMW 10kW chargers that are DIY - It isn't detecting the input voltage to the wall or of the battery. I am still chasing down how it works... maybe I just need to recalibrate it but also it could be that the DC to DC converter powering the isolated op amps are busted. I was having this problem off and on before V2 and assumed its a loose wire or something... I also know the sensor configuration is stored in EEPROM on the arduino in there - it is reasonable that the EEPROM could have gotten corrupted (then I would just calibrate). I might hardcode those gains and offsets once I successfully measure them... better yet my dream is to have the BMS available over a CANBUS and just have the charger use that data for the battery voltage.

At the moment I disabled the battery voltage checks. My computer will in theory shut the charger off before it gets to high - but I am too scared and only charge when I am home and checking it every 30 mins or so. (It's below 50% SOC).

Here's the diff under the thermal camera. I wish there was some sort of scale in the photo... this was a 1 minute no load test in the basement.

Purple Amber Sky Violet Font


Here's the 3D printed and spray painted silver "Electric" badge that's on the back of the car.
Automotive parking light Automotive tail & brake light Vehicle Grille Hood


Mostly, though, I am happy to be finished before I go back to school. That first drive where I truly put some good amps into the motor felt so good. This motor could truly live in this car for as long as I am working on it.

I am hoping to make a music video / cinematic trailer of the car this week... I'll post it if I do. And of course, thanks everyone for their help!
 
101 - 120 of 141 Posts
Top